Single and Double Skin Glazed Office Buildings

Single and Double Skin Glazed Office Buildings Analyses of Energy Use and Indoor Climate

Harris Poirazis Division of Energy and Building Design Department of Architecture and Built Environment Lund University Faculty of Engineering LTH, 2008 Report EBD-T--08/8

Lund University Lund University, with eight faculties and a number of research centres and specialized institutes, is the largest establishment for research and higher education in Scandinavia. The main part of the University is situated in the small city of Lund which has about 103 700 inhabitants. A number of departments for research and education are, however, located in Malmö. Lund University was founded in 1666 and has today a total staff of 5 500 employees and 40 000 students attending 140 degree programmes and 1 600 subject courses offered by 66 departments.

Division of Energy and Building Design Reducing environmental effects of construction and facility management is a central aim of society. Minimising the energy use is an important aspect of this aim. The recently established division of Energy and Building Design belongs to the department of Architecture and Built Environment at the Lund University, Faculty of Engineering LTH in Sweden. The division has a focus on research in the fields of energy use, passive and active solar design, daylight utilisation and shading of buildings. Effects and requirements of occupants on thermal and visual comfort are an essential part of this work. Energy and Building Design also develops guidelines and methods for the planning process.

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Single and Double Skin Glazed Office Buildings Analyses of Energy Use and Indoor Climate

Harris Poirazis

Doctoral Dissertation 1

Single and Double Skin Glazed Office Buildings

Keywords Glazed office buildings, single skin façades, double skin façades, building simulations, building performance, energy use, indoor climate, thermal environment, thermal comfort.

© copyright Harris Poirazis and Division of Energy and Building Design. Lund University, Lund Institute of Technology, Lund 2008. The English language corrected by L. J. Gruber BSc(Eng) MICE MIStructE. Layout: Hans Follin, LTH, Lund. Cover photo: Harris Poirazis Printed by KFS AB, Lund 2008 Report No EBD-T--08/8 Single and Double Skin Glazed Office Buildings. Analyses of Energy Use and Indoor Climate. Department of Architecture and Built Environment, Division of Energy and Building Design, Lund University, Lund ISSN 1651-8136 ISBN 978-91-85147-23-6 Lund University, Lund Institute of Technology Department of Architecture and Built Environment Division of Energy and Building Design P.O. Box 118 SE-221 00 LUND Sweden

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Telephone: Telefax: E-mail: Home page:

+46 46 - 222 73 52 +46 46 - 222 47 19 [email protected] www.ebd.lth.se

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To Usoa I’ve only gone this far because you tied my shoe laces

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Single and Double Skin Glazed Office Buildings

4

Abstract

Abstract

The energy efficiency and thermal performance of highly glazed office buildings are often questioned. However, nowadays glazed buildings are increasingly being built around the world, because (a) there is a growing tendency among architects to use large areas of glass in the façade, often with the aim of contributing to a better view of the outside and access to daylight, (b) users often like the idea of increased glass area, relating it to a better view of the outside and a more pleasant indoor environment and (c) many companies prefer the distinctive image of themselves (e.g. transparency or openness) that a glazed office building can provide. Due to insufficient knowledge concerning function, energy use as well as indoor environment of glazed office buildings for Scandinavian conditions, a project was initiated in order to gain knowledge of their possibilities and limitations. The aim of this thesis is to clarify and quantify how highly glazed façades affect the energy use and thermal comfort of office buildings. Another aim was to validate or identify the needed improvement of building energy simulation tools, in order to ensure the precision of the simulations. Finally, suggestions have been given for determining how the design can be improved with regard to energy efficiency and thermal comfort. The first part of this project involved establishing a reference building with different single skin glazed alternatives, choosing simulation tools and carrying out simulations for the determined alternatives. As the reference building, a moderately glazed office building representative of the late nineties was chosen. Using this building as a starting point, the window area to external wall area ratio was increased gradually, in order to meet a fully glazed office building. Results were obtained through varying the building’s orientation, the interior layout (open plan and cell type offices) and the type of glazing and solar shading devices. The different building alternatives were compared with different indoor environment classifications and a sensitivity analysis was presented regarding the occupants’ comfort and the energy used for operating the building. In the second part of the project parametric studies were carried out regarding the performance of various double skin façade cavity alterna5

Single and Double Skin Glazed Office Buildings

tives, in order to gain knowledge of the possibilities and limitations of the system’s performance. Simulations on a zone and a building level were then carried out, in order to achieve optimal integration of the system. The simulations included different glazing and shading devices for both “standard” double façades and airflow window modes. The results showed that highly glazed buildings tend to perform poorly unless designed carefully, resulting in increased energy use and poorer thermal environment. For Swedish climatic conditions during winter months, windows with low thermal transmittance are essential, in order to improve the building’s energy performance and thermal comfort, especially for highly glazed buildings. Low g and especially geffective values have a positive effect in lowering the cooling demand; externally placed shading or double skin facades can have this effect. Hybrid ventilated double façades can reduce the heating demand and improve the quality of thermal environment. Airflow windows with low E inner pane result in a radical improvement of the indoor climate, reaching the thermal comfort levels of an office building with a conventional façade. In general, double skin façades result in improved energy and thermal performance of the building mainly when applied on the south façade, but their impact is limited, since the cooling demand is rather limited for Scandinavian climatic conditions. Parameters such as the impact of temperature control set points, plan type and orientation on energy use and thermal comfort were also studied. Achieving improved building performance, when using fully glazed façades, can be a great challenge. Individual building design that takes into consideration the type of façade including the size and type of glazing, the position of shading devices, the temperature set points, the building occupancy and plan type can definitely lead to improved building performance. If this is established, even in highly glazed cases, the building performance may reach reasonable levels as to energy use and indoor climate. However, a building with low energy demand cannot be achieved by a highly glazed building in a Scandinavian climate.

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Contents

Contents

Keywords Abstract Contents Acknowledgements How to read this thesis

2 5 7 13 15

1

Introduction

19

1.1 1.2 1.3 1.4 1.5 1.6 1.7

General Energy efficiency in the building sector Energy efficient building design The “Glazed Office Building” project Aim of the thesis Limitations of the thesis Definitions and symbols

19 20 21 22 22 23 25

2

Background

31

2.1 2.2 2.3

General The performance and quality of a building as a system Building Environment

2.3.1 2.3.2

Design Criteria Indoor Environment

2.3.2.1 2.3.2.2 2.3.2.3 2.3.2.4

Thermal Comfort Conditions of thermal comfort Thermal comfort and productivity Other indoor climate parameters that influence the occupants’ health and productivity

31 32 34 34 35 35 36 43

2.3.3 2.3.4 2.3.5

Architectural quality Environmental performance Costs

2.4

Building technology

2.4.1

Glass in buildings

2.4.1.1 2.4.1.2 2.4.1.3

General Basic physics of the glass Thermal functions of the glass

45 46 47 48 49 49 49 50 52

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Single and Double Skin Glazed Office Buildings

2.4.3

Double skin façades

2.4.3.1 2.4.3.2 2.4.3.3 2.4.3.4

General Classification of double skin façades Technical description of the cavity Advantages and disadvantages of double skin façades

54 54 55 57 57 57 58 58

3

State of the art

63

3.1

Glazed office buildings in Nordic climates

3.1.1 3.1.2 3.1.3 3.1.4 3.1.5

General Layout of typical office buildings Office buildings in Sweden Energy performance of Swedish office buildings Glazed office buildings in Sweden

63 63 64 65 66 68

3.2

Double skin façades

3.2.1

Building physics of the double skin façade cavity

3.2.1.1 3.2.1.2 3.2.1.3

General Modelling approaches Measurements – test rooms and real buildings

3.2.2

Integration of double skin façades

3.2.2.1 3.2.2.2 3.2.2.3

Contribution of double skin façades to the HVAC strategy Examples of coupling double skin façades and HVAC Control strategy

3.2.3 3.2.4

Energy performance of buildings with integrated double skin façades Typical constructions - Examples of buildings

3.3

Building simulation software

3.3.1 3.3.2

Building energy simulation tools Software for DSF modelling

3.3.2.1 3.3.2.2

Façade simulation software Building simulation software

91 92 96 96 97

4

Methods

99

4.1

Generation of building alternatives

2.4.2

Single skin façades

2.4.2.1 2.4.2.2

Glazing Shading devices

4.1.1 4.1.2

Reference building (30% window to external wall area ratio) Single skin alternatives (60% and 100% window to external wall area ratios) 4.1.3 Double skin alternatives (100% window to external wall area ratio) 4.1.3.1 Pilot study on component level using WIS 3 4.1.3.2 4.1.3.3

Study on a zone level using IDA ICE 3.0 Study on a building level using IDA ICE 3.0

4.2

Description of the studied parameters

4.2.1

Single skin alternatives (30%, 60% and 100% glazed alternatives)

4.2.1.1 4.2.1.2

IDA ICE 3.0 output (zone level) IDA ICE 3.0 output (building level)

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70 70 70

71 75 77 78 81 85 86 89

99 100 102 104 104 110 113 113 113 114 114

Contents 4.2.2

Double skin alternatives

4.2.2.1 4.2.2.2 4.2.2.3

WIS 3 simulations (component level) IDA ICE 3.0 Simulations (zone level) IDA ICE 3.0 Simulations (building level)

4.3

Description of the simulation tools

4.3.1

Simulations using WIS 3

4.3.1.1 4.3.1.2

Temperatures at the centre of each layer Temperatures at different heights of the cavity

4.3.2

Simulations using IDA ICE 3.0

4.3.2.1 4.3.2.2 4.3.2.3

General description Description of double façade model Validation of IDA ICE 3.0 Double Façade model (IEA SHC Task 34/ECBCS Annex 43)

116 116 119 119 119 119 120 121 124 124 125 126

5

Description of the building model

129

5.1

Description of the reference building

5.1.1. 5.1.2. 5.1.3 5.1.4 5.1.5 5.1.6 5.1.7 5.1.8

Geometry of the building Office layouts Description of building elements Special modifications for the simulated model Control set points for indoor air temperature Occupancy Lights HVAC

5.1.8.1 5.1.8.2 5.1.8.3 5.1.8.4

Heating and cooling Ventilation Equivalent heat recovery efficiency Use of electricity

5.1.9

Electrical equipment

129 129 130 134 138 140 141 145 146 146 146 147 149 149

5.2

Description of single skin glazed alternatives

5.2.1

Description of 60% glazed building

5.2.1.1 Façade construction 5.2.1.2 Window properties

5.2.2

Description of 100% glazed building

5.3

Description of double skin glazed alternatives

150 150 150 152 155

5.3.1

WIS 3.0 simulations

5.3.1.1

Geometry of the “standard” double façade box

5.3.1.2

Geometry of the airflow window

5.3.2

IDA ICE 3.0 Input (zone level)

5.3.2.1 5.3.2.3 5.3.2.4 5.3.2.5

Office description (IDA ICE 3.0 - zone level) Geometry of the multi storey high façade Properties of the inner and outer skin Shading devices

157 157 157 157 159 159 160 160 161

5.4

Assumptions made during the calculations

163

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Single and Double Skin Glazed Office Buildings

6

Results and discussion

165

6.1

Reference building

166 166 166 169 169 170 170 174 181 182 186 190

6.1.1

Energy use

6.1.1.1 6.1.1.2 6.1.1.3

Impact of floor plan type Impact of orientation Impact of control set points

6.1.2

Indoor climate on a building level

6.1.2.1 6.1.2.2

Weighted average mean air temperatures Perception of thermal comfort

6.1.3

Indoor climate on a zone level

6.1.3.1 6.1.3.2 6.1.3.3

Mean air temperatures and potential overheating problem Directed operative temperatures Perception of thermal comfort

6.2

Single skin glazed alternatives (60% and 100% window to external wall area ratios)

6.2.1

Energy use

6.2.1.1 6.2.1.2

Impact of floor plan type and orientation Impact of windows and shading devices for the 60% and 100% glazed alternatives

6.2.2

Indoor climate on a building level

6.2.2.1

Weighted average mean air temperatures

6.2.2.2

Impact of window and shading type on the perception of thermal comfort for the 60% and 100% glazed alternatives

6.2.3

Indoor climate on a zone level

6.2.3.1 6.2.3.2

Directed operative temperatures Perception of thermal comfort

6.3

Double skin façades

6.3.1

Simulations on a component level (pilot study using WIS 3)

6.3.1.1 6.3.1.2 6.3.1.3

Pre study: reducing the number of “standard” double façade alternatives Parametric study: influence of cavity geometry on system performance Performance of the glazing alternatives

6.3.2

Parametric studies on a zone level (IDA ICE 3.0)

6.3.2.1 6.3.2.2. 6.3.2.3 6.3.2.4 6.3.2.5 6.3.2.6.

“Standard” double façade mode (naturally ventilated cavity) “Standard” double façade mode (mechanically ventilated cavity) “Standard” double façade mode (hybrid ventilated cavity) Airflow window mode Impact of the “ventilated façade” concept Impact of shading device type

199 199 200 202 209 209 210 224 224 226 233 233 234 241 252 265 266 270 274 277 282 291 295 297 300

6.3.3

Parametric studies on a building level (IDA ICE 3.0)

6.3.3.1 6.3.3.2

Energy use Thermal comfort

6.4

Comparison of single and double skin façade building alternatives 302

6.4.1

Impact of glazing size on energy use and thermal comfort of single skin buildings Impact of glazing type on energy use and thermal comfort Comparison of buildings with single and double skin façades

6.4.2 6.4.3

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302 304 306

Contents 6.4.4

Comparison of best performing alternatives

308

7

Conclusions

311

7.1

Energy use and thermal comfort for highly glazed office buildings located in Scandinavia

312 312 312 315 315 316 317 320

7.1.1 7.1.2 7.1.3 7.1.4 7.1.5 7.1.6 7.1.7

Plan type Control set points Orientation Glazing area Glazing and solar shading type Double skin façades Best performing alternatives

7.2

Methods for determining energy and indoor climate performance 321 322 Lessons learnt from the simulation work

7.2.1

7.3

Improving the energy and indoor climate performance of highly glazed buildings: general recommendations and further studies

323

8

Summary

327

8.1 8.2 8.3 8.4

Introduction Background Methods Discussion and conclusions

8.4.1 8.4.2 8.4.3 8.4.4 8.4.5 8.4.6

Glazing area Glazing and solar shading type Double skin facades Other parameters that influence the building performance Best performing alternatives Determination of energy and indoor climate performance

327 327 328 330 330 330 331 332 333 334

8.5

General recommendations for improvements of highly glazed office buildings

334

References Appendix A Appendix B Appendix C Appendix D Appendix E Appendix F Appendix G Appendix H Appendix I

337 347 357 359 365 377 381 385 387 389

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Single and Double Skin Glazed Office Buildings

Appendix J Appendix K Appendix L Appendix M

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391 393 397 403

Acknowledgements

Acknowledgements

I wish to thank my supervisors Maria Wall and Åke Blomsterberg for their guidance and the useful advice that they gave me during the research work and for the compilation of this report. I would also like to thank my colleagues at the Division of Energy and Building Design; especially Gunilla Kellgren for being so kind and helpful, Bengt Hellström for all the advice on technical issues, and Johan Nilsson for his support and friendship during the past years and Henrik Davidsson for just introducing the "Constanza" concept to me. The contribution and support of Per Sahlin and Mika Vuolle proved to be substantial for meeting the (reasonably delayed) deadlines. Special thanks to Jean Rosenfeld for believing in me and being the main driving force for starting a PhD. Along the way several people and organizations contributed to this work; I thank all of you. Finally, I would like to thank all the experts who, by making available their theses, reports and articles, have provided easy access to knowledge. I would like to express my greatest gratitude to my parents Kaiti and Stathis for their support during all the years of my study. Last but definitely not least, I wish to thank Usoa for always believing in me and for supporting my choices without considering any cost. The project was funded by the Swedish Energy Agency and SBUF (Development Fund of the Swedish Construction Industry), and supported by Skanska and WSP.

Lund, December 2007 Harris Poirazis

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Single and Double Skin Glazed Office Buildings

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How to read this thesis

How to read this thesis

When writing this thesis, a main aim was to provide enough background knowledge so that a “new” reader, less knowledgeable in this field, can read it. Since the findings of this thesis are primarily addressed to architects, HVAC engineers, glazing/façade experts and consultants in the building industry, a common language had to be established. Thus, the first three chapters were quite extensive covering different aspects of the field. In the first (Introduction) chapter a brief description is given of what energy efficient design means and why energy savings in the building sector are important. Then, the contribution of the “Glazed Office Building” project to the field is briefly explained and the main aims and limitations of this thesis (as a part of the whole project) are described. Finally, definitions and symbols used during the thesis are briefly explained. The main aim of the second (Background) chapter is to provide a theoretical background regarding different aspects of the building system and their impact on building performance. The building is described as a system consisting of the “building environment” and the “building technology”. The parameters that the “building environment” and the “building technology” comprise are described briefly in a top down organization. Emphasis is given to the aspects studied further in this thesis (such as conditions of thermal comfort and other indoor climate parameters that influence the occupants’ health and productivity), while other parameters, such as architectural quality, environmental performance and costs are described briefly. The third chapter (State of the art) aims to inform the reader about the research already carried out in the field, focusing mainly on three topics: (a) glazed office buildings in Nordic climates, (b) double skin façades and (c) building simulation software. In the first part a description of typical (glazed) office buildings in Sweden with regard to energy performance is provided. The second part deals with building physics of the double skin façade component (such as modelling approaches of the cavity) and integration techniques of double skin façades in buildings. Finally a description 15

Single and Double Skin Glazed Office Buildings

of the available building simulation software is given focusing on those that can handle double skin façade systems. A brief reference regarding the validation of these tools is also provided. In the fourth chapter (Methods) the generated building alternatives are described. The necessary reasoning concerning the alternatives selected for the parametric study is provided for better understanding. The (output) parameters of the simulated single and double skin façade alternatives are briefly discussed. Finally, the tools used for the parametric studies are briefly described and a reference to their validation is provided. The fifth chapter (Description of the building model) aims to describe the input as inserted in the two software tools used (IDA ICE 3.0 and WIS 3). The input concerns physical parameters of the building, properties of the building materials, occupancy, control set points, schedules and HVAC characteristics for the 30%, 60% and 100% glazed alternatives studied. Information regarding the construction of the double skin façade cavities, both on a component and on a building level, is also provided focusing mainly on geometrical characteristics. In the sixth chapter (Results and discussion) the results of 30%, 60% and 100% single skin glazed alternatives and 100% double skin glazed alternatives are extensively studied. The results mainly focus on energy use and thermal comfort issues. A comparison between different building alternatives takes place, in order to investigate the influence of differently varied parameters on the building performance. The parametric study of the single skin building alternatives is focused mainly on parameters such as control set points, office layout, glazing type, etc, while for the double skin façade building alternatives the glazing type and the ventilation mode are the two main issues of interest. Prior to the double skin building alternatives, a pilot study on a double skin cavity (on a component level) took place, in order to filter the simulated alternatives and reduce their number. The results of this pilot study focus on investigating the crucial (mainly geometrical) parameters that influence the cavity’s performance. Better understanding of the possibilities and limitations of the cavity configuration result in an understanding as to what can be achieved on a building level. Simulations on a building level follow considering "standard" double façade mode alternatives ((a) naturally ventilated, (b) mechanically ventilated and (c) hybrid ventilated) and airflow windows. Optimization of the integration is the main aim of this step. Discussion concurrently with the results is carried out regarding the performance of the simulated building alternatives. Single and double skin alternatives are compared with regard to energy use and thermal comfort. A Conclusions (seventh) chapter follows providing the reader with the main conclusions from the simulations. Suggestions in order to improve the building performance regarding energy use and thermal comfort are 16

How to read this thesis

provided. The main aim of the conclusion chapter is not only to understand the building’s response when design parameters vary but also to quantify its performance for office buildings located in Scandinavia. Eighth chapter: Summary

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Single and Double Skin Glazed Office Buildings

18

Introduction

1

Introduction

This PhD thesis is an important part of the “Glazed Office Building project”, a five years project initiated in 2003, with the aim to gain knowledge concerning the possibilities and limitations of glazed office buildings exposed to Swedish climatic conditions, mainly with regard to energy use and indoor climate. Both single and double skin glazed office buildings are examined, starting with a reference building (typical office building of the 90s), in Scandinavia.

1.1

General

The energy efficiency and thermal performance of highly glazed office buildings are often questioned. However, nowadays more and more glazed buildings are built for the following reasons: • there is a growing tendency among architects to use large areas of glass in the facade often with the aim of contributing to a better view of the outside and access to daylight • users often also like the idea of increased glass area, relating it to better view and a more pleasant indoor environment. However, users do not often take into account the risk of visual and thermal discomfort that can occur due to this construction type • companies who want to create a distinctive image for themselves (e.g. transparency or openness) often like the idea of being located in a glazed office building Deciding how to build with a fully glazed façade can be a complicated issue. The energy efficiency and provision of an acceptable indoor climate are issues that should be considered. Other parameters to be taken into consideration during the decision and design process are visual comfort, building aesthetics, sociological and psychological determinants (such as visual and acoustical privacy), life cycle cost, etc. By prioritizing at an early 19

Single and Double Skin Glazed Office Buildings

stage the goals to be achieved, the design team can improve the building performance and fulfil the design requirements. This thesis aims to compare the performance (as to energy use and indoor climate issues) of conventional and highly glazed façades. Through extensive parametric studies the impact of design parameters on building performance is studied. Optimizing energy and indoor climate performance of single skin highly glazed buildings is the first goal to be achieved. The proper integration of double skin façade systems is also investigated with the aim of further improvements. When large proportions of glazing are used in the façade, it is essential to know from the early design stage what is to be achieved and how to achieve it. Clear goals and sufficient knowledge of the calculation tools that should be used for predicting building performance are essential for a successful building design.

1.2

Energy efficiency in the building sector

Energy use in the building sector accounts for a large proportion of the total energy use in most countries around the world. Particularly for the EU, the building sector accounts for more than 40% of the energy use and is expanding (directive 2002/91/EC). Consequently, the building sector has a major energy-saving potential. According to the Energy Efficiency Action Plan (2006) the largest cost effective savings potential lies in the residential and commercial building sector. The full saving potential is estimated around 27% and 30% respectively. In order to achieve this, the Buildings Directive was introduced in 2002 with the aim to reduce energy use by implementing energy conservation measures in the building sector. It states that (almost all) buildings sold or rented within the EU shall have an energy performance certificate not older than 10 years. Moreover, public authority buildings and buildings frequently visited by the public should set an example by taking environmental and energy considerations into account and therefore should be subject to energy certification on a regular basis (i.e. every 10 years). According to the directive 2002/91/EC, the energy performance of buildings should be calculated on the basis of a methodology, which may be differentiated at regional level, taking into account climatic and local conditions as well as indoor climate environment and cost effectiveness. Some of the factors which determine building performance are thermal insulation, the heating and air-conditioning installations, the application of renewable energy sources and the design of the building. More specifically, according to the 2002/91/EC directive, the energy performance of a 20

Introduction

building is described as “the amount of energy actually consumed or estimated to meet the different needs associated with a standardised use of the building, which may include, inter alia, heating, hot water heating, cooling, ventilation and lighting. This amount shall be reflected in one or more numeric indicators which have been calculated, taking into account insulation, technical and installation characteristics, design and positioning in relation to climatic aspects, solar exposure and influence of neighbouring structures, own-energy generation and other factors, including indoor climate, that influence the energy demand”.

1.3

Energy efficient building design

At this point it is crucial to clarify the fundamental elements of a successful low energy building design. In order to achieve that, it is essential to understand what a low energy building is. As Nilsson, (2003) described, reducing energy use is not enough to cover the concept of energy efficiency, since the first can be achieved just by switching off the heating and cooling systems, the lighting and the ventilation. This, however, should not be the case in practice. Thus, in order to describe the concept of energy efficient building design, it is essential to understand what overall building performance is. If the building is considered as a system with input (such as location, climate, use, etc) and output (building performance), breaking it down into the parts it consists of can help us understand the interactions and their influence on the building performance. In this way energy conservation improvements can be suggested without compromising performance. The analysis of the parts that constitute the building performance is carried out in Chapter 2. Another issue to be clarified when low energy building design is discussed is what “low” means. Since this expression can often be quite unclear, a reference building has to be chosen for reasons of comparison. For example, if the topic is energy conservation in buildings, then residential, commercial and office buildings can be compared. If the topic is energy conservation in office buildings, improvements should be suggested after taking into consideration the specific building use; a parameter that can be studied in this case is whether it is energy efficient to use large areas of glazing in the external façade. If the topic is energy conservation in highly glazed office buildings (e.g. due to an architectural concept), then the use of large glazed areas in the external façade of the building is a requirement and the comparison should be limited to highly glazed office buildings. In this case comparison improvements can be suggested (e.g.) by adding

21

Single and Double Skin Glazed Office Buildings

a second skin to the building envelope. From the above it is clear that energy efficiency is a relative and not an absolute measure.

1.4

The “Glazed Office Building” project

The research project “Glazed office buildings – energy use and indoor climate” was initiated and funded in 2003 in order to gain knowledge of the possibilities and limitations of glazed office buildings exposed to the Swedish climate, with regard to: • energy use • indoor environment (thermal and visual comfort, indoor air quality, acoustics, etc) • environmental performance • architectural quality and • life cycle cost Included in the “Glazed Office Buildings” project are: • • • •

further development of calculation methods and analysis tools improvement of analysis methodology calculation of life cycle costs development of advice and guidelines for design/construction of glazed office buildings in a Swedish climate • strengthening and development of competence concerning resource efficient advanced buildings in Sweden A detailed description of the organization and the main goals of the project can be found in the “Introductory report for the Glazed Office Buildings project” (Poirazis, 2005a).

1.5

Aim of the thesis

The aim of the research presented in this thesis is to: • determine how the energy and indoor climate performance can be analysed • clarify and quantify how highly glazed façades affect energy use and thermal comfort

22

Introduction

• determine how the design can be improved with regard to energy efficiency and thermal comfort In order to achieve this, a large number of building alternatives, both with single and double skin façades, were simulated on an office room and a building level. The first part of this project involved establishing a reference building with different single skin glazed alternatives, choosing simulation tools and carrying out simulations for the determined alternatives. As the reference building, a moderately glazed office building representative of the late nineties was chosen. Using this building as a starting point, the window area to external wall area ratio was increased gradually, in order to meet a fully glazed office building. Results were obtained through varying the building’s orientation, the interior layout (open plan and cell type offices) and the type of glazing and solar shading devices. The different building alternatives were compared with different indoor environment classifications and a sensitivity analysis was presented regarding the occupants’ comfort and the energy used for operating the building. In the second part of the project parametric studies were carried out regarding the performance of various double skin façade cavity alternatives, in order to gain knowledge of the possibilities and limitations of the system’s performance. Once these results were obtained, simulations on a building level were carried out, in order to achieve optimum integration of the system. A comparison of single and double skin alternatives followed, with the main focus on energy saving potential and indoor thermal quality issues. Within the main goals of this thesis, validation and improvement of building energy simulation software was also carried out, in order to ensure the precision of the simulations. More than anything, however, this thesis aims at increasing the knowledge of how to conserve energy in highly glazed office buildings without compromising the quality of the indoor environment.

1.6

Limitations of the thesis

The present report deals mostly with energy use and indoor thermal environment calculations for a virtual reference office building, with different façade alternatives, in Nordic climates. More specifically, it deals with energy use for heating, cooling, lighting, office equipment, pumps and fans, and the server rooms (including their cooling). In terms of indoor thermal environment, importance has been given to the mean air temperatures, 23

Single and Double Skin Glazed Office Buildings

the directed operative temperatures and the perception of thermal comfort (PMV and PPD values). Daylight was taken into consideration only in order to keep a minimum and maximum illuminance level intensity at the working surface; when the illuminance exceeds these levels, artificial light was considered. A detailed separate study analyzing daylight and visual comfort was carried out within the “Glazed Office Buildings” project (Bülow-Hübe, 2007). Investment cost and LCC analysis were also carried out separately (Sjodin, 2007). Different office building alternatives i.e. different façade alternatives for office buildings were simulated and analyzed for this report. A virtual reference building was created, a building representative of office buildings built during the ninties in Sweden. The façade of this building was changed for different glazed façade alternatives. All the building elements were chosen based on commercially available products. Some of the building design parameters were assumed to remain the same during the simulations and some were changed. The parameters that were kept the same were: • the shape of the building • the roof, ground floor, interior wall and intermediate floor construction • external obstructions to the building • infiltration and exfiltration of the building envelope Parameters that varied during the simulations were: • • • • • • • • • • • •

building orientation office layout (cell type and open plan type) internal loads (number of occupants and equipment) occupancy proportion of the glazed façade area (30%, 60% and 100% glazing) glazing and frame type shading devices (type and position) thermal transmittance of the façade elements heat recovery efficiency specific fan power control set points (temperature, lighting) HVAC installations

24

Introduction

1.7

Definitions and symbols

Building Envelope: The total area of the boundary surfaces of a building through which heat, light, air and moisture are transferred between the internal spaces and the outside environment (Limb, 1992). Comfort zone: The range of indoor conditions considered acceptable by a certain proportion (e.g. usually more than 80%) of the people working or living in the space (Limb, 1992). Daylight Factor (DF): The ratio of indoor illuminance at a given point to the simultaneous outdoors illuminance on an unobstructed horizontal surface. Degree Day: The number of degrees of temperature difference on any one day between a given base temperature and the 24 hour mean outside air temperature for the particular location. The average number of degree days for a given period (i.e. during the heating season) is the sum of these degree days divided by the given period (Limb, 1992). Draught: Excessive air movement in an occupied enclosure causing discomfort (Limb, 1992). Energy Conservation: The deliberate design of a building or process to reduce its energy use or to increase its energy efficiency (Limb, 1992). Exhaust Air: The air removed from a space and not reused therein (Limb, 1992). Glare (discomfort): The sensation of annoyance caused by high or nonuniform distributions of brightness in the field of view. Glare (disability): Caused when intraocular light scatter occurs within the eye, the contrast in the retinal image is reduced (typically at low light levels), and vision is partly or totally impeded (e.g., when the eye is confronted by headlights from oncoming automobiles). Heating: The transfer of energy to a space or to the air by the existence of a temperature gradient between the source and the space of air. The process may take different forms, i.e. conduction, convection or radiation. The process is the opposite of cooling (Limb, 1992).

25

Single and Double Skin Glazed Office Buildings

Heat Recovery Efficiency (or Heat Recovery Effectiveness): The proportion of heat recovered from otherwise waste heat passing through a heat recovery system. Normally it is expressed as a percentage (Limb, 1992). Humidity, absolute (dv): The ratio of the mass of water vapour to the total volume of the sample. Humidity, relative (φ): The ratio of the mole fraction of water vapour in a given moist air sample to the mole fraction in an air sample saturated at the same temperature and pressure. Indoor Climate (or Indoor Environment): The synthesis of day to day values of physical variables in a building e.g. temperature, humidity, air movement and air quality, etc, which affect the health and/or the comfort of occupants (Limb, 1992). Illuminance (E): Expresses the amount of luminous flux that arrives at a surface and is measured in lux. Illuminance and luminance distribution: A measure of the light variation from a point to another point across a plane or a surface. Luminance: Expresses the light reflected off a surface and is measured in lumens per square meter per steradian or in candelas per square meter (cd/m²). In a way the luminance is directly related to the perceived “brightness” of a surface in a given direction. Luminous Efficacy: Refers to the ratio of total luminous flux emitted by a lamp to the energy used. It is expressed in lumens per watt (lm/W). According to Erhorn and Stoffel (1996),

n=

desired surface illuminance × floor area of considered space (lm/W) total power of lighting system

Mechanical Ventilation: Ventilation by means of one or more fans (Limb, 1992). Multizone: A building or part of a building that comprises a number of zones or cells (Limb, 1992). Natural Ventilation: The movement of outdoor air into a space through intentionally provided openings such as windows and doors, or through non powered ventilators or by infiltration (Limb, 1992).

26

Introduction

Occupancy: The time during which people are in a building, usually expressed in hours per day (Limb, 1992). Occupant Behaviour: The pattern of activity of occupants in a building, including the number of occupants, their distribution, activities and time spent within the building, the way they interact with building facilities, such as ventilation systems, window openings, etc (Limb, 1992). Outdoor Air: The air taken from the external surroundings and therefore not previously circulated through the system (Limb, 1992). PMV (Predicted Mean Vote): An index of thermal sensation since it expresses the correlation between indoor environment parameters and people’s sensation of thermal comfort (ISO Standard 7730, 1984). It is a function of activity, clothing, air temperature, mean radiant temperature, relative air velocity and humidity. The scale for PMV varies from -3 (cold) to +3 (warm) (see also Section 2.3.2.2). PPD (Predicted Percentage Dissatisfied): The PPD of a large group of people is an indication of the number of persons who will be inclined to complain about the thermal conditions (ISO Standard 7730, 1984). It is expressed as a percentage (see also Section 2.3.2.2). Radiation: The transmission of heat through space by propagation of infra red energy; the passage of heat from one object to another without necessarily warming the space in between (Limb, 1992). Single Zone: A building or a part of a building comprising one zone of uniform pressure (Limb, 1992). Solar transmittance (Tsol): The ratio of the irradiation transmitted through the window system to the irradiation impinging on the window system. Solar (total) transmittance (or solar factor) (g) The sum of the (primary) solar transmittance (τ) and the ratio of the part of the solar irradiation absorbed by the window system that is transferred to the room, to the irradiation impinging on the window system. Supply Air: Air delivered to a space and for the purpose of ventilation, heating, cooling humidification or dehumidification (Limb, 1992). Temperature, Ambient: The temperature of the air within a room or zone (Limb, 1992).

27

Single and Double Skin Glazed Office Buildings

Temperature, Dry Bulb: The air temperature indicated by a dry temperature sensing element (such as the bulb of a mercury in glass thermometer) shielded from the effects of radiation (Limb, 1992). Temperature, Effective (θeff): The temperature of a still, saturated atmosphere that would produce the same effect as the atmosphere in question. Temperature, Environmental: The temperature of the air outside a room or zone (Limb, 1992). Temperature, Operative (θop): The operative temperature empirically combines the dry bulb and the mean radiant temperatures. The operative temperature is the temperature at which a person emits the same heat output as before, but when air temperature (θa) = radiant temperature (θr) = operative temperature (θop). θop does not have the same value for all the parts of the room (when the weighting method is used) (Peterson, 1991). Temperature, Directed Operative: It is calculated in the same way as the operative temperature, the only difference being that the weighting is done only for the point where the occupant is placed and towards the surface of interest as shown in Figure 2.6, Subsection 2.3.2.2. Temperature, Radiant (or Surface) (θr): Radiant or surface temperature is the temperature of an exposed surface in the environment. The temperatures of individual surfaces are usually combined into a mean radiant temperature. Temperature, Resultant: It is similar to the effective temperature but it includes humidity effects. Temperature, Wet Bulb: The air temperature indicated by a sensing element kept wet (usually by a wick), the indicated temperature thus being related to the rate of evaporation from the wetted bulb. This wet bulb temperature is used by psychrometers to measure relative humidity (Limb, 1992). Thermal Comfort: A condition of satisfaction expressed by occupants within a building regarding their thermal environment. Since the thermal comfort condition is a subjective feeling of satisfaction, building designers attempt to satisfy as many of the occupants as possible (usually 80% or more) (Limb, 1992).

28

Introduction

Thermal Transmittance (U-value, expressed in W/m2K): The heat flow transmitted through a unit area of a given structure, divided by the difference between the effective ambient temperature on either side of the structure, under steady conditions (Limb, 1992). The U-value is only defined for dark conditions (excluding solar radiation).

29

Single and Double Skin Glazed Office Buildings

30

Background

2

Background

The main aim of this chapter is to provide a theoretical background regarding different aspects of the building system and their impact on building performance. A description of the building system’s structure is briefly given and the parts of the system are described. Emphasis is given to the aspects studied further in this thesis (such as conditions of thermal comfort and other indoor climate parameters that influence the occupants’ health and productivity), while other parameters, such as architectural quality, environmental performance and costs are briefly described. It has to be noted that the information provided regarding the latter aspects is mainly intended for “new” readers less knowledgeable in this field. It is essential to clarify that the high complexity of these issues does not allow a comprehensive description within a few pages; however, an effort has been made with the aim to bring out the properties of the parts that make up the building system and influence its performance.

2.1

General

Well defined requirements for the design of a building can be a key to a successful design. As Nilsson (2003) describes, a “good” building performance is often based on general criteria related to aesthetic attractiveness, satisfactory operation (a building that fulfils its purpose as far as users are concerned) and durability. However, in practice the requirements taken into account during the design process should be defined in greater detail. Ensuring that everybody involved in the design process is aware of the consequences of the requirements is the first step to a successful building design. Nilsson (2003) describes the requirements as performance and quality ones. Performance requirements are the ones that must be fulfilled; otherwise the building can not be used for its intended purpose. Acceptable thermal climate, air and lighting quality, restrictions on disturbances (such as draughts, noise, glare, etc) and operational reliability are considered as performance requirements. Quality requirements, on the other hand, 31

Single and Double Skin Glazed Office Buildings

ensure improved overall performance, so that the building will become a “good” building. Examples of these requirements are energy efficiency, an aesthetically attractive design, efficient use of space, minimised life cycle cost, generality and flexibility, durability and ease of maintenance. This distinction between performance and quality requirements is made, in order to clarify which parameters can be compromised to a certain extent during the design process. A detailed description of the requirements and their impact on the building performance can be found in the “Introductory Report for the Glazed Office Building Project”, (Poirazis, 2005a). Below follows a summary of this report.

2.2

The performance and quality of a building as a system

Before discussing how this thesis deals with improving some of the quality requirements, especially energy efficiency and thermal comfort, it is essential to describe the main components that constitute the building’s performance. In this way a common language between the author and the reader can be established, facilitating a precise understanding of the interaction between quality (such as energy efficiency) and performance (such as indoor environment) requirements, the aim of which is to improve the building’s overall performance. Initially, the building can be considered as a: • “Sub system” of the environment that it is located in; during its whole life the building has impacts related mainly to environmental and energy use issues. • “Hyper system” (a larger system, a system that contains other ones) influencing the comfort and productivity of the occupants. In Figure 2.1 a scheme of the building as a system is presented. The performance and quality requirements included in the “building environment” interact with each other and influence its performance. The interaction of “building technology” with “building environment” during an early design stage aims to improve the building performance. A successful holistic approach during the design stage of an office building requires consideration of the performance of individual parts that constitute the building system. Moreover, successful optimization of the building's performance requires a deep understanding of the interactions between these parts, as shown in Figure 2.1. 32

Background

Building E nvironment

Energy performance Costs

Indoor environment

Architectural quality

O utput

I nput

Environmental performance

Building T echnology

Integration of passive systems

Figure 2.1

Building simulation software

Integration of active systems

The building system.

The design team should take into account the design constraints at an early stage of the decision making process, in order to achieve an overall approach and more accurate predictions. Thereby, unpleasant surprises resulting in an increase in the building’s life cycle cost and/or impairment of its performance as to energy use and indoor climate can be avoided. These constraints (stated as input in Figure 2.1) are: • Climate (solar radiation, outdoor temperature, etc) • Site and obstructions of the building (latitude, local daylight availability, atmospheric conditions, exterior obstructions, ground reflectance, etc) • Use of the building (operating hours, occupant density, schedule and activity, etc) • Building and Design Regulations It is obvious that optimum building design (maximization of the output) can not be achieved, since the overall goodness can be defined in different ways depending both on the design constraints and on the way that the design team prioritises its goals and needs (Andersen, 2000). In sustainable 33

Single and Double Skin Glazed Office Buildings

building design the integration of solar technologies is a delicate matter. Optimal performance of passive or active solar systems can not be achieved unless their integration is considered at an early design stage. Their efficiency is highly dependent on the system’s input (such as the location and use of the building) and is directly influenced by the building’s shape and orientation. Their integration has impacts on the life cycle cost, on the environmental profile, and it can be crucial for the quality of the indoor environment. Validated building simulation software can ensure proper integration, when considered at an early stage. From the above it is clear that “building technology” can interact with the “building environment” in improving the overall performance. The main aspects studied in this thesis are the energy performance and the indoor environment. The continuous lines drawn in Figure 2.1 emphasise the interactions that were studied for the “Glazed Office Buildings” project as it will be described later.

2.3

Building Environment

2.3.1

Design Criteria

The main goal of the “Glazed Office Buildings” project was to study different types of office buildings, in order to determine if energy efficiency can be achieved without compromising performance requirements such as the indoor environment, while maintaining reasonable LCC (investment, operating and maintenance cost), low environmental impacts and good architectural quality (see Section 2.3.3). In Figure 2.2 the (top-down) hierarchy for the “Glazed Office Buildings” project is presented. The objectives at the top are quite abstract but they become more specific as one follows the hierarchy down. The bold characters emphasize the aspects studied in this thesis. E nergy E fficient O ffice Building

I ndoor E nvironment

Figure 2.2

34

Environmental Performance

Architectural Quality

Costs

Integration of Solar Technologies

Design criteria of an energy efficient office building.

Background

2.3.2

Indoor Environment

According to Wouters (2000), early building design is the most important step in achieving an acceptable indoor environment. The energy use of the technical installations constitutes an important part of the building performance. Thus, energy efficiency can be considered an important part of the building design. However, low energy use design can not be the only target, since other parameters also contribute to the improved overall performance.

2.3.2.1 Thermal Comfort Achieving an acceptable indoor environment with respect to energy use is one of the most difficult tasks when an office building is designed, especially if it is highly glazed. The main components that define the indoor environment are shown in Figure 2.3. These components affect the occupants’ productivity and consequently the total economic value of the building (see Subsection 2.3.5). I ndoor E nvironment

Acoustics

T hermal C omfort

Visual Comfort

Psychosocial Comfort

Indoor Air Quality

Productivity

Figure 2.3

Criteria of indoor environment.

As far as this thesis is concerned, thermal comfort is the main component studied (the other parameters are investigated separately within the “Glazed office buildings” project). Thermal comfort can be divided into primary and secondary factors that influence the quality of the thermal environment, as shown in Figure 2.4 (ASHRAE Fundamentals, 2005).

35

Single and Double Skin Glazed Office Buildings T hermal C omfort

Primary Factors

Figure 2.4

Secondary Factors

Main aspects of thermal comfort.

2.3.2.2 Conditions of thermal comfort As outlined above, the factors influencing thermal comfort are divided into primary and secondary ones. The primary factors are shown in Figure 2.5: Primary Factors

T emperature and radiation (dry bulb, mean radiant)

Figure 2.5

O perative and resultant temperatures

Relative humidity

Air speed and turbulence

Clothing

Perception of thermal comfort

Primary factors of thermal comfort.

• Temperature and radiation (dry bulb, mean radiant): The thermal sensation is dominated by the surrounding temperature. However, the standard dry bulb temperature is not always a sufficient indicator for establishing a good indoor thermal environment, since it does not take into account the influence of radiant energy. The mean radiant temperature, however, is a more appropriate thermal comfort indicator, since it is a measure of the average radiation exchange between the occupant and the surrounding surfaces. • Operative and resultant temperatures: The operative and mean resultant temperatures empirically combine the dry bulb and the mean radiant temperatures. The operative temperature is the temperature at which a person emits the same heat output as before, but when air temperature (θa) = radiant temperature (θr) = operative temperature (θop) (Peterson, 1991). The θop does not have the same value for all the parts of the room (when the weighting method is used).

36

Background

Near cold surfaces, the operative temperature drops since the temperatures are low and the angle factors large (the closer the measuring point is to a surface, the larger is the angle factor). The more the occupant moves away from the surface, the more the angle factor decreases and thus the smaller the effect of the cold surface becomes. Since all the surfaces of a room are weighted, the walls can have a larger effect than a cold window (although the wall temperatures can be very close to the mean air temperature). Thus, the operative temperature gives a measure of a room as a whole but it is not a sufficient indicator for showing the impact of a cold surface on the occupant’s comfort. For this reason, the directed operative temperature is preferred. This is calculated in the same way, the only difference being that weighting is performed only for the point where the occupant is placed and towards the surface of interest as shown in Figure 2.6. The operative temperature, however, can be used when persons are moving inside the space (i.e. open plan office type).

Directed operative temperature

Operative temperature

Figure 2.6

Operative and directed operative temperature.

• Relative humidity: Relative humidity is the ratio of the moisture content at a certain temperature to the maximum possible moisture content at that temperature (until condensation starts). Generally, humidity affects the heat loss by evaporation, which is most important at high temperatures and high metabolic rates (ASHRAE Fundamentals, 2005). However, questionnaires have shown that even in the comfort zones the relative humidity has a large impact on the perception of the thermal environment. High relative humidity means that the moisture content of clothing increases which alters their insulating properties. Usually the relative humidity in an office space varies between 30% and 60%. • Air velocity and turbulence: the sensation of thermal comfort is influenced by air velocity and the scale of turbulence. Often the increased velocity can be an advantage in an office space, when the temperatures 37

Single and Double Skin Glazed Office Buildings

are higher than within the comfort range. A typical way to increase the air velocity is to use circulation fans in the rooms. However, at other times, draughts cause discomfort due to localised cooling. • Clothing: clothing provides thermal insulation. Thus, it has an important influence on acceptable temperature. The choice of clothing can alter comfort preferences by as much as 2 to 3K. The unit that expresses the clothing insulation is clo; (1clo = 0.155 m2KW-1). According to ASRAE Fundamentals (2001), “because people change their clothing for the seasonal weather, ASHRAE Standard 55 specifies summer and winter comfort zones appropriate for clothing insulation levels of 0.5 and 0.9 clo respectively”. • Perception of thermal comfort: It is important to clarify that the conditions of thermal comfort are not easy to define, since thermal comfort is a very subjective value. Thus, a thermal environment that is acceptable to some people may be totally unacceptable to others. According to Andresen (2000), it is not only that people are differently dressed and have different metabolic rates, but their assessment of comfort is also influenced by their psychosocial environment, which can not easily be taken into account by any calculation method. The most commonly used calculation methods are the ASHRAE standard 55 (ASHRAE, 1992) and the ISO Standard 7730 (ISO, 1984). In order to describe this factor it is necessary to explain the concepts of Predicted Mean Vote (PMV) index and Predicted Percent Dissatisfied (PPD). Both ASHRAE and ISO standards are based on the concepts of PMV and PPD developed by Fanger (1970). o The PMV index is a measure of thermal sensation, since it expresses the correlation between indoor environment parameters and people’s sensation of thermal comfort. It is a function of activity, clothing, air temperature, mean radiant temperature, relative air velocity and humidity. As it is described in ASHRAE fundamentals, (2001) “The PMV index predicts the mean response of a large group of people according to the ASHRAE thermal sensation scale”. The ASHRAE sensation scale is presented below: +3 = hot +2 = warm +1 = slightly warm 0 = neutral -1 = slightly cool -2 = cool -3 = cold 38

Background

The Predicted Percentage Dissatisfied (PPD) of a large group of people is an indication of the number of persons who will be inclined to complain about the thermal conditions. After estimating the PMV, the predicted percent dissatisfied (PPD) with a condition can also be estimated. Those persons not scoring +1, -1 or 0 are deemed to be dissatisfied. From this part, the predicted percentage dissatisfied (PPD) of occupants could be determined. Liddament (1996) writes that “the immediate conclusion of this work was that it was not possible to define a set of thermal conditions that would satisfy everyone. Even when the average of the predicted mean vote was zero, i.e. a neutral thermal environment, 5% of the test occupants were dissatisfied”. Accepting that no single environment is judged satisfactory by everybody, the standards specify a comfort zone based on 90% acceptance or 10% dissatisfied occupants. Thus, the upper limit for operative temperature in summer is 26°C, given 50% relative humidity, sedentary activity, 0.5 clo and a mean air velocity of less than 0.15 m/s. Based on the PMV index, the PPD index can be calculated. The PPD index predicts the percentage of the occupants who will judge their thermal comfort unsatisfactory (corresponding to a vote below –2 or above +2). PPD as a function of PMV is shown in Figure 2.7:

Figure 2.7

PPD as a function of PMV (Source: Low energy Building Design, Pedersen, (2001)).

Andresen (2000) claims that “the PMV model is interpreted as a constant set-point for a given clothing, metabolic rate and air velocity. It does not consider any effects due to adaptation, cultural differences, 39

Single and Double Skin Glazed Office Buildings

climate and seasons, age, sex or psychosocial attributes”. According to the author, “recent research casts doubt upon the application of steady-state heat exchange equations to what in practice is a variable environment (Clements-Croome, 1997). People are not passive recipients of the environment, but take adaptive measures to secure thermal comfort. They may modify their clothing or activity, modify the lighting or solar heat gains, or modify the ventilation rate through opening of doors and windows. This suggests that a more “adaptable” method of comfort judgment is needed”. Other parameters such as state of health, level of physical activity, gender, working environment and individual preferences can also influence the perception of thermal comfort. Although the secondary factors of thermal comfort, apart from asymmetric thermal radiation (directed operative temperature), are not studied in the present thesis, a brief description follows. Secondary Factors

Nonuniformity of the environment

Age

Gender

Adaptation

Seasonal and Circadian Rhythms

Asymmetric thermal radiation Draught

Vertical air temperature difference

Warm and cold floors

Figure 2.8

Secondary factors of thermal comfort.

As shown in Figure 2.8, the secondary parameters that influence the thermal environment are as follows

40

Background

• Non-uniformity of the environment The non-uniform conditions that lead to local discomfort are probably the most important of the above secondary factors. According to ASHRAE Fundamentals (2001), “a person may feel thermally neutral as a whole but still feel uncomfortable if one or more parts of the body are too warm or too cold”. A number of reasons can lead to a non-uniform environment. Some of these are: o o o o

a cold window a hot surface draught a temporal variation of these

In buildings, asymmetric or non-uniform thermal radiation can be caused usually by poor and large windows, non-insulated walls, or improperly sized heating panels on the wall or ceiling, etc. In office buildings the most common reasons for discomfort due to asymmetric thermal radiation or draught are large and/or poor windows (during the heating and cooling periods) and improperly sized, installed or operated ceiling cooling systems. Draught is an undesired local cooling of the human body caused by air movement. ASHRAE Fundamentals (2001) describe draught as one of the most annoying factors in offices. Draught makes the occupants demand higher air temperatures in the room or stop the ventilation systems. This can often lead to temperatures above the comfort levels. Vertical air temperature difference: In most of the offices (or generally spaces in buildings) the air temperature is not completely uniform but increases with height above the floor. When the gradient is sufficiently large, local warm or cold discomfort can occur at the head and/or the feet, although the body as a whole is thermally neutral. Warm and cold floors: According to ASHRAE Fundamentals (2001), “due to the direct contact between the feet and the floor, local discomfort of the feet can often be caused by a too-high or too-low floor temperature. Also, the floor temperature has a significant influence on the mean radiant temperature in a room”. Often, when the floor is too cold, the occupants feel cold discomfort in their feet and as a result they increase the temperature level in the room. During the heating period, this can be a reason for the increase in energy use. A radiant system, which radiates heat from the floor, can solve this problem. A diagram of how the PPD increases due to the cold/warm ceiling and walls is shown in Figure 2.9:

41

Single and Double Skin Glazed Office Buildings

Figure 2.9

Influence of ceiling and wall temperature on the PPD (ASHRAE Fundamentals, 2001)

• Age Since metabolism decreases with age, young and old people do not always have the same preferences when it comes to thermal comfort. Often older people prefer higher ambient temperatures. However, previous research showed that sometimes the thermal environment in an office can satisfy both ages. The need for higher ambient temperature for older people in their homes can be explained by the lower level of activity. • Gender Both men and women can be satisfied with the same thermal conditions. In ASHRAE Fundamentals (2001) it is mentioned that the temperature of women’s skin and evaporative loss are slightly lower than those of men and this balances the lower metabolism of women. Experiments proved that people can not adapt to preferring warmer or colder climates. According to ASHRAE Fundamentals (2001) “it is therefore likely that the same comfort conditions can be applied throughout the world. However in determining the preferred ambient temperature from the comfort equations, a clo value that corresponds to the local clothing habits should be used”. Thus, adaptation does not really influence 42

Background

the preference of the occupants regarding the ambient temperature. However, people used to living or working in warm climates can more easily stand higher temperatures while maintaining the same levels of performance than people from colder climates. • Seasonal and circadian rhythms According to ASHRAE Fundamentals (2001) there is no difference between indoor thermal conditions of comfort during the winter and the summer. However, the preference of an occupant for thermal comfort may change during the day since the body has a lower temperature rhythm during the early morning hours and a higher one late in the afternoon.

2.3.2.3 Thermal comfort and productivity Although a lot of attempts have been made to correlate productivity with indoor climate factors, no detailed studies have been made so far that can predict accurately the interaction between these two parameters. The occupants’ efficiency is a really complicated matter, since many different parameters can influence it separately and together at the same time. Wyon (2000a) describes how discomfort conditions lead to reduced productivity. The author claims that a change from 18ºC and dry to 28ºC and humid can increase the proportion of dissatisfied from 10 to 90%. Additionally, the thermal effect is greater for clean air than for normally polluted indoor air. According to the IDA ICE 3.0 manual, Wyon (2000b), for operative temperature between 20 and 25°C no work is regarded as lost. Above and below these limits experiments show an average loss of 2% in performance per degree. Hanssen (2000) claims, that the ambient temperature can give the most specific correlation between indoor climate parameters and productivity. The author, referring to previous research by Wyon (1987), describes the correlation between air temperature and the number of accidents, productivity of manual work, finger dexterity, number of breaks and mental performance. The (lower and higher) x-axes (Figure 2.10) show the activity level and the clothing (summer and winter case) insulation of the occupants. The x-axis in the middle of the diagram can be applied both for active work (1.4 met) during the summer (0.6 clo) and for sedentary work (1 met) during the winter (1 clo). As the author describes, “For an office workplace it may be especially appropriate to examine the effect of air temperature on mental performance and manual work”. 43

Single and Double Skin Glazed Office Buildings

Figure 2.10

Correlation between air temperature and the number of accidents, productivity of manual work, finger dexterity, number of breaks, and mental performance (reference: Wyon, 1986).

It is obvious that it is not always easy to evaluate and improve the thermal conditions in order to increase the comfort and productivity of the occupants. Advanced computer simulation programs often predict • operative temperatures • temperature swings • relative humidity and air velocity in a building with “predictable” occupants. However, the behaviour and adaptability of occupants in reality are far harder to predict. A quite practical approach in order to ensure acceptable indoor thermal environment could be to ensure that the air temperature and the “cold draught” from windows stay within acceptable limits.

44

Background

2.3.2.4 Other indoor climate parameters that influence the occupants’ health and productivity • Indoor air quality According to Nathanson (1995) the quality of the indoor environment depends on the interaction between the site and the o climate o building system o potential contaminant sources (e.g. furnishings, moisture sources, work processes and activities, outdoor pollutants, etc) o building’s occupants The HVAC system is designed to provide thermal comfort, distribute outdoor air to the occupants, remove odours and contaminants, or dilute them to acceptable levels. The influence of the indoor environment on the comfort and health of the occupants has been the focus of research for many years. However, according to Hanssen (2000) there is relatively little research examining the total effect of indoor air quality on human wellbeing, employee performance and productivity at work. • Visual comfort When designing an office building attention should be paid to the visual comfort of the occupants. Although electricity savings through daylight utilisation may not be so impressive (compared for example with those for heating or cooling), correct distribution of light may create a more pleasant indoor environment and thus improve the mood and productivity of the occupants. In “Sustainable Building Technical Manual” (Public Technology Inc and US Green Building Council, 1996), it is pointed out that “daylighting creates healthier and more stimulating work environments than artificial lighting systems and can increase the productivity up to 15%. Daylighting provides also changes in light intensity colour and views that help support worker productivity”. Surveys mention that 90% of the occupants prefer to work close to the window, having a view to the outside. The comfortable visual environment depends on vision, perception and what we want to see in different room configurations and for different activities. The absence of sensation of physiological pain, irritation or distraction is the main aim, when the visual properties of an indoor environment are optimized. Christoffersen (1995) writes in his PhD 45

Single and Double Skin Glazed Office Buildings

thesis that “visual perception is an active, information-seeking process, partly conscious and partly unconscious, involving many mechanisms in a cognitive process interpreted by the eye and the brain”. When the shape and position of windows for an office building are designed, attention should be paid to the provision of visual comfort for the occupants, without forgetting the importance of solar shading to avoid overheating. The visual function parameters which determine good visibility and pleasant indoor environments are the: o o o o

illuminance, luminance (level and ratios) and daylight factor distribution - Uniformity of light across a surface glare direction

2.3.3

Architectural quality

The architectural design (essential for achieving architectural quality) of an office building has great impact on both energy use during the occupation stage and provision of comfort for the occupants. The building’s shape and location, the façade’s orientation and the integration of passive or active solar systems are some of the parameters that influence the performance of the building in terms of energy use. On the other hand the occupants’ perception of indoor environment is closely related to their sociological needs, psychological state, and individual differences influencing directly their comfort and productivity (Poirazis, 2005a). Thus, it is clear that many parameters have to be examined at the early design stage in order to succeed architectural quality (i.e. energy efficient design and attractive working environment). In order to achieve an energy efficient design, different parameters have to be considered and combined carefully. The location and orientation of the building, the area of the building’s skin in relation to the volume of space enclosed, the type of façade (proportion of glazing, structure, etc) are crucial for the building’s performance. In highly glazed office buildings, the building’s skin is obviously more sensitive to the outdoor environment. High solar gains during the summer may lead to overheating problems during the summer, increasing the energy demand for cooling. Furthermore, the greater the area of building skin in relation to the volume of space enclosed, the more the building is influenced by heat exchanges at the skin. Thus, it is a general rule that a square floor plan is thermally more efficient than a rectangular one because it contains less surface area over which to lose or gain heat. On the other hand, this building form is less efficient in terms of daylighting and passive solar heating and cooling. 46

Background

The shape and orientation of the building have also great impact upon wind driven air infiltration through the envelope. Obviously more parameters than an acceptable thermal and visual environment should be considered in order to achieve an attractive working atmosphere. Parameters related with the perception of indoor environment (such as privacy, interaction levels, territoriality and crowding) may have a great impact on the occupants responses regarding mainly sociological, psychological (such as visual and acoustic privacy and aesthetic) and physiological determinants. A more detailed description is provided by the “Design Guide for Interiors”, (U.S. Army Corps of Engineers, 1997).

2.3.4

Environmental performance

Another quality requirement that should be taken into account in a holistic approach of a building design is the environmental performance. The impacts of buildings on the environment are diverse. Not only during the construction stage, but also during the occupation and demolition stage, the building interacts with the environment in different ways. As a physical structure, the building is composed of different elements. These elements are extracted, manufactured, assembled, maintained, demolished and finally disposed of. The total environmental impact of the materials used is the sum of the impacts caused in each of the above stages. As a “living part” the building has inputs (energy use, services) and outputs (CO2 emission, wastes, etc). The environmental performance of a building depends (a) the construction (sum of the performance during the manufacturing stage of the materials, the transportation stage and the erection of the building), (b) occupation/maintenance stage (according to Adalberth (2000) for modern apartment buildings the 70-90% of the total energy use (during the life cycle) is used during the occupation stage) and (c) the refurbishment and demolition stage of an office building (obviously less important than the ones described above). The study of a whole life cycle of a product or a process (in this case a building) from the extraction of raw materials to the disposal or reconstruction is called Life Cycle Analysis (LCA). At this point, it is necessary to set out the advantages and disadvantages of this method and to make clear the importance of its use during the design stage of a building. The main benefit of the LCA is that it provides information on the environmental performance of different building concepts in a really accessible format. On the other hand, the lack of consistent and peer reviewed international level databases of Life Cycle Inventories of building related products is one of the main problems which limits the use of 47

Single and Double Skin Glazed Office Buildings

LCA. However, an LCA limited to the period from construction until deconstruction is feasible. The holistic approach during the design stage of a building involves variables that often interact with each other. Impacts on the surrounding environment, energy needed for the construction and maintenance of the building, use of recycled building components and integration of solar technologies that improve the environmental profile of the building are some of the factors that define the environmental performance of the building. The main reason for using an LCA is to insert it as part of the decision making process in order to optimize the efficiency of the system over the life span of the building. Since a lot of parameters are involved, the complexity increases and the goals should be prioritized from the early design stage in order to make the process more clear.

2.3.5

Costs

In the existing literature three ways of calculating the cost of a building are given. • Investment costs: consideration of the investment cost only • Life cycle costs: Cost over the whole life of a building • Total economic value: It goes further than life cycle costing, since it also includes more “hidden” building related costs or profits such as the productivity of the workers in the building. According to Fuller and Petersen (1996) energy conservation projects provide excellent examples for the application of LCCA. On the other hand, the total economic value is time restrictive, since it often involves very detailed calculations that require detailed input. For the ongoing “Glazed Office Buildings” project the Life Cycle Cost (LCC) has been calculated (Sjödin, 2007). The productivity of the occupants (such as lost working hours) is also calculated in a simple way taking into account thermal comfort criteria (Poirazis, 2005b). The reason for the decision to calculate the LCC is that calculation of only the investment costs for the suggested alternatives does not provide information on the energy, environmental and maintenance costs, which is crucial when it comes to energy efficient office buildings. The integration of solar technologies with alternative heating, ventilating, and air conditioning (HVAC) systems and strategies can provide a wide variety of models (some of which are considerably more energy efficient than others), interesting to study in a life time prospective. 48

Background

2.4

Building technology

At an early stage the “building technology” should be involved in the building design process (Figure 2.1) with the aim of improving the building’s performance. By integrating new technologies into the building process, the complexity of the system increases. In these cases the implications should be considered and the evaluation process should start from the beginning, considering the problem as new. As an example, in order to clarify the foregoing, a solution regarding thermal comfort problems of highly glazed buildings can also be provided by proper integration of double skin façade systems (integration of passive systems). In this way the provision of a more uniform thermal environment can be achieved (performance requirement), by controlling the cavity temperatures to avoid cold walls and temperature asymmetries. From the above it is clear that the interactions between the constituents (performance and quality requirements) of the building environment and the implications of building technology are a complicated and delicate matter. Prioritizing the main goals and the quality requirements to be fulfilled, deciding about the trade off values and creating a common understanding between the different sides of the design team is the first step to an improved building performance. The complexity of the system requires continuous focus on the main goals to be achieved without in any case compromising the performance requirements. The higher risk of facing unexpected problems, when newer and more complicated technologies are integrated, should be considered and a gradual integration process should be adapted.

2.4.1

Glass in buildings

2.4.1.1 General The main function of architectural glass is to transmit daylight. Increased glazing areas that admit daylight were achieved at the beginning of the nineteenth century, when the development of framed building structures, suspending the heavy load bearing wall, liberated the window area (Button and Pye, 1993). Glass and the steel skeleton came together as key elements in the modern architectural movement, in order to increase natural daylight, transparency, health and social well-being. For the last two centuries glass has had its own material developments, which brought new aesthetic qualities to architecture. The method of suspending glass assemblies as a curtain of glass leads to the full liberation of glass from the building structure. This liberation, however, was followed by numerous 49

Single and Double Skin Glazed Office Buildings

performance demands of the building skin. According to Button and Pye (1993) today, the building structure is no longer of primary architectural importance; of equal design consideration and equal financing investment are heating, lighting and air conditioning services. During the last decades there has been much research on variable transmission glass and new technologies in photochromic, thermochromic and electrochromic panes. This research is driven by the desire for energy savings and improved occupant comfort. The development of coated and body tinted glass aims to cover needs for appearance, view (in and out), daylight, passive solar gains, solar control and thermal insulation; laminated glass provides durability, fire resistance, safety and explosion and bullet impact protection.

2.4.1.2 Basic physics of the glass Radiation Electromagnetic radiation is the principal energy source, which provides both heat and light. The complete electromagnetic spectrum is delineated in Figure 2.11. The intermediate part of the spectrum, which extends from a wavelength of approximately 0.1 to 100 µm and includes part of the UV and all of the visible and infrared (IR) is considered as thermal radiation and is related to heat transfer. Thermal Visible

Infrared

X rays

Ultraviolet

Microwave

Gamma rays

10

-5

10

Figure 2.11

-4

10

-3

10

-2

10

-1

1

10

10

2

10

3

10

4

Spectrum of electromagnetic radiation.

All bodies emit and absorb energy in the form of electromagnetic radiation. The thermal radiation emitted by a surface varies for different wavelengths. The term “spectral” is used in order to refer to the nature of this dependence. The spectral distribution depends on the nature and temperature of the emitting surface. To properly quantify radiation heat transfer, we must be able to treat both spectral and directional effects. 50

Background

Surface absorption, reflection and transmission When the irradiation interacts with a semitransparent object (such as glass), portions of this radiation may be reflected, absorbed or transmitted, as shown in Figure 2.12. From a radiation balance of a medium, it follows that: Gλ= Gλ,ref+ Gλ,abs+ Gλ,tr

Reflection (Gλ, ref)

Irradiation (Gλ)

Absorption (Gλ,abs)

Transmission (Gλ, tr)

Figure 2.12

Reflection, absorption and transmission of solar radiation in glass.

Reflectance occurs when the surface of a material reflects an incident beam of light and it expresses the fraction of incident radiation reflected by the glass. Reflection can be specular, diffuse or a mixture of the two. Specular reflection (a)

If a material surface is microscopically smooth and flat, such as float glass, the incident and reflected light rays make the same angle with a normal one to the reflecting surface, producing specular reflection. Diffuse reflection (b)

If a material has a rough surface, that is if it is not microscopically smooth, diffuse reflections will occur. Each ray of light falling on a small particle of the surface will obey the basic law of reflection but, because these particles are randomly oriented, the reflections will be randomly distributed. A perfect diffusely reflecting surface would in practice reflect light equally in all directions, giving a perfect matt finish.

51

Single and Double Skin Glazed Office Buildings

θ θ

a

Figure 2.13

b

Specular and diffuse reflection.

Absorptance expresses the fraction of incident radiation absorbed. In other words, absorptance is that part of the incident light which is lost in the body of the glass, increasing its temperature. Transmittance expresses the fraction of incident radiation directly transmitted through the glass. Transmittance is that part of the incident light remaining after reflection and absorption. Transmitted light is subject to modification by refraction, diffusion and colouring.

2.4.1.3. Thermal functions of the glass Glass and thermal comfort Windows influence occupant comfort by: • heat gain or heat loss through the glass, which either raises or lowers the room air temperature. • radiation exchange between the glass and occupant. • increased convection close to window, thus increased cold down draught during winter. The glass surface temperature influences the thermal comfort of an occupant close to the window, due to the heat loss produced by long wave radiation exchange between the occupant and the window. During winter, the glass temperature is often lower than the other room surfaces, producing a loss of heat from the occupant’s body surface by long wave radiation and contribution to cold discomfort. During summer, the glass temperature can be higher than that of the other surfaces. The long wave radiation in combination with any shortwave solar radiation received through the

52

Background

glass is absorbed by the occupant and contributes to a sensation of hot discomfort. Heat loss Heat loss is quantified through the U value (thermal transmittance) measured in W/m2K. Thermal transmittance is the rate of loss of heat per square metre under steady state conditions for a temperature difference of one degree (Kelvin or Celsius) between the inner and outer environments separated by the glazing. Heat loss can be also quantified by the thermal resistance (R=1/U). According to Button and Pye (1993) there are three stages of heat loss through glass products: • between the internal glass surface and the room surfaces • through the glass product • between the outdoor environment and the outer glass surface Heat loss to the internal glass surface: Heat is lost to the internal glass surface from the room, whenever the glass surface is at a lower temperature than the internal air temperature and the room surface temperature, through: • exchange of long wave radiation between the glass surface and the room surfaces. • convection/conduction from the room air moving over the surface of the glass. Usually, the heat loss by radiation exchange is the greater heat loss (unless the glass surface has a low emissivity coating). Heat loss through the glass product: Generally, glass is a very poor insulating material. However, due to technological developments there are a number of ways to decrease heat loss through glazing as described in Subsection 2.4.2.1. Heat loss from the outer glass surface: The final stage of heat loss is from the outer glass surface. As with the inner glass surface, heat transfer occurs by long wave radiation exchange and by convection-conduction. The balance and magnitude of heat transfer depend on the temperature of the surrounding outside surfaces and the sky temperatures. With clear skies, sky temperatures can be extremely low; this effect is demonstrated by the formation of dew and frost on surfaces exposed to clear skies due to their cooling below ambient air temperature. 53

Single and Double Skin Glazed Office Buildings

2.4.2

Single skin façades

Nowadays, there is a growing interest in using highly glazed facades in commercial buildings. The trend of covering large portions of the façade or even the entire façade by glass has its origin in Europe and is expanding to other regions. As with many other architectural trends, understanding and improving the building performance of highly glazed buildings is very important. Prior simulation studies have shown that it should be technically possible to produce an allglass façade with sufficient energy and indoor climate performance although it is not a simple challenge (Lee, et al., 2002). This Subsection gives a brief background to the problems often met and the solutions given, in order to improve the building’s performance. When glazed façades are designed, several devices are often implemented, in order to keep the heat losses low and to avoid undesired heat gains through solar radiation (during summer). According to Compagno (2002) the two main criteria when designing a fully glazed façade are the number of glazing skins incorporated in the design (single or multiple skin façades) and the positioning of shading devices.

2.4.2.1 Glazing In energy efficient design the proper selection of glazing elements is probably the most complex task. Glazing and window design are two areas in which great technical developments have occurred over the last years. In order to achieve good window design, it is essential to find the balance between demands which are often conflicting such as passive heating and cooling functions, e.g. allow solar gains but avoid excessive solar heat, provide sufficient daylight without causing glare, allow controllable ventilation into the building but keep out the noise, allow visual contact with the surroundings but ensure acceptable privacy levels (A Green Vitruvious, 1999). This Subchapter focuses on the thermal insulation that glazing can provide and suggests a number of ways to decrease heat loss through it. Single glazing provides relatively little resistance to loss of heat, since the glass is a poor insulator. To decrease the thermal transmittance, a second pane of glass separated from the first pane by an air space can be added. This layer of enclosed air provides extra thermal resistance to long wave radiation exchange. The incorporation of an air space provides several opportunities for increasing the thermal resistance of glazing: • increasing the width of the air space: by increasing the width of the air space, extra resistance is provided. There is a limit due to convec54

Background

tion within the air space, which occurs at about 15mm width, after which little extra thermal benefit is obtained. Adding a third pane of glass to give a second air space provides further improvement. • Incorporating low emissivity coatings: The use of a low emissivity (low E) coating on the glass makes it possible to reduce the long wave radiation exchange between the panes. The higher insulating effect (lower U value) provided by a Low E coating in a double glazed unit is due to the high reflectance of long wavelength radiation. In cold climates the higher temperature of the inner glass surface of double glazed units using Low E coating diminishes the effect of long wave radiation, which causes discomfort near the window. • Using gases of lower conductivity: Sealed Low E double glazed units may contain gases with lower thermal conductivity than air such as argon, providing further decrease in U value. • Evacuating the air space: the air space may be fully or partially evacuated. The properties of glass, such as solar shading and emissivity influence the transmission through the glass (Carlsson, 2005). Drastic changes can be obtained by applying a coating on the glass. Coatings can influence the range of transmitted radiation and its absolute level. The coatings can be reflective and selective. Efficient solar shading can be obtained by reflective coatings. Increased reflection results in reduced total transmission. Currently, the total solar energy transmittance (g value) for a sealed double glazed unit can be varied between 0.2 and 0.7 with a daylight transmittance between 0.3 and 0.8 W/m2K. Lower U values can be obtained with coatings of low emissivity. The emissivity can be reduced from 0.87 to 0.04. The infrared radiation can be reduced to 20 %, without lowering daylight transmittance below 0.75. This type of coating is selective, as it allows transmittance of the main part of daylight, but has a high reflectivity of the infrared radiation. Currently the U value (middle of the glass) for a sealed double glazed unit can be varied between 2.8 and 1.1 W/m2K. In modern office buildings sealed double glazed units are preferably used, often with a reflective coating.

2.4.2.2 Shading devices In order to achieve a certain level of solar transmittance through the single skin façade, solar control glass is often used. However, since the properties of this glass are fixed, they restrict useful solar gains during cold months and they can reduce daylight levels. Thus, by providing additional adjust55

Single and Double Skin Glazed Office Buildings

able shading devices the building performance can be further improved. Some of these devices are: • exterior shading devices: The main advantage of these devices is that the heat resulting from the radiation from the device itself remains out of the building, keeping the cooling load levels lower during summer months. The main disadvantage, however, is that they are exposed to the effects of weather, often resulting in high maintenance and cleaning costs. If the exterior shading is movable, then the low solar transmittance effect could be limited to the summer months, when cooling is needed; if they are fixed, they have similar effect as the solar control glass. • interior shading devices: This type of shading device is less effective, since the radiation absorbed by the devices stays in the room raising the cooling demand. However, the cleaning and maintenance of these devices is much simpler than with exterior ones. Additionally, internal shading can provide the “clean façade” look, which is quite often required by architects. • intermediate shading devices: Shading devices placed in between the panes of glass are less common in office buildings. Costs associated with cleaning are lower than with the exterior ones but maintenance may be more expensive, mostly when the electric motors are also incorporated inside the cavity (Compagno, 2002). The increase in temperature between the panes due to absorption by the shading should be considered in order to avoid cracking of the glass due to the dramatic temperature increase. A comprehensive study of several aspects related to solar shading devices has been carried out within the “Solar Shading” project at the Division of Energy and Building Design, Department of Architecture and Built Environment, Lund University. The project included the following tasks: • determination of the primary and total solar energy transmittance (g value) of shading devices through measurements; • development of an advanced computer program (Derob-LTH) and a user-friendly design tool (ParaSol) to predict the impact of shading devices on energy use in buildings; • parametric studies as a basis for the development of design guidelines aimed at architects, engineers and consultants; • measurement of the daylight transmittance and interior illuminance/luminance conditions in rooms equipped with shading devices. 56

Background

2.4.3

Double skin façades

2.4.3.1 General The double skin façade is a system consisting of two glass skins (single or double) placed in such a way that air flows in the intermediate cavity. The distance between the skins usually varies from 0.2 m up to 2 m. For protection and heat extraction reasons the solar shading devices are placed inside the cavity. The ventilation of the cavity can be natural, fan supported or mechanical; the origin and destination of the air can also vary depending on the location, the use and HVAC strategy of the building. The advantages of double skin façades compared with single skin facades are improved acoustic insulation, protection of shading devices and provision of natural ventilation in the office spaces. However, energy reduction and provision of an improved indoor thermal environment can also be achieved, when these are designed and integrated properly. Due to the additional skin, a thermal buffer zone is formed which reduces the heat losses and enables passive solar gains. During the heating period, the solar preheated air can be introduced inside the building providing natural ventilation with a good indoor climate retained. On the other hand, during the summer overheating problems are often referred to when the façade is poorly ventilated (Poirazis, 2004). Different configurations can result in different ways of using the façade, proving the flexibility of the system and its adaptability to different climates and locations. A detailed description of this system can be found in the Literature review for “Double skin façades for office buildings” by Poirazis (2004).

2.4.3.2 Classification of double skin façades The most common way to categorize the system is according to the type (geometry) of the cavity, as described below. • Multi storey: In this case no horizontal or vertical partitioning exists between the two skins. The air cavity ventilation is provided via large openings at the bottom and top of the cavity. • Corridor: The cavity is partitioned horizontally for acoustical, fire security or ventilation reasons. • Box window: In this case horizontal and vertical partitioning divides the façade into smaller and independent boxes. • Shaft box: In this case a set of box window elements are placed in the façade. These elements are connected via vertical shafts situated in the façade. These shafts ensure an increased stack effect. 57

Single and Double Skin Glazed Office Buildings

2.4.3.3 Technical description of the cavity The most common types of glass panes used for double skin façades are described below. The internal skin is often a thermal insulating double glazed unit (when the air enters the cavity from outdoors). The panes are usually toughened or unhardened float glass. The gaps between the panes are filled with air, argon or krypton. The external skin is often a toughened (tempered) single pane of glass. Sometimes it can be a laminated glass instead. Lee et al. (2002) claim that the most common exterior layer is a heatstrengthened safety glass or laminated safety glass. The second interior façade layer consists of fixed or operable, double or single pane, casement or hopper windows. Low emittance coatings on the interior glass façade reduce radiative heat gains to the interior. Oesterle et al. (2001) suggest that for a higher degree of transparency, flint glass (glass with high refraction and low dispersion) can be used as the exterior layer. Since the number of layers and the thickness of the panes are greater than in single skin construction, it is really important to maintain a “clear” façade, if transparency is the goal. The main disadvantage in this case is the higher construction costs, since flint glass is more expensive than the normal glass. The shading devices are usually horizontal louvres placed inside the cavity for protection. In the existing literature, there is no extended description concerning the material and the geometry of the shading devices used for double skin facades. However, it is mentioned that in large scale projects it is useful to investigate the material and positioning of the glass and shading devices inside the cavity. It is also worth considering proper combination of these two elements in order to succeed in attaining the desired indoor operative temperatures.

2.4.3.4 Advantages and disadvantages of double skin façades The advantages and disadvantages outlined in the existing literature of the double skin façade system are briefly described below: • Advantages Lower construction cost compared with solutions that can be provided by the use of electrochromic, thermochromic or photochromic glass (the properties of which change according to climatic or environmental conditions). 58

Background

Acoustic insulation: In the view of some authors sound insulation can be one of the most important reasons to use a double skin façade. Reduced internal noise levels inside an office building can be achieved by reducing both the transmission from room to room (internal noise pollution) and the transmission from outdoor sources i.e. heavy traffic (external noise pollution). The type of double skin façade and the number of openings can be really critical for sound insulation concerning the internal and the external noise pollution. Thermal insulation: During the winter, the external additional skin provides improved insulation by increasing the external heat transfer resistance. The reduced air flow and the increased temperature of the air inside the cavity lower the heat transfer rate on the surface of the glass, which leads to reduction of heat losses. During the summer, the warm air inside the cavity can be extracted by mechanical, fan supported or natural ventilation. Certain façade types can cause overheating problems. However, a completely openable outer layer can solve the overheating problem during the summer months, but will certainly increase the construction cost. Night time ventilation: During the hot summer days, when the external temperature is higher than 26˚C, the interior spaces may easily become overheated. In this case, it may be energy saving to pre-cool the offices during the night using natural ventilation. In this case, the indoor temperatures will be lower during the early morning hours, providing thermal comfort and improved air quality for the occupants. Energy savings and reduced environmental impacts: In principle, double skin façades can save energy when properly designed. Often, when the conventional insulation of the exterior wall is poor, the savings that can be obtained with the additional skin may seem impressive. Better protection of the shading or lighting devices: Since the shading or lighting devices are placed inside the intermediate cavity of the double skin façades, they are protected from both the wind and rain. Reduction of the wind pressure effects: The double skin façades around high rise buildings can serve to reduce the effects of wind pressure. Transparency – Architectural design: In almost all the literature, reference is made to the desire of architects to use bigger proportions of glazed surfaces.

59

Single and Double Skin Glazed Office Buildings

Natural ventilation: One of the main advantages of the double skin façade systems is that they can allow natural (or fan supported) ventilation. Different types can be applied in different climates, orientations, locations and building types in order to provide fresh air before and during the working hours. The selection of double skin façade type can be crucial for temperatures, air velocity, and the quality of the introduced air inside the building. If designed well, the natural ventilation can lead to a reduction in energy use during the occupation stage and improve the comfort of the occupants. Thermal comfort – temperatures of the internal wall: Since the air inside the double skin façade cavity is warmer than the outdoor air during the heating period, the interior part of the façade can maintain temperatures that are closer to the thermal comfort levels (compared with single skin facades). On the other hand, during the summer it is really important that the system is well designed, so efficient heat extraction ensures that the temperatures inside the cavity do not increase dramatically, leading to high oprative temperatures. Fire escape: Claessens and De Hedre mention that the glazed space of a double skin façade may be used as a fire escape. • Disadvantages Higher construction costs compared with a conventional façade. For example, the additional skin increases the weight of the construction, which increases the cost. Additional maintenance and operating costs: When the double skin and the single skin type of façade are compared, it is easily seen that the double skin type has higher cost regarding construction, cleaning, operating, inspection, servicing, and maintenance. Fire protection: It is not yet very clear whether or not the double skin façades can be positive regarding the fire protection of a building. However, some authors refer to possible problems caused by the room to room transmission of smoke in case of fire. Reduction of rentable office space: The width of the intermediate cavity of a double skin façade can vary from 20 cm to several metres. This results in the loss of useful space. Often the width of the cavity influences the properties inside it (i.e. the deeper the cavity, the less heat is transmitted by convection when the cavity is closed) and sometimes the deeper the cavity, the greater the improvement in thermal comfort conditions next to the 60

Background

external walls. Thus, it is quite important to find the optimum depth of the façade, to be narrow enough so as not to lose space, and deep enough so as to make it possible to use the space close to the façade. Overheating problems: If the double skin façade system is not properly designed, the temperature of the air in the cavity may increase, overheating the interior space. Increased air flow velocity inside the cavity, mostly in multi storey types. The possibility of important pressure differences between offices is mentioned in the case of natural ventilation via the cavity. Daylight: The double skin façades are similar to other types of glazed facades (i.e. single skin façade). However, Oesterle et al., (2001) describe that double façades reduce the quantity of light entering the rooms as a result of the additional external skin. Acoustic insulation: It is possible that sound transmission problems (room to room or floor to floor) may arise if the façade is not designed properly.

61

Single and Double Skin Glazed Office Buildings

62

State of the art

3

State of the art

3.1

Glazed office buildings in Nordic climates

Subchapter 3.1 is based on personal communication with Åke Blomsterberg at the Division of Energy and Building design, Department of Architecture and Built Environment, Lund University.

3.1.1

General

The office buildings as known today are likely to retain their validity in the foreseeable future. Although there has been, and still is, a dramatic development of the infrastructure for communications (mobile phones, laptops, e-mails, etc.), the change in office practice is far less dramatic (Kleibrink, 2002). Nowadays, the exchange of information between and within organizations is very often achieved by e-mail and the activities are increasingly dominated by discussions and flow of information at all levels. High interaction levels may however lead to reduced occupant productivity, due to acoustic disturbance. The increase in teamwork and communication, however, can lead to activities and persons disturbing each other, especially if the spatial organisation is not appropriate. The plan of an office environment establishes the privacy (both acoustic and visual) level at which the office functions. Therefore, it is still necessary to perform concentrated individual work in undisturbed surroundings. Modern office work is characterized by quick changes between these two types of activity, so the challenge today is to provide for a combination of individual work and teamwork, while also providing for flexibility for unforeseen developments. Moreover, in new constructions the conventional envelope of office buildings tends to be replaced by a highly glazed one that can lead to a pleasant visual indoor environment. The recent trend of transparent buildings is often initiated by architects, in order to provide more daylight and view to the occupants. Depending on the task of the occupants this can increase their productivity (as stated in the Sustainable Building 63

Single and Double Skin Glazed Office Buildings

Technical Manual in 1996, productivity can increase by up to 15% when daylight is provided instead of artificial lighting). In some cases, however, the occupants can often feel distracted or even annoyed when they can be seen from outside.

3.1.2

Layout of typical office buildings

There are at least four different concepts of office layout: • • • •

unit or cell-type office open-plan and group office combination office the so-called “business club”

The cell-type office is the most traditional form, where single or double rooms are located along artificially lighted corridors. A single person office is very good for concentrated work, but does not promote informal communication between colleagues. Typical sizes for a single room are: width 1.35 m by depth 4.20 m, width 2.7 m by 4.20 m, width 3 m by depth 3.6 m or width 3 m by depth 5 m. The corridor can be 2 m wide. The open-plan and group office with hundreds of persons working was designed to encourage communication. Often, many of these offices have after some time been divided by head height cupboards and plants into almost cell-type offices. What some people perceive as a disadvantage is the lack of individual control of indoor climate and lighting. For routine processing work requiring a high degree of informal communication this type of office can be preferable. The combination office, developed in Scandinavia at the end of the seventies, combines the advantages of the cell-type offices and open-plan offices, while avoiding the disadvantages. The workplaces are located in cell-type spaces along the façade and are separated from the indirectly lit internal zones by room high glazed walls. Every workplace has access to discussion areas, direct visual contact with the outside world and the means to control the climate individually. The common space in the middle serves a number of employees and offers communal services like meeting areas, copiers, printers, facilities for coffee breaks. The glazed wall provides sound attenuation for the workplaces, while allowing visual contact with colleagues. The size of the individual workplaces/rooms is similar to the cell-type ones mentioned above. The common space can be 4.8 m deep. An office should meet the following four criteria: • Flexibility: workplaces should be standardized, but should also be adaptable to individual needs. 64

State of the art

• Functional efficiency: the working space should meet physiological requirements, ergonomic standards and statutory requirements, in order to support optimal working conditions. • Contact quality: the working spaces should contribute to the transparency of the activities, carried out in the office and encourage communication and synergetic effects between employees and departments • Corporate culture: the message conveyed by the working spaces should promote the employees’ identification with the company and its products and communicate company values internally and externally. Typical depths for office buildings are • 12 to 13 metres for a cell-type office • 13. 5 to 15.5 metres for a combination office

3.1.3

Office buildings in Sweden

Office buildings account for a significant proportion of the floor area in non-industrial buildings in Sweden. The total floor area in office buildings is approximately 30 million m2 (usable area to let) (SCB, 2001). The completed floor area is almost evenly distributed over the decades, but with less construction during the last decade (as shown in Table 3.1). Floor area, millions m2, broken down by year of completion (SCB, 2001).

Table 3.1

Year Floor area

…-1940 1941-1960 1961-1970 7,1

4,6

4,9

1971-1980 1981-1991 1991-… 5,4

5,4

2,8

Sum 30,2

Most (65%) of the existing office buildings are rather small, between 200 and 1000 m2. Many office buildings are between 1000 and 5000 m2 and some are bigger than 20 000 m2 (see Table 3.2).

Table 3.2

Number of office buildings within a certain range of floor area, m2 (SCB, 2001).

Floor area (m2)

200-999 1000-4999 5000-19999 20000-… Sum

Number of buildings

11 505

4 719

1 415

170

17 809

65

Single and Double Skin Glazed Office Buildings

Most office buildings are equipped with a heating system. However, mechanical cooling systems are also becoming rather common in office buildings. Most of the buildings are equipped with a mechanical ventilation system, usually a system with mechanical supply and exhaust air. The newer ones often have heat recovery on the ventilation. The energy source for heating office buildings can be oil furnace, district heating, electricity, local district heating, gas or biomass. The most common source is district heating (71%), as shown in Table 3.3.

Table 3.3

Area of office buildings by type of heating (SCB, 2001). Oil District Electric Local furnace heating district heating

Heated area 2,4 million, m2 Heated 7 area, %

3.1.4

Gas

Oil + el Biomass Other Sum

23,4

2

0,2

0,6

0,4

0

4,1

33,1

71

6

1

2

1

0

12

100

Energy performance of Swedish office buildings

The majority of the office buildings are heated by district heating. Among these buildings, those built between 1961 and 1970 have the highest use of district heating energy, 144 kWh/m2a (see Table 3.4). Most of the heating is space heating, hot service water accounts for 2 – 7% of the heating (Nilson, 1996).

Table 3.4

Year of completion Use of district heating kWh/m2a

Use of district heating in Swedish office buildings, broken down by year of completion (SCB, 2001). …-1940 1941-1960 1961-1970 1971-1980 1981-1991 1991-… Average 137

133

144

112

91

116

122

If cooling is included, then the buildings constructed between 1961 and 1970 have the highest energy use, 156 kWh/m2a (see Table 3.5).

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Table 3.5

Average energy use for space heating, district cooling and electricity for cooling in Swedish office buildings (SCB, 2001).

Year of completion

…-1940 1941-1960 1961-1970 1971-1980 1981-1991 1991-… Average

Use of district heating kWh/m2a

146

143

156

127

114

127

135

An analysis of energy use for heating and use of electricity in premises showed that the heating energy use has been reduced, while the total use of electricity has increased, during the last decades (Energiboken, 1995). The reduction in heating energy use is due to the improved thermal insulation (lower thermal transmittance) and introduction of heat recovery on the exhaust air flow, required by the building regulations. New premises have a lower total use of energy than older ones, but a higher share of use of electricity (see Figure 3.1). In new office buildings, i.e. those built after 1980, the use of electricity often accounts for 70% of the use of energy (Nilson, 1996). The previous building regulations, before 2006, did not have any real requirement for the use of electricity or the total energy use. 280 260 240

1970

220

Heating (kWh/am²)

200

1980

180 160

1990

140 120 100 80 60 40 20 0 0

10

20

30

40

50

60

70

80

90

100

110

120

130

Electricity (kWh/am²)

Typical office buildings

Figure 3.1

Refurbished office buildings

New office buildings

Relation between use of energy for space heating and use of electricity in Swedish office buildings, as a function of year of completion (Energiboken, 1995).

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Single and Double Skin Glazed Office Buildings

The reduction in heating demand has in many cases taken place at the expense of an increased use of electricity. Redistribution between these two energy sources has taken place both in new construction and refurbishment. There are several reasons for this, e.g. • • • •

poor knowledge as to the actual use of electricity in buildings. increased use of office appliances (PCs, printers, servers, copiers, etc) the building regulations have focused on heating demand no life cycle perspective is applied

There is quite a variation in the energy use of office buildings as shown in Table 3.6.

Table 3.6

Energy use in office buildings (REPAB, 2003).

kWh/m2year District (non-residential heating area)

Electricity Electricity Electricity Total (fans, (lighting, cooling electricity pumps etc.) PC etc.)

Total energy use

Low Normal High

10 18 30

140 223 365

80 125 205

35 50 80

15 30 50

60 98 160

There is clearly an energy saving potential, especially with regard to use of electricity for ventilation, cooling, lighting. Targets have to be specified for the use of electricity for fans, pumps, lighting etc and for the cooling demand. The users have to buy energy efficient appliances (e.g. PCs). Important savings can be achieved by adapting the operation of the HVAC system to the actual activity in the building and optimising the operation of the building with regard to ventilation, heating and cooling. The users can contribute by improving their behaviour with regard to the use of lighting, PCs etc.

3.1.5

Glazed office buildings in Sweden

Especially during the nineties, highly glazed office buildings were built in Scandinavia, some of them with single and others with double skin façades. This has been made possible by technical development regarding the construction and physical properties of glass. During the last years architects have developed an interest in applying the technology of double skin façades in Scandinavia. Buildings with double skin façades built in Sweden are described in several literature sources. A report on requirements and methods for double skin façades has been 68

State of the art

produced by Carlson in 2003. A literature review on double skin façades for office buildings has also been written by Poirazis (2004a), describing the main aspects of the system and presenting buildings from Scandinavia, Finland, Germany, United Kingdom, Belgium, etc. Buildings described from Sweden are the Kista Science Tower, The Nokia House Kista, Arlanda airport, the ABB Business centre and the GlasshusEtt. Before describing further the properties of double skin façades, it is useful to understand why office buildings with fully glazed façades are being built. Architecturally an airy, transparent and light building is created, with more access to daylight than in a more traditional office building (Svensson, 2000). Furthermore, the main argument for constructing double skin glazed façades is that a decision has been made in the first place to build a glazed building because of the transparent appearance (Svensson, 2001). The individual arguments, compared with a single skin glazed façade, are noise reduction, natural light, possibility to open windows, protected solar shading, burglary protection, night ventilation, preheated supply air, additional heat during winter and removal of solar energy via the double skin sustainable construction. This type of building enables ventilation to be adapted to the different seasons and often some kind of hybrid ventilation. It is also claimed that office buildings with double skin façades can result in a reasonable energy use and a reasonable indoor climate. There is a lack of knowledge in the building trade in Sweden concerning the design of highly glazed buildings and the calculation of energy use, thermal comfort and the influence of different technical solutions on these buildings. When highly glazed office buildings are designed, exact copies of buildings located in other climates should be avoided. Adaptation to Swedish requirements for energy use and indoor climate, as well as adjustment to Swedish climate and Swedish engineering (building and HVAC), is necessary. The complexity of building and HVAC systems requires a comprehensive view. Energy, comfort and costs must be analysed for Swedish conditions. The low outdoor temperatures and solar gains during winter in Sweden can result in low temperatures of the inner layer and hence thermal discomfort (draughts, a non-uniform indoor climate, etc). The low altitudes of the sun during the winter can cause visual discomfort due to glare problems, mostly close to the façade. For deep buildings the daylight level can be low in the core of the building, although the façade is fully glazed.

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Single and Double Skin Glazed Office Buildings

3.2

Double skin façades

The main aim of this Subsection is to provide necessary background information from previous research carried out in the field of double skin façades. Since the evaluation of the methods used (in order to determine the performance of double skin façades) is a part of this thesis, approaches and methods used for modelling and measuring the cavities are briefly described as found in the existing literature. Moreover, a description of previous research regarding proper building integration of double skin façades is provided, with the emphasis on different HVAC strategies and the contribution of double skin façades for an optimized performance. Background information regarding energy simulations of double façades that were carried out on a building level is also provided. Finally, examples of buildings and typical constructions used are given.

3.2.1

Building physics of the double skin façade cavity

In the following subchapters a brief description is given of the modelling approaches and the measurement methods used (as described in the literature). Although it is not the main aim of the thesis to develop a model for predicting the performance of the double skin façade cavity, a basic understanding of the physical model (air flows, temperatures etc.) and the methods used was required in order to evaluate the results, when validating the simulation tools used. Detailed description of the modelling methods can be found in the chapter “Double Skin Façade Modelling Approaches” of the report “Double Skin Façades; A literature review” (Poirazis, 2006).

3.2.1.1 General Accurate prediction of the airflow rates in a ventilated cavity is essential for successful modelling of the double skin façade cavity. Before describing each of the air flow simulation methods that different authors have used, it is essential to briefly describe the two possible ways of ventilating the double skin façade cavity. As Shiou Li (2001) describes double skin façades can be both naturally and mechanically ventilated. Although, according to the author, natural ventilation can provide an environmentally friendly atmosphere, it is not without risk. Unless the ventilation is designed properly the solar heat gain within the façade cavity will not be removed efficiently and will increase the cavity temperature. For the naturally ventilated cavi70

State of the art

ties the air is brought into the cavity and exhausted by two means: wind pressure and/or the stack effect. According to the author the wind effect is dominant all the year round. As the author mentions, natural ventilation systems in urban environments may also experience significant problems of noise transmission and pollution and may result in uncomfortable indoor environments in extreme weather conditions. The mechanically ventilated double skin façades often use an underfloor or overhead ventilation system in the building to supply or exhaust the cavity air to ensure good distribution of the fresh air. In this case the air is forced into the cavity by mechanical means. This air rises and removes heat from the cavity and continues upwards to be expelled or re-circulated. The mechanically assisted ventilation systems allow the building to be sealed, thereby providing more protection from traffic noise than naturally ventilated systems. In areas with severe weather conditions or poor air quality, the mechanically assisted ventilation system can keep conditions in the buffer zone nearly constant to reduce the influence of the outdoor air to the indoor environment. If the airflow in the DSF cavity is mechanically driven, the amount of air passing the cavity is known; in the case of a naturally ventilated cavity, however, it is necessary that the flow is calculated. In addition, the airflow in the cavity can be limited to maintain the necessary airflow rate in the room. Knowledge of air temperature in the double façade cavity is essential if one wants to maintain a comfortable indoor environment, especially when the cavity air is directly used for ventilation indoors. The air temperature and the airflow in the cavity are interrelated parameters and one can not be estimated properly without the other. Knowledge of the flow regime is also essential for prediction of the air temperature and air flow.

3.2.1.2 Modelling approaches This part is based on the “DSF Modelling Approaches” subchapter of the Literature review written by Poirazis (2006). Nowadays, building simulation software and developed mathematical models vary over a wide range of complexity. The simplest model is described by a few equations and the most complex one is the CFD model solving the conservation equations for mass, momentum and thermal energy. According to Champagne (2002), in the HVAC field there is a need to validate a proposed design to ensure proper performance. The two methods typically used are experimental or numerical. According to the author the experimental values are very reliable, when performed in a 71

Single and Double Skin Glazed Office Buildings

controlled environment; however, there are several major drawbacks to this approach since, for instance, it is expensive and time consuming. Numerical approaches such as computational fluid dynamics (CFD) are informative and when applicable can also save time and money. At the same time, Hensen (2002) categorizes building simulation approaches by level of resolution into macroscopic and microscopic. According to the author the macroscopic approaches deal with entire building systems, indoor and outdoor conditions over some periods, while microscopic approaches use much smaller spatial and time scales. The building simulation software is normally related to the macroscopic approaches, while the CFD has the microscopic technique which is usually restricted to the steady state condition. The macroscopic (network) method is more suitable for the time series considerations. Another direction is taken by Djunaedy, et al. (2002), which categorizes the main air flow modelling levels of resolution and complexity as: • Building Energy Balance (BEB) models that basically rely on airflow guesstimates. • Zonal Airflow Network (AFN) models that are based on (macroscopic) zone mass balance and inter-zone flow pressure relationships; typically for a whole building. • CFD that is based on energy, mass and momentum conservation in all (minuscule) cells that make up the flow domain; typically a single building zone. Hensen, et al. (2002), explain that although airflow is obviously an important issue for building performance assessment, the development of its treatment in modelling methods often lags behind the treatment applied to the other important issues, such as energy flow paths. Nowadays emphasis has been given to airflow simulations which mostly focus on the following two approaches: • Computational Fluid Dynamics (CFD) based on conservation equations for mass, momentum and thermal energy for all nodes of a two- or three-dimensional grid inside or around the object under investigation. The CFD approach is applicable to any thermo fluid phenomenon; however, in building physics applications, there are several problematic issues, such as the amount of necessary computing power, the nature of the flow fields and the occupant-dependent boundary conditions. This has often led to CFD applications being restricted to steady-state cases or very short simulation periods. • The network method, in which a building is treated as a network of nodes representing rooms, parts of rooms and system components, 72

State of the art

with inter-nodal connections. According to the authors, the assumption is made that for each type of connection there exists an unambiguous relationship between the flow through the component and the pressure difference across it. Conservation of mass for the flows into and out of each node leads to a set of simultaneous, nonlinear equations, which can be integrated over time to characterize the flow domain. The position of Park, et al. (2003), Gertis (1999), Hensen, et al. (2002), and the work of many other researchers indicates that it is very difficult to find a simple model that would describe the DSF performance appropriately. As explained in Hensen, et al. (2002) predicting the performance of a double skin façade can be quite difficult, since highly transient parameters such as cavity temperature, ambient temperature, wind velocity and direction, transmitted and absorbed solar radiation and angles of incidence govern the main driving forces. Manz and Frank (2005), point out that the thermal design of buildings with the DSF type of envelope remains a challenging task. As yet, there is no software tool that can accommodate all the following three modelling levels: optics of layer sequence, thermodynamics and fluid dynamics of DSF and building energy system. The complexity of the prediction task is the main reason for the long lasting research and application of simplifying techniques. The iterative approach of the network method became the reason to distinguish the three main issues in the DSF modelling: • Optical element – responsible for the optical properties of the DSF materials • Heat transfer element– responsible for the heat transfer processes in the DSF • Flow element – responsible for the motion of the fluid in the DSF In various network methods these elements are defined differently in terms of nomenclature. In some methods they even stay undefined. The elements (the physical processes behind them) influence each other and, as has been argued, together they govern the main heat and mass transfer processes in the DSF. Several researchers (Saelens, Faggembauu, van Paassen, Di Maio, Manz and others) suggested the separation of the flow element and the heat transfer element in the predictions, which makes for better accuracy of wind influence predictions and advanced calculations of the convective and radiative heat transfer (Saelens, 2002). Saelens (2002), performed an investigation of an accuracy change with stepwise enhancement of the network model. The diagram, depicted in 73

Single and Double Skin Glazed Office Buildings

Figure 3.2, represents the stepwise change in the network models starting from the simplest case (a) – a single zone model.

Figure 3.2

Diagram of the different models with raised shading device, (Saelens, 2002).

According to the author: •

•

•

• •

SZ (single zone) model: the cavity is represented by a single node. Radiation and convection in the cavity are combined. The heat transfer through the cavity surfaces is described by a single U-factor. The solar radiation is inserted in the air node and the cavity surface temperatures are not calculated. (SZRC) model: the previous model is somewhat improved, since the radiation and convection in the cavity are treated separately. The absorbed solar energy is inserted in the cavity layers and is a function of the angle of incidence. (AL) model: A further improvement consists of accounting for the temperature gradient along the height of the cavity. In order to allow an analytical solution, a temperature profile is chosen with a linear temperature gradient. (AE) model: An exponential temperature gradient is assumed as a further improvement for the analytical model. (NUM) model: A numerical model is developed, which is based on a cell centred finite volume method. As an improvement over the other models, the radiation heat transfer in the cavity is treated more correctly and shadowing is taken into account.

The CFD code is able to perform many tasks that the network modelling will never achieve. However, some of the CFD features are too sophisticated and unnecessary for the design stage (e.g. the grid distribution of the velocity, temperature, dissipation of energy etc., obtained when the CFD modelling is performed) and, as mentioned above, the CFD modelling is often restricted to steady state simulations. According to the authors, whose 74

State of the art

works are mentioned in this section, there is a steadily growing experience in CFD modelling in general and in CFD modelling of DSF, but still there are a number of issues which are considered to be problematic in practice (Hensen, et al., 2002; van Dijk and Oversloot, 2003; Ding, et al., 2004; Jaroš, et al., 2002; Chen, 1997): • • • •

amount of necessary computer power complex flow fields uneven boundary conditions necessity to validate the results and the difficulties to achieve satisfaction with validations • the need for users to have advanced knowledge

A more detailed description of developed network and CFD models that can be found in the existing literature is given in the report “Double Skin Façades; A literature review report” (Poirazis, 2005).

3.2.1.3 Measurements – test rooms and real buildings In this section measurements made both in test rooms and in real buildings are described. Saelens and Hens (2001) in “Experimental evaluation of Airflow in Naturally Ventilated Active Envelopes” describe the most common measurement techniques for calculating the air flow rates in both naturally and mechanically ventilated active envelopes. The airflow in ducts and cavities can be determined by measuring: • the pressure difference across an orifice, nozzle or venturi tube • the air velocity using anemometers • the air flow directly using tracer gas techniques In the same paper the airflow through naturally ventilated active envelopes has been experimentally analysed. The authors proposed a method to determine the airflow through the cavity by means of the pressure difference over the lower ventilation grid. From the pressure difference over the lower ventilation grid, the airflow rate through the cavity was determined from the pressure characteristic of the active envelope. The method has been verified by tracer gas measurements and proved to be reliable. Saelens, referring to Onur et al. (1996) in his PhD thesis writes that for mechanically ventilated cavities, the airflow rate can be determined by measuring the pressure difference across an orifice placed in the exhaust duct. However, this method is less suited for naturally ventilated cavities. As Saelens describes in “Experimental evaluation of Airflow in Naturally 75

Single and Double Skin Glazed Office Buildings

Ventilated Active Envelopes” (2001), “the driving forces are usually small and because of the high flow resistance of the orifice, the flow in the cavity would be too much affected. Furthermore, it would be difficult to find a suitable place for the orifice as no exhaust duct is available”. Saelens (2001) after studying reports of Park et al. (1989) and Faist (1998), described a second method to estimate the airflow rate by measuring the air velocity with anemometers. The author concluded that the determination of the airflow rate from velocity measurements seems obvious, but is likely to produce erroneous results, since the velocity in a naturally ventilated channel is not uniform and is influenced by lowering or raising the shading device. Furthermore, according to the author, there is no guarantee that the resulting velocity vector is perpendicular to the reference surface. Detailed information about the velocity vectors may be obtained by placing an array of individual velocity measuring points, which may however affect the development of the airflow in the cavity. Hence, determining the airflow rate in naturally ventilated active envelopes from measured velocities is a less recommendable method. A third, less common method, is the use of tracer gas measurements (Ziller (1999); Busselen and Mattelaer (2000)). Tracer gas techniques such as the constant concentration, constant emission and tracer dilution method (Raatschen, 1995 and ASHRAE, 1997) make it possible to determine the airflow rate in both naturally and mechanically ventilated active envelopes without interfering with the driving forces. In “Modelling of air and heat transport in active envelopes”, Saelens, Carmeliet and Hens (2001) compare (using measurements) five models, of varying complexity, of a mechanically ventilated active envelope. The authors claim that radiation and convection in the cavity have to be modelled separately in order to obtain reliable results. According to the authors, for an accurate prediction of active envelope performances, the vertical temperature profile has to be implemented properly (e.g. by an exponential expression). A sensitivity study performed with the numerical model reveals that the air temperature at the inlet of the cavity, the airflow rate, the distribution of the airflow in the cavity and the angle of solar incidence are the governing parameters. Saelens (2002) describes in his thesis measurements carried out at the Vliet test building (two one storey high multiple-skin façades and a traditional envelope). According to the author there are two main aims of the measurements: (a) the measurement set-up is used to extend knowledge of the thermal behaviour of multiple skin façades and (b) the data is used to evaluate modelling assumptions and to derive and check relationships for modelling parameters. The author compares different models for the convective heat transfer coefficient with the measurements. Additionally, the measurements are 76

State of the art

used to evaluate the numerical model and to assess the reliability of models with different levels of complexity. Finally, the data are used to assess how the inlet temperature should be determined. Shiou Li in 2001 wrote an MSc thesis which proposes a protocol for experimentally determining the performance of a south facing double glazed envelope system. The protocol was applied to an experimental study of a south-facing, single story double glazed ventilated system. In order to achieve that, two modular full-scale double glazed window models with naturally or mechanically assisted ventilation were constructed and monitored. The main goal was to develop and apply the test protocol by monitoring and analyzing the thermal performance of double façades. By using this test protocol the author claims average cavity heat removal rate approximately 25% higher for the active system when compared to the naturally ventilated one. Also, the passive system has a higher temperature difference between the indoor glass surface and the indoor air than the active system.

3.2.2

Integration of double skin façades

The integration of the double skin façade systems in office buildings is crucial for thermal performance and energy use during the occupation phase. Stec & Paasen (2003) presented a paper in which they describe different HVAC strategies for different double skin façade types. According to the authors, the integration procedure of double skin façades in the building should include (a) defining the functions of the double skin façade in the building, (b) selecting the type of the double skin façade, its components, materials and dimensions of the façade that fulfil the requirements, (c) optimizing the design of the HVAC system to couple it with the double skin façade, and (d) selecting the control strategy to supervise the whole system. The authors briefly introduce the concept of different cavity depths and describe its influence on the air temperatures inside the cavity. According to them, the dimensions of the façade together with the openings determine the flow through the façade; narrower cavities result in higher flow resistance and smaller flow through the cavity and a higher increase in air temperature in the cavity. The authors conclude that (a) in the cold period it is more suitable to use narrow cavities to limit the flow and increase the cavity temperature and (b) in the hot period the double skin façade should work as a screen for the heat gains from radiation and conduction. It is difficult to claim in general whether the narrow or deep cavities will perform better because in one case the cavity temperature and in the other case the temperature of the blinds will be higher. 77

Single and Double Skin Glazed Office Buildings

Examples concerning the influence of different depths on the properties of the cavity are shown in “Second Skin Façade Simulation with Simulink Code” by Di Maio and van Paassen in (2000). In “Modelling the Air Infiltrations in the Second Skin Façade” in (2001) the same authors conclude that “narrow cavities are more useful, because they can deliver a higher and hotter air flow compared to the air flow delivered by wide ones”.

3.2.2.1 Contribution of double skin façades to the HVAC strategy As Stec et al. (2003) describe, an HVAC system can be used in the following three ways in a double skin façade office building: • full HVAC system (the double façade is not a part of the HVAC) which can result in high energy use. The user can select whenever he/she prefers mechanically controlled conditions inside or natural ventilation with the use of the double skin façade). • limited HVAC system (the double façade contributes partly to the HVAC system or plays the major role in creating the right indoor climate). In this way the double façade can play the role of: o pre-heater for the ventilation air o ventilation duct o pre-cooler (mostly for night cooling) • no HVAC. The double façade fulfils all the requirements of an HVAC system. This is the ideal case that can lead to low energy use. During the heating periods the outdoor air can be inserted from the lower part of the façade and be preheated in the cavity (Figure 3.3). The exterior openings control the air flow and thus the temperatures. Then, through the central ventilation system the air can enter the building at a proper temperature. During the summer, the air can be extracted through the openings from the upper part of the façade. This strategy is usually applied to multi storey high double skin façades.

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State of the art

Summer

Winter AHU

Figure 3.3

Double skin façade as a central direct pre-heater of the supply air.

During the whole year, the double skin façade cavity can work only as an exhaust duct without the possibility of heat recovery for the HVAC system (Figure 3.4). It can be applied both during winter and summer to the same extent. The main aim of this configuration is to improve the insulation properties in the winter and to reduce the solar radiation heat gains during the summer. There are no limitations to individual control of window opening. Winter/Summer

AHU

Figure 3.4

Double skin façade as an exhaust duct.

79

Single and Double Skin Glazed Office Buildings

It is also possible to use the double skin façade as an individual supply of the preheated air (Figure 3.5). This strategy can be applied in both the multi-storey and box window types. An exhaust ventilation system improves the flow from the cavity to the room and to the exhaust duct. Extra conditioning of air is needed in every room by means of VRV system or radiators. This solution is not applicable for the summer conditions, since the air temperature inside the cavity is higher than the thermal comfort levels. Also in this case there are no limitations to individual control of window opening. Multi-storey

Figure 3.5

Box window

Double skin façade as an individual supply of the preheated air.

Finally, the double skin façade cavity can be used as a central exhaust duct for the ventilation system (Figure 3.6). The air enters through the lower part of the cavity and from each room. The supply ventilation system stimulates the flow through the room to the cavity. Heat can be recovered by means of heat pump or heat regenerator at the top of the cavity. Because the air in the cavity is not fresh air, the windows cannot be operable.

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State of the art

Winter AHU

Figure 3.6

Double skin façade as a central exhaust duct for the ventilation system.

As Stec et al. (2003) describe, generally supply façades couple better with the winter systems in which their preheating properties can be used. The exhaust façade is more efficient in cooling the cavity in the summer. Problems arise when one façade needs to couple both of the periods, in which case the construction must be adjusted for summer and winter conditions.

3.2.2.2 Examples of coupling double skin façades and HVAC In 2001, van Paassen and Stec wrote a paper “Controlled Double Façades and HVAC” that deals with the preheating aspects of double skin façades. The authors claim that for the winter period the most significant parameter should be the heat recovery efficiency. The main aim of the paper was to show the usability of the cavity air for ventilation purposes. According to the authors, it is possible to define by simulation how the heat recovery efficiency depends on the outside conditions, the dimension of the cavity, the area of inlet and outlet for outside air and the height of the building. For the simulations, the authors chose the following four double skin façade types: 1. Double skin façade with controlled airflow through the cavities (Figure 3.7). The façade is a multi-storey façade with no opening junctions that allow the air to be extracted out. There is only one inlet for the ventilation airflow at the bottom of the façade. It is controlled by an air damper such that the air supply to the cavity 81

Single and Double Skin Glazed Office Buildings

is just enough for ventilating all the rooms above. The controlled trickle ventilator delivers the desired airflow to each room (80 m3/h)

Figure 3.7

Coupling DSF and HVAC; Controlled air flow in the cavity.

2. There are no open junctions on each floor, no controlled airflow in the cavity and open dampers in this system (Figure 3.8). Additionally, the upper part of the façade is open allowing the air to be extracted.

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State of the art

Figure 3.8

Coupling DSF and HVAC; Uncontrolled air flow in the cavity.

3. There are open junctions between the outside and the cavity on each floor, which cause heat exchange between air inside the cavity and outside air. The main airflow is the same as in the second system (Figure 3.9). The authors claim that this should be the best system for summer time when cooling is required, but due to the open junctions preheating of the cavity air will be much lower than in the other systems with closed junctions.

83

Single and Double Skin Glazed Office Buildings

Figure 3.9

Coupling DSF and HVAC; Open junctions in each floor.

4. There are open junctions on each level, but the storeys are separated from each other (Figure 3.10). Consequently each storey creates its own system. The authors claim that in practice this can be the most convenient system since the same module can be used on each storey and the problems due to large temperature gradients at different levels in the cavity can be avoided (on each storey there is more or less the same temperature in the cavity).

Figure 3.10

84

Coupling DSF and HVAC; Each storey is separated.

State of the art

The conclusions drawn by the authors were that: • The dimensions of the cavity, (height and width) have the greatest influence on the heat and flow performance in the double skin façade and hence they are the most important parameters in designing the double skin façade. • High-rise buildings with very narrow cavities may not ensure the airflow in the cavity needed for ventilation purposes. • In general, a double façade with airtight junctions and proper airflow control in the cavity is an interesting pre-heater for ventilation air. In a four storey building with cavity width of 0.2 m an overall heat recovery efficiency of 40% can be obtained. According to the authors this efficiency can be increased to 72% if the ventilation flow inside the cavity is properly controlled. A disadvantage is the vertical temperature gradient inside the double façade. It gives lower comfort or higher cooling capacities at higher floors. • Splitting the cavities of high rise buildings into separate parts by combining for example four storeys with their own inlets and outlets can be essential. If this is done for each floor the efficiency can drop to 35%. • In order to use the double façade for night cooling and for heat recovery, controlled dampers in the open junctions are needed. During cooling periods they should be fully open.

3.2.2.3 Control strategy A crucial point when integrating double skin façade systems in buildings is to define a control strategy that allows the use of solar gains during the heating period and provides acceptable thermal comfort conditions during the whole year. In the case of cavities with all year round mechanical ventilation, there is a high risk of overheating the offices during the summer months, when the design of the double skin façade is not coupled properly with the strategy of the HVAC system. According to Stec et al. (2003) this system allows the outside conditions to influence the indoor climate. As the authors describe, an efficient control system can manage rapidly changing outside conditions. Successful application can only be achieved when the contributions of all the devices can be synchronized by an integral control system. According to the authors, the control system of the building should take into consideration the following principles: • the occupants should be able to influence everything, even if their intervention wastes energy. 85

Single and Double Skin Glazed Office Buildings

• energy saving can be achieved when the control system takes maximum advantage of the outside conditions before it switches over to the air conditioning system. • all control systems must be focused on realization of the required comfort with the lowest energy use. • during the unoccupied period the control system is focused only on the energy savings, while during the occupied period it must also be focused on comfort. According to the authors, the main tasks that the control system has to fulfil are to: (a) keep the right level of temperature inside the building, (b) supply sufficient amount of ventilation air to the building and (c) ensure the right amount of light inside the building.

3.2.3

Energy performance of buildings with integrated double skin façades

A complete study of energy performance was presented by Saelens, Carmeliet and Hens in “Energy performance Assessment of Multiple Skin Façades” in 2003. The authors claim that only few combinations of Multi Storey Façade modelling and building energy simulation are available. According to the authors, “most of these papers are restricted to only one MSFtypology. Müller and Balowski [1983] analyse airflow windows, Oesterle et al [2001] give a comprehensive survey of double skin façades and Haddad and Elmahdy [1998] discuss the behaviour of supply air windows”. In the above paper the authors focus on the energy saving objectives of three Multi Storey Façade typologies used in a single office. The MSFmodel is coupled with TRNSYS. According to the authors, “to simulate the energy demand of the office, a cell centred control volume model, describing the MSF, is coupled to a dynamic energy simulation program. The results of the energy simulations are compared and confronted with the objectives found in literature”. The authors focus on one storey high solutions: • • • •

a conventional façade with an insulated glazing unit (IGU) a naturally ventilated double skin façade (DSF) a mechanically ventilated airflow window (AFW) a mechanically ventilated supply air window (SUP)

The reduction of the transmission losses, the possibility of recovering the transmission losses by the airflow, the position of the shading device sheltered from climatic conditions and the ability to remove the absorbed solar heat are the most commonly mentioned energy advantages. 86

State of the art

The authors conclude that it is possible to improve the building’s energy efficiency in some way by using multiple skin façades. However, most typologies are incapable of lowering both the annual heating and cooling demand. This can be achieved only by (a) combining typologies or (b) changing the system settings according to the particular situation. This implies that sophisticated control mechanisms are essential, in order to make multiple skin façades work efficiently throughout the year. Furthermore, the authors conclude that the energy performance strongly depends on the way the cavity air is used. In order to correctly evaluate the energy efficiency of multiple skin façades, it is imperative not only to study the transmission gains and losses but also to take into account the enthalpy change of the cavity air and to perform a whole building energy analysis. Gratia and De Herde (2004), claim that there are still relatively few buildings in which double-skin façades have actually been realized, and there is still too little experience of their behaviour in operation. For this reason the authors chose to study the natural ventilation in a multi-storey double skin façade using the TAS software. The study was made on a building level for a sunny summer day. The authors have analyzed the behaviour of the double skin façade for various conditions, with the main focus on the impact of the double skin orientation and the impact of wind orientation and degree of wind protection. Hendriksen, Sørensen, Svensson and Aaqvist wrote a paper that focuses mostly on the heat loss, indoor climate and energy aspects of double skin façades. Examining four different cases of double skin façades, they provide useful information concerning daylight, climate and energy aspects. The first case is with simple double glazing and the other three with D.S.F. as described below: • • • •

Simple double glazing Double inner - single outer glazing Single inner – double outer glazing Double inner - double outer glazing

According to the authors, when a single layer of glazing is added to a double low-E glazing in a double skin façade construction the reduction in heat loss expressed by the U value is modest ( Tmean,zone is the monthly average zone temperature Azone is the zone area Nzones is the number of the zones Atotal is the total floor area The limitation of the weighted average mean monthly air temperatures is that no information is given as to the variation over time or space. For the cell type office building, only the occupied zones were included in the calculations (offices and meeting rooms, as described in detail in Chapter 5). The corridor (zone 11) was excluded, since the impact on the occupants’ comfort is limited. However, for the open plan type the whole area was considered for the calculations, since all this area was considered as working space. All the calculations (excluding those for energy) were carried out for a middle floor (in IDA ICE 3.0). • number of hours between certain (weighted) average mean air temperatures for working space: This output gives information similar to the weighted average mean air temperatures for the working area. However, this is more a quantitive indicator compared with the previous output, since the previous one only gives monthly averages and does not provide any information concerning the variation of the indoor temperatures during the year. • weighted average PMV: As already described in Subsection 2.3.2.2, the Predicted Mean Vote is a qualitative indicator of the perception of thermal comfort. Likewise, the weighted average PMV is a monthly average PMV value of each occupant multiplied by the number of occupants in each zone and the number of identical zones, divided by the total number of occupants. This factor can basically show whether or not the controls are proper for certain occupancy, since it provides information for all the year. • number of working hours for certain average PPD: As already described in subsection 2.3.2.2, the Predicted Percentage of Dissatisfied is more a quantitative indicator of the perception of thermal comfort. In a similar way weighted average PPD is the sum of the PPD of each occupant multiplied by the number of occupants in each zone and the number of identical zones, divided by the total number of occupants. This output is more a quantitative indicator for the perception of thermal environment in the working space. Although it does not show 115

Single and Double Skin Glazed Office Buildings

whether the occupant feels warm or cold, it provides the necessary information to classify an indoor thermal environment, both on a zone and on a building level.

4.2.2

Double skin alternatives

The simulations for the double skin façade alternatives were carried out at three levels: (a) component level (pilot study aiming to reduce the number of glazing alternatives initially considered using WIS 3), (b) zone level (parametric study focusing on the impact of the façade mode and construction on energy use and of a specific office zone for different orientations, using IDA ICE 3.0) and (c) building level (parametric study investigating the impact of glazing type on the system’s performance (naturally, mechanically and hybrid ventilated double façades and mechanically ventilated airflow windows), using IDA ICE 3.0). The main parameters studied at these 3 levels are briefly described below.

4.2.2.1 WIS 3 simulations (component level) The main aim of this study is to better understand the possibilities and limitations of different double skin façade constructions. This pilot study can be considered as a first step for optimizing the system’s performance and integration on a building level. During the calculations carried out on the double skin façade level, several parameters were varied (façade mode, geometry of the cavity, size of the openings, glazing type and shading device position inside the cavity – when applied). In this way, their impacts mainly on the air flow, the air temperature at different heights of the cavity and the surface temperature of different panes were investigated. Due to the large number of varied parameters a detailed methodology was developed with the aim to decrease the number of simulations (Figure 4.4). A description of the methodology is given below and, when necessary, the reasoning is set out.

116

Figure 4.4

Influence of cavity height and depth on airflows

Influence of cavity height and depth on temperature profile

Parametric study: influence of cavity geometry on system’s performance

Influence of % of opened area on airflows and temperature profile

Air temperatures (multi storey high)

Influence of glazing on optimal depth

Influence of shading devices position on the air and the inner pane temperatures

Surface temperatures

Outlet air temperatures

Preliminary study: influence of depth on air and surface temperature

Mechanically ventilated cavity

Airflow window mode

Surface temperatures (box window)

Mechanically ventilated cavity

Influence of weather conditions on optimal depth

Surface temperatures

Performance of the glazing alternatives

Air temperatures

Naturally ventilated cavity

Preliminary study: Selection of glazing combinations

“Standard” double façade mode

Double Skin Façades

Methods

Methodology of WIS 3 simulations.

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Single and Double Skin Glazed Office Buildings

“Standard” double façade mode As described in detail in the Subsection 4.1.3.1, initially seven glazing combinations were considered for each mode. However, due to the large amount of simulations a preliminary study was carried out (see Figure 4.4) for the “standard” double façade mode, and the number of glazing alternatives was reduced from seven to four. For the airflow window mode, on the other hand, all seven alternatives were studied. Influence of cavity geometry on system performance (naturally ventilated cavity): Generally, studying a naturally ventilated cavity is more complicated than studying a mechanically ventilated one, since the airflow rate depends on the characteristics of the cavity such as glazing type, geometry of the cavity, etc. For this reason a further parametric study was carried out for the naturally ventilated double façade mode, in order to study the impact of construction on the system performance (see Figure 4.4). The parameters studied were: • • • • • •

influence of cavity height and depth on airflows influence of cavity height and depth on air temperature profile influence of opened area on airflows and air temperature profile influence of weather conditions on optimal depth influence of glazing on optimal depth influence of shading device position on the air and the inner pane temperatures

Performance of the glazing alternatives (naturally and mechanically ventilated cavity): After investigating the influence of geometry on the performance of the naturally ventilated cavities, different glazing alternatives were evaluated. The outputs of these simulations were the airflow and air temperature profile along the cavity and the inner pane’s surface temperatures. A similar study was carried out for the mechanically ventilated “standard” double façade alternatives. Airflow window mode Finally, for the airflow window cases, all seven glazing alternatives were considered. As shown in Figure 4.4, for the airflow window mode only mechanical ventilation was considered. A brief parametric study was carried out to investigate the influence of cavity depth on the inner pane surface temperature and the outlet air temperatures. This was followed by an evaluation of the seven glazing alternatives.

118

Methods

4.2.2.2 IDA ICE 3.0 Simulations (zone level) The output of the parametric study on a zone level was mainly focused on (a) energy demand for heating and cooling the office (zone behind the double façade) and (b) monthly average PMV. The main aim of the parametric studies on a zone level is to evaluate the simulated alternatives, in order to select the ones for further simulations on a building level. Since it takes a long time to simulate such a complicated and detailed building model, this screening is essential for the optimization of its performance.

4.2.2.3 IDA ICE 3.0 Simulations (building level) The two parameters studied and compared on a building level are the energy use and the number of hours with certain PPD values. The energy use (absolute) values obtained from the building level serve comparison purposes with the single skin alternatives, while the PPD values give a more “quantative” way of indoor climate comparisons.

4.3

Description of the simulation tools

4.3.1

Simulations using WIS 3

The software used for calculations of the double skin façade cavity is WIS 3. According to the WIS 3 User’s Guide “WIS is a European software tool for the calculation of the thermal and solar properties of commercial and innovative window systems on the basis of known component properties and thermal and solar/optical interactions between the components. One of the unique elements in the software tool is the combination of glazings and shading devices, with the option of free or forced air circulation between the components. This makes the tool particularly suited to calculate the thermal and solar performance of complex windows and active facades”. WIS 3 has been built in algorithms based on international (CEN, ISO) standards, such as the ISO Standard 15099 (2003). As already mentioned the two main outputs of the simulations are: • temperatures at the centre of each layer. • vertical air temperature profile along the ventilated cavity.

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Single and Double Skin Glazed Office Buildings

4.3.1.1 Temperatures at the centre of each layer These values were calculated by WIS 3 and they refer to the centre of each layer. A short description of the calculated values follows. T1: Tglass1: T2: Tgap1:

temperature of the outer glass (outer surface – average temperature) average temperature of the outer glass (average temperature) temperature of the outer glass (inner surface – average temperature) temperature of the air between the outer and the intermediate glass (in the centre of the cavity) Tgap1-(a): temperature of the layer between the outer glass and the blind (in the centre of the cavity) Tgap1-(b): temperature of the layer between the blind and the intermediate glass (in the centre of the cavity) Tbo: temperature of the outer surface of the blinds (average temperature) Tblind: temperature of the blinds (average temperature) Tbi: temperature of the inner surface of the blinds (average temperature) T3 : temperature of the intermediate pane (outer surface – average temperature) Tglass2: average temperature of the intermediate glass (average temperature) T4: temperature of the intermediate pane (inner surface – average temperature) Tgap2: temperature of the layer between the intermediate and the inner glass (in the centre of the cavity) T5: temperature of the inner pane (outer surface – average temperature) Tglass3: average temperature of the inner glass (average temperature) T6: temperature of the inner pane (inner surface – average temperature)

T6 T5 Tgap2 T4 T3 Tgap1 T2

T1

Figure 4.5

120

Case without venetian blind.

Methods

T6 T5 Tgap2 T4 T3 Tgap1-(b) Tbi Tblind Tbo Tgap1-(a) T2 T1

Figure 4.6

Case with venetian blind.

4.3.1.2 Temperatures at different heights of the cavity General case According to ISO Standard 15099 (2003), by assuming that the mean velocity of the air in the space is known, the temperature profile and the heat flow may be calculated by a simple model.

121

Single and Double Skin Glazed Office Buildings

Outlet air temperature, Tgap i_out

Hi Air flow j

Average air temperature, Tgap i

v,i

Average surface temperature, Tave i

H0,i Height h

Air temperature Tgap i (h)

Figure 4.7

Inlet air temperature, Tgap i_in

Air flow in the gap of a window system.

Due to the air flow through the double skin façade cavity, the air temperature in the cavity varies with the height (see Figure 4.7). The temperature profile depends on the air velocity in the space and the heat transfer coefficient to both layers. The air temperature profile in the space i is given by:

T gap_i (h) = T av,i − (T av,i − T gap_i,in ) ⋅ e Equation 4.2

− h/H0,i

Temperature profile along the cavity

where: Tgap_i(h): H0,i: Tgap_i,in: Tav_i:

is the temperature of the air in gap i at position h, (in m); is the characteristic height (temperature penetration length, in m); is the temperature of the incoming air in gap i, (in °C); is the average temperature of the surfaces of layers i and i+1, given by equation:

T av_i =

(Tb_i + T f_i +1 )

Equation 4.3

122

2 Average temperature of the surfaces of layers i and i+1

Methods

where: Tav_i : Tb_i : Tf_i+1:

is the average temperature of the surfaces of layers i and i+1, (in °C) is the temperature of the surface of layer (pane, film or shading) i, facing the cavity i, (in °C) is the temperature of the surface of layer (pane, film or shading) i+1, facing the cavity i, (in °C)

The characteristic height (H0,i) of the temperature profile is defined by the following equation:

H 0,i =

ρi ⋅ c p ⋅ si

Equation 4.4

2 ⋅ hcv,i

⋅ Vi

Characteristic height

where: ρi : cp : si : Vi : hcv,j :

is the density of the air at temperature Tgap_j , in (kg/m3) is the specific heat capacity, in (J/kgK) is the depth of the cavity i, in (m); is the mean velocity of the air flow in the cavity i, in (m/s); is the heat transfer coefficient for ventilated cavities, in (W/m2K).

Case with no venetian blind in the cavity If there is no shading in the cavity, then Tav is the average value of T2 and T3. When the incoming air in the cavity is at 0°C, it is assumed that the air density is 1.25 and when the incoming air in the cavity is at 25°C the air density is 1.18. The heat transfer coefficient for the ventilated cavity is calculated by the following equation: hcv = 2hc + 4V Equation 4.5

Heat transfer coefficient for the ventilated cavity

where: hc : V:

is the heat transfer coefficient for the cavity if it is not ventilated (given from WIS 3) is the mean velocity of the air flow in the cavity in (m/s)

123

Single and Double Skin Glazed Office Buildings

Case with blinds in the cavity In the cases that between the outer and the intermediate pane shading is applied, then two different temperatures are calculated: the one between the outer pane (or inner pane, depending on where the ventilated cavity is situated) and the blind, and the other between the blind and the intermediate pane. In the first case the temperatures Tbi and T2 were used for Tav and in the second case the temperatures Tbi and T3 were used for Tav. For the cases with ventilated cavity no air exchange between the two subcavities was assumed.

4.3.2

Simulations using IDA ICE 3.0

4.3.2.1 General description Before a building thermal simulation tool was chosen, certain performance criteria were developed. The program was to have the following features: 1. 2. 3. 4. 5. 6. 7.

A dynamic building simulation tool User friendly interface Multi-zone capability Simple natural ventilation features Simulation of HVAC systems typical for office buildings Reasonably accurate simulations of different shading devices Possibility of adding new simulation modules developed by the user e.g. a double skin façade module 8. Good support 9. Reasonably well spread among researchers and consultants in Sweden 10. Known outside Sweden The software candidates were: • • • •

Bsim2000 developed by the Danish Research Institute (SBI) IDA ICE 3.0 developed by EQUA (Stockholm, Sweden) DEROB LTH developed by the University of Lund BV2 available from CIT Management AB (Gothenburg, Sweden)

– Bsim2000 has most of the above features (except for 7 and 9) – IDA ICE has all the above features (was therefore chosen for the simulation of the building alternatives) 124

Methods

– DEROB has some of the above features (except for 2, 4, 5, 7 and 9) – BV2 has some of the above features (except at least 3 and 7) IDA ICE 3.0 is a computational program for indoor climate studies of individual zones within a building, as well as energy use of an entire building (EQUA, 2002). IDA Indoor Climate and Energy is an extension of the general IDA Simulation Environment. This means that the advanced user can, in principle, simulate any system whatsoever with the aid of the general functionality in the IDA environment. Validation tests have shown the program to give reasonable results and to be applicable to detailed buildings physics and HVAC simulations (Acherman 2000 and 2003).

4.3.2.2 Description of double façade model After personal communication with Dr. Bengt Hellström (Division of Energy and Building Design, Lund University) a brief description of the IDA ICE 3.0 double façade model is given below. The window in IDA ICE 3.0 is divided into frame and glazing. The input data for the frame is the area fraction and the U value. For the glazing, the input parameters are the U value, the solar transmittance (Tsol) and the solar heat gain coefficient (SHGC or g) at normal incidence. Also the emittances of the outermost and innermost surfaces of the glazing are given. The solar shadings are specified by coefficients, which, when multiplied by U, T and g of the glazing, give the total values of the glazing/shading system. The surface temperatures for the frame and the glazing are calculated from heat balance equations. Absorption of solar irradiation in the glazing is assumed to occur only at the innermost pane of the window and the absorbed energy rate is calculated from the difference between the g and the T values of the glazing (with or without solar shading) and the U value. The double façade is modeled as an external window (with or without a shading device), outside an internal window and a wall. The cavity is assumed to be closed to the outside, except for four openings. One at the top, one at the bottom, whose areas can be chosen; a third opening connects the double façade cavity with the room and, finally, it is also possible to have mechanical exhaust ventilation of the cavity and its flow rate can be chosen. The air temperature of the double façade cavity is obtained from an energy balance equation, using convective heat exchange with the surfaces and air exchange with the outside. Temperature stratification is not taken 125

Single and Double Skin Glazed Office Buildings

into account, as the air inside the cavity of the double façade has one temperature node. The surface convection heat transfer coefficients are chosen as the maximum of two values, one calculated from forced convection, depending on the air speed, and one calculated from natural convection, depending on the temperature difference to the surrounding air and the slope of the surface. The natural convection driven air exchange in the cavity is calculated from the density difference between the air in the cavity and outside air, considering the pressure drops at the inlets and outlets.

4.3.2.3 Validation of IDA ICE 3.0 Double Façade model (IEA SHC Task 34/ECBCS Annex 43) Concurrently with the “Glazed Office Buildings” project, IEA SHC Task 34/ECBCS Annex 43 (Testing and Validation of Building Energy Simulation Tools) was started. The aim of the Task was to investigate the availability and accuracy of building energy analysis tools and engineering models to evaluate the performance of innovative low-energy buildings. The scope of the Task was limited to building energy simulation tools, including emerging modular type tools, and to widely used innovative low-energy design concepts. Activities include development of analytical, comparative and empirical methods for evaluating, diagnosing, and correcting errors in building energy simulation software. The objective of Subtask E (Double-Façade Empirical Tests) was to assess the suitability and awareness of building energy analysis tools for predicting heat transfer, ventilation flow rates, cavity air and surface temperatures, solar protection effect, and interaction with building services systems in buildings with double skin façades. The validation process was carried out in two steps. First comparative test cases (Kalyanova and Heiselberg, 2005) were simulated and the results were cross compared; then empirical cases (Kalyanova and Heiselberg, 2006) were carried out and the output of the different software were compared with the measurements of the test facility. The empirical tests were led by Aalborg University (AAU), Denmark, using a new facility being constructed at AAU. Detailed description of the test facility can be obtained by (Kalyanova and Heiselberg, 2005). The double skin façade configurations considered for this validation procedure are set out below (Figure 4.8): • DSF100. All façade openings closed • DSF200. Openings open to the outside 126

Methods

• DSF300. Openings open to the inside • DSF400. Bottom opening open to outside; top opening open to inside • DSF500. Top opening open to outside; bottom opening open to inside

Figure 4.8

Double skin façade configurations considered for the validation tests.

Within the test cases there are a number of variations to check the influence of various parameters, including: • driving force of airflow (buoyancy, wind, mechanical fan, combined forces) • internal (thermal)/External (thermal, solar, wind) boundary conditions • opening area (fully opened, opening area controlled by temperature and/or airflow rate) Some of the output used for the validation of the simulation tools are listed below: • • • • •

direct and diffuse solar irradiation on the window surface solar radiation transmitted from the outside into the DSF cavity solar radiation transmitted from the DSF cavity into the room energy used for cooling/heating in the room hour averaged surface temperature of external window surface facing outdoors and the DSF cavity • hour averaged surface temperature of internal window surface facing the room and the DSF cavity • hour averaged floor and ceiling surface temperature and air temperature in the room Simulation results for comparative and empirical tests were obtained by IDA ICE 3.0 (LTH-Lund, Sweden), BSim 2000(Aalborg University, Den127

Single and Double Skin Glazed Office Buildings

mark), VA114 (VABI, the Netherlands), TRNSYS-TUD (TUD, Germany) and ESPr (ESRU, UK). Conclusions of the software validation will be araible after the complitation of the IEA Task 34/ECBS Annex 43.

128

Description of the building model

5

Description of the building model

A detailed description of the building model as designed and as inserted in IDA ICE 3.0 is provided in this Chapter. The single and double skin office building alternatives designed for the “Glazed Office Buildings” project consist of 30% (reference case), 60% and 100% glazing and are assumed to be located in Gothenburg (Sweden) i.e. for the simulations the weather data chosen was recorded in Gothenburg in 1977, which is considered to be a representative year. There are no adjacent buildings shading. The design of the reference building was determined by the project team, with researchers from the Division of Energy and Building Design (LTH), architects and engineers from WSP and Skanska. First, detailed performance specifications (see Appendix B) for indoor climate and energy use were established and then typical constructions were determined for a reference office building representative of construction from the late nineties. System descriptions and drawings were prepared. The reference building was presented to a reference group and agreed upon.

5.1

Description of the reference building

The description of the reference building concerns the real (designed) building and the simulated model of the building (input for the IDA ICE 3.0 software) made for the energy and indoor climate simulations.

5.1.1. Geometry of the building The reference building is a 6 storey building as shown in Figure 5.1. In terms of geometry and installations, the floors 1, 2, 3, 4, and 5 are completely identical. However, the floors 1-4 are connected (floor, ceiling) with other internal zones of the building, while the roof of the 5th floor is

129

Single and Double Skin Glazed Office Buildings

connected to the outside and the ground floor is connected to the ground (i.e. there is no basement).

connected to the outside and the ground floor is connected to the ground i.e. there is no basement.

Figure 5.1

View of the reference building.

The height of the building is 21m, the length 66 m and the width 15.4 m. Architectural drawings (floor plans, cross sections, facades) are presented in Appendix C. The room height is 2.7 m and the distance between intermediate floors is 3.5 m. There is a suspended ceiling. The total floor area is 6177 m2 (BRA usable floor area i.e. floor area inside exterior walls) and 5448 m2 (LOA non-residential/premises floor area). The total area (on the inside including the window area and the area covered by interior walls and intermediate floors) of each of the long façades is 1386 m2 and that of the short façades 327.6 m2. Each opaque (wall) area is 957 m2 and 224 m2 respectively. The window area (including the frames) is 429 m2 (30.9% of the facade) and 104 m2 (31.6%) respectively (total window area = 31%). The roof area inside the exterior walls is 1030 m2.

5.1.2.

Office layouts

Two different common floor layouts were designed, one with cell-type offices and one with open plan offices. In practice an office building often has a mixture of these two plan types. In order to simplify the input model and thus reduce the time of simulation, it is important to create as 130

Description of the building model

few thermal zones as possible. On the other hand, the assumptions made should not influence the accuracy of the results or limit the output of the simulations. For the six-storey reference building, 3 different floor types are assumed, each one with several thermal zones (Figures 5.2 and 5.3). The zones were chosen to represent different kinds of rooms with different orientations. Adiabatic conditions were assumed for the ceiling of the ground floor, for the ceiling and floor of the 1st floor and for the floor of the 2nd floor. In this way it is assumed that below and above floors 1, 2, 3 and 4 there are identical zones. This is partly correct, since below the 1st and above the 4th floor the zones are not exactly the same. However, since the temperatures on all the floors are very similar, the influence of the connections plays a minor role. For the total energy use the simulated energy use of the 1st floor is multiplied by the factor 4.

Figure 5.2

Cell type office building as modelled in IDA ICE 3.0 showing the simulated zones.

Figure 5.3

Open plan type office building as modelled in IDA ICE 3.0 showing the simulated zones.

131

Single and Double Skin Glazed Office Buildings

A detailed description of the geometry of the zones (including their number of repetition on each floor), the HVAC installations, the occupancy, the equipment, the artificial lighting and the furniture is given in Appendix D. • Cell type office layout The floor area of the cell type office building as defined in IDA ICE 3.0 (excluding the fan room) is 6177 m2. However, the non-residential space is 5448m2. In Figure 5.4 the area of each zone type is shown.

Figure 5.4

Zone areas for cell type office building (p=persons).

As shown in Figure 5.4, 44% of the building area is corridor, 51% office space and only 4% meeting rooms. Figures 5.5 and 5.6 show the floor plans for the cell type office building (ground floor and 1st-5th floors).

1

3

2

11

10 9

Figure 5.5

132

4

8

5 7

6

Ground floor (cell type): Input for IDA ICE 3.0.

Description of the building model

1

2

3 11

10 9

Figure 5.6

4

8

7

5 6

First - fifth floors (cell type): Input for IDA ICE 3.0.

• Open plan office Figure 5.7 shows the area of each zone type.

Figure 5.7

Zone areas for open plan type office building.

In the same way, 3 floors were also considered for the open plan reference building. The first floor has 6 zones. There is airflow exchange between the zones 1, 4, 8 assuming a big opening (always open door) between them. The ground floor is shown in Figure 5.8 and floors 1 to 5 in Figure 5.9.

133

Single and Double Skin Glazed Office Buildings

2 1

8

4

9

5

Figure 5.8

Ground floor (open plan type): Input for IDA ICE 3.0.

5 8

1

4

2

Figure 5.9

5.1.3

First - fifth floors (open plan type): Input for IDA ICE 3.0.

Description of building elements

• Thermal transmittance of the building materials A description is given below of the properties of the building elements used for the reference building (see Table 5.1).

134

Description of the building model

Table 5.1

Description of the building elements used, disregarding thermal bridges.

Building Material type element (from inside to outside)

Thickness Thermal (m) conductivity (Wm-1K-1)

Density (kgm-3)

Specific U-value heat (Wm-2K-1) (Jkg-1K-1)

Gypsum board External Mineral wool wall Wood (studs) (long Gypsum board façade) Air gap Facing bricks

0.013 0.1068 0.011 0.009 0.04 0.12

0.18 0.036 0.14 0.18 0.25 0.58

758 16 500 758 1.2 1500

840 754 2300 840 1006 840

External wall (short façade)

0.2 0.145 0.04 0.12

1.7 0.036 0.25 0.58

2300 16 1.2 1500

880 754 1006 840

Gypsum Internal Air gap wall Light insulation Air gap Gypsum

0.026 0.032 0.03 0.032 0.026

0.22 0.17 0.036 0.17 0.22

970 1.2 20 1.2 970

1090 1006 750 1006 1090

0.62

Linoleum Linoleum floor Concrete Acoustic tiles

0.0025 0.3 0.012

0.156 1.7 0.057

1200 2300 720

1260 880 837

1.75

Ground Linoleum floor Concrete Expanded plastic

0.0025 0.1 0.1

0.156 1.7 0.035

1200 2300 1000

1260 880 1700

0.32

Roof Acoustic tiles above Concrete 6th floor Mineral wool Wood Under felt

0.0125 0.3 0.2 0.02 0.003

0.057 1.7 0.036 0.14 0.13

720 2300 16 500 930

837 880 754 2300 1300

0.16

Concrete Mineral wool Air gap Facing bricks

0.27

0.21

The thermal transmittance of the materials used was initially calculated by IDA ICE 3.0. However, since the thermal losses due to thermal bridges were not included in these calculations, further calculations were carried out as described in Appendix E. A comparison between the theoretical values and the practical values calculated by Swedish Building Regulations is shown in Table 5.2. Finally, it was decided that the use of the practical values, according to the calculation procedure in the Building Regulations, was preferable for the simulation of the reference building. In order to meet the requirements of the Swedish Building Regulations (overall thermal transmittance of the building), modifications were made in the IDA ICE 3.0 library (increase of insulation for the external walls and roof ).

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Single and Double Skin Glazed Office Buildings

Table 5.2.

Theoretical and applied thermal transmittance of the materials used.

Building element

Theoretical U-value (Wm-2K-1)

Applied U-value (Wm-2K-1)

0.27 0.22 0.62 0.16 0.32 1.75

0.32 0.25 0.62 0.19 0.32 1.75

External wall (long façade) External wall (short façade) Internal walls Roof (above 6th floor) Ground floor Intermediate floors

The total U · A value of the building envelope does not quite meet the requirements of the Swedish Building Regulations, but the energy use for heating meets the requirements of the Building Regulations reference building. • Windows A description of the geometry and the properties of the windows of the reference building follows. o Windows of the long façade (type A)

frame sash

1.3 m

100mm

1m

Figure 5.10

136

Typical window in the long façade.

Description of the building model Table 5.3

Properties of window in the long facade.

Window properties

Size of window Uwindow typical of 90s

1.3 m2 2 W/m2K

Glazing properties

Description

Triple glazed unit. Outer 4mm clear float, 30mm space, D4-12 inner IGU (Insulated Glazing Unit).

Size (Ag) 0.88 m2 Ug (Calculated with Parasol) 1.85 W/m2K Frame properties

Shading device*

Description

Wood covered by aluminium on the outside

Size (Ag)

0.42 m2 (32% of the total window area)

Uf

2.31 W/m2K

Description

Intermediate white venetian blind placed in the 30 mm gap (at 45 degrees)

Uglazing effective

1.65 W/m2K

* Shading device: it is assumed that the venetian blind closes (100%), when the incident light inside the glass exceeds 100W/m2. The Uglazing effective was calculated by the Parasol software.

o Windows in the short façade (type B)

frame sash

100mm

2.7 m

1.6 m

Figure 5.11

Typical window in the short façade.

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Single and Double Skin Glazed Office Buildings

Table 5.4

Properties of window in the short facade.

Window properties Glazing properties

Size of window

4.32 m2

Uwindow typical of 90s

1.94 W/m2K

Description

Triple glazed unit. Outer 4mm clear float, 30mm space, D4-12 inner IGU (Insulated Glazing Unit).

Size (Ag)

3.5 m2

Ug (Calculated with Parasol) 1.85 W/m2K Frame properties

Shading device*

Description

Wood covered by aluminium on the outside

Size (Ag)

0.82 m2 (19% of the total window area)

Uf

2.31 W/m2K

Description

Intermediate white venetian blind placed in the 30 mm gap (at 45 degrees)

Uglazing effective

1.65 W/m2K

* Shading device: it is assumed that the venetian blind closes (100%), when the incident light inside the glass exceeds 100W/m2. The Uglazing effective was calculated by the Parasol software.

5.1.4

Special modifications for the simulated model

In order to input the real (virtual) building into IDA ICE 3.0 some special modifications had to be made. • Office volume IDA ICE 3.0 calculates the thermal losses only for the interior of a room (inside part of the internal walls, upper part of the floor to lower part of the ceiling, etc). Thus, in order to include the transmission losses through the external wall above the suspended ceiling and the concrete floor (part b in Figure 5.12), the room height was increased from 2.7 m (real room height) to 3.5 m (Figure 5.13). The same assumption was made for the internal walls. Since the construction of the internal walls is light, in the same way the internal walls were included, when the office geometry was defined.

138

Description of the building model

Concrete (0.3 m) Air (0.5 m) Acoustic tiles

b

room (2.7 m) Office room m)

a

External wall

Figure 5.12.

Transmission losses calculated by IDA ICE 3.0 for 2.7 m floor height

Real office model.

Concrete (0.3 m) Acoustic tiles

Office room (3.2 m) m)

c

Transmission losses calculated by IDA ICE 3.0 for 3.5 m floor height

External wall

Figure 5.13.

Equivalent office model.

• Windows Equivalent windows were also assumed, in order to save time for the simulations. For each façade of every thermal zone only one window is assumed. The size of the equivalent window is equal to the sum of the real ones, while the proportion of the frame area to the window area remains the same. The equivalent window is placed 0.8 m from the floor and 15 in the middle of each zone. • Internal boundary conditions On each floor it is assumed that each zone is connected with an identical one. This was achieved, since adiabatic conditions were assumed from 139

Single and Double Skin Glazed Office Buildings

the computing program. The same assumption was made between the floors. This was achieved by keeping the distance between the zones at a minimum level of 0.5 m. • Infiltration rates The infiltration rate assumed for the reference building is 0.1 ach (air changes per hour) for the whole building. The easiest way to insert infiltration into IDA ICE 3.0 is to increase the mechanical supply and exhaust air by 0.1 ach, and reduce the heat recovery efficiency. The efficiency calculations are described in the HVAC Subsection 5.1.8.

5.1.5

Control set points for indoor air temperature

Three control set points were chosen for the simulations of the reference building, as shown in Table 5.5. The normal control set point is considered the standard (reference) case, since the lower and upper temperature limits meet the requirements for indoor temperatures according to practice in modern Swedish offices (VVS, 2000). However, the two other control set points can provide useful information concerning variation in energy use as a function of the mean air and directed operative temperature and the perception of thermal comfort. Another parameter changed with the three control set points is the artificial light provided at the workplace. For the strict control it is assumed that the lights are switched on according to the occupants’ schedule, regardless of the amount of daylight inside the offices. For the normal and poor control set points, however, set points of 500 lux and 300 lux respectively were assumed at the workplace. The main reason that these set points were assumed is to calculate the savings in electricity for artificial lighting for different control set points, glazing, shading devices and proportion of glass in the building.

140

Description of the building model

Table 5.5

Classification of the indoor environment.

Classification (control set points)

Minimum Air Temperature ºC (winter)

Maximum Air Temperature ºC (summer)

Daylight at workplace (lux)

Poor

21

26

Normal

22

24.5

Strict

22

23

Setpoints+Schedule 300-5000 Setpoints+Schedule 500-5000 Schedule

5.1.6

Occupancy

• Occupant density o Cell type For the cell type office building the number of occupants is shown in Table 5.6. Table 5.6

Occupants for cell type (p=persons).

Zone type

Corner offices Double office rooms Single office rooms Meeting rooms (6p) Meeting rooms (8p) Meeting rooms (12p) Storage room Corridor (1st floor) Corridor (2nd-6th floor) Total

Number of occupants for each zone

Total (theoretical) number of occupants for each zone type

Total (real) number of occupants (during working hours)

1 2 1 6 8 12 0 0 0

22 166 156 66 8 36 0 0 0

17.6 132.8 124.8 24.6 3.2 14.4 0 0 0

454

319.2

The total floor area of the building (inside the external walls) for the number of working places (only office rooms) is 18 m2/occupant. According to personal communication with the architect involved in the “Glazed Office Buildings” project, Christer Blomqvist, it was assumed that 80% 141

Single and Double Skin Glazed Office Buildings

of the occupants are present during office hours. The distribution of the occupants in the building is shown in Figure 5.14.

Figure 5.14.

Occupants (real) per zone for cell type.

m²/real occupant

The density of the occupants for the cell type office building is shown in Figure 5.15. 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

18,9

12,6 9,6

5,4

Corner office Double office Single office rooms rooms rooms

Meeting rooms (6p)

6,3 5,2

Meeting rooms (8p)

Meeting rooms (12p)

Zone type

Figure 5.15

142

Density of each zone for cell type (real number of occupants, p=persons).

Description of the building model

o Open plan type The total floor area of the building (inside the external walls) for the number of working places (only office rooms) is 15.5 m2/occupant. For the open plan type it is assumed that there is a 20% increase in the occupants for the offices (compared with the cell type), while the density of the meeting rooms remains the same. The number of occupants is shown in Table 5.7.

Table 5.7

Occupants for the open plan.

Zone type

Typical corner zones Reduced corner zone Intermediate zones Meeting rooms Storage rooms Total

Number of occupants for each zone

Total (theoretical) number of occupants for each zone type

Total (real) number of occupants (during working hours)

16 12 24 8 0

211.2 14.4 172.8 192 0

169 11.5 138.2 76.8 0

590.4

395.2

The distribution of the occupants in the building is shown in Figure 5.16.

Figure 5.16

Occupants (real) per zone for open plan.

143

Single and Double Skin Glazed Office Buildings

m²/real occupant

The density of the occupants for the open plan type office building is shown in Figure 5.17. 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

22,4 21,2

16,2

6,3

Typical corner zones Reduced corner zone

Intermediate zones

Meeting Rooms

Zone type

Figure 5.17

Density of each zone for open plan (real number of occupants).

The total real increase of the occupants in the open plan type is 15.5% (for the offices the increase is 20%), since the design and use of the two plan types (cell and open) are not the same (for example the cell type has 2 meeting rooms on floors 1-5 for 6 persons each, while the open plan has 4 meeting rooms for 8 persons each for the same floors). Thus, an equivalent number of occupants (interior of the open plan with density of the cell type) had to be considered in order to calculate the relative increase in the occupants in the open plan. • Occupant load The occupants’ schedule, activity level, clothing and use of the rooms are shown in Table 5.8.

144

Description of the building model Table 5.8

Occupant load.

Schedule

Schedule for offices: 08:00 -12:00, 13:00 – 17:00 Typical winter occupant schedule (01/01-31/04, 01/10-31/12): 50% working during the Christmas vacations, otherwise 100% weekends closed. Typical summer occupant schedule (01/5-30/09):50% working during July, 75% working during June and August, otherwise 100%, weekends closed. Schedule for meeting rooms: 10:00 -12:00, 13:00 – 15:00 Typical winter occupant schedule (01/01-31/04, 01/10-31/12): 50% working during the Christmas vacations, 100% rest, weekends closed. Typical summer occupant schedule (01/5-30/09):50% working during July, 75% working during June and August, 100% rest, weekends closed.

Activity level

Office activity1 met = 108 W / occupant (1 met corresponds to 58.2 W / m2 body surface)Task: sitting, reading

Clothing

For winter conditions: 1 clo For summer conditions: 0.6 clo

Use of rooms

For the offices it is assumed that 80% of the office workers are present during the working hours (since people can work at home or be absent for some other reason). For the meeting rooms it is assumed that they are used 50% of the time and used to 80% of their capacity (total 40% comparing with the offices).

5.1.7

Lights

For the artificial lighting, energy efficient lighting (fluorescent tubes with HF fittings) was assumed. For the cell plan this means an installed power of 12 W/m2 for the offices and the meeting rooms and desired illuminance at the desk of 500 lux (according to personal communication with Dr. Helena Bülow-Hübe, Division of Energy and Building Design, Lund University). For the corridors and the rest of the spaces an installed power of 6 W/m2 and desired illuminance of 250 lux was assumed. However, for the open plan the installed power of 12 W/m2 was assumed for all the working space. The luminous efficacy of the lights is set to 41.7 lm/W.

145

Single and Double Skin Glazed Office Buildings

5.1.8

HVAC

5.1.8.1 Heating and cooling The heating was provided by water radiators, while the cooling by chilled beams as described in Appendix D. For the water radiators proportional control and for the chilled beams PI control was assumed.

5.1.8.2 Ventilation The airflow rates were set after discussions with the HVAC engineer Lars Sjöberg. • For the cell type: The air is supplied in the offices and extracted from the corridors. For the offices there is a CAV (constant air volume) control, supplying 10 l/s air (typical design value for cell type plan offices) for each person. For the meeting rooms VAV (variable air volume) CO2 control is assumed. • For the open plan: In this case the air is supplied and exhausted from the office space (since there is no separation between offices and corridors). The supply air for each person is assumed to be 7 l/s (normal design value for open type plan offices) for the office space (CAV control) and a VAV CO2 control is assumed for the meeting rooms. In order to keep the supply and exhaust air flow rates balanced in IDA ICE 3.0, it was assumed that the air is supplied in the rooms through the Air Handling Unit and passes to the corridor through transfer air devices (simulated as air leakage paths) to be exhausted. Thus, the amount of the exhaust air (from the corridor) is equal to the mechanical and natural ventilation of the offices. However, since the exact amount of air supplied in the meeting rooms is not known (due to the VAV CO2 control), in order to keep the balance between the total supply and exhaust air, it was assumed that the amount of air supplied is also exhausted from the meeting rooms. The infiltration and exfiltration of the whole building was assumed to be 0.1 ach. This rate corresponds to 2.7 m room height. For the meeting rooms (VAV CO2 control), however, since the mechanical supplied air in the meeting rooms can not be increased manually (assuming that it is natural ventilation) the infiltration of the meeting rooms was added to the infiltration of the offices depending on the size of each office. For the cell type building there is a similar problem with the corridor. Since there is only exhaust air, the infiltration of the corridor was added to the offices. 146

Description of the building model

It is important to consider an assumption that was made for the Air Handling Unit’s efficiency; the easiest way to insert infiltration in IDA ICE 3.0 is to increase the mechanical supply and exhaust air by 0.1 ach, and reduce the Heat Recovery Efficiency. However, since the mechanical ventilation of the meeting rooms is not known, it is assumed that the airflow for each one depends on the schedule and the number of occupants. The theoretical heat recovery efficiency for the AHU is 60%. For the cell type, the efficiency drops to 53.8%, due to the natural ventilation, as discussed in Section 5.14. The supply air temperature of the AHU varies with the outdoor temperature, which is also inserted in IDA ICE 3.0 as shown in Figure 5.18:

Figure 5.18

Set point for supply air temperature (IDA ICE 3.0 input).

More detailed description of the ventilation rates of each zone is given in Appendix F.

5.1.8.3 Equivalent heat recovery efficiency The infiltration rate decided for the reference building is 0.1 ach for the whole building. As already mentioned, the easiest way to insert infiltration in IDA ICE 3.0 is to increase the mechanical supply and exhaust air by 0.1ach, and reduce the heat recovery efficiency. The theoretical value of the efficiency was 60%, and the mechanical air flow (excluding the natural one) was: 147

Single and Double Skin Glazed Office Buildings

o 3997 l/s for the cell plan o 3307 l/s for the open plan The total airflow (including natural airflow) was: o 4459 l/s for the cell plan o 3521 l/s for the open plan Therefore, the practical value for the heat recovery efficiency is 53.8% and 52.4% respectively. The AHU is on from 5:30 till 22:00 during weekdays (100%) and weekends (50%). However, there is natural ventilation (infiltration and exfiltration) during the rest of the hours. Thus, the off value (natural ventilation during the hours that the AHU is not working) is set to 0.1038 for the cell type according to the following equation:

natural ventilation total ventilation off value = 100 − heat recovery efficiency 100 Equation 5.1.

Off value for the AHU .

Likewise, for the open plan the off value (natural ventilation during the hours that the AHU is not working) is set to 0.1314 (heat recovery efficiency for the off value is 0, since the off value for the heat exchanger is set equal to 0). The on value during the weekends is calculated as follows:

on value =

50% mechanical ventilation + natural ventilation total ventilation

Equation 5.2. On value for the AHU

The schedule of the AHU is presented in Table 5.9.

148

Description of the building model

Table 5.9

Schedule of AHU unit

AHU Properties Air Handling Unit schedule On Value Off Value

Cell type

Open plan

Week days: Weekends: 06:00 – 20:00 08:00 – 17:00

Week days: Weekends: 06:00 – 20:00 08:00 – 17:00

1

0.552 0.1038

1

0.5679 0.1314

5.1.8.4 Use of electricity Regarding the electricity for ventilation, specific fan power of 2.5 kW/m3s was assumed, which is representative value of a well performing building of the nineties.

5.1.9

Electrical equipment

In this chapter, a brief description of the electrical equipment used is given. For the cell type office building, the corner offices (1 occupant) are equipped with 1 PC (125 W), 1 printer (30 W) and 1 fax (30 W). The double and single offices are equipped only with PCs (2 and 1 respectively). No electrical equipment is assumed for the meeting rooms. Four copiers (500 W), 4 printers and 2 faxes are placed in each corridor for general use. The annual energy use of equipment for the cell type office building is 22 kWh/m2. For each floor of the open plan office building it is assumed that there is 1 PC (30 W) per occupant, while the printers (8 units of 30 W and 4 units of 50 W), the faxes (8 units of 30 W) and the copiers (4 units of 500 W) are mainly used by everybody. No equipment was assumed for the meeting rooms. The annual energy use of equipment for the open plan office building is 21 kWh/m2. The lower annual energy use for the equipment of the open plan alternatives is inconsistent with the higher density. As one would expect, the larger number of occupants would increase the need for equipment use; however, the common use of equipment and the more and bigger meeting rooms of the open plan decrease this need. The schedule assumed for the use of the equipment is from 08:0012:00 (80%), from 12:00-13:00 (15%) and from 13:00-17:00 (80%) for a typical workday. During the Christmas vacations and July 50% of the typical use was assumed and 75% during June and August. During the weekends no use of equipment was assumed. The number and schedule of the units were decided after personal comunication with WSP architect

149

Single and Double Skin Glazed Office Buildings

Christer Blomqvist. The energy used by the office equipment is suggested by Wilkins (2000). For both (cell and open) plan types a server room was assumed with energy use of 175 kWh/occupant (Jensen, 2003). Thus, the annual energy use is 10 kWh/m2 for the cell and 13 kWh/m2 for the open plan type. The cooling of the server room is also included in the energy use calculations. Energy use of 87.5 kWh/occupant was assumed for both plan types. The energy use is 5 kWh/m2 for the cell and 6kWh/m2 for the open plan type. The server rooms were not modelled by IDA ICE 3.0 (unlike, the energy use for the fans and pumps).

5.2

Description of single skin glazed alternatives

5.2.1

Description of 60% glazed building

The 60% glazed building is identical with the reference one, with the only difference that the glazed area increases from 30% to 60% as shown in Figure 5.19. A detailed description of the façade construction follows.

Figure 5.19

60% glazed alternative.

5.2.1.1 Façade construction • Façade with internal or intermediate shading devices

150

Description of the building model

A view of the façade of the 60% glazed building (with intermediate or internal shading devices) is shown in Figure 5.20. The 60% window area refers to a floor height of 3.5 m (exterior façade). The windows can be opened for natural ventilation of the building. The total window area of a single office is 5.04 m2 out of 8.4 m2 wall area (60%). The glass area is 3.6 m2 (72.5% of the window area) and the frame area 1.4 m2 (27.5% of the window area; see Figure 5.20).

300mm 450mm 50mm 60mm

580mm

openable

1880mm

1130mm

openable

openable

60mm 50mm 650mm

1150mm

1200mm

2400mm

Figure 5.20

60% glazed façade construction (with intermediate or internal shading devices).

• Façade with external horizontal louvres The main difference of the façade for the alternative with fixed horizontal louvres is that 2 of the 3 windows are not openable, as shown in Figure 5.21. This results in a higher glass to window area ratio. Additionally, the Uf of the frame for the openable window is 1.8 W/m2K instead of 1.6 W/m2K. The total window area of a single office remains 5.04 m2 out of 8.4 m2 wall area (60%). The glass area is 4.3 m2 (84.7% of the window area) and the frame area 0.7 m2 (15.3% of the window area). The openable frame is 0.27 m2 (38.5% of the frame).

151

Single and Double Skin Glazed Office Buildings

300 mm 450 mm 50 mm

700 mm

2000 mm

1130 mm

openable 50 mm 650 mm

1150 mm

1200 mm

2400 mm

Figure 5.21

60% glazed facade with external fixed horizontal louvres.

5.2.1.2 Window properties The window properties for the 60% glazed alternatives are shown in Tables 5.10 and 5.11. The rationale for the choice of alternatives is given in Subsection 4.1.2. For the given Uglazing and Uframe the Uwindow was calculated according to the following equation:

U window = Equation 5.3

U glazing × A glazing + U frame × A frame A glazing + A frame Thermal transmittance of the window.

Uframe includes the edge losses of the glass. For the 7th alternative there are two frames used in the façade as shown in Figure 5.21. The U-value was calculated as a weighted average. The window properties (glazing and frame) for the 60% glazed alternatives are shown in Table 5.10.

152

Description of the building model

Table 5.10 Building alternative 1 2 3 4 5 6 7

Window properties (glazing & frame). Uwindow (W/m2K)

Uglazing (W/m2K)

Uframe (W/m2K)

Aglazing (m2)

Aframe (m2)

1.97 1.27 1.27 1.27 1.27 1.27 1.26

1.85 1.14 1.14 1.14 1.14 1.14 1.14

2.31 1.6 1.6 1.6 1.6 1.6 1.6 1.8 1.65

3.6 3.6 3.6 3.6 3.6 3.6 3.82

1.4 1.4 1.4 1.4 1.4 1.4 0.89 0.27 1.16

Table 5.11 sets out the impact of the shading devices for different glazing alternatives. The “effective” value refers to the cases in which the shading devices are used. The default value (set point) of IDA ICE 3.0 was used for the simulations. This value corresponds to a maximum limit of 100 W/m2 on the inside of the glass. Above this value the shading devices are used 100% (45° slat angle). The Uglazing, g, Tsol, Ugl. effective, ggl.effective and Tgl,effective (effective solar transmittance) are calculated for perpendicular ray angle “standardized” with the “Parasol” software (Wall and Kvist 2003), while Tvis is taken from Pilkington Catalogue (2004). When the glazing properties are inserted in IDA ICE 3.0, however, the Tvis is not needed, since the software calculates the daylight availability taking into account the direct solar transmittance and not the visual one. For the case with external louvres the solar and direct solar transmittance used are monthly average values calculated by Parasol software. The reason for this additional calculation is that since the horizontal external louvres are fixed (and thus operating all year round) monthly solar factor values can better approximate the reality compared with the yearly g value that IDA ICE 3.0 uses for the calculations. Using the mentioned computing program the gsystem and the Tsystem for every month were calculated as shown in Table 5.12. More information about the glazing units (e.g. daylight transmittance, commercial names of the panes, etc) is given in Table 4.2. These monthly values were inserted in IDA ICE 3.0 (schedule of external shading devices).

153

Single and Double Skin Glazed Office Buildings

Table 5.11 Building alternative 1 2 3 4 5 6 7

Table 5.12

Impact of shading on glazing alternatives. Uglazing (W/m2K)

g

Tsol

Ugl. effective (W/m2K)

1.85 1.14 1.14 1.11 1.14 1.14 1.14

0.69 0.59 0.35 0.23 0.58 0.35 0.35

0.58 0.44 0.30 0.22 0.44 0.30 0.30

1.65 1.08 1.07 1.04 1.08 0.92 1.14

ggl.effective Tgl,effective 0.30 0.23 0.28 0.22 0.47 0.19 0.20

0.13 0.10 0.08 0.06 0.12 0.08 0.17

Solar factor and solar transmittance for the fixed horizontal external louvres.

Month

g-mean sunshade (%)

g-mean window (%)

g-mean system (%)

Tmean sunshade (%)

Tmean window (%)

Tmean system (%)

1 2 3 4 5 6 7 8 9 10 11 12

84.6 74.4 58.5 44.2 45.2 49.0 51.1 40.5 48.9 68.3 80.5 87.1

34.4 34.1 33.9 33.6 33.1 33.0 32.9 33.2 33.4 33.9 34.4 34.5

29.1 25.4 19.8 14.9 15.0 16.2 16.8 13.4 16.3 23.1 27.7 30.0

84.4 74.0 57.9 43.5 44.7 48.7 51.0 40.2 48.5 68.1 80.2 86.8

29.4 29.4 29.2 29.1 29.0 28.9 28.9 29.1 29.1 29.3 29.3 29.4

24.8 21.7 16.9 12.7 13.0 14.1 14.7 11.7 14.1 19.9 23.5 25.5

A detailed description of the frame construction is given in Appendix G.

154

Description of the building model

5.2.2

Description of 100% glazed building

A view of the 100% glazed building is shown in Figure 5.22.

Figure 5.22

100% glazed alternative.

The U values and g values for the windows are the same as for the 60% alternative, since the same ratio between glazing and frame area was assumed. The façade construction of the 100% glazed building with internal or intermediate shading devices is shown in Figure 5.23.

155

Single and Double Skin Glazed Office Buildings

300 mm 450 mm 50 mm 60 mm

580 mm

openable

1880 mm

1130 mm

openable

openable

60 mm 50 mm 600 mm

50 mm 1150 mm

1200 mm

2400 mm

Figure 5.23

100% glazed façade construction (with intermediate or internal shading devices).

The façade construction of the 100% glazed building with fixed external horizontal louvres is shown in Figure 5.24.

156

Description of the building model

300 mm 450 mm 50 mm

700 mm

2000 mm

1130 mm

openable 50 mm 600 mm

50 mm 1150 mm

1200 mm

2400 mm

Figure 5.24

100% glazed facade with external fixed horizontal louvres.

5.3

Description of double skin glazed alternatives

5.3.1

WIS 3.0 simulations

5.3.1.1 Geometry of the “standard” double façade box Two double skin façade construction types were assumed: a multi storey type and a box window type. Since the software used for the current simulations (WIS 3) is a two dimensional computing tool the cavity width does not influence the output of the simulations. For all the cases, however, the width was assumed to be 3.5 m. The cavity height in the case of a multi storey high façade was assumed to be 10 m, 20 m, and 30 m, while for the box window it was assumed 3.5 m. The depth varies from 0.2 m up to 1.6 m. No frame was considered for the WIS 3 simulations.

5.3.1.2 Geometry of the airflow window For the airflow window cases a box window façade was assumed with a total height and width of 3.5 m. The mechanically ventilated cavity is 157

Single and Double Skin Glazed Office Buildings

0.3 m deep. In the airflow window cases air is supplied (11.4 l/sec) to the room and exhausted through the cavity to the heat exchanger for heat recovery purposes.

5.3.1.3 Description of the openings The openings for the multi storey high double façade are assumed to be horizontal at the top and the bottom of the cavity. At the top of the façade dampers are applied (as shown in Figure 5.25), in order to control the openable area all year round. Since the dampers occupy some area, when the cavity is fully opened the actual ventilated area (for even cavity depths) is the 87% of the area if no dampers were applied. When the cavity depth is uneven (e.g. 0.3 m, 0.5 m, etc) the actual opening area is the same as if the cavity depth was 0.1 m smaller.

Figure 5.25

Dampers for the multi storey high façade.

For the box window the height and width of the cavity were assumed to be 3.5 m. The cavity depth varied (depending on the case) from 0.2 m up to 1.6 m. The openings of the façade in this case are vertical. However, since WIS 3 can not handle vertical openings, equivalent horizontal openings were assumed.

158

Description of the building model

5.3.2

IDA ICE 3.0 Input (zone level)

5.3.2.1 Office description (IDA ICE 3.0 - zone level) In order to carry out the parametric study on a zone level, a typical single office room was considered. The office was considered to be on the second floor of the building. The occupancy, the equipment and the other internal loads (with their schedules) are described in detail in Appendix D. All the installations were considered to be the same as in the reference building.

5.3.2.2 Geometry of the box window A box window façade was assumed, covering both the window and wall area of total height of 3.5 m and width of 2.4 m. The depth of the cavity was assumed to be 0.8 m for the “standard” double façade and 0.3 m for the airflow window case. At the upper and lower parts of the cavity, dampers were assumed (same as those described in the WIS 3 input). When the cavity is fully open the actual opening area with the dampers is the 87%. When the cavity is closed a very small opening of 0.01 m2 was assumed, since the cavity is not completely sealed. A discharge coefficient of 0.65 for the top and 0.55 for the bottom opening was assumed (Kalyanova et. al, 2006).Thus, the equivalent leakage area (ELA) is calculated from: ELA = A × C d × free area where A: is the area of the opening, with the dampers considered (m2) Cd: is the discharge coefficient free area: actual opening area (with the dampers considered)

The Equivalent Leakage Area (ELA) for each zone is given in Table 5.13, while more detailed cavity characteristics are presented in Appendix J.

159

Single and Double Skin Glazed Office Buildings

Table 5.13

Equivalent Leakage Area (ELA) for double façade opennings of different zones.

Zone type Corner offices (short façade) Corner offices (long façade) Double office rooms (long façade) Double office rooms (short façade) Single office rooms Corridors

ELA (m2) – bottom leak

ELA (m2) – upper leak

1.84 1.58 1.84 1.58 1.06 0.70

2.18 1.87 2.18 1.87 1.25 0.83

5.3.2.3 Geometry of the multi storey high façade A multi storey high façade (0.8m deep) was assumed covering the whole building façade. In order to simulate correctly the air temperature stratification along the 24 m of the cavity, five box window cavities (floors 1, 2, 3, 4 and 5) were linked (the ground floor was assumed with a single skin façade). Since the airflow model in IDA ICE 3.0 is a one node one, the cavity air temperatures calculated are the average air temperature of each level. The dampers were placed at the top opening of the façade. Grills inside the cavity and between the different floors (used for maintenance purposes) were also assumed. The actual top opening (inserted in IDA ICE 3.0) was calculated as before; 87% for fully open and 0.01 m2 for fully closed cavity. The equivalent leakage area (ELA) for the upper and lower openings is calculated as before and presented i detail in Appendix J.

5.3.2.4 Properties of the inner and outer skin In order to insert the properties of the glazing in IDA ICE 3.0 the thermal transmittance and the total and direct solar transmittance had to be calculated. These calculations were carried out in WIS 3 for normal angle of incidence. The inner and outer skin properties are presented in Tables 5.13 and 5.14 and described further in section 4.1.3.

160

Description of the building model

Table 5.14

Inner and outer skin properties for the “standard” double façade alternatives.

DSF Case

U value Outer skin Inner skin

g value Outer skin Inner skin

Tsol Outer skin Inner skin

A D E F

5.79 5.79 5.79 5.79

0.789 0.532 0.532 0.789

0.742 0.389 0.389 0.742

Table 5.15

2.90 2.74 1.46 1.31

0.746 0.746 0.655 0.215

0.685 0.685 0.565 0.179

Inner and outer skin properties for the airflow window alternatives

AW Case

U value Outer skin Inner skin

g value Outer skin Inner skin

Tsol Outer skin Inner skin

A D E F G

2.87 2.71 1.45 1.30 1.31

0.688 0.419 0.369 0.213 0.214

0.624 0.338 0.299 0.169 0.176

5.92 5.92 5.92 5.92 5.66

0.846 0.846 0.846 0.846 0.738

0.82 0.82 0.82 0.82 0.677

The properties of the panes used are presented in more detail in Appendix H. The properties of the “standard” double façade and airflow window modes (when no ventilation occurs in the cavity) are described in Appendix I. The frame to window ratio was assumed to be 0.28 for the inner and 0.18 for the outer skin. Uframe was assumed to be 1.6 W/m2K.

5.3.2.5 Shading devices Two types of shading device were considered (white and blue venetian blind with a slat angle of 45°), in order to study their impact on the energy use and thermal comfort; their properties are described further in Appendix K. The thermal and solar transmittance (g and Tsol) have been calculated with the Parasol software. Since the shading is used mostly during summer, an average multiplier value (for the U, g and Tsol values) was assumed. This average includes a five month period, from May to September. The multiplier is inserted in IDA ICE 3.0 as the inner shading coefficient of the outer skin (outer pane for the “typical” double façade cases and intermediate one for the airflow window mode). Eight orientations were taken into account for the calculations: north, northwest, west, 161

Single and Double Skin Glazed Office Buildings

southwest south, southeast, east and northeast as shown in Figures 5.26 and 5.27. The multipliers of the total and direct solar transmittance are also presented in Appendix K. 0.9 0.88 0.86 0.84 0.82 0.8 0.78 0.76 0.74 0.72 0.7 0.68 0.66 0.64 0.62 0.6 0.58 north

Figure 5.26

northeast

east

southeast

south

southwest

west

northwest

DF A,F White blinds

DF A,F Blue blinds

DF D,E White blinds

DF D,E Blue blinds

AW A White blinds

AW A Blue blinds

AW D White blinds

AW D Blue blinds

AW E White blinds

AW E Blue blinds

AW F,G White blinds

AW F,G Blue blinds

Multipliers for the gshading as used in the IDA ICE 3.0 simulations.

The multipliers for direct solar transmittance are almost the same when dark (blue) shading devices are applied. For white venetian blinds, however, the multipliers follow the same trend as before: the shading effect is higher for outer panes with larger Tsol.

162

Description of the building model

0.3 0.28 0.26 0.24 0.22 0.2 0.18 0.16 0.14 0.12 0.1 0.08 north

Figure 5.27

5.4

northeast

east

southeast

south

southwest

west

northwest

DF A,F White blinds

DF A,F Blue blinds

DF D,E White blinds

DF D,E Blue blinds

AW A White blinds

AW A Blue blinds

AW D White blinds

AW D Blue blinds

AW E White blinds

AW E Blue blinds

AW F,G White blinds

AW F,G Blue blinds

Multipliers for the Tsol shading.

Assumptions made during the calculations

Condensation issues were not considered during this study. For the double façade mode the double pane (thermal barrier) is placed as inner skin. In reality, during winter, when the openings are closed the increased air temperature inside the cavity decrease the risk of condensation, while in the mechanically ventilated cases the cold outdoor air could be an issue. For naturally ventilated cavities the stack effect was considered to be the main driving force all year round. During summer, the main driving force is the thermal buoyancy, while during winter is the wind effect (Saelens 2002). However the naturally ventilated double facades are most often closed during the winter, in order to increase the air temperature inside the cavity providing higher surface temperatures of the inner skin. Moreover, simulations carried out during the IEA Task 34 (Testing and Validation of Building Energy Simulation Tools) show that the impact of wind effect does not influence much the energy use for heating and cooling the zone behind the double façade or the surface temperatures of the inner layer. Another assumption made, was that no heat absorption by the grills (in between the floors of a multi storey high facade) was considered. In the cases in which shading devices are applied this mistake is decreased since 163

Single and Double Skin Glazed Office Buildings

the grills are shaded (mostly when the shading devices are placed close to the external pane). In the cases, however, when no shading devices applied (mostly during winter), the absorption by the grills result in an increase of the air temperature inside the cavity.

164

Results and discussion

6

Results and discussion

In this chapter the results of the simulations are presented and discussed in three parts: • reference building • single skin glazed alternatives • double skin glazed alternatives In the first Section (results from the reference building alternatives) the parameters varied are the building orientation, the control set points and the plan type. The output of the simulations concerns the energy use, the mean air temperatures, the directed operative temperatures and the thermal comfort indices (PMV and PPD). The results are studied and discussed on both a building and a zone level. In the second Section the glazing and shading device type are varied for building alternatives of 60% and 100% window to external wall area ratios. The simulations were carried out for both open plan and cell type office buildings for different control set points. The studied parameters were the same as in the reference building and the simulations were carried out on both a building and a zone level. The third Section is divided into three parts: (a) simulations of double skin façades on a component level for steady state boundary conditions, (b) all year round simulations on a zone level and (c) all year round simulations on a building level with integrated double skin façades. The main aim of the first part (pilot study) was to study the possibilities and limitations of different double skin façade constructions, while reducing the amount of alternatives to be further simulated. The second part focuses on the proper integration of double skin façades regarding energy use and thermal comfort issues. Several alternatives were simulated varying the façade mode (naturally, mechanically and hybrid ventilated double façades and airflow windows) and the glazing and shading device type used. In the third part double skin façade alternatives were selectively simulated, in order to provide output values for purposes of comparison (especially with the single skin façade glazed building alternatives).

165

Single and Double Skin Glazed Office Buildings

6.1

Reference building

6.1.1

Energy use

As stated in Subsection 4.1.1, 18 building alternatives were generated with 30% window to external wall area ratio (2 plan types, 3 orientations and 3 control set points). The energy use for each alternative is presented in Appendix L, while the results are discussed below.

6.1.1.1 Impact of floor plan type For the reference building (identical long and short façades), the building’s orientation does not really influence its energy use, neither for the cell nor the open plan type (as described in Subsection 6.1.1.2). Thus, in order to decrease the number of comparisons, an average energy use was assumed for the 3 building orientations. Due to the higher internal loads of the open plan, the energy use for heating is slightly lower than for the cell type (see Figure 6.1); the open plan has a higher occupant density and different set points and power for lights used (6 W/m2 for the corridors of the cell type and 12 W/m2 for all the open plan space), as described in Subsection 5.1. For the same reason, the cooling demand of the building and the server rooms is higher for the open plan (the energy demand for the operation and cooling of the server rooms is proportional to the number of occupants (Jensen, 2003)). As described in Subsection 5.1.7, for the normal set points (cell type) the lights were switched on, in order to ensure a minimum level of 500 lux at the workplace, while for the open plan the lights were always switched on (since IDA ICE 3.0 can not handle any set point for artificial lighting in the non rectangular zones of the open plan type). Additionally, power of 12 W/m2 was assumed for the working spaces (offices and meeting rooms for the cell type and the whole space of the open plan), while power of 6 W/m2 was assumed for the corridor of the cell type. As a result, the energy use for lighting the open plan is 5 kWh/m2a higher; most of it due to the different installed power, since the impact of lighting control set points is limited at least for the reference (30% window to external wall area ratio) case. Although the occupancy level of the open plan is higher and one could assume that the energy use for the equipment would be higher, the larger number of meeting rooms of the open plan reduces the number of printers and faxes (see Subsection 5.1.9), bringing the internal loads (equipment) of the two layouts to almost the same level.

166

Results and discussion

140 130

123 127

120

Energy use (kWh/m²a)

110 100 90 80 70 60 50

52 45

40 30

17

20

11

14

19

22 21 8

10

6

10

13 5

6

0

Space heating

Cooling

Lighting

Equipment

SS-30%-Cell-average-normal

Figure 6.1

Pumps, fans

Server rooms

Cooling server rooms

Total

SS-30%-Open-average-normal

Impact of plan type on the energy use of the reference building (normal control set points).

In Figure 6.2, the difference in energy use for heating, cooling and lighting is compared between the two plan types for the three control set points. The energy use for heating the cell type office building (with strict set points) is 5.6 kWh/m2a (10%) higher than for the open plan one. The increase in energy use for the normal and poor control is 7.4 kWh/m2a (14%) and 8.9 kWh/m2a (19%) respectively. The positive value in Figure 6.2 shows higher energy use for the cell plan. As expected, in all the cases the energy use for heating is higher for the cell type due to the lower internal gains. On the contrary, the cooling demand of the open plan type is much higher (42%, 56%, and 48%). It can be concluded that the higher internal loads of the open plan result in more “useful” heat that can be stored in the cases with wider temperature variation (such as in poor set points); for the same reason the effect is the opposite for the cooling demand. At this point the difference in the ventilation strategy of the two plan types should be noted. As described in Subsection 5.1.8, the air supplied to the offices (cell type) passes through the doors (or leaks) to the corridor from where it is extracted, while for the open plan type the air is supplied and exhausted from the same zone. Since in the cell type office building there are no cooling beams installed in the corridor, the air temperature in the corridor at times rises above the upper control set point limit. This may cause an increase in the air temperature in the corridors, but since there are no occupants (used as sensors) placed in that zone, no discomfort is considered. On the other hand, for the open plan type building, the 167

Single and Double Skin Glazed Office Buildings

whole floor area is considered as working area and thus cooled according to the upper set point temperature limit. The corridor of the cell type plan is almost 44% of the total floor area and the rated input per unit (light) is 6 W/m2 instead of 12 W/m2 (open plan and working spaces of cell plan). For the strict set points the lights are assumed switched on during the working hours for both the cell and open plan types. However, the increased demand for proper lighting of the working area results in a 32% increase in energy use. For the normal and poor set points this difference increases, up to 35% and 36% respectively, due to the light control set points (500 lux and 300 lux) applied for the offices and meeting rooms of the cell plan. Finally, there is a 24% higher energy demand for the operation and cooling of the server rooms (regardless of the set point) for the open plan, due to the increased number of occupants (the assumed energy use is 175 kWh/am2 per occupant for operating the server rooms and 87.5 kWh/am2 per occupant for cooling the server rooms (Jensen, 2003)). The higher internal gains of the open plan type result in 6% higher total energy use for the strict set point and in 3% increase for the normal one. For the poor set point the cell plan uses slightly less energy as shown in Figure 6.2. As expected, the stricter the set points, the higher the impact of the plan type on the total energy use.

10 8,9

Energy difference between cell and open plan (kWh/m²a)

9 7,4

8 7 6

5,6

5 4 3 2 0,5

1 0 -1 -2 -3 -3,1

-4

-4,0

-5

-4,6

-6

-5,0

-5,1

-6,2

-7 -8

-7,6

-8,3

-9 -10

Energy use for heating

Strict control set points

Figure 6.2

168

Energy use for cooling

Energy use for lighting

Normal control set points

Total energy use

Poor control set points

Impact of plan type on the energy use of the reference building.

Results and discussion

6.1.1.2 Impact of orientation As pointed out above, the orientation has a very small (negligible) impact on the energy use for the reference building. The main reason is that the two long and two short facades are identical (including the shading devices used). If the façades were different, there would of course have been an impact of orientation.

6.1.1.3 Impact of control set points

Energy difference (%)

For the cell type office building the energy use for heating decreases by 7% for the normal and by 16% for the poor temperature set points (compared with the strict one) as shown in Figure 6.3. For the open plan type the heating demand decreases by 11% and 24%. Although the lower temperature limit is the same for the strict and normal control set points (22ºC), the strict set points reduce the capacity for storing heat (thermal mass), increasing the heating demand. For the normal control set points the maximum permissible air temperature is 24.5°C, while for the strict and poor set points it is 23°C and 26°C respectively. The cooling demand for the normal (compared with the strict) set point is 45% lower for the cell plan and 40% lower for the open plan type. The decrease for the poor type is 65% and 64% respectively. 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0

65

64

45 40

24 21 17

16 11

10

7 2

Space heating

Cooling

Strict - normal (cell plan) Strict - normal (open plan)

Figure 6.3

12

3 0

0

Lighting

Total

Strict - poor (cell plan) Strict - poor (open plan)

Impact of control set points on the energy use of the reference building.

169

Single and Double Skin Glazed Office Buildings

The minimum limit of 500 and 300 lux applied for the normal and poor set points results in an almost negligible decrease in energy use for lighting, 2% and 3% for the two control set points for the cell type plan. The impact of different set points on the energy use for lighting is calculated for the whole cell type building, although the set points are applied only to the working space. Thus, out of 14.7 kWh/am2 (total energy use for the strict control) 10.5 kWh/am2 (72%) are used in the working areas and 4.2 kWh/m2a (28%) in the common spaces. For the normal set points the energy decrease (0.3 kWh/am2) refers only to the working areas, so the energy use is reduced for this control to 10.2 kWh/am2, and to 10 kWh/am2 for the poor set points. For the open plan type, the lights were assumed switched on during the working hours for all the three types of control set points, thus the energy use remains the same. It can be concluded that the three different lighting strategies (for the reference building alternatives) result in small differences in energy use for lighting. Finally, as can be expected, the total energy use is lower for alternatives with less strict temperature control set points. The total energy use of the cell type reference building decreases by 10% for the normal and by 17% for the poor set point, compared with the strict control set points. For the open plan type, the decrease is 12% and 21% respectively.

6.1.2

Indoor climate on a building level

The mean air temperatures and thermal comfort indices are studied, in order to evaluate the indoor climate of the different building alternatives. In general, monthly average values, as presented below, are good indicators of the indoor climate building performance but do not provide any information about the variation over the year in individual zones. Thus, in this section monthly average air temperatures and thermal comfort indices were studied on a building level, while more detailed discussion focusing on specific zones is carried out in Subsection 6.1.3.

6.1.2.1 Weighted average mean air temperatures As can be expected, control set points have a larger influence on average mean air temperatures of the working area of the reference building, compared with the orientation and plan type. As shown in Figure 6.4, the mean air temperature difference between the cell and open plan type of the reference building is very small for strict set points and it increases as the permissible air temperature variation (normal and poor set points)

170

Results and discussion

26,5 26,0 25,5 25,0 24,5 24,0 23,5 23,0 22,5 December

November

October

September

August

July

June

May

April

March

February

22,0 January

Weighted average mean air temperature (°C)

increases. As expected, the open plan type is warmer due to the higher internal loads.

SS-30%-Cell-average-strict

SS-30%-Open-average-strict

SS-30%-Cell-average-normal

SS-30%-Open-average-normal

SS-30%-Cell-average-poor

SS-30%-Open-average-poor

Figure 6.4

Weighted average mean air temperatures for the working area of the reference building.

For the normal control set point the maximum permissible air temperature (24.5°C) results in higher air temperature differences during February (0.6 °C) while the poor set point (26°C) results in higher differences during April (1.4°C). The impact of orientation on the (weighted average) mean air temperatures of the building is almost negligible (see Figure 6.5), due to the identical short and long façades and the moderate window areas; further studies, however, are carried out, in order to study the impact of orientation on specific zones.

171

26,0 25,5 25,0 24,5 24,0 23,5 23,0 22,5

SS-30%-Cell-NS-poor

Figure 6.5

SS-30%-Cell-NS45-poor

December

November

October

September

August

July

June

May

April

March

February

22,0 January

Weighted average mean air temperature (°C)

Single and Double Skin Glazed Office Buildings

SS-30%-Cell-EW-poor

Impact of the orientation on the weighted average temperature (cell type, poor control set points).

Although the diagrams above are a good indicator of the average temperature variation during the year, they do not provide any information concerning the number of hours with a certain air temperature. Therefore, the number of hours between certain (weighted) average mean air temperatures for the working space of the reference building (for the cell and open plan and for the three control set points) is presented below. The open plan office building (normal control set point) is warmer than the cell type one as shown in Figure 6.6. The number of hours close to the upper permissible temperature limit is as high as 45% for the cell and 70% for the open plan type, increasing the risk of potential overheating.

172

24.8 - 24.9

24.6 - 24.7

24.4 - 24.5

24.2 - 24.3

24.0 - 24.1

23.8 - 23.9

23.6 - 23.7

23.4 - 23.5

23.2 - 23.3

23.0 - 23.1

22.8 - 22.9

22.6 - 22.7

22.4 - 22.5

22.2 - 22.3

22.0 - 22.1

21.8 - 21.9

900 850 800 750 700 650 600 550 500 450 400 350 300 250 200 150 100 50 0 21.6 - 21.7

Number of working hours

Results and discussion

Weighted average mean air temperature (°C) SS-30%-Open-average-normal SS-30%-Cell-average-normal

Figure 6.6

Number of working hours in a year with certain average weighted air temperatures for the reference building (normal set points).

26.1 - 26.2

25.9 - 26.0

25.7 - 25.8

25.5 - 25.6

25.3 - 25.5

25.1 - 25.2

24.9 - 25.0

24.7 - 24.8

24.5 - 24.6

24.3 - 24.4

24.1 - 24.2

23.9 - 24.0

23.7 - 23.8

23.5 - 23.6

23.3 - 23.4

23.1 - 23.2

22.9 - 23.0

22.7 - 22.8

22.5 - 22.6

22.3 - 22.4

22.1 - 22.2

21.9 - 22.0

21.7 - 21.8

21.5 - 21.6

21.3 - 21.4

950 900 850 800 750 700 650 600 550 500 450 400 350 300 250 200 150 100 50 0 21.1 - 21.2

Number of working hours

The number of hours between certain air temperatures for the three control set points of the cell type office plan is shown in the Figure 6.7. As can be noticed the temperature variation increases for poorer set points. For the poor set points only 18% of the working hours are close to the upper limit for the cell and 44% for the open plan type.

Weighted average mean air temperature (°C) SS-30%-Cell-average-strict

Figure 6.7

SS-30%-Cell-average-normal

SS-30%-Cell-average-poor

Number of working hours in a year with a certain average weighted air temperatures for the reference building (normal set points, cell plan).

173

Single and Double Skin Glazed Office Buildings

6.1.2.2 Perception of thermal comfort The PMV and PPD values were calculated differently for the cell and open plan type office buildings. Due to the non rectangular geometry of the zones (of the open plan type), the simulations were simplified (energy model of IDA ICE 3.0). Therefore, an average radiant temperature of the external walls was assumed, diminishing the importance of occupants’ position, when the operative temperature is calculated. This can be considered an acceptable assumption, since for the open plan type the distance of the occupants the surrounding walls is larger. For the simulations of the cell type building the position of the occupants is important, since the climate model used (in IDA ICE 3.0) takes into account the radiant temperature of each surface (glazed area and opaque wall) of the façade. • Impact of office layout on the perception of thermal comfort For the strict control set points the weighted average PMV varies form -0.58 to -0.05 for the cell and from -0.51 to 0 for the open plan type as shown in Figure 6.8. As expected, due to the higher internal loads the open plan is slightly warmer than the cell type. However, the average difference in the weighted average PMV values for the two plan types is very small (less than 0.1) throughout the year. 0

Weighted average PMV

-0,1 -0,2 -0,3 -0,4 -0,5

SS-30%-Cell-average-strict

Figure 6.8

174

December

November

October

September

August

July

June

May

April

March

February

January

-0,6

SS-30%-Open-average-strict

Weighted average PMV for strict set points of the reference building.

Results and discussion

24-26%

22-24%

20-22%

18-20%

16-18%

14-16%

12-14%

10-12%

8-10%

6-8%

4-6%

2-4%

900 850 800 750 700 650 600 550 500 450 400 350 300 250 200 150 100 50 0 0-2%

Number of working hours

The number of working hours for certain average PPD values for strict set points of the reference building is shown in Figure 6.9. According to ISO Standard 7730 (1984) PPD values of 10% (or less) for 90% of the (working) time can ensure a very good thermal environment. For the cell type an average PPD of 10% or less corresponds to 66% of the working hours, while for the open plan the same PPD corresponds to 78%. For the cell type a maximum average PPD of 15% corresponds to 93% and for the open plan to 95% of the working hours. PMV values closer to zero (open plan type) mean lower PPD values and improved thermal conditions.

Weighted average PPD SS-30%-Open-average-strict SS-30%-Cell-average-strict

Figure 6.9

Number of working hours for certain average PPD for strict set points of the reference building.

For the normal control set points, the weighted average PMV of the open plan varies between -0.4 and +0.4, while for the cell type it varies between -0.55 and +0.3, as shown in Figure 6.10. The difference in the weighted average PMV values between the two plan types is slightly higher during the winter. The tendency can be explained by the lower occupancy during the summer months. For the normal control set points the lower average PPD values of the open plan imply a better indoor thermal environment, as shown in Figure 6.11. For the cell type a maximum average PPD of 10% corresponds to 73% of the working hours, while for open plan the same PPD corresponds to 82%. For the cell type an average PPD of 15% (or less) corresponds to 93% and for the open plan to 96% of the working hours. The yearly weighted average PMV difference is 0.13.

175

Single and Double Skin Glazed Office Buildings

0,4 0,3

Weighted average PMV

0,2 0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5

SS-30%-Cell-average-normal

December

November

October

September

August

SS-30%-Open-average-normal

Weighted average PMV for normal set points of the reference building.

24-26%

22-24%

20-22%

18-20%

16-18%

14-16%

12-14%

10-12%

8-10%

6-8%

4-6%

2-4%

800 750 700 650 600 550 500 450 400 350 300 250 200 150 100 50 0 0-2%

Number of working hours

Figure 6.10

July

June

May

April

March

February

January

-0,6

Weighted average PPD SS-30%-Cell-average-normal

Figure 6.11

SS-30%-Open-average-normal

Number of working hours for certain average PPD for normal set points of the reference building.

The weighted average PMV values for the poor control set points vary between -0.6 and +0.72 for the open plan and between -0.77 and +0.6 for the cell type as shown in Figure 6.12. The difference in the PMV values between the two interior types increases even more during the winter. The 176

Results and discussion

SS-30%-Cell-average-poor

Figure 6.12

December

November

October

September

August

July

June

May

April

March

February

0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6 -0,7 -0,8 January

Weighted average PMV

yearly weighted average PMV difference is 0.23, which is higher than for the strict and normal set points. This can be explained by the wider air temperature variation allowed by the poor set points. For the poor control set points, the weighted average PMV of the open plan results in slightly lower PPD values as shown in Figure 6.13. For the cell type an average PPD of 10% corresponds to 39% of the working hours, while for open plan the same PPD corresponds to 43%. For both the cell and open plan types an average of 15% PPD corresponds to 63% of the working hours.

SS-30%-Open-average-poor

Weighted average PMV for poor set points of the reference building.

177

Single and Double Skin Glazed Office Buildings

400

Number of working hours

350 300 250 200 150 100 50

34-36%

32-34%

30-32%

28-30%

26-28%

24-26%

22-24%

20-22%

18-20%

16-18%

14-16%

12-14%

10-12%

8-10%

6-8%

4-6%

2-4%

0-2%

0

Weighted average PPD SS-30%-Open-average-strict SS-30%-Cell-average-strict

Figure 6.13

Number of working hours for certain average PPD for poor set points of the reference building.

• Impact of control set points on the perception of thermal comfort The impact of the different control set points on the perception of the thermal environment is presented in Figures 6.14 and 6.15 (cell type). From January until May and from the middle of September to the end of December the normal set points result in a more neutral thermal environment, since the weighted average PMV values are closer to zero. From the end of May until the beginning of September, however, the strict set points ensure an indoor air temperature that improves the perception of comfort for the occupants. Both controls are very close to the recommendations of ISO Standard 7730 (1984), since the PMV hardly exceeds the limits of ±0.5. For the poor control set points, however, the PMV varies from -0.8 to +0.6, exceeding the comfort levels. Lower cooling and higher heating air temperature set points (as in normal or strict set points) are preferable for providing an acceptable thermal environment. For the strict set points a maximum average PPD of 10% corresponds to 66% of the working hours, while for the normal and poor ones the same PPD corresponds to 73% and 40% respectively. The same values for maximum average PPD of 15% correspond to 93%, 93% and 63% of the working hours for the three set points.

178

December

November

October

August

July

June

September

SS-30%-Cell-average-poor

SS-30%-Cell-average-normal

SS-30%-Cell-average-strict

Figure 6.14

May

April

March

February

0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6 -0,7 -0,8 January

Weighted average PMV

Results and discussion

Weighted average PMV for the cell type plan of the reference building.

650 600

Number of working hours

550 500 450 400 350 300 250 200 150 100 50 34-36%

32-34%

30-32%

28-30%

26-28%

24-26%

22-24%

20-22%

18-20%

16-18%

14-16%

12-14%

10-12%

8-10%

6-8%

4-6%

2-4%

0-2%

0

Weighted average PPD SS-30%-Cell-average-strict

Figure 6.15

SS-30%-Cell-average-normal

SS-30%-Cell-average-poor

Number of working hours for certain average PPD for cell plan (reference building).

The impact of strict, normal and poor control set points on the perception of thermal comfort for the open plan type is presented in Figures 6.16 and 6.17. As already stated, due to the higher internal loads in the open plan the weighted average PMV values slightly increase. From January until the beginning of May and from the middle of September to the 179

Single and Double Skin Glazed Office Buildings

SS-30%-Open-average-strict

Figure 6.16

180

SS-30%-Open-average-normal

December

November

October

September

August

July

June

May

April

March

February

0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6 -0,7 -0,8 January

Weighted average PMV

end of December the normal set points provide a more neutral thermal environment. From May till the beginning of September the PMV values of the normal set points increase, causing slight discomfort. The weighted average PMV of the normal control set points varies between ±0.4, while those for the strict set points vary between -0.5 and 0. For the poor control the variation is from -0.6 to +0.75, exceeding the comfort levels (ISO Standard 7730, 1984). For the strict set points a weighted average PPD of 10% corresponds to 78% of the working hours while for the normal and poor set points the same average corresponds to 82% and 43% respectively. The same values for a weighted average PPD of 15% (or less) correspond to 95%, 96% and 63% of the working hours.

SS-30%-Open-average-poor

Weighted average PMV for the open type plan of the reference building.

32-34%

30-32%

28-30%

26-28%

24-26%

22-24%

20-22%

18-20%

16-18%

14-16%

12-14%

10-12%

8-10%

6-8%

4-6%

2-4%

900 850 800 750 700 650 600 550 500 450 400 350 300 250 200 150 100 50 0 0-2%

Number of hours

Results and discussion

Weighted average PPD SS-30%-Open-average-strict

Figure 6.17

SS-30%-Open-average-normal

SS-30%-Open-average-poor

Number of working hours for certain average PPD for open plan (reference building).

From the above it can be concluded that a narrow variation in PMV values can be achieved by strict temperature set points, which will however result in an increased energy use. The selection of correct upper and lower temperature limits is essential for the provision of an improved thermal environment, in order to avoid creating too cold or too warm thermal conditions. In order to ensure that the optimal upper and lower temperature limits are selected, parameters such as internal loads, thermal mass, etc, should be considered. The stricter set points require more attention to these limits.

6.1.3

Indoor climate on a zone level

The mean air temperature, the directed operative temperature and thermal comfort indices on a zone level for the reference building are studied. North, east, south and west oriented zones were considered for the three control set points. The zones studied are all the occupied ones of the cell type office building (i.e. double and single office rooms, meeting rooms and corner office rooms). The mean air temperatures were studied, in order to investigate their variation within the limits defined by the set points. The number of hours with certain directed operative temperatures works as a “link” between the mean air temperatures and the way the occupants perceive their thermal environment. Finally the monthly average weighted 181

Single and Double Skin Glazed Office Buildings

PMV values describe whether the occupants feel “warm” or “cold” during the year, while the average PPD values are a quantitive way of evaluating the quality of thermal environment.

6.1.3.1 Mean air temperatures and potential overheating problem The window to external wall area ratio of the reference building is 30% as described in Subsection 5.1.1. However, the meeting rooms are the only zones that have a higher glazing area than the rest of the zones (65% window to external wall area ratio, while this is 30% is for the other zones). In order to study the impact of orientation on the mean air temperatures, the meeting rooms were selected. As shown in Figure 6.18 there is a peak for the number of working hours with air temperatures close to the upper permissible limit, which is very little dependent on the orientation. The results are similar for zones with 30% window to external wall area ratio. 500

Number of working hours

450 400 350 300 250 200 150 100 50 24.5 - 24.6

24.3 - 24.4

24.1 - 24.2

23.9 - 24.0

23.7 - 23.8

23.5 - 23.6

23.3 - 23.4

23.1 - 23.2

22.9 - 23.0

22.7 - 22.8

22.5 - 22.6

22.3 - 22.4

22.1 - 22.2

21.9 - 22.0

21.7 - 21.8

0

Mean air temperature (°C) Meeting room-North

Figure 6.18

Meeting room-East

Meeting room-South

Meeting room-West

Working hours with certain mean air temperatures for the meting room (reference building, cell type plan, and normal control set points), which has 65% window to external wall area ratio.

Due to the large peak number of working hours with air temperatures close to the upper permissible mean air temperature limit, the potential overheating problem was studied. This could have been studied by calculating the cooling load for each zone; since, however, the output (regarding energy use) from IDA ICE 3.0 is available only on a building level and 182

Results and discussion

simulation of individual zones would have been far too time consuming, an alternative way had to be found. Thus, the number of hours close to the upper permissible temperature limit (hours with cooling demand, in order to keep the air temperature within the permissible limits) was calculated instead. This indicator is not precise but in a comparative study it can show the risk of overheating problems for different orientations, glazed areas, control set points and internal loads for each zone type (Figure 6.19). As expected, the south orientated zones are slightly warmer. Due to the relatively high internal gains and the low upper air temperature limit of 23ºC (strict set points), the single and double offices have similar number of hours with cooling demand. Mainly due to the lower internal gains (lower occupant density), the corner office reaches the temperature limit of 23ºC for fewer hours as shown in Figure 6.19. The different occupancy of the meeting rooms (occupied only 4 instead of 8 hours per day) makes the comparison of this zone type with the rest useless. However, useful conclusions can be drawn, when the impact of orientation on a zone with larger glazing area (such as the meeting rooms with window area to room volume ratio of 0.67 m2/m3) and the rest of the zones (e.g. single and double office room with window area to room volume ratio of 0.258 m2/m3 and 0255 m2/m3 respectively) are compared. As shown in Figure 6.19, the peak of the curve in the south oriented façade of the meeting room is slightly larger than for the other zones. The high internal gains of the single and double office rooms, combined with the low upper temperature limit, result in a large number of hours with cooling demand, decreasing the effect of the orientation (for the single room, the difference between the north and south oriented single office is 3% and for the double office 1%). The lower internal gains of the corner room and the larger glass area of the meeting rooms, however, result in a somewhat larger difference in the number of hours when cooling might be needed. Regardless of the zone type, the south orientation is the warmest, and the north orientation is the one with the lowest cooling demand, as expected.

183

Number of working hours between 23.9 and 23.1°C

Single and Double Skin Glazed Office Buildings

2000 1800 1600

1751 1719

1769

1753

1737

1778

1724

1352

1400 1200

1742

1257

1235 1156

1000 800

751 632

637

North

East

656

600 400 200 0

Double room

Figure 6.19

Single room

South

Meeting room

West

Corner room

Potential overheating problem of the reference building for the strict control set points. The meeting room has 65% window to external wall area ratio and the offices 30%.

When normal set points (with upper air temperature limit 24.5ºC) are applied, the number of hours with potential cooling demand drops dramatically, regardless of the type of zone (as shown in Figure 6.20). When Figures 6.19 and 6.20 are compared it can be seen that for strict set points the curves for the single and double offices are fairly similar, while for the normal ones, the curve of the single office zone is somewhat lower than the double one. This means that narrow temperature variations with lower upper temperature limits diminish the impact of internal loads on the cooling demand (mostly in zones that are already quite densely occupied). Another interesting conclusion that can be drawn when these two graphs are compared is that strict set points reduce the impact of orientation on the cooling mainly in densely occupied zones or in zones with larger glazed areas, such as meeting rooms (since in both cases the temperature could easily rise up to 23ºC).

184

Number of working hours between 24.4 and 24.6°C

Results and discussion

1200

1132 1075

1100 1000

930

932

1036 978 880

900 800

756 680

700 600

457

433

392

400

648

557

511

500

692

300 200 100 0 North

Double room

Figure 6.20

East

Single room

South

Meeting room

West

Corner room

Potential overheating problem of the reference building for the normal control set points. The meeting room has 65% window to external wall area ratio and the offices 30%.

For the poor set points the number of hours when cooling is used drops dramatically, mainly due to the higher upper temperature limit (26ºC), as shown in Figure 6.21. The increased glass area of the meeting room, however, keeps the values relatively high, compared with the other zone types. This means that the impact of poor set points on cooling demand is smaller for zones with larger glass areas (regardless of the internal loads of the zone). The curve type of the offices has changed for this set point, since the number of hours with air temperatures up to 26ºC in the south facing offices is lower than in the east facing ones (due to the occupants’ schedule and the upper temperature limit).

185

Number of working hours between 25.9°C and 26.1°C

Single and Double Skin Glazed Office Buildings

550 492

500

467

450

470

446 423 427

400 386

350 300 250

266 267

274

316 277

230

244

200 150

292

114

100 50 0 North

Double room

East

Single room

South

Meeting room

West

Corner room

Figure 6.21. Potential overheating problem of the reference building for the poor control set points. The meeting room has 65% window to external wall area ratio and the offices 30%.

6.1.3.2 Directed operative temperatures The directed operative temperatures for different zones (double, corner office and meeting room), control set points and orientations are studied for the different zones of the reference building, in order to find their impact on the occupants’ comfort. The occupants are placed 1 m from the façade in all the zones. The corner offices have two external walls, one with window and one opaque. The one denoted by capital letters (see Figure 6.22) refers to the orientation where the window is placed; the other one refers to the opaque wall. For the strict control set points (22ºC-23ºC) the directed operative temperature varies from 21.5ºC to 25ºC for the double and corner offices and from 20ºC to 28ºC for the meeting rooms as shown in Figure 6.22 (south orientation). As expected, the variation in the directed operative temperature in the meeting room (due to the larger window area) is larger than in the rest of the zones. It can be noticed that although the orientation has limited impact on the mean air temperatures, the directed operative temperatures vary considerably. This can be explained by the nature of the set points used (based on mean air and not operative temperatures) and also by the fact that solar gains vary considerably with the orientation.

186

Results and discussion

225

Number of working hours

200 175 150 125 100 75 50 25 27.7 - 27.8

27.4 - 27.5

27.1 - 27.2

26.8 - 26.9

26.5 - 26.6

26.2 - 26.3

25.9 - 26.0

25.6 - 25.7

25.3 - 25.4

25.0 - 25.1

24.7 - 24.8

24.4 - 24.5

24.1 - 24.2

23.8 - 23.9

23.5 - 23.6

23.2 - 23.3

22.9 - 23.0

22.6 - 22.7

22.3 - 22.4

22.0 - 22.1

21.7 - 21.8

21.4 - 21.5

21.1 - 21.2

20.8 - 20.9

20.5 - 20.6

…-20.1

20.2 - 20.3

0

Directed oprerative temperature Operative temperature (°C)(°C) Double-South

Figure 6.22

Meeting room-South

Corner SOUTH-West

Number of working hours between certain directed operative temperatures for south oriented zones for the reference building (strict control set points). The lower case letters refer to the opaque wall. The meeting room has 65% window to external wall area ratio and the offices 30%.

In Figure 6.23 a diagram of the number of hours with certain directed operative temperatures is presented for meeting rooms with strict control set points for the north and south orientations. The results for the east and west facing meeting rooms are quite similar and they vary somewhere in between the north and south oriented alternatives (maximum temperature 26.5ºC and 27ºC respectively). The north facing meeting room is cooler (maximum directed operative temperature 25.4ºC), while the directed operative temperature of that facing south reaches 28ºC. The tendencies for the other zones are similar, but somewhat lower due to the smaller glazing areas used. The reason for selecting the meeting rooms for this comparison is that due to the larger glazed area (65% instead of 30% for the rest of the zones) the tendencies are more evident.

187

Single and Double Skin Glazed Office Buildings

45

Number of working hours

40 35 30 25 20 15 10 5 27.7 - 27.8

27.4 - 27.5

27.1 - 27.2

26.8 - 26.9

26.5 - 26.6

26.2 - 26.3

25.9 - 26.0

25.6 - 25.7

25.3 - 25.4

25.0 - 25.1

24.7 - 24.8

24.4 - 24.5

24.1 - 24.2

23.8 - 23.9

23.5 - 23.6

23.2 - 23.3

22.9 - 23.0

22.6 - 22.7

22.3 - 22.4

22.0 - 22.1

21.7 - 21.8

21.4 - 21.5

21.1 - 21.2

20.8 - 20.9

20.5 - 20.6

…-20.1

20.2 - 20.3

0

Directed oprerative temperature Operative temperature (°C) (°C) Meeting room-North

Figure 6.23

Meeting room-South

Number of working hours between certain directed operative temperatures for the 65% (reference) glazed meeting room (strict control set points). The meeting room has 65% window to external wall area ratio.

In order to study the impact of temperature set points on the directed operative temperatures, the north and south single offices are compared, as shown in Figure 6.24. Since the lower permissible air temperature limit for both cases is the same (22°C), the minimum directed operative temperature is the same. For the north orientation the maximum directed operative temperature reaches 24°C for the strict set points and 25.4°C for the normal ones. For the south orientation the temperature reaches 25°C and 26.4°C respectively. For both set points the directed operative temperature is 1°C higher than the permissible air temperature limit for the north orientation and 2°C higher for the south orientation.

188

Results and discussion

250

Number of working hours

225 200 175 150 125 100 75 50 25 26.1 - 26.2

25.9 - 26.0

25.7 - 25.8

25.5 - 25.6

25.3 - 25.4

25.1 - 25.2

24.9 - 25.0

24.7 - 24.8

24.5 - 24.6

24.3 - 24.4

24.1 - 24.2

23.9 - 24.0

23.7 - 23.8

23.5 - 23.6

23.3 - 23.4

23.1 - 23.2

22.9 - 23.0

22.7 - 22.8

22.5 - 22.6

22.3 - 22.4

22.1 - 22.2

21.9 - 22.0

21.7 - 21.8

0

Operative temperature (°C)(°C) Directed oprerative temperature Strict-North

Figure 6.24

Strict-South

Normal-North

Normal-South

Impact of control set points on directed operative temperature in north and south oriented single offices of the reference building. The offices have 30% window to external wall area ratio.

A comparison of the number of working hours with certain directed operative temperatures (Figure 6.25) is carried out for the north facing single offices and the meeting rooms (strict and normal control). For the meeting rooms, the large impact of the glass area on the directed operative temperatures is evident. For the single offices the difference (between maximum permissible air and directed operative temperature) is 1°C (regardless of the set point), while for the meeting rooms it is 2.5°C for the strict and 3°C for the normal set points. The impact of the glass area on the directed temperature is larger for the south oriented zones.

189

Single and Double Skin Glazed Office Buildings

250

Number of working hours

225 200 175 150 125 100 75 50 25 27.7 - 27.8

27.4 - 27.5

27.1 - 27.2

26.8 - 26.9

26.5 - 26.6

26.2 - 26.3

25.9 - 26.0

25.6 - 25.7

25.3 - 25.4

25.0 - 25.1

24.7 - 24.8

24.4 - 24.5

24.1 - 24.2

23.8 - 23.9

23.5 - 23.6

23.2 - 23.3

22.9 - 23.0

22.6 - 22.7

22.3 - 22.4

22.0 - 22.1

21.7 - 21.8

21.4 - 21.5

21.1 - 21.2

20.8 - 20.9

20.5 - 20.6

…-20.1

20.2 - 20.3

0

Directed oprerative temperature Operative temperature (°C) (°C) Meeting room-Strict

Figure 6.25

Meeting room-Normal

Single office-Strict

Single office-Normal

Impact of control set points on directed operative temperature in single offices and meeting rooms for the reference building (north orientation, 3rd alternative). The meeting room has 65% window to external wall area ratio and the offices 30%.

6.1.3.3 Perception of thermal comfort The thermal comfort indices (PMV and PPD) for zones with different orientations and set points are studied in this Section. As stated above, the occupants were placed 1m from the external wall (window). For strict temperature set points the PMV and PPD values are quite similar for the simulated alternatives. The monthly average PMV for the south oriented zones is always below 0 for the offices, while for the meeting rooms (higher glazing area) it is positive from early May to late September (as presented in Figure 6.26). Clearly, the corner office room is the one with the lower PMV values, due to the lower internal gains and higher external wall area to room volume ratio.

190

Results and discussion

0,2 0,1

Monthly average PMV

0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6

Double office

Figure 6.26

Single office

Meeting room

December

November

October

September

August

July

June

May

April

March

February

January

-0,7

Corner office

Monthly average PMV for south oriented zones of the reference building with strict set points. The meeting room has 65% window to external wall area ratio and the offices 30%.

For the north oriented zones, the meeting room is slightly colder than the single and double offices during winter (while for the south oriented ones, it was warmer almost throughout the year) as shown in Figure 6.27. The monthly average PMV values for the offices do not change much, when the north and south oriented façades are compared, due to the strict set points and the small (compared at least with the meeting rooms) glazed area; the difference in the PMV values is larger, however, for the meeting rooms.

191

Single and Double Skin Glazed Office Buildings

0,2 0,1

Monthly average PMV

0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6

Double office

Figure 6.27

Single office

Meeting room

December

November

October

September

August

July

June

May

April

March

January

February

-0,7

Corner office

Monthly average PMV for north oriented zones of the reference building with normal set point. The meeting room has 65% window to external wall area ratio and the offices 30%.

Regardless of the orientation it appears that the strict temperature set point (22ºC - 23ºC) is quite low for the cell type reference building, since the PMV values exceed the recommended limit of -0.5 (ISO Standard 7730, 1984) during winter, while during summer the monthly average PMV values do not exceed zero. The lower PMV values during July (compared with June and August) are due to the lower internal gains (75% of the occupants are working during June and August and 50% during July) and not to lower outdoor temperatures. In Figure 6.28 a diagram of the number of hours with certain PPD for north facing zones is presented. The single and double offices perform similarly, while the corner office results in higher PPD values due to the lower internal loads and the larger external wall area. The PPD values of the meeting room have a larger spread due to the larger glazing area. It has to be noted that in this case the total amount of working hours is smaller, since the meeting rooms are occupied only 50% of the time.

192

Results and discussion

600 550

Number of working hours

500 450 400 350 300 250 200 150 100 50 26-28%

24-26%

22-24%

20-22%

18-20%

16-18%

14-16%

12-14%

10-12%

8-10%

6-8%

4-6%

2-4%

0-2%

0

PPD Double office

Figure 6.28

Single office

Meeting room

Corner office

Number of working hours with certain PPD for north facing zones of the reference building with strict set points. The meeting room has 65% window to external wall area ratio and the offices 30%.

The impact of orientation on the PPD is limited for the strict set points due to the narrow permissible air temperature variation (as with PMV values). In Figure 6.29 the percentage of working hours with PPD of 10% and 15% (or lower) is presented. Regardless of the orientation, the corner office has the lowest PPD values. The single and double offices perform quite well, while the south oriented meeting room has similar values for PPD of 10% (or less). Taking into account the low PMV values discussed earlier and the PPD values presented below, it is obvious that the low upper temperature limit (e.g.23°C) combined with the narrow permissible temperature variations of the strict set points results in a cold thermal environment all year round (PMV values between -0.7 and 0). This is evident for the corner zones, in which the low internal gains (and thus lower air temperatures) reduce drastically the number of working hours with PPD values of 10 and 15%. The larger glazing area of the south oriented meeting room, however, increases the operative temperatures and results in a warmer thermal environment, more acceptable to the occupants (due to the non-optimal strict set point).

193

Single and Double Skin Glazed Office Buildings

100

89

90

% of working hours

70 60

63

66 67

66 60

69

57

54

77

65 67 63

63

51

81

77

75

72 72

82

82

79

80

93 95

95 96

93 96

92 95

53

50 40 30 20 10 0 North

East

South

West

PPD of 10%

Double office

Figure 6.29

North

East

South

West

PPD of 15%

Single office

Meeting room

Corner office

% of working hours with PPD of 10% and 15% (or less) for zones with strict control set points (reference building). The meeting room has 65% window to external wall area ratio and the offices 30%.

For the normal control set points the monthly average PMV values of the south oriented zones are shown in Figure 6.30. The meeting room appears to be warmer (compared with the single and double offices) between the middle of March and the middle of October. The monthly average PMV values in this case vary between -0.65 and +0.53, while for the same case (but for strict set points) they vary between -0.65 and +0.15. For the other zones the monthly average PMV values exceed zero (while for the strict set points they are negative all year round, see Figure 6.26) from May to September. During the winter months the PMV for the normal set points is similar to that for the strict set points, since the lower permissible temperature limit of 22ºC is kept the same.

194

Results and discussion

0,6 0,5 0,4

Monthly average PMV

0,3 0,2 0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6

Double office

Figure 6.30

Single office

Meeting room

December

November

October

September

August

July

June

May

April

March

February

January

-0,7

Corner office

Monthly average PMV for south oriented zones of the reference building with normal set points. The meeting room has 65% window to external wall area ratio and the offices 30%.

For the north oriented zones the monthly PMV values are presented in Figure 6.31. The meeting room is once more warmer than the single and double offices between April and September and all year round compared with the corner office. The PMV in this case varies between -0.7 and +0.5, while for the same case (but for strict set points) the PMV is between -0.7 and +0.1.

195

Single and Double Skin Glazed Office Buildings

0,5 0,4

Monthly average PMV

0,3 0,2 0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6

Double office

Figure 6.31

Single office

Meeting room

December

November

October

September

August

July

June

May

April

March

February

January

-0,7

Corner office

Monthly average PMV for north oriented zones of the reference building with normal set points. The meeting room has 65% window to external wall area ratio and the offices 30%.

The large glazing area of the meeting rooms results in a wide variation in the monthly average PMV values. However, it is only the south oriented meeting room that slightly exceeds the recommended PMV limit of +0.5 (ISO Standard 7730, 1984). The effect of the normal set points on the rest of the zones is similar (but on a lower scale). The number of working hours with PPD of 10% and 15% (or less) is presented in Figure 6.32. When Figures 6.29 and 6.32 are compared, it can be noticed that the number of hours with PPD of 15% or less is similar for normal and strict set points, regardless of the zone type and the orientation. The number of hours with PPD of 10% or less, however, is larger for the normal control cases mostly for the offices (single, double and corner with 30% window area) for all the orientations i.e. the thermal comfort is better. This shows that the choice of a narrow variation in permisible air temperature for zones with small window to external wall area ratios requires very careful selection of the higher and lower limits; in this case the upper air temperature limit for the strict set points was selected lower than it should have been, resulting in higher discomfort of the occupants (due to the low PMV values). Thus, a narrow air temperature set point is not necessarily recommended, since it is quite difficult to know precisely a priori the parameters that determine the selection of upper and lower air temperature limits. A comparison of the number of working hours with PPD lower than 10% for zones with large window to external wall area 196

Results and discussion

ratios (Figures 6.29 and 6.32), however, shows that strict set points are essential, in order to lower the PPD values (since the difference between the directed operative temperatures and the air temperatures increases regardless of the zone type and the orientation). In this case the lower upper air temperature limit ensures the low PPD values. 100

93

95

95 97

94 96

94 95

90 80

77

75

% of working hours

71

80 79

76

74

78

75

75

78 77

80

83

80

77

70 60

60 50

57 53

55 49

46

48

42

40 30 20 10 0 North

East

South

West

North

PPD of 10%

Double office

Figure 6.32

Single office

East

South

West

PPD of 15%

Meeting room

Corner office

Number of working hours with PPD of 10% and 15% (or less) for zones with normal control set points (reference building). The meeting room has 65% window to external wall area ratio and the offices 30%.

For the poor control set points the monthly average PMV values exceed the recommended values for an acceptable indoor thermal environment (ISO Standard 7730, 1984), as shown in Figure 6.33. The variation in monthly average PMV values for the south oriented zones is between -0.9 and +0.9, with a smaller variation for the cell office rooms. The results for the north, east and west oriented zones are similar.

197

Double office

Figure 6.33

Single office

Meeting room

December

November

October

September

August

July

June

May

April

March

February

0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6 -0,7 -0,8 -0,9 January

Monthly average PMV

Single and Double Skin Glazed Office Buildings

Corner office

Monthly average PMV for south oriented offices and meeting room with poor set points (reference building). The meeting room has 65% window to external wall area ratio and the offices 30%.

The unsatisfactory thermal environment resulting from the poor set points can be proved by the low number of working hours with PPD values lower than 10% and 15%. Mostly for the meeting rooms, it is for no more than 27% of the working hours that PPD values are lower than 10% (the PPD values of 15% do not exceed 43%), as shown in Figure 6.34. For this reason the PMV and PPD are not studied further in this section.

198

Results and discussion

100 90

% of working hours

80 71

69

70

67

66

63

67 62

60

60

55

50

43 39

40

49

48

45 39 32

30

34

34 27

22

50

49 43

42 37

36

40

35

31

27

24

22

20 10 0 North

East

South

West

North

PPD of 10%

Double office

Figure 6.34

Single office

East

South

West

PPD of 15%

Meeting room

Corner office

Number of working hours with PPD of 10% and 15% (or less) for zones with poor control set points (reference building). The meeting room has 65% window to external wall area ratio and the offices 30%.

6.2

Single skin glazed alternatives (60% and 100% window to external wall area ratios)

6.2.1

Energy use

As stated in Subsection 4.1.2, 42 building alternatives were generated with 60% window to external wall area ratio (7 windows and shading device types, 2 plan types and 3 control set points) and another 42 for alternatives with 100% window to external wall area ratio. A detailed description of the window alternatives used was given in Subsection 4.1.2, while their properties were presented in Subsection 5.2.1.2. The energy use for the highly glazed alternatives is presented in Appendix L, while the results are discussed below. In the first 100% glazed alternative (with clear panes) the high thermal transmittance of the windows resulted in insufficient heating capacity. The opposite problem (insufficient cooling capacity) is noticed in the fifth alternative (mostly in the cell type) due to the high total solar transmittance (and also geffective) of the glazing. These 9 extreme cases were simulated 199

Single and Double Skin Glazed Office Buildings

once more with increased heating and cooling capacity, in order to determine the energy use for keeping the air temperature in the working areas within the set point limits. However, since the original reference building was designed with a certain heating and cooling capacity, the parametric study is carried out considering the original alternatives. In Appendix L the energy use for alternatives with increased heating and cooling capacity is presented.

6.2.1.1 Impact of floor plan type and orientation For the 60% and 100% glazed alternatives the impact of plan type on energy use for heating and cooling is similar to that for the reference building (higher heating demand for the cell type and higher cooling demand for the open type) as described in Subsection 6.1.1.1. The energy use for lighting depends on the visual transmittance of the window system (with and without the use of the shading devices). As mentioned in Subsection 5.2.1.2, however, the daylight availability in IDA ICE 3.0 depends on the direct solar transmittance, since Tvis is not considered. The tendency, regarding the energy for lighting the different glazing alternatives, is quite correct, since in almost all the simulated cases, windows with lower g values also have lower Tvis values (see Table 5.11), resulting in increased energy demand for artificial lighting. In Figure 6.35 the difference in heating and cooling demand between the cell and open plan types is presented (the absolute values are given in Appendix L). Once more it can be noticed that the wider temperature set points allow more “useful” heat to be stored; thus, the effect on the cooling demand is the opposite.

200

Energy difference (kWh/m2a)

Results and discussion

11,0 10,0 9,0 8,0 7,0 6,0 5,0 4,0 3,0 2,0 1,0 0,0 -1,0 -2,0 -3,0 -4,0 -5,0 -6,0 -7,0 -8,0 heating

cooling

Strict Alternative 1

Figure 6.35

Alternative 2

heating

cooling

Normal Alternative 3

Alternative 4

heating

cooling

Poor Alternative 5

Alternative 6

Alternative 7

Impact (difference between cell and open types) of plan type on the heating and cooling demand of 60% glazed alternatives with different window types.

When the total energy demand difference between the cell and open plan type alternatives is compared (Figure 6.36), it can be noticed that the impact of plan type on the energy use regardless of the window type used is increased for strict control set points (60% glazed alternatives). 6,0 5,0

Energy difference (kWh/m2a)

4,0 3,0 2,0 1,0 0,0 -1,0 -2,0 -3,0 -4,0 -5,0 -6,0 -7,0 Strict Alternative 1

Figure 6.36

Alternative 2

Normal Alternative 3

Alternative 4

Poor Alternative 5

Alternative 6

Alternative 7

Impact (difference between cell and open types) of plan type on the total energy use of 60% glazed alternatives with different window types.

201

Single and Double Skin Glazed Office Buildings

Regarding the impact of orientation, the difference in energy use for the north south and east-west oriented 100% glazed alternatives (3) increases by up to 3% (from 0.1 of the reference building). Due to the small impact of the orientation on the total energy use of the building (because of the identical long and short façades), no further study of the influence of orientation on the total energy use has been made on a building level.

6.2.1.2 Impact of windows and shading devices for the 60% and 100% glazed alternatives An energy use comparison of the 60% and 100% single skin glazed alternatives with different windows and shading devices applied is presented in this Subsection. For the comparison, only cell type alternatives with normal control set points are described. The results are similar for the other set points and the open plan. The absolute energy use values of alternatives with strict and poor set points are presented in Appendix L, as well as the open plan type cases. A brief description of the window alternatives used is given below. The first (60% and 100%) glazed alternatives have a triple clear pane window of Uwindow=1.97 W/m2K (as described in Subsection 5.2.1.2). When its thermal transmittance is reduced to 1.27 W/m2K in the second alternative (and the total solar transmittance from 0.69 to 0.58), the total energy use decreases by 12% for the 60% and by 14% for the 100% glazed alternative as shown in Figure 6.37). For the second (60% glazed) alternative the energy use for heating drops by 31%, while for the 100% glazed alternative it is slightly higher (33%). The reduced thermal transmittance of the window results in a 20% increase in cooling demand for the 60% and in a 17% increase for the 100% glazed alternatives. Although the total solar transmittance slightly drops in the second case, the much lower thermal transmittance insulates the building in such a way that it doesn’t allow the heat to “escape” during summer, resulting in increased cooling demand. The energy use for lighting (with a set point of 500 lux at the desktop) increases by 4% for the 60% and by 5% for the 100% glazed building alternatives, due to the reduced (in the second case) direct solar transmittance (Tsol) of the glazing system (see Table 5.11), since, as already stated in Subsection 5.2.1.2, the daylight availability in IDA ICE 3.0 is calculated by the direct solar and not the visual transmittance.

202

Results and discussion

200 180

Energy use (kWh/m2a)

160

45

140 120

45 45

100

13,4

80

20

45

30

13,5

13,8

37

24

60 40

12,9

92 72

59

50

20 0 normal (1)

normal (2)

normal (1)

60% glazed alternatives

Space heating

Figure 6.37

normal (2)

100% glazed alternatives

Cooling

Lighting

Rest

Comparison of energy use for the 1st and 2nd glazed alternatives (cell type).

In the third alternative the triple glazing is replaced by double glazing with a lower total solar transmittance (g=0.35 instead of g=0.58). The intermediate venetian blinds (geffective=0.225) are also replaced by internal ones (geffective=0.276). The total energy use drops only by 1% for the 60% and by 4% for the 100% glazed alternative (Figure 6.38). For the third alternative the energy use for heating increases by 6% for the 60% and by 10% for the 100% glazed alternative due to the lower total solar transmittance of the glazing (the U value was not changed). For the same reason cooling demand drops by 26% for the 60% and by 25% for the 100% glazed building alternative. It has to be noted that in the third alternative the blinds are internal, while for the second they are intermediate resulting in a lower geffective for the second case (0.23 vs. 0.28 for the third case), which explains the rather small drop in cooling demand. The energy use for lighting the 60% glazed offices increases (by 3% for the 60% and by 4% for the 100% glazed building alternative) in the third alternative due to the lower direct solar transmittance (see Table 5.11).

203

Single and Double Skin Glazed Office Buildings

160 140

Energy use (kWh/m2a)

45

45

120 45

45

13,5

100 80

13,8

14,2

60

24

18

50

normal (2)

14,0

37

27

54

59

65

normal (3)

normal (2)

normal (3)

40 20 0

60% glazed alternatives

Space heating

Figure 6.38

100% glazed alternatives

Cooling

Lighting

Rest

Comparison of energy use for the 2nd and 3rd glazed alternatives (cell type).

In the fourth alternative the double glazing is replaced by one with a lower total solar transmittance (g=0.23 instead of g=0.35). The total energy use drops only by 2% for the 60% and by 3% for the 100% glazed building alternative as shown in Figure 6.39. The heating demand for the fourth 60% and 100% glazed building alternatives increases by 3%. The cooling demand drops by 26% for the 60% glazed alternative and by 27% for the 100% glazed one. The decrease in cooling demand in this case is larger due to the lower geffective (0.22 instead of 0.28), since the position of the blinds was kept the same in the third and fourth alternatives. The energy use for lighting the 60% glazed offices slightly increases (by 1% for the 60% and by 2% for the 100% glazed building alternative) in the fourth alternative, due to the lower direct solar transmittance (see Table 5.11).

204

Results and discussion

160 140

Energy use (kWh/m2a)

45

45

120 45

100

45 14,0

80

14,2

14,4

60

18

13

54

55

normal (3)

normal (4)

14,2

27

19

65

68

normal (3)

normal (4)

40 20 0

60% glazed alternatives

Space heating

Figure 6.39

100% glazed alternatives

Cooling

Lighting

Rest

Comparison of energy use for the 3rd and 4th glazed alternatives (cell type).

In the fifth alternative the double glazing is replaced by one with a solar factor higher than in the third alternative (g=0.58 instead of g=0.35). The total energy use increases by 9% for the 60% and by 12 % for the 100% glazed building alternative Figure 6.40. The heating demand drops by 10% for the 60% and by 12% for the 100% glazed building alternative (case (5) compared with case (3)), while the cooling demand increases dramatically (by 99% for the 60% and by 102% for the 100% glazed building alternative). The energy use for lighting the 60% glazed offices drops (by 3% for the 60% and by 5% for the 100% glazed building alternative), in the fifth alternative due to the higher direct solar transmittance (see Table 5.11).

205

Single and Double Skin Glazed Office Buildings

180 160 45

Energy use (kWh/m2a)

140 45 45

120

13,4

45

100

14,0 13,8

80

14,2

60

18

36

54

48

normal (3)

normal (5)

40 20

54

27

65

58

0 normal (3)

60% glazed alternatives

Space heating

Figure 6.40

normal (5)

100% glazed alternatives

Cooling

Lighting

Rest

Comparison of energy use for the 3rd and 5th glazed alternatives (cell type).

A comparison between the second and fifth glazed building alternatives is carried out, in order to study the impact of shading device position on energy use (since U and g values are kept the same). In the second alternative the blinds are intermediate, while in the fifth they are internal. When the venetian blinds are placed in between the panes, the solar factor of the system (window and shading device) is much lower than when they are internal (geffective=0.225 instead of geffective=0.469). The total energy use for the 60% glazed buildings increases by 8% for the fifth 60% glazed building alternative and by 10% for the 100% glazed building, as shown in Figure 6.41. Since the shading devices are not often used during the heating period, the higher geffective of the fifth alternative has a limited impact on the heating demand. The energy use for heating the 60% glazed buildings is almost the same for the second and fifth alternatives, while for the 100% glazing alternatives the heating demand drops by 3%. During the cooling periods, however, the cooling demand of the fifth alternative increases dramatically since the venetian blinds are used more often. The increase is 47% for the 60% and 45% for the 100% glazed building alternative. The energy use for lighting the 60% and 100% glazed offices is almost the same, due to the similar direct solar transmittance (Tsol) of the two alternatives (see Table 5.11).

206

Results and discussion

180 160 45

Energy use (kWh/m2a)

140

45 45

120

13,4

45

13,5

100 13,8

80

13,8

60

24

54

37 36

40 20

50

48

normal (2)

normal (5)

59

58

normal (2)

normal (5)

0

60% glazed alternatives

Space heating

Figure 6.41

100% glazed alternatives

Cooling

Lighting

Rest

Comparison of energy use for the 2nd and 5th glazed alternatives (cell type).

In the sixth alternative internal screens were applied. When this case is compared with the third one (same glazing system but with internal blinds which gives a geffective of 0.19 instead of 0.28), there is a slight decrease in cooling demand and there is not much effect on the heating demand (Figure 6.42). 160

Energy use (kWh/m2a)

140 45

45

14,0

13,9

27

24

65

66

normal (3)

normal (6)

120 45

45

100 80

14,2

14,2

60

18

16

54

54

normal (3)

normal (6)

40 20 0

60% glazed alternatives

Space heating

Figure 6.42

100% glazed alternatives

Cooling

Lighting

Rest

Comparison of energy use for the 3rd and 6th glazed alternatives (cell type).

207

Single and Double Skin Glazed Office Buildings

In the seventh alternative the internal blinds (of the third alternative) are replaced by fixed external louvres (with lower effective total solar transmittance). The heating demand increases by 9% for the 60% and by 11% for the 100% glazed building alternative (when compared with the third one) as shown in Figure 6.43. This can be explained by the fact that the shading in the seventh case is applied all year round and consequently geffective=g=0.19. The shading in the third alternative, however, is applied 100% when the incident light inside the glass exceeds 100W/m2. The cooling demand drops by 60% for the seventh 60% glazed building alternative and by 66% for the 100% glazed one. The total energy use for the 60% glazed buildings decreases by 4% for the seventh 60% and by 7% for the 100% glazed building alternative. The energy use for lighting is slightly higher in the seventh alternative, since the shading devices are applied throughout the year (by 2% and 3% for the 60% and 100% glazed cases). The seventh alternative results in the lowest total energy use, due to the lower g value of the system (since the shading is applied all year round and thus the total solar transmittance is equal to the effective one). Another parameter that has to be further noticed, is that although the shading for the seventh case is always applied, the total solar transmittance varies considerably during the year due to the monthly average g and Tsol values inserted in IDA ICE 3.0 (e.g. 0.13 during May and 0.28 during January). This permits valuable heat gains during the winter (resulting in a small increase in heating demand), while having the opposite effect during summer (resulting in a large drop in cooling demand). 160 140

Energy use (kWh/m2a)

45

120

45 45

100

45

14,0 14,3

80

14,2

60

18

7

54

59

65

normal (3)

normal (7)

normal (3)

27

14,4

9

40 20

72

0

60% glazed alternatives

Space heating

Figure 6.43

208

normal (7)

100% glazed alternatives

Cooling

Lighting

Rest

Comparison of energy use for the 3rd and 7th glazed alternatives (cell type).

Results and discussion

A cross comparison of the 60% and 100% glazed alternatives with different windows and shading devices applied, shows that the difference in total energy use (compared with the reference building) is reduced, when the thermal and total solar transmittance decrease. As expected, lower gglazing values result in lower cooling and slightly higher heating demand (e.g. alternatives 2 and 3). The value of geffective (total solar transmittance when shading is applied) is crucial for the cooling demand. When the alternatives 2 and 5 (same glazing but different position of shading results in different geffective) are compared, the cooling demand differs considerably (higher cooling when the shading is applied indoors). The low window thermal transmittance results in lower heating demand (as expected), which can be seen, when the first and the remaining glazing alternatives are compared.

6.2.2

Indoor climate on a building level

6.2.2.1 Weighted average mean air temperatures In order to carry out parametric studies (on a building level) for studying the impact of window and shading device type on average air temperatures, 100% glazed alternatives with normal control set points were considered. In the case of the reference building (30% window to external wall area ratio) the mean air temperature greatly depends on the set point applied in each case (as discussed in Subsection 6.1.2.1). When the glazing area increases, however, (60% and 100% glazed alternatives) the potential number of hours outside the permissible air temperature limits may increase, due to the insufficient heating and/or cooling capacity. For example in the first alternative (high thermal transmittance of the window system) and the fifth case (double pane with low thermal transmittance and relatively high geffective value with internally placed blinds) the air temperature exceeds the limits set by the control set points. Although in most of the cases the number of working hours exceeding the temperature limits is lower than 5%, for the first 100% glazed alternative the temperatures are lower for almost 10% of the working hours, while the opposite problem (high air temperatures) occurs in the fifth alternative, due to the increased g and geffective values of the window. In Figure 6.44 the weighted average mean air temperatures of the first and fifth alternatives are compared. The temperature difference between these two cases is obvious, with the fifth alternative exceeding the upper permissible air temperature limit during the summer months. The insufficient heating and cooling capacity are examined in greater detail on the zone level. The energy use for these two 209

Single and Double Skin Glazed Office Buildings

cases (both cell and open plan) is recalculated (and presented in Appendix L) with increased heating and cooling capacity, in order to calculate the energy demand needed for each alternative. For the rest of the parametric study the original alternatives were used in order to study the impact of window type on the perception of thermal comfort. Weighted average mean air temperature (°C)

26,5 26,0 25,5 25,0 24,5 24,0 23,5 23,0 22,5 22,0 21,5

Strict (1)

Figure 6.44

Normal (1)

Poor (1)

Strict (5)

Normal (5)

December

November

October

September

August

July

June

May

April

March

February

January

21,0

Poor (5)

Weighted average air temperatures for the 1st and 5th 100% glazed alternatives.

6.2.2.2 Impact of window and shading type on the perception of thermal comfort for the 60% and 100% glazed alternatives Since the poor control set points result in high PPD values (not acceptable according to ISO standard 7730, 1984), the perception of thermal comfort indices are studied only for the strict and normal set points of the two plan types. A comparison of the weighted monthly average PMV values and the number of hours with certain PPD values for the 60% and 100% alternatives follows, in order to study the influence of the façade elements on the perception of the thermal environment. A table with the number of hours with PPD values lower than 10% and 15% for the 3 control set points for the cell and open plan type 30%, 60% and 100% glazed buildings are presented in Appendix M. When the thermal transmittance of the first 60% glazed alternative is reduced (alternative 2 compared with alternative 1), the weighted monthly average PMV values improve during the heating season (for the strict set points, during January the weighted average PMV of the first alternative 210

Results and discussion

Strict set point (1)

Figure 6.45

Strict set point (2)

Normal set point (1)

December

November

October

September

August

July

June

May

April

March

February

0,5 0,4 0,3 0,2 0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6 -0,7 -0,8 -0,9 January

Weighted monthly average PMV

is -0.67, while for the second one it is -0.55; for the normal set points the weighted average PMV of the first alternative is -0.67, while for the second one it is -0.51), as shown in Figure 6.45. During the summer months, however, the weighted average PMV values for the strict set points are around 0 and for the normal set points they are between 0.3 and 0.4.

Normal set point (2)

Weighted monthly average PMV for the 1st and 2nd 60% glazed alternatives (strict and normal control set points).

For the 100% glazed alternatives the PMV values are reduced even more during the heating season (for the strict set points, during January the weighted average PMV of the first alternative is -0.82, while for the second one it is -0.62; for the normal set points the weighted average PMV of the first alternative is -0.81 while for the second one it is -0.59), as shown in Figure 6.46. During the summer months, however, the weighted monthly average PMV values for the strict set points are around 0.1 and for the normal set points they are between 0.4 and 0.5.

211

Single and Double Skin Glazed Office Buildings

0,5

Weighted monthly average PMV

0,4 0,3 0,2 0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6 -0,7 -0,8

Strict set point (1)

Figure 6.46

Strict set point (2)

Normal set point (1)

December

November

October

September

August

July

June

May

April

March

February

January

-0,9

Normal set point (2)

Weighted monthly average PMV for the 1st and 2nd 100% glazed alternatives (strict and normal control set points).

The increase in glazed area results in a greater difference in the weighted average PMV values between the alternatives 1 and 2 mostly during the heating periods (for the strict set points of the 60% glazed alternative the difference is 0.12 during January, while for the 100% glazed one it is 0.2; for the normal set point the difference is 0.16 and 0.22 respectively). This can be partly explained by air temperature difference between the two alternatives but mainly it is caused by the difference in the radiant temperature (which could be expected from the difference in U value). The directed operative temperature is used, in order to study this effect. Since the difference in the weighted average directed operative temperatures between the first and second alternative is larger than the weighted average air temperatures (Figure 6.47), it is evident that the impact of the radiant temperature is greater (the negative values show that the 1st alternative is colder than the 2nd).

212

Directed Operative Temp. Strict 1-2 Air Temp. Strict 1-2

Figure 6.47

December

November

October

September

August

July

June

May

April

March

February

0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6 -0,7 -0,8 -0,9 -1,0 -1,1 -1,2 -1,3 January

Temperature difference (°C)

Results and discussion

Directed Operative Temp. Normal 1-2 Air Temp. Normal 1-2

Difference between weighted average directed operative temperature and air temperature for the 1st and 2nd 100% glazed alternatives.

A diagram with the number of hours with certain (weighted average) directed operative temperatures is shown in Figure 6.48. The lower thermal transmittance of the window of the second alternative increases the number of hours with directed operative temperatures closer to the maximum permissible temperature limit for each set point.

213

24.8 - 24.9

24.6 - 24.7

24.4 - 24.5

24.2 - 24.3

24.0 - 24.1

23.8 - 23.9

23.6 - 23.7

23.4 - 23.5

23.2 - 23.3

23.0 - 23.1

22.8 - 22.9

22.6 - 22.7

22.4 - 22.5

22.2 - 22.3

22.0 - 22.1

21.8 - 21.9

21.6 - 21.7

21.4 - 21.5

21.2 - 21.3

800 750 700 650 600 550 500 450 400 350 300 250 200 150 100 50 0 21.0 - 21.1

Number of hours

Single and Double Skin Glazed Office Buildings

Directed operative temperature (°C) Strict (1)

Figure 6.48

Normal (1)

Strict (2)

Normal (2)

Number of hours with certain (weighted average) directed operative temperatures for 1st and 2nd 100% glazed alternatives.

For the 60% glazed buildings with strict control set points the (weighted average) PPD values are lower than 10% during 72% of the working hours for the second alternative, and during 61% of the working hours for the first alternative (Figure 6.49). For the normal set points the number of hours decreases to 70% and 57% respectively. The number of hours with (weighted average) PPD values lower than 15% increases by up to 94% for the second and by 83% for the first alternative (for the strict control set points). For the normal set point the number of hours is 94% and 82% for the two alternatives.

214

32-34%

30-32%

28-30%

26-28%

24-26%

22-24%

20-22%

18-20%

16-18%

14-16%

12-14%

10-12%

8-10%

6-8%

4-6%

2-4%

800 750 700 650 600 550 500 450 400 350 300 250 200 150 100 50 0 0-2%

Number of hours

Results and discussion

Weighted average PPD Strict (1)

Figure 6.49

Strict (2)

Normal (1)

Normal (2)

Weighted average PPD for the 1st and 2nd 60% glazed alternatives.

For the 100% glazed building, the (weighted average) PPD values are lower than 10% during 68% of the working hours for the second alternative, and during 46% of the working hours for the first alternative for the cell type (Figure 6.50). For the normal set point the number of hours decreases to 55% and 31% respectively. The number of hours with (weighted average) PPD values lower than 15% increases by up to 87% for the second and by 65% for the first alternative (for the strict control set points). For the normal set point the number of hours is 84% and 60% for the two alternatives.

215

38-40%

36-38%

34-36%

32-34%

30-32%

28-30%

26-28%

24-26%

22-24%

20-22%

18-20%

16-18%

14-16%

12-14%

10-12%

8-10%

6-8%

4-6%

2-4%

750 700 650 600 550 500 450 400 350 300 250 200 150 100 50 0 0-2%

Number of hours

Single and Double Skin Glazed Office Buildings

Weighted average PPD Strict (1)

Figure 6.50

Strict (2)

Normal (1)

Normal (2)

Weighted average PPD for the 1st and 2nd 100% glazed alternatives.

When the triple window is replaced by a double one (with a lower total solar transmittance) and the blinds are placed internally (third alternative), the weighted monthly average PMV values of the 100% glazed alternatives decrease (more for the normal than for the strict set points, as shown in Figure 6.51). Since the thermal transmittance of the glazing was kept the same, the difference in the PMV values is small during the winter months. The results for the 60% glazed buildings are similar.

216

Results and discussion

0,5

Weighted monthly average PMV

0,4 0,3 0,2 0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6

Strict set point (2)

Figure 6.51

Strict set point (3)

Normal set point (2)

December

November

October

September

August

July

June

May

April

March

February

January

-0,7

Normal set point (3)

Weighted average PMV for the 2nd and 3rd 100% glazed alternatives.

For the 60% glazed building with strict set points, the (weighted average) PPD values are lower than 10% during 72% of the working hours for the second and during 68% of the working hours for the third alternative (Figure 6.52). For the normal set points the number of hours decreases to 70% and 70% respectively. The number of hours with (weighted average) PPD values lower than 15% increases by up to 94% for the second and by 93% for the third alternative (for the strict control set points). For the normal set points the number of hours is 94% and 93% for the two alternatives.

217

24-26%

22-24%

20-22%

18-20%

16-18%

14-16%

12-14%

10-12%

8-10%

6-8%

4-6%

2-4%

800 750 700 650 600 550 500 450 400 350 300 250 200 150 100 50 0 0-2%

Number of hours

Single and Double Skin Glazed Office Buildings

Weighted average PPD Strict (2)

Figure 6.52

Strict (3)

Normal (2)

Normal (3)

Weighted average PPD for the 2nd 3rd 60% glazed alternatives.

For the strict control set points of the 100% glazed buildings, the (weighted average) PPD values are lower than 10% during 68% of the working hours for the second and during 62% of the working hours for the third alternative (Figure 6.53). For the normal set points the number of hours decreases to 55% and 57% respectively. The number of hours with (weighted average) PPD values lower than 15% increases by up to 87% for the second and by 84% for the third alternative (for the strict control set points). For the normal set point the number of hours is 84% and 82% for the two alternatives.

218

32-34%

30-32%

28-30%

26-28%

24-26%

22-24%

20-22%

18-20%

16-18%

14-16%

12-14%

10-12%

8-10%

6-8%

4-6%

750 700 650 600 550 500 450 400 350 300 250 200 150 100 50 0 2-4%

Number of hours

Results and discussion

Wighted average PPD Strict (2)

Figure 6.53

Strict (3)

Normal (2)

Normal (3)

Weighted average PPD for the 2nd and 3rd 100% glazed alternatives.

A further decrease and increase in the total solar transmittance of the fourth and fifth alternatives respectively, results in lower and higher weighted average PMV values as shown in Figure 6.54. The weighted average PMV values of the fifth alternative vary between the recommended limits ±0.5 (which correspond to lower than 15% of weighted average PPD values), but on the other hand they exceed the limits of ±0.3 (which correspond to lower than 10% of PPD values) for a longer time.

219

Single and Double Skin Glazed Office Buildings

0,5

Weighted monthly average PMV

0,4 0,3 0,2 0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5

Strict set point (3) Normal set point (3)

Figure 6.54

Strict set point (4) Normal set point (4)

December

November

October

September

August

July

June

May

April

March

February

January

-0,6

Strict set point (5) Normal set point (5)

Weighted average PMV for the 3rd, 4th and 5th 60% glazed alternatives (strict and normal control set points).

For the 60% glazed building, the (weighted average) PPD values are lower than 10% during 66% of the working hours for the fourth and during 71% of the working hours for the fifth alternative for strict set points (Figure 6.55). For the normal set points the number of hours increases for the fourth to 71% and drops for the fifth to 65%. The fifth alternative gives lower PPD values for the strict set points, since the (weighted average) PMV is between ±0.3 between the beginning of April and the end of October, while for the fourth one the PMV varies between these limits between the end of April and the middle of October. For the normal set points, however, the PPD values are lower for the fourth alternative, since the high total solar transmittance (of the fifth alternative) results in higher than +0.3 PMV values from the middle of May until the end of August, while for the fourth alternative they are lower than +0.3 during these months. The number of hours with PPD values lower than 15% increases by up to 92% for the fourth and by 93% for the fifth alternative (for the strict control set points). For the normal set point the number of hours is 93% and 90% for the two alternatives. The number of hours with PPD values lower than 15% is lower in the fourth alternative mostly due to the higher directed operative temperatures during January, February and December (PMV higher than -0.5). For the strict control set points of the 100% glazed buildings, the PPD values are lower than 10% during 60% of the working hours for the fourth, and during 64% of the working hours for the fifth alternative for the cell 220

Results and discussion

28-30%

26-28%

24-26%

22-24%

20-22%

18-20%

16-18%

14-16%

12-14%

10-12%

8-10%

6-8%

4-6%

2-4%

750 700 650 600 550 500 450 400 350 300 250 200 150 100 50 0 0-2%

Number of hours

type (Figure 6.56). For the normal set points the number of hours decreases to 59% and 50% respectively. The number of hours with PPD values lower than 15% increases by up to 83% for the fourth and by 84% for the fifth alternative (for the strict control set points). For the normal set point the number of hours is 83% and 78% for the two alternatives.

Weighted average PPD Strict (5)

Strict (4)

Figure 6.55

Normal (4)

Normal (5)

Weighted average PPD for the 4th and 5th 60% glazed alternatives.

650 600 550

Number of hours

500 450 400 350 300 250 200 150 100 50 28-30%

26-28%

24-26%

22-24%

20-22%

18-20%

16-18%

14-16%

12-14%

10-12%

8-10%

6-8%

4-6%

2-4%

0-2%

0

Weighted average PPD Strict (4)

Figure 6.56

Strict (5)

Normal (4)

Normal (5)

Weighted average PPD for the 4th and 5th 100% glazed alternatives.

221

Single and Double Skin Glazed Office Buildings

The sixth and seventh alternatives have the same glazing as the third alternative. Instead of internal blinds, the sixth alternative has internal screens and the seventh one fixed external louvres. The effective g value of both alternatives is lower than in the third alternative, as described in Subsection 5.2.1.2. The main difference between the alternative with the fixed external louvres and the other two is that in the first the shading devices are always applied, while in the others they are drawn for a set point of 100 W/m2 on the surface of the glass. As shown in Figure 6.57, the weighted monthly average PMV for the strict set points of the seventh alternative is quite low. However, the 6th alternative does not really differ from the 3rd one. For this reason, the sixth alternative is be studied further. 0,5

Weighted monthly average PMV

0,4 0,3 0,2 0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6

Strict set point (3) Normal set point (3)

Figure 6.57

Strict set point (6) Normal set point (4)

December

November

October

September

August

July

June

May

April

March

February

January

-0,7

Strict set point (7) Normal set point (7)

Weighted average PMV for the 3rd, 6th and 7th 100% glazed alternatives (strict and normal control set points).

For the seventh 60% glazed alternative, the PPD values are lower than 10% during 68% of the working hours for the strict and during 71% for the normal set point. The number of hours with weighted average PPD values lower than 15%, increases by up to 93% for the strict and by 92% for the normal set point. For the strict control set points of the 100% glazed buildings, the PPD values are lower than 10% during 57% of the working hours for the strict and during 60% for the normal set point (Figure 6.58). The number of hours with PPD values lower than 15%, increases by up to 82% for the strict and by 83% for the normal set points respectively.

222

28-30%

26-28%

24-26%

22-24%

20-22%

18-20%

16-18%

14-16%

12-14%

10-12%

8-10%

6-8%

4-6%

2-4%

700 650 600 550 500 450 400 350 300 250 200 150 100 50 0 0-2%

Number of hours

Results and discussion

Weighted average PPD Strict (60%)

Figure 6.58

Strict (100%)

Normal (60%)

Normal (100%)

Weighted average PPD for the 7th 60% and 100% glazed alternatives.

The first glazed alternative (triple clear glazing) results in both high and low PMV values due to the high thermal and total solar transmittance. When the thermal transmittance of the windows (second alternative) increases, the heating demand drops and the (minimum) PMV values during the winter increase. The (maximum) PMV values during the summer months are almost the same, since the solar factor values were kept the same. When the solar factor of the glazing in the third alternative is reduced the PMV values drop during the summer, resulting in a lower number of hours with PPD up to 10% (for a PPD of 15% the number of hours for the 2nd and 3rd alternatives is almost the same). A further decrease in the solar factor of the fourth alternative brings similar results as before, increasing the number of dissatisfied occupants. When the effective total solar transmittance increases (as in the second alternative but with inner venetian blinds) overheating problem occurs. For the strict set points the fifth alternative appears to provide a better thermal environment, while for the normal set points the temperature increases causing discomfort problems. The alternative with internal screens (sixth) provides thermal environment of quality similar to that in the third alternative. Finally, when the fixed horizontal external louvres are applied (seventh alternative) the upper limit of 23°C appears to be very low, increasing the PPD values. For the normal control however the PMV increases, giving PPD values similar to those in the third alternative.

223

Single and Double Skin Glazed Office Buildings

For strict set points the best performing alternative is the 2nd (since the high total solar transmittance “corrects” the mistaken, low upper air temperature limit of 23°C). For normal set points the alternatives 2, 3, 4, 6 and 7 perform similarly due to the low U, g and geffective values (PPD lower than 15% for 90% of the working hours). The 7th alternative, however, gives a larger number of hours with PPD values lower than 10% (which correspond to PMV values between ±0.3). In general, the upper permissible air temperature of 23°C appears to be fairly low, since the monthly average PMV during summer hardly reaches the neutral conditions (= 0). The air temperature set points are crucial for the provision of improved thermal environment since (a) the air temperature variation influences the PMV variation and (b) the correct selection of upper and lower permissible air temperature limits can place the PMV closer to the neutral condition (0) axis (in such a way that the PPD values will minimize). The large glazing area has a similar effect to the “less strict” set points since the large variation in the radiant temperatures will affect the operative temperatures, increasing the PMV variation. In order to minimize this effect, the use of “stricter” set points (with correct selection of upper and lower temperature limit) in highly glazed buildings is preferable.

6.2.3

Indoor climate on a zone level

Directed operative temperatures and thermal comfort indices on a zone level are studied in this section. The orientation of the zones is north, east, south and west for the strict, normal and poor control set points. The studied zones are double and single office rooms, meeting rooms and corner office rooms of the cell type 100% glazed office building. The third building alternative (typical construction for a glazed facade) was chosen as a 100% glazed reference case for the comparisons on a zone level, in order to study the impact of glazing on each orientation. The potential overheating problem for zones with increased glazing area (i.e. meeting rooms with 65% of window to external wall area ratio) is discussed in Subsection 6.1.3.

6.2.3.1 Directed operative temperatures Zones with different set points and orientations were studied (third 100% glazed alternative), in order to investigate the impact of increased glazed area on the directed operative temperatures. The number of working hours with certain directed operative temperatures of the 100% glazed meeting rooms is presented in Figure 6.59 (strict 224

Results and discussion

27.8 - 27.9

27.5 - 27.7

27.2 - 27.3

26.9 - 27.0

26.6 - 26.7

26.3 - 26.4

26.0 - 26.1

25.7 - 25.8

25.4 - 25.5

25.1 - 25.2

24.8 - 24.9

24.5 - 24.6

24.2 - 24.3

23.9 - 24.0

23.6 - 23.7

23.3 - 23.4

23.0 - 23.1

22.7 - 22.8

22.4 - 22.5

22.1 - 22.2

21.8 - 21.9

21.5 - 21.6

70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 21.2 - 21.3

Number of working hours

set points). The orientations selected are the north and south (the east and west vary in between). The minimum directed operative temperatures are almost 21ºC for all orientations; the maximum values, however, differ by 3ºC (24.5ºC for the north and 27.5ºC for the south facing meeting room). For the normal control set points the directed operative temperature varies from 21ºC to 31ºC for the south oriented meeting room with 9% of the working time being higher than 27.5ºC. For the north oriented meeting room the directed operative temperature varies from 21ºC to 26ºC.

Directed operative temperature (°C) Meeting room-North

Figure 6.59

Meeting room-South

Number of working hours between certain directed operative temperatures for the 100% glazed meeting room (strict control set points, 3rd alternative).

The impact of window to floor area ratio on the directed operative temperatures is presented in Figure 6.60 for a south oriented double and corner office zone with strict set points. For the double office with one external wall the directed operative temperature starts at 21ºC and it exceeds 27ºC only 1% of the time. For the corner office, however (with the external wall area twice than in the double office) the directed operative temperature is lower than 21ºC for 25% and higher that 27ºC for 8% of the working time. For the normal control set points, the directed operative temperatures vary even more.

225

Single and Double Skin Glazed Office Buildings

100

Number of working hours

90 80 70 60 50 40 30 20 10 27.7 - 27.8

27.4 - 27.5

27.1 - 27.2

26.8 - 26.9

26.5 - 26.6

26.2 - 26.3

25.9 - 26.0

25.6 - 25.7

25.3 - 25.4

25.0 - 25.1

24.7 - 24.8

24.4 - 24.5

24.1 - 24.2

23.8 - 23.9

23.5 - 23.6

23.2 - 23.3

22.9 - 23.0

22.6 - 22.7

22.3 - 22.4

22.0 - 22.1

21.7 - 21.8

21.4 - 21.5

21.1 - 21.2

20.8 - 20.9

20.5 - 20.6

…-20.1

20.2 - 20.3

0

Directed operative temperature (°C) Double-South

Figure 6.60

Corner South-West

Number of hours between certain directed operative temperatures for the 100% glazed south oriented zones (strict control set points, 3rd alternative).

From the above Figures it is evident that, in order to keep the directed operative temperatures at reasonable levels, strict set points should be applied in zones with fully glazed external walls (see number of hours above 24.5°C in Figure 6.59). For corner office zones (with increased external wall area to room volume ratio) not even strict set points can ensure directed operative temperatures within accepted levels (see number of hours above 28°C in Figure 6.60).

6.2.3.2 Perception of thermal comfort In this part the glazing and type of shading device were also varied (while for the study of the directed operative temperature only the third case was considered), in order to investigate the thermal comfort indices of different zones. Beginning with the third widow alternative (considered as reference for the 100% glazed building cases) with strict set points, the monthly average PMV value varies for different zone types, as shown in Figure 6.61. The wider monthly PMV variations occur for the corner offices due to the increased external wall area to room volume ratio. The values for the southwest oriented corner office vary from -1 to 0.4, while for the

226

Results and discussion

Corner (southwest)

Figure 6.61

Double (southwest)

Single (southwest)

December

November

October

September

August

July

June

May

April

March

February

0,4 0,3 0,2 0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6 -0,7 -0,8 -0,9 -1,0 January

Monthly average PMV

rest they vary from -0.6 to 0.2. For the rest of the glazing alternatives the tendency is similar.

Meeting room (southeast)

Monthly average PMV for zones of the third 100% glazed building with strict set points.

Since the more extreme monthly average PMV values occur for the corner office rooms, mainly this zone type was considered for further comparison. In the first 100% glazed case, with three clear panes and intermediate venetian blinds, the high thermal transmittance of the windows resulted in insufficient heating capacity. Thus, the case was simulated once more with increased heating and cooling capacity, in order to determine the energy use for keeping the air temperature in the working areas within the permissible set point limits. A comparison of the double and corner office zones with normal and increased heating capacity is presented in Figure 6.62. The lack of sufficient heat capacity results in differences in PMV values only for the corner offices, since the values for the double office are completely identical. During the winter months the difference reaches 0.8 (monthly average PMV of -1.7 during December for the alternative with real heat capacity), while during summer the values are the same, as expected.

227

Single and Double Skin Glazed Office Buildings

0,6 0,4

Monthly average PMV

0,2 0,0 -0,2 -0,4 -0,6 -0,8 -1,0 -1,2 -1,4 -1,6

Corner (real h.c.)

Figure 6.62

Double (real h.c.)

Corner (incresed h.c.)

December

November

October

September

August

July

June

May

April

March

February

January

-1,8

Double (incresed h.c.)

Monthly average PMV for the corner and double office of the first glazing case with real and increased heating capacity (100% glazed building, strict set points, southwest oriented zones).

The opposite problem (insufficient cooling capacity) is noticed in the fifth alternative due to the high solar factor (and also high geffective) of the window. The corner and double offices (case with real and increased cooling capacity) are compared in Figure 6.63. Once more the insufficient cooling capacity is considered only for the corner zones since the monthly average PMV values for the double office are identical. For the corner zone, however, the monthly average PMV reaches 1.1 with real and 0.6 with increased cooling capacity. There is also a small difference in PMV values during spring and autumn, since cooling is needed occasionally due to the strict control.

228

Results and discussion

1,2 1,0

Monthly average PMV

0,8 0,6 0,4 0,2 0,0 -0,2 -0,4 -0,6 -0,8

Corner (real c.c.)

Figure 6.63

Double (real c.c.)

Corner (incresed c.c.)

December

November

October

September

August

July

June

May

April

March

February

January

-1,0

Double (incresed c.c.)

Monthly average PMV for the corner and double office of the fifth glazing case with real and increased cooling capacity (100% glazed building, strict set points, southwest oriented zones).

In order to study the impact of window and shading device type on the perception of thermal comfort, the highly glazed corner offices with southwest facing alternatives (1-7) were compared (Figure 6.64). When the heating capacity is increased, the first alternative with the triple clear pane gives quite high monthly average PMV values during the summer due to the high thermal transmittance of the windows (otherwise the PMV values are very low). The second alternative is the second warmest due to the high solar factor of the glazing; g=0.584 and the lower (compared with the first alternative) thermal transmittance. The only alternative warmer than the second one is the fifth. In this alternative the same glazing was used while the intermediate blinds were replaced by internal ones, increasing the effective solar factor and thus the directed operative temperatures and the PMV values (as in the first alternative, the case with increased cooling capacity was chosen; otherwise the PMV values would have been much higher as shown in Figure 6.62). The monthly average PMV values of the fourth alternative are much lower than those of the third one due to the lower solar factor of the glazing (g=0.28 instead of g=0.35). The sixth alternative, with the same total solar transmittance as the third one, is slightly warmer due to the internal screens (lower geffective than the internal blinds). Finally, the seventh alternative with the fixed external louvres is colder throughout the year due to the fixed external louvres (low geffective all year round). 229

Single and Double Skin Glazed Office Buildings

0,6

Monthly average PMV

0,4 0,2 0,0 -0,2 -0,4 -0,6 -0,8

1st alt.

Figure 6.64

2nd alt.

3rd alt.

4th alt.

5th alt.

6th alt.

December

November

October

September

August

July

June

May

April

March

February

January

-1,0

7th alt.

Monthly average PMV for 100% glazed southwest corner offices (strict set points).

The impact of set points on the perception of thermal comfort (number of hours with PPD lower than 10% and 15%) for different zones is presented in detail in Appendix M. In general the number of hours with PPD lower than 15% is somewhat lower when normal set points are applied as shown in Figure 6.65. A larger difference between the two set points can be noticed in the “warmer” alternatives (alternatives with higher PMV values), since the higher permissible temperature limits combined with the higher g and geffective values cause higher discomfort. The highest percentage of working hours with PPD lower than 15% for normal set points occurs for alternative 7 (with low geffective), while alternatives 2, 4 and 6 have similar values. All these alternatives have low geffective and U values. For the strict set points the result is slightly different and the percentages are all higher. The poorest alternatives are the ones with high U and geffective values.

230

Results and discussion

% number of hours with PPD lower than 15%

100 90

90 80 70

85

87

87 82

85

88 82

85

86 87

6th alt.

7th alt.

75

74 70

60 50 40 30 20 10 0 1st alt.

2nd alt.

3rd alt.

4th alt.

strict

Figure 6.65

5th alt.

normal

Percentage of working hours with PPD lower than 15% for the southwest corner office zones.

When the percentage of working hours with PPD values lower than 10% is examined (for the corner offices with strict and normal set points), the positive effect of narrow air temperature variation is evident (Figure 6.66). The percentage difference in this case increases which shows that “quality wise” the strict set points are essential for zones with large glazing areas, such as corner offices (since PPD lower than 10% corresponds to PMV values between ±0.3, while PPD lower than 15% corresponds to PMV values between ±0.5).

231

Single and Double Skin Glazed Office Buildings

% number of hours with PPD lower than 10%

100 90 80 70 60 49

50

46

46

44

42

40

37 32

30

34

33

30

42

31 25

24

20 10 0 1st alt.

2nd alt.

3rd alt.

4th alt.

strict

Figure 6.66

5th alt.

6th alt.

7th alt.

normal

Percentage of working hours with PPD lower than 10% for the southwest oriented corner office zones.

A similar comparison of the percentage of working hours with PPD lower than 10% for strict and normal set points for the double offices (Figure 6.67) shows that the thermal environment improves drastically due to the lower ratio of external wall area to room volume. Since the difference (in % of working hours with PPD lower than 10%) between strict and normal set points decreases, it is also evident that the importance of narrower permissible air temperature variation (such as in strict set points) increases as the glazing area increases.

232

Results and discussion

% number of hours with PPD lower than 10%

100 90 80 71

70

65 59

57

60

64 59

68

66 62

62

61

62

53 47

50 40 30 20 10 0

1st alt.

2nd alt.

3rd alt.

4th alt.

strict

Figure 6.67

5th alt.

6th alt.

7th alt.

normal

Percentage of working hours with PPD lower than 10% for the southwest oriented double office zones.

6.3

Double skin façades

6.3.1

Simulations on a component level (pilot study using WIS 3)

Before the results obtained by the pilot study are analyzed, it would be useful to briefly describe the construction types on which the WIS 3 simulations are based. The simulations were carried out for a box window and a multi storey façade as shown in Figure 6.68. For the “standard” double façade mode during summer the air is extracted through the cavity to the outside either naturally (A-B-C) or mechanically (A-B-D-C); during winter the air remains in the cavity for increased thermal insulation, or after preheated in the cavity it is used as inlet supply air for the AHU (AB-D-E) respectively. For the airflow window cases the indoor air enters the cavity and is driven (through the cavity) to the AHU (E-B-D); during the heating season heat is recovered while during summer the air is just conducted to the outside.

233

Single and Double Skin Glazed Office Buildings

C

D

AHU

AHU

C

D

B

B

B E

E

B A

Figure 6.68

A

Multi storey and box window constructions.

6.3.1.1 Pre study: reducing the number of “standard” double façade alternatives Seven glazing alternatives were initially considered for the “standard” double façade and airflow window modes, as described in Subsection 4.1.3.1. A pre study, however, was carried out in order to reduce the number of glazing alternatives as described in this section. The main parameter studied, in order to achieve this is the temperature of different layers at the horizontal and vertical centres of the cavity of the double skin façade. For this study a box window 3.5 m high and 800 mm deep was assumed. Cases with opened and closed cavity opening were considered; for the cases in which the cavity is opened no dampers are applied (100% opened cavity). The air inside the cavity is naturally ventilated and the only driving force assumed is the thermal buoyancy (wind effects are neglected). The air enters the cavity from the outdoors and leaves to the outdoors. The shading devices (when applied) are assumed at the horizontal centre of the ventilated cavity. The simulations were carried out (see also Table 4.1 in Subsection 4.1.3.1) for a: • typical summer day (open cavity - with and without shading devices) • extreme summer day (open cavity - with and without shading devices) • winter day (open – closed cavity - without shading devices) 234

Results and discussion

The properties of the “standard” double façade glazing systems are described in Table 6.1 and in more detail (e.g. visual transmittance) in Appendix I.

U value inner skin W /m²K

g value

T sol

1.15

1.46

0.551

0.447

Clear pane 4mm

1.85

2.73

0.516

0.326

Argon

Clear pane 4mm

1.85

2.74

0.404

0.279

Clear pane 4mm

Argon

Low E Coated 4mm

1.15

1.46

0.354

0.264

A

Clear pane 8mm

Ventilated cavity

Clear pane 4mm

Air

B

Clear pane 8mm

Ventilated cavity

Clear pane 4mm

Argon

C

Clear pane 8mm

Ventilated cavity

Optigreen (solar control tinted) 6mm

Argon

Ventilated cavity

Clear pane 4mm

Ventilated cavity

D

E

Optigreen (solar control tinted) 8mm Optigreen (solar control tinted) 8mm

I nternal pane

0.53

G ap (12mm)

0.627

I ntermediate pane

2.87

G ap (800mm)

1.93

E xternal pane

U value glazing system W /m²K, closed cavity

Properties of the “standard” double façade glazing systems as calculated by WIS 3.

D SF C ase

Table 6.1

Clear pane 4mm Low E Coated 4mm

F

Clear pane 8mm

Ventilated cavity

Solar control + lowE (soft coated) 6mm

Argon

Clear pane 4mm

1.04

1.31

0.301

0.15

G

Solar control +lowE (hard coated) 8mm

Ventilated cavity

Clear pane 4mm

Argon

Low E Coated 4mm

1.14

1.46

0.443

0.335

The temperatures at the vertical and horizontal centres of different layers, for an opened cavity without shading during a typical summer day, were calculated as shown in Figure 6.69. In these cases it has to be noted that, since the cavity is ventilated, the thermal transmittance of the system (for each alternative) is the thermal transmittance of the inner skin (see Table 6.1). In order to compare the simulated alternatives, the first case (A) with 3 clear panes is considered as a reference case. When the low E pane replaces the inner clear one (case B), a slight increase in temperature (1°C, from 28°C to 29°C) can be noticed at the inner pane, due to a substantial decrease in the thermal transmittance of the inner skin. In the third case (C) the intermediate solar control pane results in an increase 235

Single and Double Skin Glazed Office Buildings

of almost 8°C (at the intermediate pane) and almost 3°C (to 31°C) at the inner one (when compared with the reference case, due to the increased indirect solar transmittance). When the solar control (body tinted) pane is placed as the outer one (case D and E), the increase in temperature (at this pane) is approximately 8°C. When these two cases are compared, it is evident that the low g values of the outer skin reduce the effect of low thermal transmittance (see U values of the inner skin for the cases D and E), resulting in slightly lower inner pane temperatures (compared with the inner pane temperatures of the cases A and B with clear outer pane). This can be explained as being due to the larger proportion of solar radiation that is absorbed at the outer skin. In the sixth case (F) only one advanced intermediate pane (with solar control and low E coating) was applied, resulting in an inner pane temperature 4°C higher than the indoor air temperature (and similar ones as the reference case). Both cases C and F have solar control intermediate panes. When these two cases are compared, however, the temperature of the intermediate pane is higher for the case F due to the low E coating (lower thermal transmittance). The position (facing to the inside) of the low E coating for the case F is crucial for the inner pane temperature. The additional insulation that the low E coating provides allows the inner pane to maintain lower temperatures (similar to the reference case). Finally, when a solar control and low E coated pane is placed as external pane, the temperature of the external pane increases as expected. The low E coating at the inner pane has similar effect. Due to the well ventilated cavity the cases (G) and (E) perform in a similar way. Thus the lowest inner surface temperature was achieved with alternative D, because of a low g-value, not the lowest, and a high U value (allowing the heat to be transmitted from indoors to the cavity). However, the inner pane temperature of the case E is similar due to the same low total solar transmittance of the outer skin; the impact of lower thermal transmittance, on the other hand, is limited.

236

Results and discussion

42 40

Temperature (°C)

38 36 34 32 30 28 26 24 22

Figure 6.69

A1

B1

C1

D1

E1

F1

Indoor air temperature

Indoor surface temperature

Internal pane (centre)

border

window airgap (centre)

border

Intermediate pane (centre)

border

Ventilated cavity

border

External pane (centre)

Outdoor surface temperature

Outdoor air temperature

20

G1

Calculated temperatures for different layers at the vertical and horizontal centres of a naturally ventilated double skin façade for a typical summer day, opening depth: 800mm – no shading devices.

When shading devices are applied inside the cavity, part of the transmitted radiation is absorbed increasing the temperature inside the cavity. According to the existing literature (Poirazis, 2006), sufficient heat extraction can ensure low air and inner surface temperatures. The influence of the air temperature on the inner pane’s temperature is studied later in this Subsection. In Figure 6.70 the temperatures of the different layers are presented for the different glazing alternatives during a typical summer day, when the movable solar shading in the cavity is applied. When the cases with and without shading devices are compared, an increase in the cavity air temperature is obvious. As shown in Figure 6.70 the inner layer’s temperatures are only slightly higher than the indoor air temperatures due to the decreased geffective value of the system and the heat extraction through the cavity. The tendency for the different glazing alternatives is similar to the case without the shading devices, but at a smaller scale. The results for an extreme summer day are similar (yet more significant).

237

Single and Double Skin Glazed Office Buildings

38 36

Temperature (°C)

34 32 30 28 26 24 22

Figure 6.70

A1s

B1s

C1s

D1s

E1s

F1s

Indoor air temperature

Indoor surface temperature

Internal pane (centre)

border

window airgap (centre)

border

Interediate pane (centre)

border

Internal subcavity (centre)

border

Shading device (centre)

border

External subcavity (centre)

border

External pane (centre)

Outdoor surface temperature

Outdoor air temperature

20

G1s

Calculated temperatures for different layers at the vertical and horizontal centres of a double façade for a typical summer day, opening depth: 800mm – shading devices.

During winter, the cavity of the “standard” double façade mode is closed, in order to reduce the system’s thermal transmittance and hence the heating demand. At other times (usually in mechanical ventilated cavities) the air is preheated before reaching the Air Handing Unit (AHU). Furthermore, in the existing literature (Poirazis, 2006) buildings with fully opened cavities during all the year are also mentioned. In this case the inner skin is crucial for the performance of the double façade. For a ventilated cavity without shading devices, as shown in Figure 6.71, the cases with low E inner pane (B, E, F and G) are the most appropriate in terms of surface temperatures, as the U value of the inner skin is the lowest. The cases with clear inner and intermediate panes are the ones with the lowest inner surface temperatures, as expected, since they have the highest U values.

238

A3

Figure 6.71

B3

C3

D3

E3

F3

Indoor air temperature

Indoor surface temperature

Internal pane (centre)

border

window airgap (centre)

border

Intermediate pane (centre)

border

Ventilated cavity

border

External pane (centre)

Outdoor surface temperature

24 22 20 18 16 14 12 10 8 6 4 2 0 Outdoor air temperature

Temperature (°C)

Results and discussion

G3

Calculated temperatures for different layers at the vertical and horizontal centres of a double façade for a winter day, opening depth: 800mm – no shading devices.

When the cavity is closed, the temperatures at the vertical and horizontal centres of each layer for cavities with closed openings are shown in Figure 6.72. The inner surface temperature of the reference case is slightly above 20°C, while the air temperature inside the cavity (centre) is approximately 10°C. The inner surface temperature of the second case increases due to the low E coating (lower U value). The air temperatures, however, are lower than in the reference case, since the insulation of the low E coating lowers the heat flow from indoors to the cavity. The solar control body tinted intermediate pane of the third alternative (C) results in high air temperatures in the cavity and inner surface temperatures slightly above 23°C. The curve of the sixth alternative (F) with the intermediate solar control and low E coating is very similar. The main reason for that is the high absorption of the body tinted pane. Since the temperatures of the inner and intermediate panes are very similar, the insulation that the low E coating provides seems not to be needed; however, in cases with lower solar gains, the increased thermal insulation that the low E pane (case F) provides can lead to reduced thermal losses. When the solar control body tinted pane is placed as external pane and the inner and intermediate panes are clear ones (case D), the air temperatures are slightly below 16°C and the inner surface temperatures slightly above 20°C. When a low E coating is placed at the inner pane (case E) the air temperature decreases and the inner surface temperature increases (similar effect with cases A and B). 239

Single and Double Skin Glazed Office Buildings

A3

Figure 6.72

B3

C3

D3

E3

F3

Indoor air temperature

Indoor surface temperature

Internal pane (centre)

border

window airgap (centre)

border

Intermediate pane (centre)

border

Ventilated cavity

border

External pane (centre)

Outdoor surface temperature

26 24 22 20 18 16 14 12 10 8 6 4 2 0 Outdoor air temperature

Temperature (°C)

Finally, for the case (G) due to the solar control and low E external pane the air temperature is 11°C, and due to the inner low E coated pane the inner surface temperature is around 23°C. The two low E coated panes (external and inner ones) of the latter case result in a low temperature inside the cavity but a sufficient one at the inner pane. The highest inner surface temperature is obtained for cases C and F, due to the intermediate solar control pane which leads to higher indirect solar transmittance. Lower inner pane temperatures occur in the cases A and D with high thermal transmittance values.

G3

Calculated temperatures for different layers at the vertical and horizontal centres of a double façade for a winter day, opening depth: 0 mm – no shading devices.

During night the best performing alternatives are the ones with the lowest U value, since the g value does not have any impact on the inner pane temperatures. The inner pane temperatures during night are of no interest (the building is occupied during day), so no further study was carried out on a component level. For the “standard” double façade the alternatives chosen were: • Case A: Selected as a reference case. The first case has the highest thermal transmittance (1.93 W/m2K) (when the cavity is closed) and the highest total solar transmittance (0.627). • Case D: This case has the solar control body tinted pane as an exterior layer and clear intermediate and inner panes. The thermal transmittance of this alternative is 1.85 W/m2K (closed cavity) and the total solar transmittance is 0.404. This case was chosen as a first improvement of the case A by adding a solar control pane. 240

Results and discussion

• Case E: In this case both a solar control body tinted (external) and a low E pane (intermediate) was applied. In this way the temperatures at the inner layer are kept within reasonable levels. The thermal transmittance for this alternative is 1.15 W/m2K (closed cavity) and the total solar transmittance 0.354. This is a second improvement by adding a low E intermediate pane to increase the insulation. • Case F: This alternative has the lowest thermal (1.04 W/m2K with closed cavity) and total solar transmittance (0.301). Only the intermediate pane is an advanced one (low E and solar control coatings), while the inner and external panes are clear. This alternative has the same coatings as the case E but their position changes; as a result, the intermediate advanced pane results in increased indirect transmittance.

6.3.1.2 Parametric study: influence of cavity geometry on system performance In this case a multi storey standard double façade cavity (with different height and depth) was chosen, in order to study the airflows and the vertical air temperature profile along the ventilated cavity. The parameters varied were the cavity height and depth, the size of openings and the position of shading device inside the cavity. The cavity depth varied from 200 to 1600 mm. In the cases with fully open cavity it could be expected that the depth of the openings is equal to the depth of the cavity. However, since the dampers occupy space (see Subsection 5.3.1.3) the opening depth to cavity depth percentage is presented in Table 6.2.

Table 6.2

Cavity and opening depth for the multi storey façade (even depths).

Cavity depth (mm)

Opening depth (mm)

% of opened area

200 400 400 600 800 1000 1200 1400 1600

173 346 346 519 692 865 1038 1211 1384

87 87 87 87 87 87 87 87 87

241

Single and Double Skin Glazed Office Buildings

Air velocity (m/s per m cavity width)

Influence of cavity height and depth on the airflows The height of the façade influences the airflow inside the naturally ventilated cavity and consequently the air temperatures. Initially the first double façade case with three clear panes (case A) was considered, in order to study the airflow rate for 10 m, 20 m and 30 m high cavities of different depths. The air velocity inside the cavity (10 m, 20 m and 30 m high) is shown in Figure 6.73. As expected, the higher cavities result in higher air velocities (for the same cavity depth), since the stack effect is stronger. 1,6 1,5 1,4 1,3 1,2 1,1 1,0 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0,0 0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

Cavity depth 10m

Figure 6.73

20m

30m

Calculated air velocity for 10, 20 and 30m high multistorey facades (case A, cavity depths 0.2-1.6 m, typical summer day).

The airflow rate (l/s per metre cavity width) for the 10 m, 20 m and 30 m high cavities is shown in Figure 6.74. As expected, the wider cavities (with larger openings) provide larger airflows (absolute numbers). A comparison of the airflow per meter of cavity height, however, shows that shorter cavities can ventilate more efficiently, since as shown in Figure 6.75 the airflow rate per metre of cavity height is larger. However, the total air flow will increase with the height of the cavity.

242

Results and discussion

1200 1100

Airflow (l/s per m cavity width)

1000 900 800 700 600 500 400 300 200 100 0 0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

Cavity depth (m) 10m

Figure 6.74

20m

30m

Calculated air flows as a function of cavity depth for 10, 20 and 30m high multistorey façades (case A).

Airflow (l/s per m cavity height and width)

60 55 50 45 40 35 30 25 20 15 10 5 0 0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

Cavity depth (m) 10m

Figure 6.75

20m

30m

Calculated air flows per metre of cavity height as a function of cavity depth for 10, 20 and 30m high multistorey facades (case A).

The diagram in Figure 6.76 shows the differences in airflow rates between cavities 10 and 20 m high and 20 and 30 m high façades. 243

Single and Double Skin Glazed Office Buildings

Airflow difference (l/s/ m cav. height and width)

10 9 8 7 6 5 4 3 2 1 0 0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

Cavity depth (m) 10-20m

Figure 6.76

20-30m

Calculated airflow differences (per m of cavity height) between cavities 10 and 20 m high and 20 and 30 m high.

It can be noticed that: • The airflow difference is higher in the first case than in the second one independently of the cavity depth (since the first curve is higher than the second one). This means that the more the cavity height increases the smaller is the influence of the height on the airflow. • The airflow difference increases when the cavity depth increases (since the deeper the façade, the larger the difference). This means that the influence of cavity depth is smaller in higher cavities.

Influence of cavity height and depth on the temperature profile along the cavity The air temperature profile inside a 10 m high cavity (case A, typical summer, no shading devices) is presented in Figure 6.77. The cavity is assumed fully opened (87%). As expected, the wider cavities provide lower air temperatures at the top of the cavity due to the larger airflows. The air temperature differences decrease as the cavity depth increases. In this case, as noticed in Figure 6.77, when the cavity gets wider than 1 m, the temperature differences along the cavity become very small. 244

Results and discussion

25,0 24,5

Air temperature (°C)

24,0 23,5 23,0 22,5 22,0 21,5 21,0 20,5 20,0 0

1

2

3

4

5

6

7

8

9

10

Cavity height (m) 0.2m

Figure 6.77

0.4m

0.6m

0.8m

1m

1.2m

1.4m

1.6m

Calculated air temperature as a function of height along a 10m high cavity for different cavity depths (case A, typical summer, no shading devices).

The results for a 20 and a 30 m high cavity are similar as shown in Figure 6.78.

27

Air temperature (°C)

26 25 24 23 22 21 20 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Cavity height (m) 0.2m

Figure 6.78

0.4m

0.6m

0.8m

1m

1.2m

1.4m

1.6m

Calculated temperature in the cavity as a function of height along a 30m high cavity for different cavity depths (case A1, typical summer, no shading devices).

245

Single and Double Skin Glazed Office Buildings

When Figures 6.77 and 6.78 are compared, it appears that, independently of the cavity depth, the air temperature at the 10th metre of a 10 m high cavity is higher than that at the 10th metre of a 30 m high one. This can be explained by the stronger stack effect that takes place in the taller cavity. In terms of temperature profile the cavity height is not very important for finding the optimal cavity depth, since similar results can be obtained regardless of the cavity height. Optimal cavity depth can be considered the minimum depth after which the air temperature decrease drops, ensuring sufficient heat extraction. However, this may vary for different weather conditions and glazing combinations. Another interesting result is the non linear curve type of the 0.2 m deep cavity (for 10 m high cavity) and the curves of the 0.2 and 0.4 m deep cavities (for the 30 m high cavities). Due to the lower airflows, the narrower the cavity (of a certain height), the more intense is the air temperature increase at lower heights. The tendency as the cavity height increases is similar. Larger airflows result in a lower rise in air temperature in the cavity. The air in the cavity is heated by energy losses from the inside and solar radiation from the outside, absorbed in the glass panes surrounding the gap. If the flow is low, the gap air temperature approaches the average temperature of the surrounding panes at a lower height than if the airflow is high. The temperature rise will then be curved as seen in Figure 6.78. Influence of percentage of opened area on the airflows and the temperature profile along the cavity Due to the construction type of dampers, when they are fully opened, the % of opened area is 87% for even opening size (0.2 m, 0.4 m, 06 m, etc) but it varies for odd ones. In Table 6.3 the opening area for different cavity depths (0.5, 0.7 and 0.9 m) is presented.

Table 6.3

Cavity and opening depth for the multistorey façade (even and odd depths).

Cavity depth (mm)

Opening depth (mm)

% of opened area

400 500 600 700 800 900

346 346 519 519 692 692

87 69 87 74 87 77

246

Results and discussion

The airflow difference between the 0.4 and 0.5 m (20m high) cavity is almost negligible as it is for the 0.6 and 0.7 and for the 0.8 and 0.9 m deep ones (cavities with the same opening size). The small differences are caused by the higher flow resistance of the narrower cavities. Due to the larger cavity depth, however, the air velocity is higher at the even cavities as shown in Figure 6.79. The larger differences in the air velocities in narrower cavities can be explained by the higher flow resistance of the narrower cavities. 1,00 0,95 0,90 0,85 0,80 0,75 0,70 0,65 0,60 0,55 0,50 0,45 0,40 0,35 0,30 0,25 0,20 0,15 0,10 0,05 0,00 0,4

0,5

0,6

0,7

0,8

0,9

Cavity depth air velocity (m/sec per m width)

Figure 6.79

airflow (m3/sec per m width)

Calculated cavity air velocity and airflow for different cavity depths for a 20 m high multistorey facade (case A, cavity depths 0.4-0.9 m, typical summer day, no shading).

The higher air velocity in the cavities with even depth results in lower air temperatures, since the air can be extracted easier. The temperature profile along a 20 m high cavity is shown in Figure 6.80. The temperature difference between the cavities with even and odd depths decreases as the depth increases.

247

Single and Double Skin Glazed Office Buildings

25,0 24,5

Air temperature (°C)

24,0 23,5 23,0 22,5 22,0 21,5 21,0 20,5 20,0 0

1

2

3

4

5

6

7

8

9

10 11 12 13 14 15 16 17 18 19 20

Cavity height (m) 0.4m

Figure 6.80

0.5m

0.6m

0.7m

0.8m

0.9m

Calculated air temperature as a function of height for different cavity depths for a 20 m high multistorey facade (case A, no shading).

It can be concluded that: • The opening size is very crucial for the size of the air flows. Airflows in cavities with the same opening size are almost the same (independently of the cavity depth). The air temperatures however tend to increase more in narrower cavities due to the lower air velocity.

Influence of glazing on cavity depth In this section the influence of glazing type on the airflow and temperature profile along a 20 m high cavity are studied. For a typical summer day the cavity depths studied were 0.6, 0.8, 1 and 1.2 m, while for an extreme summer day the cavity depths considered were 0.6, 0.8, 1, 1.2, 1.4 and 1.6 m. The influence of glazing type on the optimal depth (minimum depth for efficient heat extraction) is presented in Figure 6.81. In this case only the temperatures at the exit were considered for an extreme summer day. As expected, due to the lower absorptivity, the case with the three clear panes results in the lowest temperatures at the exit of the cavity. The cases with the solar external pane (with clear or low E coated internal pane) are somewhat warmer and the one with the highest temperatures is the one with the intermediate advanced coating (low E and solar control). 248

Results and discussion

From the Figure below, it can be concluded that the solar control pane increases the need for wider cavities, in order to achieve efficient heat extraction (air temperature difference for 0.6 m is higher than the one for 1.6 m); this effect is stronger, when the solar control pane is placed as intermediate one (case F instead of outer pane in cases D and E), since a larger part of the absorbed heat is transmitted into the cavity. 40

Air temperature at exit (°C)

39 38 37 36 35 34 33 32 0,6

0,8

1,0

1,2

1,4

1,6

Cavity depth (m) case A

Figure 6.81

case D

case E

case F

Temperatures at the exit of a 20 m high cavity during an extreme summer day (cases A, D, E, F, no shading).

When shading devices are applied the vertical air temperature profile is calculated in both the external (1) and internal (2) sub cavity. The external sub cavity is the one between the external pane and the shading devices and the internal one is that between the shading devices and the intermediate pane. At this point the shading devices are assumed to be placed in the middle of the ventilated cavity. For the case with the three clear panes (case A) the air temperatures in the two sub cavities are very similar as shown in Figure 6.82. The results are also very similar for a typical summer day. With shading the cavity air temperature is higher, but less solar energy enters the room behind the double skin façade.

249

Single and Double Skin Glazed Office Buildings

40 39

Air temperature (°C)

38 37 36 35 34 33 32 31 30 0

1

2

3

4

5

6

7

8

9

10 11 12 13 14 15 16 17 18 19 20

Cavity height (m) ext 0.6m ext 1m

Figure 6.82

int 0.6m int 1m

ext 0.8m ext 1.2m

int 0.8m int 1.2m

Air temperature profile along the internal and external sub cavity for different cavity depths for an extreme summer day (case A, shading).

The vertical air temperature profile was calculated also for the cases D, E and F. In order to reduce the number of simulations, only a 0.8 deep cavity was assumed. The difference in the air temperature between the internal and external sub cavity is minimum for the case with the three clear panes (case A), as shown in Figure 6.83. The difference in the case with the advanced intermediate pane (solar control and low E) is slightly larger, since the external pane is a clear one. Finally, the sub cavities in the cases with the solar control outer pane (cases D and E) show the largest air temperature difference. The solar control outer pane performs best during a summer day, since the temperatures at the external sub cavity are high and at the inner one low (when shading is used). During winter, however, shading is off and the solar control outer pane gives rise to high temperatures inside the cavity (as wanted).

250

Results and discussion

42 41 40

Air temperature (°C)

39 38 37 36 35 34 33 32 31 30 0

1

2

3

4

5

6

7

8

9

10 11 12 13 14 15 16 17 18 19 20

Cavity height (m) case A ext case E ext

Figure 6.83

case A int case E int

case D ext case F ext

case D int case F int

Air temperature profile along the internal and external sub cavity for the cases A, D, E and F for an extreme summer day (depth 0.8m, shading).

Influence of the position of shading device on the air temperatures In the existing literature (Poirazis, 2006) it is mentioned that the position of shading devices inside the cavity can have a relatively large impact on the energy and on the thermal performance of double skin façades. In order to investigate the impact of the position of shading device on the inner layer temperatures, a 20 m high and 0.8 m deep cavity was selected and the cases A, D, E and F were simulated for an extreme summer day. In Figure 6.84 the air temperature (at the vertical centre) of the internal sub cavity for different depths, and the inner layer temperatures for the cases A, D, E and F, are presented. The main aim of this comparison was to investigate the influence of shading device position on the thermal comfort. As shown in Figure 6.84, the variation in air temperature for the internal sub cavity ranges from 5°C (case D) to 9°C (case F) depending on the depth. However, the variation in the inner pane’s surface temperature is much smaller for all glazing alternatives. From the above it can be concluded that in the naturally ventilated cavities (with double pane glazing unit as inner skin) the position of shading devices is not important for the thermal comfort during the summer unless the inner skin is openable (box window cases) for natural ventilation purposes.

251

Single and Double Skin Glazed Office Buildings

42 40 38

Temperature (°C)

36 34 32 30 28 26 24 22 20 case A

case D

case E

case F

air temperatures (°C)

0.1m

Figure 6.84

0.2m

case A

case D

case E

case F

inner surface temperatures (°C)

0.3m

0.4m

0.5m

0.6m

0.7m

Air temperature (at the vertical centre) of the internal sub cavity and inner surface temperatures for different depths of the inner sub cavity for the cases A, D, E and F (extreme summer day).

6.3.1.3 Performance of the glazing alternatives Double façade mode Summer function (naturally ventilated cavity)

The temperature was calculated at the vertical and horizontal centres of each layer of a box window façade 800 mm deep and 3.5 m high. The calculations were carried out for an extreme summer day. For the cases that shading devices are not applied, all alternatives except the one with the three clear panes (case A) perform similarly in terms of the inner pane surface temperature (32°C for the cases D, E and F and 36°C for case A, with indoor air temperature of 25°C). For the cases D and E a large part of the absorption takes place at the outer pane, while for the case F the intermediate solar control and low E coated pane results in a dramatic increase in temperature (of the intermediate pane), as shown in Figure 6.85.

252

Figure 6.85

A

D

E

Indoor air temperature

Indoor surface temperature

Internal pane (centre)

border

window airgap (centre)

border

Intermediate pane (centre)

border

Ventilated cavity

border

External pane (centre)

Outdoor surface temperature

62 60 58 56 54 52 50 48 46 44 42 40 38 36 34 32 30 28 26 24 22 20 Outdoor air temperature

Temperature (°C)

Results and discussion

F

Calculated temperatures for different layers at the vertical and horizontal centres of a double façade for an extreme summer day, naturally ventilated cavity-no shading devices.

When shading is applied, the surface temperature of the inner pane decreases as expected, since part of the solar radiation is absorbed by the venetian blinds. As shown in Figure 6.86 for the cases that no low E was applied (cases A and D) (i.e. high U values of the inner skin) the inner pane temperature is slightly higher (approximately 2°C) than in the cases with inner and intermediate one (cases E and F).

253

Figure 6.86

A

D

E

Indoor air temperature

Indoor surface temperature

Internal pane (centre)

border

window airgap (centre)

border

Interediate pane (centre)

border

Internal subcavity (centre)

border

Shading device (centre)

border

External subcavity (centre)

border

External pane (centre)

Outdoor surface temperature

62 60 58 56 54 52 50 48 46 44 42 40 38 36 34 32 30 28 26 24 22 20 Outdoor air temperature

Temperature (°C)

Single and Double Skin Glazed Office Buildings

F

Calculated temperatures for different layers at the vertical and horizontal centres of a double façade for an extreme summer day, naturally ventilated cavity-shading devices.

Winter function (closed cavity)

For the winter case a box window cavity was selected, in order to study the air temperatures inside the cavity and the temperatures at the inner layer. In Figure 6.87 temperature at the horizontal and vertical centres of the layers for the cases A, D, E and F is presented assuming that no shading devices were applied. The cavity was assumed completely closed. At the inner layer the surface temperatures vary from 20°C to 24°C for the different cases, while the air temperatures inside the cavity vary from 10°C to 17°C. The case F (with the advanced low E and solar control intermediate pane) has the highest air and surface temperatures. The higher inner pane temperatures (when the alternatives E and F are compared) can be explained by (a) the lower U value and (b) the higher indirect solar transmittance of the F case. As shown in Table 6.1 the g values for the alternatives E and F are 0.35 and 0.3 respectively. The indirect transmittance is however 0.09 and 0.15 (g, Tsol) for the two cases. This means that even if the total solar transmittance is lower in the F case, the indirect transmittance is higher resulting in higher temperatures of the inner pane. Thus, the position of the solar control pane in a double façade system can be important for the inner pane temperatures.

254

case A

Figure 6.87

case D

case E

Indoor air temperature

Indoor surface temperature

Internal pane (centre)

border

window airgap (centre)

border

Intermediate pane (centre)

border

Ventilated cavity

border

External pane (centre)

Outdoor surface temperature

26 24 22 20 18 16 14 12 10 8 6 4 2 0 Outdoor air temperature

Temperature (°C)

Results and discussion

case F

Calculated temperatures for different layers at the vertical and horizontal centres of a double façade for a winter day, closed cavity- no shading devices.

When shading devices are applied (Figure 6.88), the variation in the air temperature inside the cavity is between 20°C and 25°C, while the inner surface temperatures vary from 20°C to 22°C. The increase in air temperature inside the cavity is caused by the absorption of the shading devices.

255

case A

Figure 6.88

case D

case E

Indoor air temperature

Indoor surface temperature

Internal pane (centre)

border

window airgap (centre)

border

Interediate pane (centre)

border

Internal subcavity (centre)

border

Shading device (centre)

border

External subcavity (centre)

border

External pane (centre)

Outdoor surface temperature

26 24 22 20 18 16 14 12 10 8 6 4 2 0 Outdoor air temperature

Temperature (°C)

Single and Double Skin Glazed Office Buildings

case F

Calculated temperatures for different layers at the vertical and horizontal centres of a double façade for a winter day, closed cavityshading devices.

A parametric study with different positions of shading devices inside the closed cavity was carried out for winter conditions for the cases A, D and F; as expected, the shading device position does not influence the temperatures at the inner surface. Summer – winter function (mechanically ventilated cavity)

The main purpose of the mechanically ventilated DSF mode is to preheat the air inside the cavity during the heating season and to distribute it through the AHU into the zones as supply air (if needed it can be further heated in the AHU, in order to meet the required supply temperature). The increase in air temperature should lead to energy savings during the heating season. These simulations will be carried out in IDA on a building level, in order to reduce the energy use all year round. However, simulations are carried out in WIS 3, in order to study the increase in temperature with different glazing alternatives with and without shading devices. In order to calculate the air temperatures at the outlet of the cavity, a 20 m high multistorey façade was chosen and the simulations were carried out for a typical winter day (in order to study the warmest case); the airflows needed for ventilation of the office zones are shown in Table 6.4. The two airflow rates picked for the simulations are the minimum (typical single office) and the maximum (meeting room for 12 persons). 256

Results and discussion

Table 6.4

Airflow rates for mechanically ventilated cavities (double façade mode). The airflow rates are chosen according to the ventilation rates of the different zones.

Zone type

Typical single office (1 occupant) Double office (2 occupants) Corner office (1 occupant) Meeting room (6 occupants) Meeting room (8 occupants) Meeting room (12 occupants)

Total ventilation rate (l/s)

10 20 15 21 28 42

Ventilation Ventilation per m of per m of width for the width for the box window 20m high cavity (l/s/m cavity (l/s/m width) width) 4.2 5.6 4.2 5.8 5.2 6

24 32 24 33 30 34

For the winter case the air temperatures at the exit for the different glazing alternatives are presented in Figure 6.89. In the cases with shading devices (placed at the middle of the cavity) an average temperature of the two sub cavities was assumed. As expected, in all the cases there is a small decrease in the air temperature at the exit, when the airflow rate increases from 24 l/s/per m cavity width to 34 l/s/per m cavity width. The outlet air temperature of the case A (thee clear panes) is around 9°C when shading devices are not applied and around 16.5°C with shading devices. When a solar control external pane is applied (case D) the air temperature at the exit increases (around 11°C) for the cases without shading devices due to the higher absorption of the external pane. For the same reason the air temperature difference for the cases with and without shading drops (by approximately 4.5°C) compared with the case A. The results are similar when a low E internal pane is applied (case E). The lower air temperatures in case E (compared with the case D) can be explained by the lower heat transmission from indoors to the cavity. When the cases D and E with shading applied are compared, it can be noticed that the air temperatures at the exit slightly decrease. This can be explained by the larger absorption of the external pane. Finally, in the case with the advanced intermediate pane (low E + solar control pane) the air temperature increase is the highest both in the cases with (approximately 18 to 17°C) and without (approximately 15°C) shading devices. In this case, the air temperature increases due to the solar control pane treatment, while the low E coating reduces the heat transmission to or from the indoors. Since shading devices 257

Single and Double Skin Glazed Office Buildings

Air temperature at exit (°C)

are usually not applied during winter, the preferred cases for the winter conditions should be the cases F and D. On the other hand it is likely that there will be energy losses through the windows due to the higher U values then for E and F. This energy aspect is analyzed and discussed on a zone level using IDA ICE 3.0 (Subsection 6.3.2). 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

18,2 17,5

17,2 16,4

16,0

15,3

11,5 9,3

11,0

14,7

14,6

10,4

9,7

9,0

24 l/s/m width

34 l/s/m width

A3 A

24 l/s/m width

34 l/s/m width

D3 D

no shading

Figure 6.89

15,3

15,3

24 l/s/m width

34 l/s/m width

E3 E

24 l/s/m width

34 l/s/m width

F3 F

with shading

Calculated air temperatures at the exit of the mechanically ventilated cavity during a typical winter day (800mm deep cavity).

In order to calculate the inner pane’s surface temperatures, a box window façade (3.5 m high and 0.8 m deep) was considered. The surface temperature of the inner layer was calculated for both winter and (extreme) summer conditions. For the winter case the maximum airflow (6 l/sec per m width) was assumed, while for the summer case the minimum one was considered (4.2 l/sec per m width). The main reason for these assumptions was to study the worst possible cases causing thermal discomfort problems. Both winter cases (with and without shading devices) were simulated as shown in Figure 6.90.

258

Inner surface temperature (°C)

Results and discussion

25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

21,9 20,1

23,1 21,5

22,0

22,7

20,9

19,8

no shading

shading

Winter

case A

Figure 6.90

case D

case E

case F

Calculated inner surface temperatures of mechanically ventilated box window facades (winter/extreme summer, with/without shading devices).

During a typical winter day the inner pane surface temperatures are quite close to the indoor air temperatures (23°C), mostly for the alternatives E and F, with low U values. For the other two alternatives the surface temperatures are close to 20°C, when shading is not applied. In the cases A and D the inner pane temperature is somewhat higher, when shading is applied, due to the clear inner pane. In the cases E (inner low E pane) and F (intermediate low E pane), however, the inner surface temperature remains almost the same for the cases with and without shading devices. During an extreme summer day the difference between the inner surface temperature and the indoor air temperature is 10 to 12°C for the cases without the shading devices and 9 to 14°C for the cases in which shading is applied. Simulations were carried out with naturally ventilated box window cases, in order to study the influence of the reduced airflows (mechanical ventilated cases) on the inner surface temperatures for an extreme summer day. For the naturally ventilated cavities the airflow rate is much larger (than in the assumed mechanically ventilated ones) resulting in lower inner surface temperatures as shown in Figure 6.91. The airflow rates for the naturally ventilated cases are presented in Table 6.5 (the air flow rate for the mechanically ventilated cavities is 4.2 l/sec per m of width of the façade). Regardless of whether shading is applied or not, a drop in the surface temperature can be noticed for the naturally ventilated cases due 259

Single and Double Skin Glazed Office Buildings

Inner surface temperature (°C)

to the highest airflow rates inside the cavity. In the mechanically ventilated cases A and D, when shading is applied, the inner surface temperature slightly increases, while for the cases E and F it decreases. The absorbed radiation in the blinds results in higher air temperatures inside the cavity. In the cases with intermediate and inner clear panes (A and D) the air temperature increase has a considerable effect on the inner surface temperatures (resulting in higher inner surface temperatures when shading is applied), while for the cases E and F the influence is much smaller (resulting in lower inner surface temperatures when shading is applied). In the naturally ventilated cases, however, the increase in air temperature inside the cavity when shading is applied results in a more intense stack effect and thus higher airflows. The inner surface temperatures in all cases drop when shading is applied (most often cases during extreme summer days). 42 40 38 36 34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 case A

case D

case E

no shading mechanical vent. shading mechanical vent.

case F

no shading natural vent. shading natural vent.

Figure 6.91

Calculated inner surface temperatures for box window facades (extreme summer day).

Table 6.5

Airflow rates for naturally ventilated box window facades.

no shading shading

260

case A (l/sec per m of width)

case D (l/sec per m of width)

case E (l/sec per m of width)

case F (l/sec per m of width)

167 255

242 267

248 248

274 284

Results and discussion

Finally, a comparison between a naturally and a mechanically ventilated cavity during an extreme summer day shows that (especially when shading is applied) the sufficient heat extraction can reduce the inner surface temperatures. The drop in temperature can reach 9°C in the cases with clear inner and intermediate panes and 6°C in the cases with a low E coated pane. Moreover it is obvious that in order to ensure low inner surface temperatures during extreme summer days, sufficient airflow in the cavity should be provided. If the temperature does not drop enough with a naturally ventilated cavity, then the possibility of fan supported ventilation (Poirazis, 2006) should be examined. Airflow window mode For the airflow window cases the exhaust air (of the office space) enters the cavity and through the cavity is driven to the AHU. Thus, the temperature of the inlet air (to the cavity) is constant (i.e. 23°C for a winter day, 24°C for a typical summer and 25°C for an extreme summer day, same as the indoor air temperatures ). Only box window façades were studied for the airflow window mode, focusing on (a) the (inner surface) temperatures of the inner pane, for thermal comfort purposes and (b) the air temperatures at the exit from the cavity, for heat recovery purposes. The different glazing alternatives used are described in more detail in Subsection 4.1.3.1. A brief parametric study was initially carried out, regarding the impact of cavity depth on the inner surface temperatures and the air temperatures at the vertical and horizontal centres of the cavity. The calculations were made for a typical winter and an extreme summer day for cases without shading devices. The study showed that neither the air nor the surface temperatures are influenced by the depth of the mechanically ventilated cavity. For this reason a 200 mm deep cavity was selected for the simulations. The properties of the airflow window glazing systems are described in Table 6.6 and in more detail (e.g. visual transmittance) in Appendix I.

261

Single and Double Skin Glazed Office Buildings

C

D

E

F

G

Air

Argon

Argon

Argon

Argon

Ventilated

Ventilated

Ventilated

Ventilated

Ventilated

Clear pane 4mm Clear pane 4mm Clear pane 4mm Clear pane 4mm Clear pane 4mm

U value glazing system W/m²K, closed cavity U value inner skin W/m²K

Internal pane

Gap (200 mm)

Intermediate pane Clear pane 4mm Low E 4mm Optigreen 6mm Clear pane 4mm Low E 4mm

Tsol

B

Clear pane 8mm Clear pane 8mm Clear pane 8mm Optigreen 8mm Optigreen 8mm Solar control+low E 8mm Solar control+low E 8mm

g value

A

Gap (12 mm)

AW Case

External pane

Table 6.6 Properties of the airflow window glazing systems as calculated by WIS 3.

1.93

5.92

0.627

0.53

1.15

5.92

0.561

0.447

1.83

5.92

0.529

0.326

1.85

5.92

0.404

0.297

1.15

5.92

0.354

0.264

Argon

Clear pane 8mm

Ventilated

Clear pane 4mm

1.04

5.92

0.195

0.157

Argon

Clear pane 4mm

Ventilated

Low E 6mm

0.824

5.66

0.191

0.149

Inner surface temperatures of airflow window façades

In order to carry out the parametric studies with the different glazing alternatives a typical winter and an extreme summer day were considered (where the results are more evident). Cases with and without shading were considered for the extreme summer conditions, in order to study the potential overheating problem, while the airflows were selected for the worst case in terms of heat gain or extraction (6 l/sec per m width of façade for winter and 4.2 l/sec per m width of façade for summer conditions). During a typical winter day the inner surface temperature of all the simulated alternatives varies from 21°C to 24°C, as shown in Figure 6.92 (the inlet air temperature is the same as the indoor air temperature, 23°C). The highest inner surface temperature is noticed in the third (C) case with an intermediate solar control pane and clear inner and outer panes (its performance regarding energy use is studied all year round on a zone level in Subsection 6.3.2 using IDA ICE 3.0 software) . The lowest temperature is noticed in the fourth (D) case in which the solar control pane was placed as an outer pane and the inner and intermediate panes are clear. For an extrene summer day the highest surface temperatures are still noticed in the third case, while the lowest are noticed in the seventh (G) case with an advanced (low E + solar control) outer pane, a clear intermediate pane and 262

Results and discussion

a low E inner pane (case with the lowest U and g values). The inner surface temperature variation of the simulated alternatives is from 32°C to 47°C, without shading, and from 33°C to 50°C when shading is applied. When three clear panes are applied (case A) the inner surface temperature is almost 22°C, while for the extreme summer case the temperature rises up to 37°C when shading is not applied and up to 48°C for the case with shading. The surface temperatures for the second (B) case in which the clear intermediate pane was replaced by a low E coated one are slightly higher. By replacing the intermediate clear pane with a solar control one (case C) the surface temperature slightly rises even more during a typical winter day. For an extreme summer day, however, the highly absorbing intermediate pane results in increased air temperatures inside the cavity, and consequently (due to the relatively high thermal transmittance of the inner clear pane) high inner surface temperatures. When shading is applied the inner surface temperature increase is lower than in the cases A and B, since the solar control intermediate pane reduces the effect of shading devices. When a body tinted solar control pane is placed as an outer one (cases D and E) the surface temperatures drop to 21°C in the case D and to 22°C in the case E, for the typical winter day. During an extreme summer day (without shading devices) the inner surface temperatures are 38°C for the case D (clear intermediate pane) and 36°C for the case E (low E coated intermediate pane). A larger drop in inner surface temperatures (compared with the cases A, B and C) can, however, be noticed when shading devices are applied during an extreme summer day. In this case the temperatures rise to 42°C and 41°C respectively (i.e. much lower than the alternatives studied before), since the absorption takes place at the outer pane (same effect as case C but this time at the outer pane). When the cases D and E are compared it is obvious that the low E coated pane (with lower U value) placed as intermediate pane (case E) replacing the clear one (case D) results in a slightly higher (1°C) surface temperature during winter, while during the summer this slight temperature increase brings the opposite results. The difference between the two alternatives is however quite small. In the last two cases an advanced solar coated (low E + solar control) pane is applied. In the case F the intermediate and inner panes are clear ones, while in the case G the inner pane is replaced by a hard coated low E one. In these two cases the inner surface temperature during the winter is around 22°C (slightly higher for the case G), while for an extreme summer day the temperature rise is the lowest (compared with all previous cases) as it does not exceed 32°C (no shading applied). When shading is applied, 263

Single and Double Skin Glazed Office Buildings

Temperature (°C)

the increase in the inner surface temperature is very small especially in the case with the inner low E coated pane (case G). 52 50 48 46 44 42 40 38 36 34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 typical winter surface temperature (no shading)

A

Figure 6.92

extreme summer

B

C

D

E

extreme summer surface temperature (shading)

F

G

Inner surface temperatures for an airflow box window (with and without shading devices).

Outlet air temperatures of airflow window façades

The outlet air temperatures are calculated only for the winter case, since in this case the air is brought to the AHU for heat recovery. In order to study the influence of glazing combination on the outlet air temperature a 200 mm deep box cavity was selected with airflow of 6 l/sec per m width of façade. The airflow window alternatives are studied both with and without shading device. When shading is not applied, the highest outlet air temperature is noticed when the solar control pane is placed as intermediate pane (case C) as shown in Figure 6.93. The lowest temperatures are noticed for the case A, in which three clear panes are applied (case with the highest thermal transmittance). When shading is applied the cases with clear outer pane are the ones with the highest air temperatures at the exit of the cavity (cases A, B and C). In more detail, when shading is not applied the air temperature at the exit for the first case (A) is 19°C (4°C of temperature drop), while, when shading is applied, the air temperature rises to 27.5°C. When a low E coated pane is applied as intermediate pane (case B) resulting in a lower U value, the air temperature increases to 23°C and 28.5°C respectively. The advanced low E and solar control intermediate pane (case C) results 264

Results and discussion

in a higher air temperature when shading is not applied (24°C) but in a lower one (26°) when shading is applied, due to the higher absorption at this pane. When a solar control pane is applied as outer pane (case D), the air temperature at the exit is 19°C, without shading, and 21.5°C with shading. When a low E pane is applied as intermediate one (case E), replacing the clear pane of the case D, the air temperature at the exit increases to 22°C and 24.5°C respectively. The temperatures are somewhat lower when the advanced coated pane (low E + solar control) is used as the outer one (cases F ad G). 30 28

Air temperature at the exit (°C)

26 24 22 20 18 16 14 12 10 8 6 4 2 0

A A1

B B1

C C1 no shading

Figure 6.93

D D1

E E1

F F1

G G1

shading

Air temperature at exit for different airflow window cases (winter day).

In general, solar control panes result in smaller air temperature differences between the cases with and without shading devices, since by absorbing a larger amount of radiation (than clear panes) they reduce the effect of shading. The concept of heat recovery is studied more extensively in the IDA ICE 3.0 simulations and conclusions are further discussed below.

6.3.2

Parametric studies on a zone level (IDA ICE 3.0)

As described in Subsection 4.1.3.2, a parametric study of different double skin façade alternatives was carried out, in order to evaluate their performance and better understand the influence of design parameters on energy use and thermal comfort. A typical cell office (for one person) zone with normal control set points was selected for this study. Due to the large amount of output data, the results are presented selectively. 265

Single and Double Skin Glazed Office Buildings

6.3.2.1 “Standard” double façade mode (naturally ventilated cavity) For the naturally ventilated “standard” double façade mode the alternatives selected for the IDA ICE 3.0 simulations were A, D, E and F (see Subsection 6.3.1.1). Two types of shading devices were used (see Subsection 5.3.2.6) in the cavity with a depth of 0.8 m (see Subsection 5.3.2.3). The cavity depth was selected after consideration of minimum depth to ensure efficient heat extraction from the cavity as discussed in Subsection 6.3.1.2. For the naturally ventilated cavities nine different damper control set points were considered. For the first case the dampers were assumed always open. For the second case (set point of 10°C) the dampers were completely closed for cavity air temperature below 8°C and completely open above 12°C; between 8 and 12°C the dampers open linearly. The dampers for the other set points (12, 14, 16, 18, 20 and 22°C) are similar. In the last case the openings were considered always closed. The output parameters studied for the naturally ventilated cavities are related to energy use and indoor climate issues. In more detail, the study focuses on the influence of design parameters (such as glazing and shading device type and the opening control of dampers) on energy use and inner pane temperatures. Furthermore their impact on operative temperature and comfort indices is presented. Energy use The design parameters studied are the façade orientation and the type of glazing and shading device. Each of these cases was simulated for the different damper control set points mentioned above and the alternatives with minimum total energy use were selected as optimal ones. The glazing type is crucial for energy savings. As shown in Figure 6.94, the alternative F (solar control + low E coating intermediate pane) performs best regardless of the façade orientation. The alternatives A and D have increased heating demand (due to the high U value of the system). The lower g value of the alternative D (solar control outer pane), results in a lower cooling and a higher heating demand. In total there is a slightly higher total energy demand for the north and east but a lower one for the south and west oriented façades. The alternative E has a lower heating demand due to the low E inner coating (lower thermal transmittance); the lower thermal transmittance of the inner skin of the alternative E (1.46 instead of 2.74 W/m2K, see Table 6.1) does not have much influence on the cooling demand. The alternative F with the intermediate solar control and low E coating performs better during both the heating and cooling seasons, 266

Results and discussion

101

138

134

89

18

12

12

16

13

13

9

20

9

14

13

9

DSF A

DSF D

DSF E

DSF F

DSF A

DSF D

DSF E

DSF F

DSF A

DSF D

DSF E

DSF F

89

91

97

104 92 9

DSF F

DSF E 11

DSF D 10

north

east

cooling

Figure 6.94

134

132

143

137 108

149

141 17

160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0

DSF A

Heating and cooling demand (kWh/m2a)

due to the lower U and g values. The performance of the cases with blue (instead of white) venetian blinds is similar; the impact of shading devices is studied further in Subsection 6.3.2.6.

south

west

heating

Energy use (heating and cooling) for a cell office for cases with white venetian blinds (“standard” double façade mode, naturally ventilated cavity with optimal temperature damper control).

Indoor Climate In order to study the thermal performance of the double façade alternatives, the inner pane temperatures and the monthly average PMV values were studied. Although similar output was obtained by WIS 3.0 simulations, this time all year round simulations were carried out, providing a more realistic view of the double façade thermal performance as to Scandinavian climatic conditions. For the simulations, cavities with optimal (as to energy use) temperature damper control were chosen. Inner pane temperatures

For studying the inner pane temperatures a south oriented façade was selected, with optimal (as to energy use) damper control. The glazing type has a considerable influence on the inner pane temperatures of the ventilated cavity as shown in Figure 6.95, which was also shown by the WIS 3.0 simulations. The best choice for glazing is alternative F, with a low U and g value of the inner skin. The inner pane temperature distribution is larger for the alternatives (A and D) without low E pane (higher U value) and as expected somewhat colder than the ones with low E panes. 267

Single and Double Skin Glazed Office Buildings

1200 1100 1000

Number of hours

900 800 700 600 500 400 300 200 100 0 14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

Inner pane temperature (°C) DSF A

Figure 6.95

DSF D

DSF E

DSF F

Number of hours (in a year) for certain inner pane temperatures for different glazing alternatives for a cell office (south orientation, ventilated cavity with optimal temperature damper control, white venetian blinds).

Monthly average PMV

The Predicted Mean Vote (monthly average PMV values during the working hours) was studied in this section. North, east, south and west oriented single offices with ventilated façades were simulated. All four glazing alternatives were selected with white venetian blinds. Due to the lower U value (when the dampers are closed) the alternatives E and F perform better than the A and D during the winter months (north oriented façades, see Figure 6.96). The higher indirect transmittance and slightly lower U values of the case F further improve the PMV values during winter (when compared with the case E), as explained in Subsection 6.1.3.1. During summer on the other hand the warm air is extracted through the ventilated cavity (cooling the intermediate pane), so the performance of alternative F is similar to that with the case E (see Figures 6.85 and 6.86). In the PMV comparison, however, it can be seen that the PMV values are lower in the case F. This can be explained by damper control set points, in combination with the fact that the cavity air temperatures tend to be higher in the case F. The dampers in this case are opened for more hours during the summer months resulting in lower U values (1.31 instead of 1.15 W/m2K of case E) and lower inner pane temperatures. The alternative with the outer solar control pane (D) also performs well during the summer but it has pretty low PMV values during 268

Results and discussion

winter, due to a high U value. The lower PMV values (during summer) of the alternative D compared with those of alternative E during summer can be explained with the higher transmission losses from the zone to the cavity (due to the lack of the inner low E pane). Finally, the alternative A performs poorly during both winter and summer due to the high U and g values. 0,3 0,2

Monthly average PMV

0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6

DSF A

Figure 6.96

DSF D

DSF E

December

November

October

September

August

July

June

May

April

March

February

January

-0,7

DSF F

Monthly average PMV values for the north oriented naturally ventilated cases for a cell office (white venetian blinds).

The monthly average PMV values during summer of the south oriented alternatives are somewhat lower (better being closer to zero) than those of the north oriented ones, as shown in Figure 6.97, due to the increased use of shading devices. Since the shading (due to the daylight control) is used more in the south oriented façade (e.g. 31% for the south and 1% for the north oriented alternative F during the summer months), the system g value drops, lowering the inner pane temperatures and consequently the monthly average PMV values. Another conclusion that can be drawn by observing the curves in Figure 6.97 is that the PMV values of the south oriented A and F alternatives (with clear outer pane) tend to decrease even more (compared with D and E that have outer solar control pane). Since the shading is used more for the cases with clear outer pane (due to the daylight control), the g values of the south oriented cases A and F are lower during the summer months. Furthermore, the more often the shading is applied, the warmer the cavity gets and the greater is the number of hours with opened dampers, resulting in lower inner pane temperatures and lower monthly average PMV values for the south oriented cases. 269

Single and Double Skin Glazed Office Buildings

0,3 0,2

Monthly average PMV

0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6

DSF A

Figure 6.97

DSF D

DSF E

December

November

October

September

August

July

June

May

April

March

February

January

-0,7

DSF F

Monthly average PMV values for the south oriented naturally ventilated cases for a cell office (white venetian blinds).

6.3.2.2. “Standard” double façade mode (mechanically ventilated cavity) For the mechanically ventilated “standard” double façade mode the four glazing alternatives selected were the same as for the naturally ventilated one. For this mode the air enters the AHU in three ways: (a) from outdoors, (b) from the double skin façade cavity or (c) from both. All year round, the outlet air from the double skin façade cavity is warmer than the outdoor air. During the heating season the use of this air as supply air may have a positive effect on energy demand, while during summer the outdoor air should be preferred, in order to avoid increasing the cooling demand. In order to mix the outdoor air and cavity air properly, so as to meet the supply air temperature (into the zones), a mixing box was designed in IDA ICE 3.0. The parameters studied for the mechanically ventilated cavities are similar to those for the naturally ventilated ones. Energy use The design parameters studied are the façade orientation and the type of glazing. As for the naturally ventilated cases the glazing type is crucial for the energy savings. As shown in Figure 6.98, the DSF F (solar control + low E coated intermediate pane) performs best regardless of the façade orientation, while due to the high U value the alternatives A and D have increased heating demand. The total energy demand for the north and 270

Results and discussion

north

21

19

13

DSF E

DSF F

13

DSF F

DSF D

18

DSF E

south

DSF A

20

DSF D

32

78

80

89

93

129

124 124

119

cooling

Figure 6.98

28 12

DSF F

east

DSF A

16

DSF E

17

DSF D

DSF A

9

DSF F

DSF E 11

DSF D 11

26

86

82

102

97

134

128

142

133 19

160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0

DSF A

Heating and cooling demand (kWh/m2a)

east is slightly higher, while for the south and west oriented façades it is lower. The heating demand of the DSF E case is lower due to the low E inner coating. When the alternatives E and F are compared it is obvious that the position of the solar control pane is as crucial for the mechanically ventilated cases, as it was for the naturally ventilated ones. The intermediate solar control + low E pane results in a lower heating demand due to reduced transmission losses through the outer skin, while the lower g value of the alternative F results in a lower cooling demand during summer.

west

heating

Energy use (heating and cooling) for cases with white venetian blinds for a cell office (standard double façade mode, mechanically ventilated cavity).

Indoor Climate The parameters studied in this section were the inner pane temperatures and the monthly average PMV values. Inner pane temperatures

As for the naturally ventilated cavity a south oriented façade was selected for studying the inner pane temperatures. The glazing type considerably influences the inner pane temperatures of the ventilated cavity as shown in Figure 6.99 (cases with white venetian blinds). The low U and g values of the alternative F result once more in narrower temperature variation of the inner pane; the distribution is larger for the alternatives A and D without low E pane (higher U value) and as expected somewhat colder. When the inner pane temperatures for the south oriented naturally (Figure 6.89) and mechanically (Figure 6.99) ventilated cavities are compared it 271

Single and Double Skin Glazed Office Buildings

is obvious that the latter ones are much higher. This can be explained by the insufficient heat extraction due to the low airflow rates. 1200 1100 1000

Number of hours

900 800 700 600 500 400 300 200 100 0 15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

Temperature (°C) DSF A

Figure 6.99

DSF D

DSF E

DSF F

Number of hours (in year) for certain inner pane temperatures for different glazing alternatives for a cell office (south orientation, white venetian blinds, mechanically ventilated cavity).

Monthly average PMV

The monthly average PMV is presented for the north and south oriented double skin alternatives. As expected, for the north oriented façade the DSF F appears to be closer to the zero axis (due to the low U and g values) both during winter and summer (as shown in Figure 6.100. The low E coating of the DSF E results in higher PMV values (compared with the DSF D), while the solar control outer pane results in similar PMV values during summer. The clear outer pane of the DSF A results in slightly higher PMV values (than DSF D) all year round.

272

Results and discussion

0,3 0,2

Monthly average PMV

0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6

DSF A

Figure 6.100

DSF D

DSF E

December

November

October

September

August

July

June

May

April

March

February

January

-0,7

DSF F

Monthly average PMV values for the north oriented mechanically ventilated cases for a cell office (white venetian blinds).

The trend for the monthly average PMV values for the south oriented façade is similar as shown in Figure 6.101. As expected, when the naturally and mechanically ventilated cases are compared, the PMV values are somewhat higher during summer due to the lower air flow rates (mainly during the summer months) inside the cavity. Higher airflow rates can partly solve this problem but they will increase the energy demand for fans. The lack of efficient heat extraction through the cavity has also another effect on the PMV values of the south oriented façades. While for the naturally ventilated cases the larger amount of absorbed radiation during the summer months, combined with the efficient heat extraction, resulted in lower PMV values, for the mechanically ventilated cases the insufficient ventilation rates lead to increased air temperatures inside the cavity, which influences the inner pane temperatures (as shown in Figure 6.99) and increases the PMV values.

273

Single and Double Skin Glazed Office Buildings

0,3 0,2

Monthly average PMV

0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6

DSF A

Figure 6.101

DSF D

DSF E

December

November

October

September

August

July

June

May

April

March

February

January

-0,7

DSF F

Monthly average PMV values for the south oriented mechanically ventilated cases for a cell office (white venetian blinds).

6.3.2.3 “Standard” double façade mode (hybrid ventilated cavity) For the hybrid ventilated “standard” double façade mode the same four glazing alternatives (as for the naturally and mechanically ventilated ones) were simulated in IDA ICE 3.0. For this mode the cavity is mechanically ventilated all year round, using the same mixing box as the one described in Subsection 6.3.2.2. In the hybrid ventilated case, however, the dampers open when the cavity air temperature exceeds a certain limit (for more efficient heat extraction purposes); this temperature limit was selected in such a way that the total (heating and cooling demand) is minimized. The main aim of the “hybrid” mode is to combine efficient heat recovery (as in the mechanically ventilated cases) and reduced cooling demand due to the better ventilated cavity (as in the naturally ventilated cases). Energy use The design parameters studied are the façade orientation and the type of glazing. As shown in Figure 6.102, the DSF F (solar control+low E coating intermediate pane) performs best once more regardless of the façade orientation , while due to the high U value the alternatives A and D have increased heating demand. The total energy demand for the north and east is slightly higher, while for the south and west oriented façades it is

274

Results and discussion

98

134

130

14

DSF E

82 14

DSF D

DSF F 11

20

13

DSF E

south

DSF A

13

DSF D

82 15

DSF A

DSF F 10

86

cooling

Figure 6.102

94

101 13

DSF E

east

DSF F 10

DSF D 11

89

107

DSF E 10

DSF D 10

north

129

140

17

DSF A

127

133 9

DSF F

145

137 17

160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0

DSF A

Heating and cooling demand (kWh/m2a)

lower. The heating demand of the DSF E case is lower due to the low E inner coating.

west

heating

Energy use (heating and cooling) for cases with white venetian blinds for a cell office (standard double façade mode- hybrid ventilated cavity).

Indoor Climate The parameters studied in this section were the monthly average PMV values for the north and south oriented façades. Monthly average PMV

For the north oriented façades the alternative A (clear panes) has the highest monthly average PMV values during the summer months due to the high g values. The alternative with the inner low E and outer solar control pane (E) is next, while the alternatives D and F appear to perform best during the cooling period. As for the naturally ventilated cases, the inner low E pane prevents the transmission losses from the office space to the cavity resulting in slightly warmer conditions during the cooling period. During the heating season the alternatives with the lowest U values (E and F) perform best, while the intermediate solar control + low E pane (case F) results in more hours with open cavity, due to the increased air cavity temperatures and thus lower monthly average PMV values.

275

Single and Double Skin Glazed Office Buildings

0,3 0,2

Monthly average PMV

0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6

DSF A

Figure 6.103

DSF D

DSF E

December

November

October

September

August

July

June

May

April

March

February

January

-0,7

DSF F

Monthly average PMV values for the north oriented hybrid ventilated cases for a cell office (white venetian blinds).

The south oriented alternatives follow a similar trend. As for the naturally ventilated cases the increased use of shading devices combined with efficient heat extraction (caused partly by the more intense stack effect during the summer) results in lower monthly average PMV values during the summer months for the south oriented façades; the effect is larger for the cases with clear outer pane (A and F).

276

Results and discussion

0,3 0,2

Monthly average PMV

0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6

DSF A

Figure 6.104

DSF D

DSF E

December

November

October

September

August

July

June

May

April

March

February

January

-0,7

DSF F

Monthly average PMV values for the south oriented hybrid ventilated cases for a cell office (white venetian blinds).

6.3.2.4 Airflow window mode In the airflow window cases the air from the office zone is exhausted through the cavity to the heat exchanger for heat recovery purposes. The supply air to the zone is 11.5 l/s (equal to the airflow rate inside the cavity). More information concerning the geometry of the airflow window cases can be found in Subsection 5.3.1.2, while a description of the type and position of shading devices can be found in Subsection 5.3.2.6. The glazing properties of the studied alternatives are described in Appendices H and I. Energy use In Figure 6.105 the energy use of the airflow window alternatives is presented. In general, the north facing alternatives tend to perform slightly better than the rest mainly due to the lower cooling demand. As expected, AW A (case with three clear panes) has the highest total (heating and cooling) demand, due to the high U and g values (1.93 W/m2K and 0.627, as shown in Appendix I). The outer solar control pane (AW D) results in a lower cooling and in a slightly higher heating demand (due to the lower g value of the outer skin). For the south and west orientation the decrease in total demand reaches 11%. When a low E intermediate pane replaces the clear one (AW E), decreasing the U value of the system (1.15 W/m2K), the heating demand drops drastically (approximately 33% regardless of 277

Single and Double Skin Glazed Office Buildings

116

82

75

70

83

24

AW G

44 23

AW F

AW E

AW A

AW D

26

AW G

34

60

65

78 25

46

south

AW F

AW E

59 35

cooling sum

AW A

19

east

AW D

18

AW F

AW G

33

26

AW D

AW E

AW A

AW G 11

73

88

86 77 45

93

91 17

AW F 10

AW E

north

Figure 6.105

122

108 127

115

121 135

127 26

13

AW D

180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0

AW A

Heating and cooling demand (kWh/m2a)

orientation, compared with AW D), since the air temperature drop inside the cavity is smaller due to the better insulation of the outer skin. The cooling demand, however, increases (although the g value is lower than in the two previous cases), since during the cooling period the low E intermediate pane does not allow the heat to transmit from the cavity to the outside. When the advanced low E + solar control pane is placed as the outer one (AW F), the cooling demand drops, while the heating demand increases due to the lower g value of the outer skin (compared with AW E); the decrease in total demand is more noticeable in the south, west and east orientations due to the larger cooling demand. Finally, when the clear inner pane (of the E case) is replaced by a low E pane the total demand drops further. The cooling demand in this case slightly increases (although the solar transmittance slightly drops) due to the improved insulation of the inner skin (less heat transmission from indoors to the cavity). AW G results in the lowest energy use for heating and cooling, due to the low thermal transmittance (both outer and inner skin).

west

heating sum

Energy use (heating and cooling) for cases with white venetian blinds for a cell office (AW cases).

Indoor Climate Inner pane temperatures The inner pane temperatures have been studied in this section for the different glazing alternatives. For all the cases white venetian blinds were assumed (when applied). As shown in Figure 6.106 the inner pane temperatures of the north facing alternatives hardly exceed 28°C. For the 278

Results and discussion

cases without low E pane (AW A and AW D) the temperature of the inner pane is somewhat lower due to the high thermal transmittance. The inner pane temperature of the alternatives E and F (with U of 1.15 and 1.04 W/m2K and g values of 0.354 and 0.195) increases, when low E panes are applied. The temperature variation is smaller in the case F due to the lower g value, while the slightly lower U value does not affect the lower inner pane temperatures. When the inner clear pane is replaced with a low E pane (case G), a slight decrease in the U value results in higher inner pane temperatures. 1300 1200 1100

Number of hours

1000 900 800 700 600 500 400 300 200 100 0 14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

Inner pane temperature (°C) AW A

Figure 6.106

AW D

AW E

AW F

AW G

Inner pane temperatures for north facing AW alternatives for a cell office (white venetian blinds).

The inner pane temperatures, however, increase dramatically in the south, west and east orientations, as shown in Figure 6.107. When no solar control pane is applied (AW A), the number of hours with temperatures above 30°C is 860 for the south, 650 for the west and 400 for the east oriented façade. As expected, the solar control outer pane (AW D) causes a decrease in the inner pane temperatures, especially for the south facing zone. When a low E intermediate pane replaces the clear one (AW E), the inner pane temperature slightly increases, although the solar transmittance of AW E is lower than that of AW D (0.354 and 0.404 respectively). The increased thermal insulation of the intermediate pane in combination with the low airflow rates results in higher air temperatures inside the cavity and thus higher inner pane temperatures. Finally, the number of hours with inner pane temperatures higher than 30°C is much lower for the last two AW alternatives (AW F and AW G), mainly due to the lower total solar 279

Single and Double Skin Glazed Office Buildings

Number of hours with inner pane temperature above 30°C

transmittance. The low E inner pane of AW G results in somewhat lower inner pane temperatures. 900 850 800 750 700 650 600 550 500 450 400 350 300 250 200 150 100 50 0

868

535 465 426

406

275 229 142 107 48

116

65 24

East

South

AW A

Figure 6.107

645

627

AW D

AW E

West

AW F

AW G

Number of hours with inner pane temperatures above 30°C for a cell office (white venetian blinds).

Monthly average PMV

The monthly average PMV values for the north oriented facades are presented in Figure 6.108. As expected, the cases without low E pane (AW A and AW D) have the lowest PMV values during the winter months, due to high U values. During spring and autumn, however, the PMV values of AW A increase due to the high total solar transmittance. AW D (case with outer solar control pane) is a somewhat cooler option during summer compared with AW A. When the low E pane is placed as the intermediate one (AW E) the PMV improves during the heating season but not during summer (compared with AW D), since less heat can be transmitted to the outdoors through the outer skin, increasing the air temperature and consequently the inner pane temperature. Finally, the monthly average PMV values are improved by AW F and AW G with the solar control+low E outer pane. The PMV during winter improves further, when the inner low E pane (AW G) is applied.

280

Results and discussion

0,4 0,3

Monthly average PMV

0,2 0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6

AW A

Figure 6.108

AW E

AW D

December

November

October

September

August

July

June

May

April

March

February

January

-0,7

AW G

AW F

Monthly average PMV values for the north oriented AW cases for a cell office (white venetian blinds).

For the south oriented façade the monthly average PMV values are shown in Figure 6.109. The tendencies remain the same as in the north oriented façade but in this case the PMV values are somewhat higher during the whole year. The alternatives performing best are the ones with the solar control + low E outer pane (AW F and AW G) for both the north and south oriented façades. 0,4 0,3

Monthly average PMV

0,2 0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6

AW A

Figure 6.109

AW D

AW E

AW F

December

November

October

September

August

July

June

May

April

March

February

January

-0,7

AW G

Monthly average PMV values for the south oriented AW cases for a cell office (white venetian blinds).

281

Single and Double Skin Glazed Office Buildings

6.3.2.5 Impact of the “ventilated façade” concept In order to estimate the energy savings and the indoor climate improvements achieved by different ventilated facade concepts, a comparison between “standard” double façades, airflow window cases and a non-ventilated façades was carried out at a zone level. The “standard” double façade mode (naturally, mechanically and hybrid) ventilated glazing alternatives were compared with the same ones in which no ventilation occurs. According to personal communication with Dr. Bengt Hellström (Division of Energy and Building Design, Lund University) the difference in thermal transmittance values between a closed double skin façade (with cavity depth of 0.8 m) and a single skin one with the same glazing (but cavity depth of 0.012 m) is 0.1 W/m2K. This difference is also what IDA ICE 3.0 results in. So consideration of the all year round closed double façade as a single skin one is reasonable. Similar comparisons have been carried out for the airflow window cases. This comparison can be considered as a comparison between (triple glazed) single skin and double skin alternatives with intermediate venetian blinds. In order to reduce the size of output, south and north oriented façades were selected for the comparisons. Energy use When the cooling demand of the different north and south oriented alternatives is compared, it is obvious that the naturally and hybrid ventilated double façades use less energy than the mechanically ventilated and the closed double skin facades (see Figure 6.110). As expected, the effect of ventilated cavities is larger for the south oriented facades, with the alternative F giving the lowest energy use. When the naturally and hybrid ventilated façades are compared with the (all year round) closed ones, a larger drop in cooling demand can be observed in the case A (with the higher total solar and thermal transmittance; 52% lower cooling demand in the naturally ventilated case compared with the one with a closed cavity, for the south oriented zone). This can be explained by the fact that the heat extraction is more important due to the higher total solar transmittance of the outer skin (which results in increased air temperatures in the cavity) and the high thermal transmittance of the inner skin (increased heat transmission from the cavity to indoors). The outer solar control pane (case D) reduces the effect of ventilation, decreasing the cooling demand by 46% (naturally ventilated south oriented zone compared with the case with closed dampers). When the inner low E inner pane replaces the clear one (case E) the drop is 40%, while for the case with the advanced intermediate pane (case F) the drop is 42% (slightly higher drop due to

282

Results and discussion

north

closed

Figure 6.110

DSF F

DSF E

DSF D

DSF A

DSF F

DSF E

DSF D

34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 DSF A

Cooling demand (kWh/m2a)

the higher indirect solar transmittance, when the cavity is closed). The results for the hybrid ventilated cases are similar.

south

naturally

mechanically

hybrid

Cooling demand for façades with natural, mechanical, hybrid and no ventilation for the north and south oriented zones for a cell office (normal set points, white venetian blinds).

A comparison between a closed cavity and cavities with natural, mechanical and hybrid ventilation (Figure 6.111) shows that the closed and the mechanically ventilated cavities are the ones performing slightly better during winter. It should be stated, however, that for the naturally ventilated cavity the dampers are not completely closed (sealed), allowing a low airflow inside the cavity. This assumption was made, since it is similar to the real case. The hybrid ventilated case has also slightly higher energy use for heating due to the damper control used (depending on the cavity air temperature); as a result, in some of the cases where the dampers are open to allow natural ventilation, heating is still needed. A more sophisticated damper control was assumed on a building level.

283

north

closed

Figure 6.111

DSF F

DSF E

DSF D

DSF A

DSF F

DSF E

DSF D

150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 DSF A

Heating demand (kWh/m2a)

Single and Double Skin Glazed Office Buildings

south

naturally

mechanically

hybrid

Heating demand for façades with natural, mechanical, hybrid and no ventilation for the north and south oriented zones for a cell office (normal set points, white venetian blinds).

As shown in Figure 6.112 the impact of ventilated façade on the total energy demand is limited. For the north facing alternatives the closed and mechanically ventilated cases perform best regardless of the glazing case, since the heating demand is the dominating factor; increased heating demand due to small openings, when the dampers are assumed closed can lead to slightly higher total energy use. For the south oriented cases the hybrid ventilated cavities perform slightly better than the rest (except in the case F in which the mechanically ventilated case is slightly better). The savings for the naturally ventilated case can reach 4% (south oriented, case A), for the mechanically ventilated case 4% (south oriented, case F) and for the hybrid case 7% (south oriented, case A).

284

north

naturally

Figure 6.112

DSF F

DSF E

DSF D

DSF A

DSF F

DSF E

DSF D

170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 DSF A

Total demand (kWh/m2a)

Results and discussion

south

mechanically

hybrid

closed

Total (heating and cooling) demand for cavities with natural, mechanical, hybrid and no ventilation for the north and south oriented zones for a cell office (normal set points, white venetian blinds).

Regarding the airflow window cases, a comparison between these and the closed double façades was carried out (Figure 6.113). The U and g values of the system are kept the same, while the geffective is slightly different due to the position of shading devices. Regardless of the orientation, the cooling demand for the north facing airflow window cases increases, while the heating demand drops. Due to the reduced heating demand, the total demand is lower for the airflow window cases.

285

13

11

17

11

10

9

92

93

91 20

aw

df (closed)

aw

df (closed)

aw

df (closed)

aw

df (closed)

case A

case D

cooling

Figure 6.113

108

148

135

140

127

170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0

26

Total demand (kWh/m2a)

Single and Double Skin Glazed Office Buildings

case E

case F

heating

Total demand (heating and cooling) for the double façade and airflow window north oriented zones for a cell office with normal set points.

When the south oriented zones are compared, however, the cooling demand increases dramatically due to the small airflow rates and the increased inlet air temperatures (Figure 6.114). Another reason for the increased cooling demand is the position of shading devices. The shading devices for the airflow window cases are placed between the intermediate and inner panes (while for the double façade cases they were placed between the outer and intermediate panes), increasing the amount of transmitted heat through the inner skin; the effect of shading devices is more important for the south oriented zones, since in this case they are used more. When the heating demand is examined, there is a drop regardless of the glazing case. The total demand is in most of the cases increased for the south facing façades.

286

86

78

96

case A

aw

df (closed)

case D

cooling

aw

aw

case E

13

25

46

df (closed)

20

18

df (closed)

35

27

aw

Figure 6.114

75

132

115

128

108

170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0

59

Total demand (kWh/m2a)

Results and discussion

df (closed)

case F

heating

Total demand (heating and cooling) for the double façade and airflow window south oriented zones for a cell office with normal set points.

Indoor climate For the indoor climate comparisons, monthly average PMV for the south oriented façades were considered, while PPD values were examined on a building level. For the case with the three clear panes the naturally and hybrid ventilated cavities perform similarly resulting in lower monthly average PMV values as presented in Figure 6.115. For these cases the PMV values vary from -0.6 to 0.26.

287

Single and Double Skin Glazed Office Buildings

0,3 0,2

Monthly average PMV

0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6

closed

Figure 6.115

naturally

mechanically

December

November

October

September

August

July

June

May

April

March

February

January

-0,7

hybrid

Monthly average PMV values for the south oriented alternatives for a cell office (case A, normal set points, white venetian blinds).

The trend for the glazing alternatives D and E is similar (but lower), in which the monthly average PMV values vary from -0.6 to 0.2 and from -0.55 to 0.2 respectively (Figure 6.116). For the case F (with solar control and low E intermediate pane), however, a difference can be noticed in the naturally and hybrid ventilated cases. This difference can be explained by the increased number of hours with open cavity for the naturally ventilated cases. Since the temperature set point for the dampers (hybrid ventilate case) is set, in order to decrease the total energy demand, it was decided to have a much higher set point (in order to use the preheated air for heat recovery purposes for more hours).

288

Results and discussion

0,3 0,2

Monthly average PMV

0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5

closed

Figure 6.116

naturally

mechanically

December

November

October

September

August

July

June

May

April

March

February

January

-0,6

hybrid

Monthly average PMV values for the south oriented alternatives for a cell office (case F, normal set points, white venetian blinds).

The airflow window cases tend to be warmer as discussed previously (Subsection 6.3.2.4). The monthly average PMV values were compared with the closed and naturally ventilated double façades, in order to investigate the impact of façade mode on thermal comfort. As shown in Figure 6.117 for the south oriented case A the monthly average PMV values are higher for the airflow window than for the double façade alternatives during the whole year. The tendency for the cases D, E and F is similar. The impact of the increased PMV values on thermal comfort is examined quantatively on a building level.

289

Single and Double Skin Glazed Office Buildings

0,5 0,4

Monthly average PMV

0,3 0,2 0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6

closed df

Figure 6.117

naturally ventilated df

December

November

October

September

August

July

June

May

April

March

February

January

-0,7

aw

Monthly average PMV values for the south oriented (closed and naturally ventilated) double façade and airflow window alternatives for a cell office (case A, normal set points, white venetian blinds).

The tendency for the north facing alternatives is similar. The difference in PMV values between the double façade and airflow window alternatives is smaller (than for the south oriented ones) as shown in Figure 6.118. Since the shading devices are used less than in the south facing cases, the increased heat transmission (due to the application of shading devices) through the inner skin is limited during the summer months, resulting in smaller differences in PMV values during the whole year. The differences are reduced for the other glazing alternatives D, E and F.

290

Results and discussion

0,4 0,3

Monthly average PMV

0,2 0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6

closed df

Figure 6.118

naturally ventilated df

December

November

October

September

August

July

June

May

April

March

February

January

-0,7

aw

Monthly average PMV values for the north oriented (closed and naturally ventilated) double façade and airflow window alternatives for a cell office (case A, normal set points, white venetian blinds).

6.3.2.6. Impact of shading device type Two types of shading devices were used for the parametric studies. Their properties are given in Appendix K and also described in Subsection 5.3.2.6. The impact of shading type is larger for the closed and mechanically ventilated cases, due to the low airflow rates (of the latter one), which result in high air temperatures inside the cavity (Figure 6.119). On the other hand, the impact of shading device type on the cooling demand for the naturally and hybrid ventilated cases is limited due to the efficient heat extraction from the cavity. For the case with three clear panes the increase is substantial (up to 56% in cases with closed or mechanically ventilated cavity) due to the high total solar transmittance of the outer skin (large amount of radiation is absorbed by the shading) and the high thermal transmittance of the inner skin (large proportion of the created heat is transmitted to the indoors). The solar control outer pane (case D) reduces the effect of shading devices, while the number of hours when shading is used drops (since the daylight sensor is at the inner skin). For the mechanically ventilated case there is a slight drop in cooling demand, since even the low ventilation rate is enough in this case to extract the increased heat created by the high absorbing shading device. The impact of shading on cooling demand is very small for the case with solar control outer and low E inner pane, while finally due to the clear outer pane the 291

Single and Double Skin Glazed Office Buildings

Increase in cooling demand (kWh/m2a)

closed and mechanically ventilated case F has increased cooling demand (due to the low total solar transmittance of the outer pane, the shading effect is more intense). 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 -1 -2 DSF A

DSF D

closed

Figure 6.119

naturally

DSF E

mechanically

DSF F

hybrid

Increase in cooling demand when the blue shading devices replace the white ones for a cell office (normal set points, south oriented zones).

The impact of shading type on heating demand is almost negligible. For the cases A and F (high total solar transmittance of the outer skin) the shading there has a positive effect for the closed façade, while for the mechanically ventilated cases the effect is negative. In general, darker shading devices (with higher absorptance) have a negative effect on the total energy demand for the different double façade alternatives as shown in Figure 6.120. The increase for the case A is larger due to the increased cooling demand. For the cases with efficient heat extraction (naturally and hybrid ventilated cavities) the effect is very small.

292

Increase in total demand (kWh/m2a)

Results and discussion

17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 -1 -2 DSF A

DSF D

closed

Figure 6.120

naturally

DSF E

mechanically

DSF F

hybrid

Increase in total demand when the blue shading devices replace the white ones for a cell office (normal set points, south oriented zones).

A comparison between white and blue venetian blinds regarding energy use has been carried out for air flow windows as well. For the north oriented facades the difference in energy use is very small, (since the venetian blinds are applied for fewer hours). For the south oriented façade, however, there is an increase in total demand in the cases with the darker shading devices due to the increased cooling demand, as shown in Figure 6.121. The heating demand, however, slightly increases due to the higher absorbtivity of the blinds, which results in an increase in air temperatures in the cavity. The differences in the cases with high U and g values are larger.

293

106

65

65

78

AW A

51

white

blue

AW D

26

46

blue

26

43

white

25

35

blue

25

84

white

white

blue

white

blue

AW E

cooling sum

Figure 6.121

78

75

75

115

114

108

200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0

59

Total demand (kWh/m2a)

Single and Double Skin Glazed Office Buildings

AW F

AW G

heating sum

Energy use (heating & cooling) for air flow window cases with white and blue venetian blinds for a cell office (normal set points, south orientation).

The impact of shading device type on thermal comfort is also studied for the ventilated cavities. Since the mechanically ventilated and closed cavities perform similarly, and the shading device type does not really influence the inner pane temperatures of the naturally and hybrid ventilated façade (since the damper control is dependent on the cavity air temperature), only the south oriented mechanically ventilated case was examined. Further PPD comparisons were carried out on a building level. The larger differences in monthly average PMV values are noticed in the south oriented case A (with the three clear panes), as shown in Figure 6.122. The difference in PMV values is still rather small; thus, no further investigation of the impact of shading device on thermal comfort was carried out.

294

Results and discussion

0,3 0,2

Monthly average PMV

0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5

DSF A white

Figure 6.122

December

November

October

September

August

July

June

May

April

March

February

January

-0,6

DSF A blue

Monthly average PMV values for the mechanically ventilated, south oriented case A, for a cell office.

For the airflow window cases the darker shading devices have a negative effect on thermal comfort, since they increase the monthly average PMV values when applied (during summer months). This increase can be noticed mostly for the south oriented zones, in which the shading is applied more often. For this reason, the impact of shading devices was not studied further.

6.3.3

Parametric studies on a building level (IDA ICE 3.0)

As described in Subsection 4.1.3.3, buildings with different fully glazed double skin façades were studied. The parameters varied for this study were the façade type (multi storey and box window), mode (“standard” double façade and airflow window) and ventilation strategy (naturally, mechanically and hybrid ventilated cavities). The two best performing “standard” fully glazed double skin façade alternatives were selected for further study on a building level (cases E and F). Both cases have low U and g values due to low E and solar control panes (outer and intermediate for case E and advanced intermediate for F). When these two cases are compared with regard to optical and thermal properties it can be noted that:

295

Single and Double Skin Glazed Office Buildings

• the thermal transmittance is slightly lower in case F than in E (1.04 instead of 1.14 W/m2K) • the total solar transmittance is somewhat lower in case F than in E (0.3 instead of 0.354), while the difference for the direct solar transmittance is higher (0.151 instead of 0.264) • the light transmittance of case F is lower than for case E (0.416 instead of 0.551) The best performing alternative, with regard to energy use and thermal comfort, on a zone level was F. However, due to the low light transmittance (according to personal communication with the WSP consultant Peter Pertola low light transmittance is below 0.5) and the high temperatures noticed at the intermediate advanced pane (which can lead to possible cracks) the case E was also selected as an alternative solution. For the airflow window cases the glazing alternatives chosen for simulations on a building level are E (low E inner, clear intermediate and solar control outer pane), F (clear inner and intermediate and solar control + low E outer pane) and G (low E inner, clear intermediate and solar control + low E outer pane). The best performing alternative according to the simulations on a zone level is G, with F and E next. The light transmittance of the cases F and G is low (0.357 and 0.344 respectively), so case E was also selected (with a light transmittance of 0.551). The case G, on the other hand, has very low thermal transmittance and a comparison with the “standard” double façade and single skin alternatives would be quite “unfair”; that is why case F (with similar thermal and optical properties to those of the double façade F) was selected. Finally, the case G was simulated on a building level, in order to investigate the importance of inner low E pane on energy use. The thermal and optical properties of the different glazing alternatives can be found in more detail in Appendix I. As stated in Subsection 5.3.2.2, the ground floor of the building has a single skin façade (for both the “standard” double façade and airflow window alternatives). The glazing assumed for the ground floor has the same properties as the reference single skin glazing alternative (third case, see Figure 4.2). For the rest of the floors a double skin façade was assumed with glazing as stated above. For the “standard” double façade mode white shading devices are selected for the southwest and southeast orientations (in order to reduce the increased cooling demand) and blue for the northeast and northwest (in order to avoid increasing the heating demand); for the airflow window cases only white venetian blinds were selected. The cavity depth of the “standard” double façade mode on a building level was assumed 0.8 m and for the airflow windows 0.3 m.

296

Results and discussion

A brief description of the naturally, mechanically and hybrid ventilated double façade and the airflow window building alternatives is given below. Naturally ventilated, box window “standard” double façade: The air in this case is inserted from the lower opening of the cavity (when the façade is ventilated) and is extracted through the upper opening of the box window construction. The dampers were set to open, when the indoor (office zone) mean air temperature reaches 23°C (while for the simulations on the zone level the dampers were functioning depending on the cavity air temperatures as described in Subsection 6.3.2.1). Naturally ventilated, multi storey “standard” double façade: The air in this case is inserted from the lower opening of the cavity of the second floor (when the façade is ventilated) and is extracted through the upper opening of the top floor. The dampers were set to open when the indoor (office zone) mean air temperature of the zones of the last floors reach 23°C. Mechanically ventilated “standard” double façade: The outdoor air enters the cavity at a controlled rate and ends up in the AHU. A mixing box that mixes the outdoor and cavity air, in order to bring air temperatures as close as possible to the supply air temperature is installed in the AHU. If further heating or cooling is needed, then this is provided by the heating and cooling coils. The cavity air is used as supply air (when needed), while the exhaust air from the zone is driven to the AHU for heat recovery purposes. Hybrid ventilated “standard” double façade: The hybrid ventilated case is a “combination” of the natural and mechanical cases. A temperature control opens the cavity dampers allowing natural ventilation, when the indoor air temperature exceeds 23°C (naturally ventilated case). When the indoor air temperature is below 23°C, the ventilation inside the cavity is the same as in the mechanically ventilated “standard” double façade, with a mixing box optimizing the mixing of outdoor and cavity air for minimizing the energy demand. Airflow windows: For the airflow windows the exhaust air from the office zones enters through a bottom opening and passes through the cavity to the AHU for heat extraction purposes. The airflow rates in the cavity for each zone are the same as the exhaust rates, as stated in Appendix F.

6.3.3.1 Energy use A comparison regarding the total energy use of the two best performing glazing alternatives is carried out in this section. The main purpose of this comparison is to investigate the impact of ventilated façades for already 297

Single and Double Skin Glazed Office Buildings

well performing glazing alternatives on a building level. It has to be noted that for this simulations the same glazing and ventilation modes were applied for all the orientations and no optimization for each orientation was considered. In practice the optimal façade type for each orientation should be considered. However, a comparison of the energy performance between single skin (with intermediate venetian blinds) and double skin alternatives can still be carried out. In Figure 6.123 a comparison for case E (solar control outer, low E intermediate and clear inner pane) is carried out. The larger drop in heating demand (compared with the case with closed cavity) can be noticed for the airflow window and the mechanically ventilated “standard” double façade cavity, while a smaller drop can be seen in the hybrid ventilated case. As expected, the heating demand for the naturally ventilated cavity is higher, due to the realistic assumption that closed dampers are leaky (higher thermal transmittance). The results are opposite regarding the cooling demand. The naturally and hybrid ventilated façades perform best while the mechanically ventilated façade is slightly higher. Finally, the airflow window case has the highest cooling demand due to the low airflow rates and the increased inlet air temperatures (during the spring and autumn months) and the low thermal transmittance of the inner skin. The decrease in total energy use is larger for the hybrid ventilated case (138 instead of 145 kWh/m2a noticed for the case with closed cavity), while for the airflow window case the total energy use increases to 148 kWh/m2a. When the multi storey and box window naturally ventilated “standard” double façades are compared an increase of 12 kWh/m2a of heating and a drop of 5 kWh/m2a of cooling demand can be seen. This can be explained by the temperature set points of the dampers. In order to avoid overheating of the cavity air, the dampers open when the indoor air temperature of the office of the last floor reaches 23°C. The cavity air temperature influences the inner pane temperature and the indoor air one. Since the cavity air temperature is higher at the top floors than in the first ones, if the damper set points are connected with the top floors, more hours they will be opened resulting higher heating and lower cooling demand; opposite would have been the effect if the damper set points were connected with the first floors.

298

Energy use (kWh/m2a)

Results and discussion

150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0

45

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naturally (box naturally mechanically window) (multi storey)

Space heating

Figure 6.123

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45

45 45

Cooling

Lighting

Rest

Total energy use for the glazing alternative E (closed, naturally, mechanically and hybrid ventilated “standard” double façade and airflow window, normal set points).

Similar comparisons are carried out for case F (clear inner and outer pane and solar control + low E intermediate pane). As shown in Figure 6.124 the decrease in cooling demand of the naturally ventilated cavity (when compared with the closed one) is 8 kWh/m2a. In case F the intermediate pane tends to overheat resulting in increased heat transmission to the inside; when natural ventilation occurs the temperature of the intermediate pane drops resulting in much lower cooling demand. For the same reason, a slight increase in heating demand can be noticed. As in case E, the mechanically ventilated case (when compared with the naturally ventilated one) results in increased cooling and decreased heating demand. The hybrid case is the one performing best (136 instead of 143 kWh/m2a for the case with closed cavity), with the heating demand slightly higher than in the mechanically ventilated case and with the cooling demand the same as in the naturally ventilated case. Finally, the airflow window case performs worst in terms of total energy use.

299

Single and Double Skin Glazed Office Buildings

150 140 130

Energy use (kWh/m2a)

120

45

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Space heating

Figure 6.124

Cooling

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Rest

Total energy use for the glazing alternative F (closed, naturally, mechanically and hybrid ventilated “standard” double façade and airflow window, normal set points).

From the Figures above it can be concluded that the decrease in total energy use is rather small, when double skin facades are used instead of single skin ones. However, the impact of ventilated façades on a zone level (Subsection 6.3.2.5) can give a better understanding as to which are the energy saving possibilities, since the study was focused only on heating and cooling demand (for which the savings occur) and was carried out for different oriented zones to point out the energy saving possibilities of each mode for each orientation. Although optimal double skin façade integration should definitely include consideration of the orientation, the comparison carried out above can give an understanding of the energy saving possibilities mostly for the hybrid ventilated case which can perform differently for the north, south, west and east oriented facades.

6.3.3.2 Thermal comfort When the monthly average PMV values of the different modes are compared for the glazing alternative E, it can be noticed that the cases with closed and mechanically ventilated cavities perform similarly (with the mechanically ventilated case giving slightly lower PMV values than the case with closed cavity), while the naturally and hybrid ventilated ones perform 300

Results and discussion

the same (giving slightly lower PMV values); finally, the airflow window cases give the highest values during the whole year (Figure 6.125). 0,4 0,3

Monthly average PMV

0,2 0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6

closed hybrid ventilated

Figure 6.125

naturally ventilated airflow windows

December

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October

September

August

July

June

May

April

March

February

January

-0,7

mechanically ventilated

Monthly average PMV for the glazing alternative E (closed, naturally, mechanically and hybrid ventilated “standard” double façade and airflow window, normal set points).

Regarding the number of hours (%) with PPD values lower than 10% and 15%, the double façade alternatives perform similarly to the case with closed cavity (62% and 85%) while for the airflow window cases there is a slight increase (67% and 90%) due to the higher (and closer to the 0 axis) PMV values during the winter months. For case F with the advanced (low E + solar control) intermediate pane the monthly PMV values slightly drop during the summer months due to the lower total solar transmittance of the glazing unit. The percentage of working hours with PPD values lower than 10% is 64% for the closed and mechanically ventilated cavities, while for the naturally and hybrid ventilated ones it is 63%. For the airflow window the percentage increases to 72%. Weighted average PPD values lower than 15% are noticed for 86% of working hours for the double façade and for 92% for the airflow window alternatives.

301

Single and Double Skin Glazed Office Buildings

6.4

Comparison of single and double skin façade building alternatives

6.4.1

Impact of glazing size on energy use and thermal comfort of single skin buildings

In order to study the impact of glass area on the energy use, 30%, 60% and 100% glazed alternatives with triple clear glazing (as in the reference building) were generated (in reality windows used for highly glazed alternatives have lower thermal transmittance). A cross comparison diagram of energy use of the 30%, 60% and 100% glazed alternatives (cell type) with strict and normal set points is presented in Figure 6.126. The increase in the total energy use for the 60% glazed building is 23% regardless of the set point (compared with the reference building). The increase for the 100% glazed alternatives is 45% for the strict and 47% for the normal set points. Both the heating and cooling demand increase in the highly glazed building alternatives as shown in Figure 6.126. However, the increase in cooling demand of the 100% glazed building, which reaches 112% for the strict and 177% for the normal set points, is substantial. One of the main arguments for using increased glazed areas in buildings is the provision of better indoor environment due to daylight. However, the increased window area does not necessarily lead to a reduction in energy use for lighting the building properly. To make use of daylight more efficiently, attention has to be paid to how the daylight is controlled and brought into the building. Traditional control of solar shading and lighting was applied to the cases studied in this report.

302

Energy use (kWh/m2a)

Results and discussion

200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0

45 45 45

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20 14,4

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92

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30%

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100%

strict set points

Space heating

Figure 6.126

13,4

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12,9

30%

60%

100%

normal set points

Cooling

Lighting

Rest

Impact of glazing size on energy use (triple clear pane with intermediate shading devices, strict and normal set points).

As already stated, the perception of thermal comfort depends on the permissible mean air temperatures, but also on the surface temperatures that surround the occupant. Thus, the size of the window is crucial for the perception of thermal comfort as seen in Figure 6.127. The considered glazed alternative with the triple clear glazing tends to give both high and low PMV values due to the high thermal and total solar transmittance. For the reference building alternative the monthly average PMV varies from -0.55 to 0.3, while for the 60% and 100% glazed alternatives the monthly average PMV varies from -0.68 to 0.36 and from -0.84 to 0.43 respectively.

303

Single and Double Skin Glazed Office Buildings

0,5 0,4 0,3

Monthly average PMV

0,2 0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6 -0,7 -0,8

30%

Figure 6.127

6.4.2

60%

December

November

October

September

August

July

June

May

April

March

February

January

-0,9

100%

Monthly average PMV for the 30%, 60% and 100% glazed alternatives with triple clear pane and intermediate shading devices with normal set points.

Impact of glazing type on energy use and thermal comfort

In order to study briefly the impact of the windows and shading devices on the energy use, the seven 100% single skin glazed alternatives with normal set points (cell type plan) are compared (Figure 6.128). For the best performing case the total energy use of the glazed alternative is only 20 % higher than for the reference building, (122 kWh/m²a with three clear panes and normal set points). A decrease in the thermal transmittance of the window (alternatives 2-7) results in a reduction in the energy use for heating and a smaller increase in cooling demand (comparison of alternatives 1 and 2). The alternatives (2nd and 5th) with high glazing solar factor values (0.584) have also a slightly lower heating demand (compared with the 3rd one with g=0.354), while the one (4th) with lower g values (0.27) has a slightly higher heating demand. The effect on cooling demand is the opposite; the 4th alternative uses less energy for cooling than the 3rd and 5th. Another parameter studied was the position of shading devices on the energy use. Intermediate blinds result in lower geffective values and thus lower energy use for cooling. When the 2nd and 5th alternatives (same window and shading device properties) are compared, it is obvious that the cooling demand increases dramatically (37%), when the blinds are 304

Results and discussion

Energy use (kWh/m2a)

placed intervally (5th alternative). The heating demand is almost the same (slightly higher in the 2nd alternative), since the blinds were used mostly during the warm periods. When fixed external louvres are applied (7th alternative), the cooling demand reduces dramatically while the heating demand increases. Different types of internal shading (blinds in the 3rd and screens in the 6th) with similar properties do not much influence the energy use. The type of glazing (solar factor values) influences the energy use for lighting in the building. For a set point of 500 lux at the work place the energy use increases up to 14.3 kWh/m2a, when fixed external louvres are applied (seventh alternative), from 12.9 kWh/m2a (first alternative). Often, the low g and geffective values lead to increased lighting demand. 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0

45 45 12,9 30

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2nd alt

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92

1st alt

Space heating

Figure 6.128

45

Cooling

58

5th alt

Lighting

Rest

Impact of glazing type and shading device position on energy use (100% glazed alternatives, normal control set points).

The first glazed alternative (triple clear glazing) tends to give both high (during summer) and low (during winter) monthly average PMV values due to the high thermal and total solar transmittance (Figure 6.129). Although the g value of the windows slightly increases in the second alternative, the PMV values are still slightly higher due to the much lower thermal transmittance; the effect during winter is similar. When the total solar transmittance of the glazing in the third alternative is reduced the PMV values drop during the summer, resulting in lower PPD values. A further decrease in the total solar transmittance of the fourth alternative brings similar results as before, lowering the PMV values during the cooling period. When geffective increases (the fifth case is the same as the second 305

Single and Double Skin Glazed Office Buildings

1st alt

Figure 6.129

6.4.3

2nd alt

3rd alt

4th alt

5th alt

6th alt

December

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June

May

April

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February

0,7 0,6 0,5 0,4 0,3 0,2 0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6 -0,7 -0,8 -0,9 January

Monthly average PMV

one but the shading is placed internally instead of between the panes), the PMV values increase dramatically. The alternative with internal screens (sixth) has PMV values similar to the third one. Finally, when the fixed horizontal external louvres are applied (seventh alternative) the PMV is lower all year round.

7th alt

Impact of glazing type and shading device position on monthly average PMV values (100% glazed alternatives, normal control set points).

Comparison of buildings with single and double skin façades

In Figure 6.130 single and double skin alternatives with the same thermal and optical properties are compared (thermal transmittance of glazing 1.14 kWh/m2a and solar transmittance of glazing 0.354). In the first case internal shading was applied resulting in a high geffective value. When fixed horizontal external louvres (second case) replace the internal venetian blinds (first case) the heating demand increases (7 kWh/m2a), while the cooling demand drops drastically (18 kWh/m2a) resulting in lower energy use. Intermediate placed shading devices (third case) result in lower heating (due to the increased solar gains during the heating season) and increased cooling demand (due to the increased indirect solar transmittance and to the daylight solar control of the shading that allows shading not to be used, when cooling is needed). A hybrid ventilated double façade (fourth case) with venetian blinds results in a slight decrease (when compared with the third case) in both heating (due to the reduced transmission losses 306

Results and discussion

Energy use (kWh/m2a)

from the cavity through the outer skin) and cooling demand (due to the heat extraction from the cavity when open). Finally, the airflow window (fifth case) has the lowest heating but increased cooling demand (due to the low airflow rates and the increased inlet to the cavity air temperature) that leads to high total energy use. 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0

45 45

45

14,0 14,3 27

65

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72

67

Space heating

14,4

14,4

9

single skin single skin internal shading external shading

Figure 6.130

45

45

12

66

single skin intermediate shading

Cooling

25

63

double skin airflow window hybrid ventilated

Lighting

Rest

Energy use for single and double skin alternatives with similar thermal and optical properties of the glazing (100% glazed alternatives, normal control set points).

When the monthly average PMV values (Figure 6.131) of these alternatives are compared, it can be noted that the case with internal shading devices has low values during winter and high values during summer. For the case with external shading the PMV values drop during summer (values closer to the 0 axis), but also during spring and autumn resulting in higher PPD values. The monthly average PMV values for the single skin case with intermediate venetian blinds are placed in between the previous two cases, while for the hybrid ventilated cases they are slightly lower mainly during the spring and summer. Finally, the airflow window case results in similar (with the case with internal shading) values during summer but somewhat increased values during winter, improving the thermal comfort.

307

Single and Double Skin Glazed Office Buildings

0,5 0,4

Monthly average PMV

0,3 0,2 0,1 0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6

single skin internal shading double skin hybrid ventilated

Figure 6.131

6.4.4

single skin external shading airflow window

December

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September

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May

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-0,7

single skin intermediate shading

Monthly average PMV values for single and double skin alternatives with similar thermal and optical properties of the glazing (100% glazed alternatives, normal control set points).

Comparison of best performing alternatives

Finally, a comparison of the “best performing” alternatives as to energy use and thermal comfort is carried out (Figure 6.132). An improved version of the reference (30% glazed) single skin building was simulated. The Uglazing and Uframe were assumed 1.14 W/m2K and 1.6 W/m2K, while the g value was set to 0.354 (for the initial reference case with triple clear pane the values were 1.85 W/m2K, 2.31 W/m2K and 0.69 W/m2K respectively). The low thermal transmittance and smaller area of widows result in a very low (compared with the rest of the cases) heating and cooling demand and the lowest total demand (113 kWh/m2a). The next two alternatives have the same glazing type but larger window to external wall area ratio (60% and 100% respectively). For buildings with larger glazed area the heating, cooling and thus total energy use increases by 18 kWh/m2a for the 60% and by 38 kWh/m2a for the 100% glazed alternative (from 113 to 131 and 151 kWh/m2a). On considering the fully glazed case for comparison, it is seen that fixed externally placed shading devices reduce the total energy use by 10 kWh/m2a (to 141 kWh/m2a) due to a drastic decrease in the cooling demand. A hybrid ventilated double façade (with the same glazing type as in the two previous cases) can result in a further drop of 3 kWh/m2a in total energy use compared with the case with fixed 308

Results and discussion

Energy use (kWh/m2a)

external louvres; for a more “fair” (considering the concept of clean, highly glazed façade) comparison, the total demand decreases by 13 kWh/m2a compared with the case with internal shading devices (total energy use of 138 kWh/m2a). Finally, an airflow window case with even lower thermal and optical transmittance was considered (U=0.824, g=0.191, Tvis=0.344; inner low E coated, and advanced solar control + low E outer pane); this case results in even lower energy use (132 kWh/m2a), but the low visual transmittance can often be a drawback. Energy wise, the poorer performance of highly glazed office buildings is inevitable. Careful selection of shading and glazing, however, can decrease the difference, resulting in reasonable solutions. 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0

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60% (3rd) 100% (3rd) 100% (7th) 100% (E) 100% (G) glazed single glazed single glazed single glazed double glazed airflow skin building skin building skin building skin hybrid window ventilated

Space heating

Figure 6.132

45

Cooling

Lighting

Rest

Comparison of the energy use for the “best performing” alternatives, normal set points.

Regarding the quality of indoor environment it is evident that smaller glazing areas provide a more stable environment with fewer dissatisfied occupants. In more detail, PPD values lower than 10% and 15% are achieved for 81% and 97% of the working hours for the improved reference building, while for the alternatives with larger glazed area (and the same window type) these values drop to 70% and 93% (for the 60% glazed building) and to 57% and 82% (for the 100% glazed building). The improvement is rather small when external shading is applied, since PPD values lower than 10% and 15% occur for 60% and 83% of the working hours; the improvement with a hybrid ventilated double façade cavity (63% and 85% respectively) is similarly small. Finally, due to the increase in the already low PMV values during winter, the airflow window 309

Single and Double Skin Glazed Office Buildings

case provides clearly improved thermal environment resulting in the same PPD values as the improved reference alternative (PPD values lower than 10% and 15% are achieved for 81% and 97% of the working hours).

310

Conclusions

7

Conclusions

The energy efficiency and thermal performance of highly glazed office buildings are often questioned. However, nowadays glazed buildings are increasingly being built around the world, because (a) there is a growing tendency among architects to use large areas of glass in the façade, often with the aim of contributing to a better view of the outside and access to daylight, (b) users often like the idea of increased glass area, relating it to a better view of the outside and a more pleasant indoor environment and (c) many companies prefer the distinctive image of themselves (e.g. transparency or openness) that a glazed office building can provide. Achieving good building performance, when using fully glazed façades is a great challenge. The energy efficiency and provision of an acceptable indoor climate are issues that should be considered. This thesis compares the performance (as to energy use and indoor climate issues) of an office building with different façade alternatives, both conventional and highly glazed ones. Optimizing the energy and indoor climate performance of highly glazed buildings by achieving proper construction and integration of single and double skin façade systems is an important and challenging goal. This chapter is divided into three main sections: • Energy use and thermal comfort for highly glazed office buildings located in Scandinavia. Within this section the main conclusions from the simulations are described. The aspects discussed are the impact of plan type, orientation, control set points, glazing area and type and façade (single and double skin) on energy use and thermal comfort. • Methods used to determine the energy and indoor climate performance of single and double skin façade glazed office buildings. • Improving the energy efficiency and thermal comfort of office buildings with highly glazed façades. Suggestions are given for further studies that can be carried out regarding the components and their efficient integration. The possibilities of double skin façade systems are further discussed. 311

Single and Double Skin Glazed Office Buildings

7.1

Energy use and thermal comfort for highly glazed office buildings located in Scandinavia

7.1.1

Plan type

The plan type of office buildings plays a considerable role in building performance regarding energy use and indoor environment issues. There are two clearly distinguishable plan types: the open plan and cell office. The use of the office space, ventilation rates, occupant density and the quantity of office equipment are some of the main parameters that differ between these two types. Due to the higher internal loads, mainly caused by higher occupancy and lower ventilation rates, an open plan office building is likely to have higher cooling and lower heating demand. In this study the increase in cooling demand for an open plan compared to a cell office reference building (30% window to external wall area ratio) was 57% (6 kWh/m²a) for the normal set points for the indoor air temperature, while the decrease in heating demand was 14% (7 kWh/m²a). The energy use for lighting the open plan office space increases (5 kWh/m²a), since all the space is considered to be working area. The tendencies for the highly glazed building alternatives are similar. The risk of discomfort increases in cell office zones, compared with zones of the open plan type, due to the larger external wall to occupied office floor area ratios (the occupants of the open plan are more evenly distributed within the whole floor space). In fully glazed building alternatives the risk of comfort problems is higher; especially in cases when windows with high thermal, total solar and effective solar transmittance were applied. The variation in operative temperatures increased, leading to an unacceptable thermal environment. The increased floor to external wall area ratio of the open plan type, combined with the position of the occupants within the working area (in the open plan some occupants are distributed more evenly in the working space, decreasing the impact of radiant temperature on the perceived thermal comfort), results in a more stable thermal environment.

7.1.2

Control set points

The control set points for the indoor air temperature are crucial for the energy and the thermal performance of a given building alternative. The 312

Conclusions

three mean air temperature set points considered within this thesis were the strict (22-23°C), the normal (22-24.5°C) and the poor (21-26°C). In general, the energy use increases when strict set points are applied. For the studied typical cell type reference building with 30% window to external wall area ratio (with 3 clear panes) the difference in energy use for heating between the strict – normal and strict - poor set points respectively is 7% (4 kWh/m²a) and 16% (9 kWh/m²a) . This difference tends to decrease as the glazing area increases (e.g. 5% and 7% are the corresponding values for a 100% glazed alternative); the difference for cooling demand is similar. When windows with lower thermal and total solar transmittance are used, the difference in energy use between the different set points drops. Despite a common perception that strict control set points often lead to an improved thermal environment, this study has shown that the key to choosing proper set points is the consideration of design parameters such as plan type, internal loads and glazing area and type. In general, the choice of set point requires the determination of (a) the permissible air temperature variation and (b) the minimum and maximum permissible air temperature. Two of the main parameters that highly influence the PMV values are the indoor air and operative temperatures. For a given position of an occupant inside the office space, the operative temperature depends on the surrounding surface temperatures. In order to achieve an improved thermal environment (assuming that the indoor air is well mixed), the optimal indoor air temperature should take into consideration the surface temperatures of, mainly, the external walls. In general, a wide variation in indoor air temperatures results in PMV curves with larger difference between minimum and maximum PMV, while the maximum and minimum air temperature limits influence the absolute PMV levels. Since, however, the PMV values are also influenced by the radiative temperatures of the surrounding surfaces and the occupant’s position, it is obvious that the indoor air temperature is not the only factor that determines the quality of thermal environment. As mentioned before, the two parameters that should be determined when deciding the set points are (a) the permissible air temperature variation and (b) the minimum and maximum air temperatures. Three of the most important input design parameters to be considered for this selection are (a) the internal loads (e.g. the open plan requires lower maximum air temperature limits due to the increased occupancy), (b) the window size (since a larger variation in surface temperatures results in a larger variation in PMV values) and (c) the glazing and shading device type used (since the different thermal and optical properties have a large impact on the radiative temperatures). 313

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For the reference building alternatives (30% window to external wall area ratio) strict set points may lead to comfort problems with excessive energy use, when the maximum and minimum temperature limits are not chosen properly (e.g. the strict set points with maximum air temperature limit of 23°C resulted in negative PMV values all year round, while the increased PMV values of the normal set points with maximum air temperature limit of 24.5°C resulted in similar PPD values with reduced cooling demand). Thus, for building alternatives with lower window to external wall area ratios, the PMV values can still vary within the acceptable PMV limits of ±0.5 (ISO Standard 7730), when set points with wider variation are allowed. For highly glazed facades narrow variations may have to be chosen. When the glazing area increases, windows with low thermal transmittance can ensure inner pane temperatures closer to the indoor air ones. For the cases when low inner pane temperatures occur, increasing the minimum temperature limit can only improve the situation to some extent, since cold drafts can still occur, lowering the quality of thermal environment. During summer, attention should be paid to the selection of the maximum permissible air temperature, in order to avoid excessive cooling of the office space. Windows with low total solar transmittance and/or shading devices that result in low geffective values (i.e. externally placed louvres or naturally ventilated double façades with venetian blinds) partly lower the inner pane temperatures. The maximum permissible air temperature should be decided according to the PMV values given for a certain window alternative. For cases with internally placed shading devices the maximum air temperature of 23°C was considered sufficient, while for cases with lower g and geffective values the air temperature limit of 24.5°C was preferred. Another parameter that should be considered in highly glazed buildings is the larger inner pane temperature variation that occurs during the year. Thus, stricter set points (narrower air temperature variation) should be preferred in general, requiring more careful consideration of the input parameters, leading to optimal selection of maximum and minimum limits that will ensure acceptable PMV values throughout the year. The selection of optimal temperature set points that ensure an acceptable thermal environment (avoiding at the same time excessive heating or cooling) is a complicated task. The selection of strict set points does not always guarantee improved indoor thermal environment, since if the input design parameters (e.g. occupancy, internal loads, window type and size, etc) are not considered thoroughly and the maximum and minimum permissible temperatures are not selected correctly, both discomfort and excessive heating or cooling may occur. Highly glazed buildings are more likely to lead to comfort problems and the selection of proper temperature 314

Conclusions

set points is more difficult. However, in any case the set points should be selected individually for each building and in cases with increased glazing areas further analysis should be carried out.

7.1.3

Orientation

The orientation of a building may have an effect on the energy use; however, if the design is the same for the opposite sides of the façades the effect is negligible. Strict temperature control set points (22-23°C) decrease the impact of orientation on energy use. Although the orientation of a zone has limited impact on the mean air temperatures, the directed operative temperatures may vary considerably. Wider permissible air temperature variations increase impact of the orientation in each zone (wider variation in operative temperature), mostly for zones with highly glazed areas. It is evident that, in order to achieve an acceptable indoor thermal environment, proper set points should be selected after considering zones with different orientations. For buildings with larger window to external wall area ratios the need for careful set point selection increases, since in these cases the impact of orientation on the perception of thermal comfort increases.

7.1.4

Glazing area

As expected, the total use of energy increases with the glazing area. Assuming a triple clear glazed window, the increase in energy use of a studied typical 60% single skin glazed building, compared with the studied typical reference building, is 28 kWh/m²a (23%) for the normal indoor temperature control set points. The increase for the studied typical 100% single skin glazed alternatives is 57 kWh/m²a (47%). This difference in energy use would of course decrease if glazed facades with lower thermal and total solar transmittance (including solar shading, which results in lower geffective values) were chosen. Increased window area does not necessarily mean a substantial decrease in the electricity for lighting. When the 30% and 100% alternatives are compared the decrease in energy does not exceed 1.3 kWh/m²a for the normal (with a set point of 500 lux at desktop) and 1.9 kWh/m²a for the poor set points (with a set point of 300 lux at desktop) and is even smaller for glazing with lower visual transmittance. Thus, the energy savings for lighting highly glazed buildings are often very small. The access to daylight might be higher with increased glazing area, but the quality of visual comfort could be compromised due to glare problems. 315

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The larger the window to external wall area ratio, the larger the comfort problems are during the whole year, especially when the comparison is based on triple-glazed (clear glass) windows. During the winter the PMV drops from -0.55 (reference building) to -0.82 (100% glazed alternative) and during the summer it increases from 0.3 (reference building) to 0.45 (100% glazed alternative). This corresponds to a number of hours with PPD values lower than 10% of 73% for the reference building, 57% for the 60% glazed alternative and 31% for the 100% glazed alternative (with normal control set points). Thus, the need of glazing with lower thermal and total solar transmittance is evident, especially for highly glazed alternatives.

7.1.5

Glazing and solar shading type

The window properties (U, g and geffective) have, as expected, a remarkable impact on energy use, which is also a main conclusion from this study. However, one of the main aims of the study was also to quantify the impact for Scandinavian climatic conditions. A description of the energy use, as simulated for the cases with normal control set points for the indoor air temperature, is given below. Large glazing areas with three clear panes (with high U and g values) result in a high energy use for heating and cooling. When the three clear panes were replaced by glazing with lower U values (from 1.85 to 1.14 W/m2K), the total energy use for the studied fully glazed building with normal control set points dropped from 180 to 155 kWh/m²a mainly due to reduced heating. By decreasing the total solar transmittance of the glazing (0.35 instead of 0.58), the energy use for cooling dropped (from 37 to 27 kWh/m²a), while the energy use for heating increased (from 59 to 65 kWh/m²a); a further decrease in the total solar transmittance had a similar effect. The position of shading, however, had a positive effect, with the intermediate placed shading decreasing the cooling demand, while having almost no effect on the heating demand. Simulations have shown that for intermediate blinds the cooling demand (of a 100% glazed alternative with normal control set points) is 37 kWh/m²a, while when the blinds are internally placed, it increases to 54 kWh/m²a (both cases have Uglazing of 1.14 and gglazing of 0.58). Finally, externally placed shading devices decreased substantially the cooling demand compared with intermediate shadings. The cooling demand then dropped from 27 to 9 kWh/m²a, although the heating demand increased by 7 kWh/m²a, for alternatives with Uglazing of 1.14 and gglazing of 0.35. This case resulted in the lowest total energy use (141 kWh/m²a). 316

Conclusions

For 100% glazed alternatives (a) a decrease in thermal transmittance of the windows can lead to considerable energy savings for heating, (b) low total solar transmittance of the glazing unit results in lower cooling and higher heating demand and (c) low effective total solar transmittance by using intermediate or external shading devices can achieve a lower cooling demand, while it doesn’t have much effect on the energy use for heating. As to indoor climate, highly glazed single skin alternatives give a wide variation in PMV values resulting in a poorer thermal environment. In general, narrower PMV variation can be achieved by applying windows with low thermal transmittance and low g and geffective values. However, the PMV values during winter still exceed the PMV comfort limit of 0.5 due to the low radiant temperatures. Fixed, external shading devices lower the PMV values during summer months but also during spring and autumn.

7.1.6

Double skin façades

In order to reduce the energy use and improve the indoor thermal environment of highly glazed buildings, double skin façades can be implemented. The double skin façade is a system consisting of two glass skins (single or double) placed in such a way that air can flow through the intermediate cavity. In principle the main purpose of the double skin façades, as to energy use and thermal comfort, is to allow the useful solar gains into the building when shading is not needed, and to extract, through the ventilated cavity, the heat absorbed by the shading to lower the cooling demand of the building. The distance between the skins usually varies from 0.2 m up to 2 m. For protection and heat extraction reasons the solar shading devices are placed inside the cavity. The ventilation of the cavity can be natural, fan supported or mechanical; the origin and destination of the air can also vary depending on the location, the use and HVAC strategy of the building. The two modes considered in this study were the “typical double façade” and the “airflow window” mode. In the “typical double façade” air always enters the cavity from outdoors. The cavity can be (a) closed during the heating season for increased thermal insulation and opened during the cooling season for heat extraction purposes (naturally ventilated cavity), (b) used for preheating the air supplied in the AHU (as supply air) during the heating season and extracted during cooling periods (mechanically ventilated case) or (c) opened during the cooling periods, as in the naturally ventilated cases and used for preheating the air supplied in the AHU, as in the mechanically ventilated cases (hybrid ventilated cavity). 317

Single and Double Skin Glazed Office Buildings

For the “airflow window” mode, the air always enters the cavity from the indoor office space (exhaust air) all year round. The aim is to improve the inner glass temperatures for extreme winter and extreme summer conditions. During the heating season the cavity air ends up in the AHU for heat recovery purposes, while during the cooling season the air is extracted to the outside. A main requirement to be fulfilled when ventilated cavities of double skin façades are designed is efficient heat extraction during the summer months. For naturally ventilated cavities the key parameters for achieving this are the characteristic height of the cavity (height to depth ratio) and the inlet and outlet opening size of the dampers. In general, the area occupied by the dampers when the cavity is fully open should be as small as possible, since the opening size is crucial for the size of the air flows. Cavities with the same opening size result in almost the same airflows independently of the cavity depth. Another parameter that has to be considered is the type and position of panes, since they have a considerable impact on the minimum cavity depth that ensures efficient heat extraction. During the parametric studies on a component level it was noted that solar control outer and especially intermediate panes require wider cavities, due to the increased cavity air temperatures that result in high inner pane temperatures. Finally, for naturally ventilated cases, the position of shading device inside the cavity has limited impact on the thermal comfort; the lower the thermal and indirect solar transmittances of the inner skin, the smaller is the impact. However, if the operable cavity is used for natural ventilation of the office space, then the shading position should be considered. The ventilation rate is crucial for the inner pane temperatures. Low airflow rates in the ventilated cavity can increase the risk of overheating the air and influence the inner pane temperatures. Especially in cases when no low E coated pane is applied at the inner skin, sufficient heat extraction reduces the risk of thermal discomfort. This problem is more evident in mechanically ventilated cavities with lower airflow rates. In airflow window cases, in which the air enters the cavity from the office zone, the overheating risk of the cavity air increases; especially when the indoor air temperature is lower than the outdoor air temperature, which is typical for Scandinavia. In that case a low E coated pane could reduce the heat transmission through the inner skin, keeping the cooling demand at reasonable levels. Office zones with all year round closed, naturally, mechanically or hybrid ventilated cavities perform well, mainly due to a decreased heating demand, when equipped with a window with an advanced intermediate pane (solar control and low E coated). Reducing the heating demand is essential for office buildings located in Nordic countries. The position 318

Conclusions

of the advanced pane in this case is essential for its performance, since the increased indirect solar transmittance results in reduced transmission losses though the outer skin when the cavity is closed. This is true at least compared with an alternative with an outer solar control and low E intermediate pane. On the other hand, during the summer months, the sufficient ventilation results in efficient heat extraction and low cooling demand. The performance is better for a north oriented office zone, since the heating demand is normally larger for a zone facing north. The effect is similar on thermal comfort; PMV values are higher in the winter and slightly lower during summer due to the lower total solar transmittance. Similar but less intense is the trend for the mechanically and hybrid ventilated cavity, with an advanced (low E + solar control) intermediate pane performing best. A single skin case with intermediate blinds compared with the naturally and hybrid ventilated double skin case shows that the savings in cooling demand of the south oriented zones are important, while for the north they are very small. Larger are the savings in the glazing alternatives with high thermal and total solar transmittance values. The heating demand tends to increase, however, due to (a) leaky dampers in the case when the cavity is considered closed and (b) not optimal damper control set points (dependence of the dampers’ temperature set points on the cavity air temperature). When the total energy use is compared, the single skin façades perform better than the double for the north oriented zones for the two reasons mentioned above. This can be explained by the fact that the simulations were carried out for Sweden where the heating demand is a dominating factor. However, for the south oriented zones a decrease in energy use can be noted with the double façade cases, with the hybrid ventilated one performing best. In general, hybrid ventilated cases tend to perform best as to energy use (regardless of the orientation), while airflow windows provide a better indoor thermal environment, mostly with north oriented façades, due to the higher PMV values during winter. The energy savings, which can be achieved for a highly glazed office building by using double skin façades instead of single skin façades, are rather small. A typical double façade hybrid building (best performing) has a total energy use of 137 kWh/m2a vs. 144 kWh/m2a for a single skin façade building (same glazing cases with low U and geffective values, non-ventilated cavity and intermediate shading). As regards thermal comfort, the double façade alternatives perform similarly to the single skin ones (PPD values), while the airflow window cases perform slightly better due to the higher (and closer to the 0 axis) PMV values during the winter months. Airflow windows with the same thermal and optical properties, on the other hand, result in high energy use (but still lower than the inter319

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nally placed shading devices) due to increased cooling demand. However, when the inner clear pane is replaced with a low E hard coated pane, the performance increases dramatically. In airflow window cases with low E inner pane the quality of the thermal environment can improve drastically, reaching the comfort levels of a 30% glazed building with improved window thermal and optical properties.

7.1.7

Best performing alternatives

Often, highly glazed buildings perform poorly when compared to a traditional building with e.g. 30% glazed facade (reference case) with regard to energy use and thermal comfort. As to energy use, windows with low thermal and total solar transmittance are essential for improving the building’s performance, especially since the energy use may vary substantially in highly glazed buildings, depending upon design. The position of shading devices also plays a major role. Fixed external louvres decrease the cooling and increase the heating demand. The effect is opposite for the internally placed venetian blinds resulting in the highest total energy use due to the drastic increase in the cooling demand. Glazed façades with intermediate venetian blinds can perform slightly poorer than those with externally placed ones due to the larger cooling demand. However, if a double skin façade is used and the cavity with the shading device is ventilated, the total demand can drop further. The difference in total energy use between a reference building (30% glazed alternative) and a highly glazed hybrid ventilated double skin façade, could for the studied cases be reduced by 25 kWh/m2a, (113 kWh/m2a vs. 138 kWh/m2a), if the glazing properties are kept the same. When external louvres are placed in a single skin alternative (100% glazed) with the same window properties, the building performs similarly (increase in total demand by 3 kWh/m2a). The same alternative but with internal venetian blinds instead results in a further increase by 10 kWh/m2a giving a total energy use of 151 kWh/m2a. An airflow window alternative with further improved glazing properties results in a total demand of 132 kWh/m2a; only 19 kWh/m2a higher than in the reference case. As regards the quality of indoor environment it is evident that smaller glazing areas provide a more stable environment with fewer dissatisfied occupants. If the glazing is selected carefully (i.e. low U values), the percentage of dissatisfied occupants will still increase mainly due to the low inner surface temperatures during winter. The reference building can provide a thermal environment, in which there will be fewer than 15% of dissatisfied occupants for 97% of the working hours. This value drops for the alternative with the hybrid ventilated double façade to 85% of the 320

Conclusions

working hours. However, if the glazing is further improved it is possible that the quality of thermal environment can reach the level of the reference case by using an airflow window.

7.2

Methods for determining energy and indoor climate performance

Energy and indoor climate simulations of an office building should preferably be carried out already at an early design stage and then be refined during the actual design. This will ensure improved energy and indoor climate performance of the building. In order to achieve energy efficient buildings and improved thermal environment, it is essential that the steps described below should be followed: • Validation of the calculation methods used should be the first step in a successful energy efficient building design. Understanding of the possibilities and limitations of the computing tools and the physical models used, enables accurate predictions. Validation tests that have been carried out in the past can help the user recognize the strengths and weaknesses of each tool and use the right tool for the right purpose or even combine different ones when needed. • Simulations on a component level (such as those carried out for the double skin façade alternatives) can provide the necessary background to the possibilities and limitations of the system used. These simulations can often be very detailed and require a lot of time and effort, in order to meet a certain level of accuracy. In practice, however, deciding the acceptable level of accuracy is not an easy task, since this depends on the scale and complexity of the project, the experience of the user and the available time. • Performance and quality specifications have to be fulfilled. Once the validation of the calculation methods has been completed and a deeper understanding of the integrated components has been achieved, it is essential that the client and the design team, including the engineer responsible for energy and thermal simulations, prioritize the goals and decide to what extent achieving low energy and improved thermal environment can and should influence the building design. In practice, many mistakes may originate from the lack of communication and clear goals of the design team. • Parametric studies on a zone level: A clear view of the parameters that can be varied, in order to lower the energy use and improve the thermal performance is the first step for selecting the simulated 321

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alternatives. In general, parametric studies on a zone level can provide useful information regarding the impact of different design parameters on the building performance, especially regarding comfort. The reduced simulation time can allow the user to investigate a larger number of alternatives, but can not predict absolute values for the whole building performance. • Simulations on a building level: Once the best performing alternatives on a zone level are selected, the whole building should be modelled. However, if the implimented building model is too simplified (e.g. assuming the whole floor as one zone or calculating the average cavity air temperature of a multi storey façade), this can lead to wrong values and overestimation of the building performance. Simulations on a building level can predict and improve the building performance, as long as input parameters (e.g. internal loads, thermal mass, control set points, ventilation rates, etc) are correctly estimated.

7.2.1

Lessons learnt from the simulation work

A challenge in this thesis has been to correctly simulate buildings with double skin façades, since the modelling of especially naturally ventilated double skin façades is a complicated task. On a component level the software tool WIS 3 was used. WIS 3 can provide a wide range of output values but on the other hand the simulations are carried out for steadystate boundary conditions, which do not allow the user to investigate the façade performance throughout the year. The determination of input parameters, such as cavity geometry, position of shading devices inside the cavity etc, allows the user to carry out an extensive parametric study, in order to understand the influence of the key parameters on the façade performance. Energy and indoor climate simulations on a zone and building level were carried out using IDA ICE 3.0. The dynamic building energy simulation tool IDA ICE 3.0 allows energy and indoor climate simulations of complicated buildings with integrated double skin façades during the whole year. The input options regarding a double skin façade e.g. cavity geometry, shading position, are not so many and certain values (such as discharge coefficients for the openings, etc) have to be calculated by the user before being input in the software. At the advanced level of IDA ICE 3.0 the user has a great variety of options. Some of these options, used within this study, were (a) different modelled ventilation modes (such as the naturally, mechanically and hybrid ventilated double facades and airflow windows), (b) different damper controls, e.g. dampers opening 322

Conclusions

according to the cavity air temperature for the zone simulations, while on a building level they were dependent on the indoor air temperature and (c) multi storey façades simulated by connecting cavities at different floors. In general IDA ICE 3.0 allows a wide variety of configurations, since the user can build his/her own case. The main drawback, however, is that the user has to be quite experienced, since most of the models have to be developed at the advanced level. Correct modelling of office buildings can be a complicated task. The large number of office zones can be a drawback for the speed of simulation, often limiting the number of parametric studies. On the other hand, simplifying the building model too much can lead to wrong assumptions which diminish the quality of output results and mislead the design team regarding the energy and thermal building performance. Further improvement of the advanced building simulation tools, which includes easier interfaces, reduced simulation time, but also more options for the user to create individual building components and insert them into the building model, are essential for broader use. In order to correctly use building simulation software, documentation of the physical and mathematical models included should be available to the user. In this way, the possibilities and limitations would be clear when the user attempts to do his/her own modelling.

7.3

Improving the energy and indoor climate performance of highly glazed buildings: general recommendations and further studies

Low energy building design would be a relatively easy task, if it were always prioritized as one of the main performance requirements to be achieved. However, in practice the building “concept” is often initially created leading to a building design that does not always take into account energy and thermal performance. An example of this is the increasing number of highly glazed office buildings built all around the world during the last decades. Despite their poorer energy and thermal performance, most architects (following the trend of highly glazed areas), companies (which want to create a distinctive image for themselves) and users (who relate highly glazed façades to a more pleasant environment) prefer this building type. Before anything else, it has to be stated that the low energy building design is directly connected with the location of the building, since the 323

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climatic conditions are essential to its performance; especially for buildings with large glazing areas, general recommendations should be avoided. Thus, careful and individual design is an indisputable requirement, in order to achieve improved building performance. For Swedish climatic conditions, windows with low thermal transmittance are essential. This is especially true for highly glazed buildings, in order to improve the building’s performance as to energy use and thermal comfort during the winter months. The results have shown that in cases with windows with low g values, the increase in heating demand is unavoidable; this is not the case when windows with relatively high g but low geffective (when shading is used) values are applied. Similar results were obtained for the perception of thermal comfort, since the cold pane surfaces result in negative PMV values during winter. Hybrid ventilated double façades, however, can reduce the heating demand and improve the quality of thermal environment. Airflow windows have a positive effect on thermal comfort mainly during winter due to the increased PMV values. The results show that airflow windows may perform better in north facing façades. Air flow windows with (hard coated) low E inner pane result in a radical improvement of the indoor climate, since the PPD values are the same as for a 30% glazed building with windows of low U and g values. On the other hand, glazing with low total solar transmittance values reduces the cooling demand and decreases the risk of overheating. Fixed external louvres have definitely a positive effect on cooling, but since they are applied all year round they have a negative effect during winter, increasing the heating demand. Internally placed venetian blinds have the opposite effect, but the radical increase in cooling demand and radiant temperatures leads to poor all-year performance. Intermediate placed movable shading improves the building’s performance, since they result in higher g values when the shading is not in use and solar heat gain is needed, but also due to low geffective values that result in acceptable performance during summer. When the cavity in which the shading is placed in the double façade is ventilated, a further improvement can be noticed. When integrated properly, double skin façades result in improved (compared with single skin facades) energy and thermal performance of the building, mainly when used on the south façade. However, since the cooling demand is rather limited for Scandinavian climatic conditions, their impact is also limited. Hybrid ventilated façades perform better than naturally or mechanically ventilated ones, since they efficiently combine heat recovery during winter and efficient heat extraction by natural ventilation during summer. Optimal damper control set points and sufficiently sealed cavities when dampers are closed are essential to the system’s performance. The usually higher construction cost of double skin façades, on the other hand, makes 324

Conclusions

their application in buildings located in Scandinavia questionable. Further investigation of their possibilities for buildings located in warmer climates, however, should be carried out, since their impact on the building performance may be promising. Individual building design that takes into consideration the type of façade including the size and type of glazing and the position of shading devices, the temperature set points, the building occupancy and plan type, can definitely lead to improved building performance. A holistic view that takes into account the interaction of the different building components is essential for low energy building design. If this is established, even in highly glazed cases, the building performance can reach reasonable levels as to energy use and indoor climate. Further studies are suggested in the following fields: • impact of building shape on the energy and thermal performance of highly glazed buildings • detailed CFD calculations on double skin facades; influence of geometrical characteristics on airflows • optimization of DSF constructions and modes for different climates to study the potential of energy savings due to the use of double skin façades • optimization of damper control set points for double skin façades (cavity air, indoor air, operative temperatures, etc) • further development of dynamic building energy simulation tools with integrated double façade • further validation of tools for double skin façade cases with venetian blinds

325

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326

Summary

8

Summary

8.1

Introduction

Highly glazed office buildings are considered to be airy, light and transparent with more access to daylight than traditional buildings, but their energy efficiency is often questioned. However, nowadays glazed buildings are increasingly being built around the world, because (a) there is a growing tendency among architects to use large areas of glass in the façade, often with the aim of contributing to a better view of the outside and access to daylight, (b) users often like the idea of increased glass area, relating it to a better view of the outside and a more pleasant indoor environment and (c) many companies prefer the distinctive image of themselves (e.g. transparency or openness) that a glazed office building can provide. Achieving low energy use and improved thermal environment when using a fully glazed façade can be a great challenge; energy efficiency and the provision of an acceptable indoor climate are essential for improved building performance. Other parameters to be taken into consideration during the decision and design process are visual comfort, building aesthetics, sociological and psychological determinants (such as visual and acoustical privacy), life cycle cost, etc. By prioritizing at an early stage the goals to be achieved, the design team can improve the building performance and fulfill the design requirements.

8.2

Background

Today, there is insufficient knowledge of the function, energy use and indoor environment of office buildings with highly glazed facades for Scandinavian conditions. Therefore, a project was initiated to gain knowledge of the possibilities and limitations of glazed office buildings in Scandinavian climates. This means further development of calculation methods and analysis tools, improvement of analysis methodology, calculation of life-cycle costs (LCC), compilation of advice and guidelines for the construction of glazed offices, and strengthening and improving the 327

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competence regarding sustainable buildings in Sweden. This thesis, which is a part of the “Glazed Office Buildings” project, aims to (a) determine how the energy and indoor climate performance can be analysed, (b) clarify and quantify how highly glazed façades affect the energy use and thermal comfort and (c) determine how the design can be inproved with regard to energy efficiency and thermal comfort. Through extensive parametric studies the impact of design parameters on building performance has been studied. Optimizing energy and indoor climate performance of single skin highly glazed buildings was the first goal to be achieved. The proper integration of double skin façade systems was also investigated with the aim of further improvements.

8.3

Methods

A virtual reference building was initially created, which was considered to be representative of Swedish office buildings built in the late nineties with regard to design, energy and indoor climate performance. The design of the building was determined by researchers from the Division of Energy and Building Design, architects and engineers from WSP and Skanska. First, detailed performance specifications for energy and indoor climate were established and then typical constructions were determined for the reference building. System descriptions and drawings were prepared. The building was approved by a reference group. Finally a validation of the simulated performance of the reference building showed that the performance specifications were fulfilled. The reference building is a 6 storey building of rectangular shape (21 m high, 66 m long and 15.4 m wide; the room height is 2.7 m) and the distance between floors is 3.5 m. Two plan types were assumed for the simulations; cell and open plan. In order to reduce the simulation time in IDA ICE 3.0, but still be able to analyse the indoor climate for individual rooms, the number of zones was reduced to 11 per floor for the cell type and to 7 per floor for the open plan type. Input parameters such as occupancy, HVAC strategy, internal loads, etc, were decided after thorough consideration and long discussions with experts of the working group; these parameters are described in great detail in the report. Three different control set point intervals for the indoor temperature were chosen for the simulations of the building alternatives. The normal control set point (22 - 24.5°C) is considered the standard (reference) case, since the lower and upper temperature limits are common practice in modern Swedish offices. However, the two other control set points (21 - 26°C (poor) and 22 - 23°C (strict)) can provide useful information concerning 328

Summary

the variation in energy use with indoor temperature and the perception of thermal comfort. For this building, a parametric study of energy use and indoor climate was carried out. The building construction, the HVAC system, the occupancy, etc were modelled in great detail. Parameters such as the building’s orientation, plan type, control set points, façade elements (window type and area, shading devices, etc) and façade type (single and double skin) were varied during the simulations, while others such as building shape, occupants’ activity and schedules, etc were kept the same. A sensitivity analysis based on the simulated alternatives was carried out regarding the occupants’ comfort and the energy use for operating the building. The window to external wall area ratio of the simulated single skin building alternatives varied from 30% (reference case), to 60% and 100%. For the 30% glazed alternatives a triple-glazed (clear glass) window with a venetian blind between two of the panes was assumed, while the building’s construction was kept the same. The simulations were carried out for three orientations, three control set points (strict, normal and poor) and two plan types (cell and open). For the 60% and 100% single glazed alternatives, 7 different (commercially available) window constructions were studied. The rest of the building construction was kept the same as for the 30% glazed alternative. Each case was then simulated for both cell and open plan type and for strict, normal and poor control set points. In total 84 (60% and 100%) glazed alternatives were simulated. The simulation tools used were (a) IDA ICE 3.0, a dynamic building energy simulation tool, and (b) WIS 3, a calculation tool developed to calculate the thermal and solar characteristics of window systems and components. Validation tests have shown that both programs give reasonable results and are applicable to detailed simulations. In order to analyse the large amount of output data from the IDA ICE 3.0, simulations a post processor in MS Excel was developed. The performance parameters examined on a building level in this report are (a) heating demand, cooling demand and electricity for lighting, pumps and fans, etc, (b) weighted (average) air temperatures for the working area, (c) number of hours between certain (weighted) average air temperatures for the working space, (d) weighted average PMV and (e) number of working hours for certain average PPD. On a double skin façade component level the main parameters calculated were the temperatures of different layers at the vertical and horizontal centre and the airflow rates and temperatures along the ventilated cavity.

329

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8.4

Discussion and conclusions

8.4.1

Glazing area

In general, the total use of energy increases with increased glazing area. Assuming a triple clear glazed window the energy use of the studied typical 60% single skin glazed building is 23% higher for the strict and normal indoor temperature control set points, compared with the studied typical reference building. The increase for the 100% single skin glazed alternatives is 45 % and 47 % respectively. This difference in energy use would of course decrease if glazed facades with lower thermal and total solar transmittance (including solar shading, which results in lower geffective values) were chosen. Furthermore, increased window area does not necessarily mean a substantial decrease in the electricity for lighting. According to the simulations the maximum savings did not exceed 2 kWh/m²a. Additionally, the larger the window to external wall area ratio, the larger are the comfort problems during the whole year, especially when triple-glazed (clear glass) windows are used. Thus, the need of glazing with lower thermal and total solar transmittance is evident, especially for highly glazed alternatives.

8.4.2

Glazing and solar shading type

The window properties (U, g and geffective values) have a remarkable impact on energy use, as concluded from the study and as already expected. For the Swedish climatic conditions, windows with low thermal transmittance are essential, in order to improve the building’s performance during the winter months regarding energy use and thermal comfort. The results have shown that in cases with windows with low g values, the increase in heating demand is unavoidable. Similar results were obtained for the perception of thermal comfort, since the cold pane surfaces result in negative PMV values during winter. On the other hand, glazing with low total solar transmittance values reduces the cooling demand and decreases the risk of overheating. Fixed external louvres have definitely a positive effect on cooling, but since they are applied all year round they increase the heating demand during winter. Movable shading and efficient heat extraction (as in the case of exterior shading) can be achieved with the use of venetian blinds in double skin façades. Internally placed venetian blinds have the opposite effect. The radical increase in cooling demand and radiant temperatures leads to poor year- round performance. Intermediate moveable shading improves performance, since they result in higher g values when

330

Summary

the shading is not in use and solar gain is needed, but also due to low geffective values that provide acceptable performance during summer.

8.4.3

Double skin facades

In order to reduce energy use and improve the indoor thermal environment, double skin façades were introduced. The double skin façade is a system consisting of two glass skins (single or double) placed in such a way that air can flow through the intermediate cavity. In principle the main purpose of the double skin façades (as to energy use and thermal comfort) is to allow the useful solar gains into the building when shading is not applied, and to extract through the ventilated cavity the heat absorbed by the shading to lower the cooling demand of the buildings. The distance between the skins usually varies from 0.2 m up to 2 m. For protection and heat extraction reasons the solar shading devices are placed inside the cavity. The ventilation of the cavity can be natural, fan supported or mechanical; the origin and destination of the air can also vary depending on the location, the use and HVAC strategy of the building. A main requirement when ventilated cavities of double skin façades are designed, is efficient heat extraction during the summer months. For naturally ventilated cavities the key parameters for achieving that are the characteristic height of the cavity (height to depth ratio) and the inlet and outlet opening sizes of the dampers. Another parameter that has to be considered is the type and position of panes, since they have a considerable impact on the minimum cavity depth that ensures efficient heat extraction. For naturally ventilated cases, the position of shading device inside the cavity has limited impact on the thermal comfort, unless the openable cavity is used for natural ventilation of the office space. The energy savings achieved for a glazed office building by using double skin façades instead of single skin façades are rather small. When the double façade hybrid case (best performing as to energy use) is compared with single skin façade buildings (same glazing cases with low U- and geffective values, no ventilated cavity and intermediate shading), the total energy use decreases by 7 kWh/m2a (137 instead of 144 kWh/m2a). Regarding thermal comfort, the double façade alternatives perform similarly to the single skin ones (PPD values), while the airflow window cases perform slightly better due to the higher (and closer to the 0 axis) PMV values during the winter months. Airflow windows with the same thermal and optical properties, on the other hand, result in high energy use due to increased cooling demand, but still lower than for the case with internally placed shading devices. However, when the inner clear pane is replaced with a low E hard coated pane, the performance improves dramatically. 331

Single and Double Skin Glazed Office Buildings

As to thermal comfort the airflow windows perform better than the rest of the cases due to the increased PMV values during winter months. In cases with low E inner pane the quality of the thermal environment can improve drastically, reaching the comfort levels of a 30% glazed building with improved window thermal and optical properties.

8.4.4

Other parameters that influence the building performance

The plan type of office buildings plays a considerable role in the building performance regarding energy use and indoor environment issues. The two clearly distinguishable plan types studied in this thesis were the open plan and cell office. The use of the office space, ventilation rates, occupant density and the quantity of office equipment are some of the main parameters that differ between these two types. This results in (a) often higher cooling and lower heating demand of the open plan office building due to higher internal loads, mainly caused by higher occupancy and lower ventilation rates and (b) the risk of discomfort increases in cell office zones, compared with zones of the open plan type, due to the larger external wall to office floor area ratios (the occupants of the open plan are more evenly distributed within the whole floor space). In fully glazed building alternatives the risk of comfort problems is higher, especially in cases when windows with high thermal, total solar and effective (i.e. shading is applied) solar transmittance were applied. The control set points for the indoor air temperature are crucial for the energy and the thermal performance of a given building. Despite a common perception that strict control set points lead to an improved thermal environment, this study has shown that the key to choosing proper set points is the consideration of design parameters such as plan type, internal loads and glazing area and type. In general, the choice of set point requires the determination of (a) the permissible air temperature variation and (b) the minimum and maximum permissible air temperature limits. The selection of strict set points does not always guarantee an improved indoor thermal environment, since if the input design parameters (e.g. occupancy, internal loads, window type and size, etc) are not considered thoroughly and the maximum and minimum permissible temperature limits are not selected correctly, both discomfort and excessive heating or cooling may occur. Highly glazed buildings are more likely to lead to comfort problems and the selection of proper temperature set points is more difficult. In any case, the set points should be selected individually for each building and in cases with increased glazing areas further analysis should be carried out.

332

Summary

The orientation of a building may have an effect on the energy use; however, if the design is the same for the opposite sides of the façades the effect is negligible. The orientation of a zone has limited impact on the mean air temperatures, but the directed operative temperatures may vary considerably. The wider the permissible air temperature variation, the bigger is the impact of the orientation in each zone (wider variation in operative temperature) mostly for zones with highly glazed areas. This could provide useful information for the choice of the permissible air temperature variation of certain zone types, in order to keep the operative temperature within acceptable limits.

8.4.5

Best performing alternatives

Often, highly glazed buildings perform poorly when compared to a traditional building with e.g. 30% glazed facade (reference case) with regard to energy use and thermal comfort. As to energy use, the use of windows with low thermal and total solar transmittance is essential for improving the building’s performance, since especially in highly glazed buildings the energy use may vary substantially, depending upon design. The position of shading devices also plays a major role; fixed external louvres decrease the cooling and increase the heating demand. The effect is opposite for internally placed venetian blinds resulting in the highest total energy use due to the drastic increase in the cooling demand. Glazed façades with intermediate placed venetian blinds can perform slightly poorer than externally placed shadings due to the larger cooling demand, unless the cavity where the shading devices are placed is ventilated. In this case the total demand can drop further. The difference in total energy use between the reference building (30% glazed alternative) and the best performing highly glazed building (hybrid ventilated double façade), could be limited to only 25 kWh/m2a in cases when the glazing properties were kept the same. When external louvres are placed in a single skin alternative with the same window properties, the building performs similarly. The same alternative but with internal venetian blinds instead results in a further increase by 10 kWh/m2a (total energy use of 151 kWh/m2a). An airflow window alternative with further improved glazing properties results in a total demand of 132 kWh/m2a; only 19 kWh/m2a higher than in the reference case. Regarding the quality of the indoor environment, it is evident that smaller glazing areas provide a more stable environment, with fewer dissatisfied occupants. If the glazing is selected carefully, the percentage of dissatisfied occupants will still increase mainly due to the low inner surface temperatures during winter. For the reference case with the same window 333

Single and Double Skin Glazed Office Buildings

properties as described above, the reference building can provide a thermal environment, in which there will be fewer than 15% dissatisfied occupants for 97% of the working hours. This value drops for the alternative with the hybrid ventilated double façade to 85% of the working hours. However, if the glazing is further improved, it is possible that the quality of thermal environment may reach the level of the reference case.

8.4.6

Determination of energy and indoor climate performance

In principle, energy and indoor climate simulations have to be carried out already at an early design stage and then be refined during the actual design. This will ensure improved energy and indoor climate performance of the building. In order to achieve energy efficient building design and improved thermal environment it is essential to (a) validate the calculation methods, (b) carry out simulations on a component level in order to gain the necessary background to the possibilities and limitations of the system, (c) prioritize the performance and quality requirements to be fulfilled and (d) carry out simulations on a zone and on a building level. Parametric studies on a zone level can provide useful information regarding the impact of different design parameters on the building performance, while parametric studies on a building level predict absolute values of the building.

8.5

General recommendations for improvements of highly glazed office buildings

In general, low energy building design would be a relatively easy task if it were always prioritized as one of the main performance requirements to be achieved. However, in practice the building “concept” is often initially created leading to a building design that does not always take into account energy and thermal performance. An example of this is the increasing number of highly glazed office buildings built all around the world during the last decades. Within this study, however, an effort has been made to quantify the performance of highly glazed office buildings, as to energy use and indoor climate issues, for Scandinavian climatic conditions and suggest improving solutions. It is always required that the low energy building design is directly related to the building location, since the cli334

Summary

matic conditions are essential to its performance. Especially for buildings with large glazing areas, general recommendations should be avoided. For instance a double façade performing well in a south European country could be unacceptable for Scandinavia, and vice versa. Thus, careful and individual design is an indisputable requirement, in order to achieve improved building performance. For Swedish climatic conditions during the winter months, windows with low thermal transmittance are essential, especially for highly glazed buildings, in order to improve the building’s performance as to energy use and thermal comfort. Glazing with low total solar transmittance values reduces the cooling demand and decreases the risk of overheating. The best solution is external movable solar shading to arrive at low g-values during periods with warm weather, as in winter low g values are not needed and the solar gains can contribute to space heating. However, if the g value of the glazing is too low, the light transmittance might be insufficient. The external movable solar shading can also be located in the cavity of a double skin façade, in order to be protected. When g values and U values are chosen for a façade, the area and orientation of the glazing have to be taken into account. The total solar gains and total thermal losses of a zone are important. When integrated properly, double skin façades result in improved energy and thermal performance of the building mainly when applied on the south façade, but since cooling is not the main issue for Scandinavian climatic conditions, their impact is limited. Individual building design that takes into consideration the type of façade including the size and type of glazing, the position of shading devices, the temperature set points, the building occupancy and plan type, can definitely lead to improved building performance. If this is established, even in highly glazed cases, the building performance can reach reasonable levels as to energy use and indoor climate. However, a building with low energy demand cannot be achieved with a highly glazed building in a Scandinavian climate.

335

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336

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Saelens, D. (2002). Energy Performance Assessments of Single Storey MultipleSkin Facades. PhD thesis, Laboratory for Building Physics, Department of Civil Engineering, Catholic University of Leuven, Belgium. Saelens, D., Carmeliet, J., & Hens, H. (2003). Energy performance assessment of multiple skin facades. International Journal of HVAC&R Research 9 (2): 167-186. Web address: http://www.bwk.kuleuven. ac.be/bwf/pdf_artikels/I_J_HVACR_DS_2003.pdf Saelens, D., Blocken, B., Roels, S., Hens, H. (2005). Optimization of the energy performance of the multiple skin facades. Proceedings of the Ninth International IBPSA Conference, MOndreal, Canada SCB, (2001). Energy statistics for non-residential premises. Statistics Sweden, Statistiska meddelande EN 16 SM 0203 (in Swedish). Sjodin L., (2007). LCC Calculations of Glazed Office Buildings. WSP Management Internal Report, Malmö, Sweden (in Swedish) Stec, W., & van Paassen, A.H.C. Integration of the Double Skin Façade with the buildings. Energy in Built Environment, Energy Technology, TU Delft, Mekelweg 2, 2628 CD, Delft, The Netherlands. Stec, W., and van Paassen, A.H.C. (2003). Defining the Performance of the Double Skin Facade with the Use of the Simulation Model. Proceedings of Building Simulation '03, 1243-1250, Netherlands. Svensson, A. (2000). Glazed facades – a question of image or? Journal Byggkontakt May 2/2000 (in Swedish). Svensson, A., & Åqvist, P. (2001). Double skin glazed facades – Image or at step on the road to a sustainable society? Arkus skrift nr 37, Stockholm (in Swedish) TAS software (v.907). EDSL Ltd. Web address: http://ourworld.compuserve.com/homepages/edsl Travesi, J. G., Maxwell, K., Klaassen, M. & Holtz. (2001). Empirical Validation of Iowa Energy Resource Station Building Energy Analysis Simulation Models, A report of Task 22, Subtask A Building Energy Analysis Tools Project A.1 Empirical Validation, June 2001. TRISCO software. Physibel, Belgium. Web address: http://www.physibel. be/ TRNSYS software (v16.037). University of Wisconsin, USA Web address: http://sel.me.wisc.edu/trnsys

344

References

U.S. Army Corps of Engineers, (1997). Design Guide for Interiors. DG 1110-3-122 van Dijk, D. H.A.L. & Henk Oversloot, H.P. (2003). WIS, the European Tool to Calculate Thermal and Solar Properties of Windows and Window Components. Proceedings of Building Simulation '03, 259-266, Netherlands.Web address: http://www.ibpsa.org/PDFs/ BS03%20Papers/BS03_0259_266.pdf van Paassen, A.H.C., & Stec, W. (2001). Controlled Double Facades and HVAC. 7th world congress Clima 2000/Napoli 2001, September 1518 (CD-ROM). Indoor environment technology: towards a global approach (Napels), REHVA, Brussels, 2001, p. 1-15 VVS, (2000). Classification of indoor climate systems. Guidelines and specifications. R1, Swedish HVAC association (in Swedish). Wall, M., & Bülow-Hübe, H. (2001). Solar protection in buildings. (Report TABK- 01/3060). Lund: Lund University, Dept of Construction and Architecture. Wall, M., & Bülow-Hübe, H. (2001). Solar Protection in Buildings. Part 2: 2000 – 2002 (2003). (Report EBD-R—03/1). Lund, Sweden: Energy and Building Design, Dept of Construction and Architecture, Lund Institute of Technology, Lund University. Wall, M., & Kvist, H. (2003), SunSpace- a user friendly design tool to predict temperatures and energy demands for different types of glazed spaces. Report EBD-R--03/2, the department of Energy and Building Design, Lund Institute of Technology, Lund University. Wilkins, C., & Honsi, M. H. (2000). Heat Gain from Office Equipment. ASHRAE Journal. Wouters, P. (1999-2000). Quality in Relation to Indoor Climate and Energy Efficiency. An analysis of trends, achievements and remaining challenges. PhD thesis in Université Catholique de Louvain (UCL), Faculté des Sciences Appliquées, Département Architecture et Construction (ARCH), Belgium. Wyon, D. (1986). The effects of indoor climate on productivity and performance. Simplified summary of results: ‘Indoor climate, accidents, human efficiency and comfort’, Revised version of a summary prepared by the author for Scandinavian Indoor Climate Year, published in Swedish in VVS & Energi, 59-65.

345

Single and Double Skin Glazed Office Buildings

Wyon, D. (1987). The importance of our indoor climate. Fläkt Review No. 71, Indoor climate systems, Fläkt AB, Stockholm, Sweden, ISSN 0015-3400. Wyon, P. D. (2000a). Enhancing Productivity While Reducing Energy Use in Buildings. Proceedings of the Conference held at The Ronald Reagan Building and International Trade Center Washington, D.C Wyon, D. (2000b). Individual control at each workplace: the means and the potential benefits In: Clements-Croome, D. (editor). Creating the productive workplace. E&FN Spon. London and New York.

346

Appendix A

Appendix A Germany

347

348

Headquarters of Commerzbank Compagno, (2002) Eurotheum Lee et al., (2002)

Building Düsseldorf city gate (Düsseldorfer Stadttor) BBRI, (2002), Oesterle et al., (2001), Lee et al., (2002), Compagno, (2002) ARAG 2000 Tower Oesterle et al., (2001), Compagno, (2002)

Free window ventilation is possible for 50- 60% of the year. During winter, the airextract shaft is also designed to be closed if required

Two variations on the principle of the “buffer zone” for natural ventilation of the offices were used: as a double skin façade and as a winter garden. Fresh air is supplied through 75-mm diameter holes in the vertical metal fins on each side of the glazing unit. Warm air is extracted through an exterior opening at the ceiling level.

Shaft-box system

Multi storey high

Box window

Ventilation strategy The façade was designed to naturally ventilate the rooms with outside air during long periods of the year. The first years of operation show that the building can be naturally ventilated for roughly 70-75% of the year.

Façade type Corridor façade

The façade grid is 1350 mm wide 3350 mm tall and 340mm deep. Each unit, which is prefabricated offsite, consists of a 6-grid span, one-storey tall.

Three storey sealed outer skin, a continuous cavity and an inner façade with operable windows.

The façade is roughly 70 cm deep. Each of the box windows has its own 15 cm high airintake opening in the form of a closable flap

Construction Two corridor widths are encountered in the building (90 cm and 140 cm). The entire building is enclosed in a glass skin so that a 56-meter-high atrium space is created at the centre.

The internal skin consists of thermally-broken aluminum frames and double-pane, manually-operated, tilt-and-turn windows. The external skin consists of single-pane, fixed glazing. Power-operated blinds are applied.

The outer skin consists of 8 mm toughened glass. Air louvres were provided at the lower and upper ends of the cavity.

The inner façade layer is constructed with conventional vertically pivoting aluminum casements with low-E glazing. Louvred blinds were installed in the outer third of the façade.

Panes and shading devices The outer layer consists of a 12 mm safety glass and the inner is a low –E glazing with a wooden frame. The solar blinds are situated near the outer glazing layer.

Only part of the building is designed with a double-skin façade, which provides natural ventilation for most of the year.

During periods of extreme weather conditions, a high level of thermal comfort can be attained with mechanical ventilation. None

Comments No complete air conditioning of the office room was installed. The office rooms are equipped with chilled ceiling.

Single and Double Skin Glazed Office Buildings

Façade type Corridor façade

Multi storey high

Corridor façade

Building Debis headquarters Lee et al., (2002), Crespo, Oesterle et al. (2001)

(GSW) Headquarters Lee et al., (2002)

Halenseestraße Lee et al., (2002)

Ventilation strategy The external skin is openable. Opening the external skin to a greater degree has a positive influence on the ventilation, since it helps to remove the heat in the intermediate space. The users can open the interior windows for natural ventilation. A mechanical ventilation plan was installed to provide partial air conditioning for those periods in winter and summer when extreme weather conditions prevail. Cross ventilation; the double façade operates as a thermal shaft. During the heating season, the air cavity acts as a thermal buffer when all operable windows are closed. Warm air is returned to the central plant via risers for heat recovery. During the summer, the cavity is mechanically ventilated. At night, internal heat gains are removed with mechanical ventilation. During the winter, solar gains pre warm the air in the interstitial space.

The cavity is 0.85 m deep.

The cavity is 0.9 m deep.

Construction Walkway grills occur at every floor within the 70-cm wide interstitial space and are covered with glass to prevent vertical smoke spread between floors.

Interior double pane windows that are operated both manually and automatically and a sealed 10-mm exterior glazing layer. Wide, vertical, perforated aluminum louvres are located in the cavity and are automatically deployed and manually adjustable. The 12-mm single-pane external skin of this double-skin façade is completely sealed while the internal skin consists of sliding double pane glass doors. A blind was installed within the 1-storey high interstitial space.

Panes and shading devices The inner skin consists of a double low-E insulating glazing in aluminum frames. The exterior skin consists of 12mm thick laminated glass louvres. Sliding louvre blinds were installed in front of the inner façade.

Only the top westfacing seven stories of this ten storey building are designed with a double skin façade. The double-skin façade reduces noise from the adjacent highway towards the west.

Comments Night-time cooling is automated. The main objective of the clients and the planner was to create an environmentally sustainable and userfriendly building. To achieve these goals, large scale investigations and research work were undertaken. Radiant heating and cooling are provided to the building. Various building systems such as lighting and diffusers are integrated.

Appendix A

349

350

Box window

Corridor type

Potsdamer Platz 1 Oesterle et al., (2001)

Deutscher Ring Verwaltungsgebäude Lee et al., (2002) Print Media Academy Bohren and Boake, (2001)

Box window

Façade type Corridor façade

Building Galleries Lafayette Compagno, (2002)

The top of the four-storey façade has a rainproof opening with overlapping glass panes that allow air exchange. The cavity is naturally ventilated for heat extraction Cross ventilation. A cross ventilation control system moderates the buffer space between the outer and inner glazing.

Ventilation strategy The inlet and outlet vents are placed at each floor. The openings remain permanently open. The façade enables natural ventilation of the offices for most of the year. If the outside temperature is too low or too high, a mechanical ventilation system is switched on. The ventilation of the cavity and the internal rooms is effected via a 6 cm high gap beneath the outer pivoting casement.

Some of the interior windows are operable to allow for cleaning within the interstitial space. Walkway grills occur at every floor within this interstitial space. The cavity is roughly 0.46 m deep.

The cavity is roughly 0.22 m deep.

Construction The cavity is 0.2 m deep.

The internal window is a low-E glazing in an oak frame and with aluminum cover strips externally. A louvred blind is installed, the location of which was optimized in respect of its rear ventilation by designing the upper louvres to be fixed at a flatter angle, so that they remain permanently open, even when the blind is lowered. The exterior skin is toughened, solar control, single pane. The interior skin consists of a low-E coated, double-glazed, window. Blinds are positioned interior to the internal glass windows Single glass exterior pane and a sealed double glass pane on the inner side. The shading system is a mechanical aluminium blind system that controls solar heat gain.

Panes and shading devices The 29 mm thick insulating glass unit with an 8 mm glass on the outside and a 6 mm low –E coated glass on the inside, has a cavity filled with argon. Perforated louvres of stainless steel are fitted as solar control.

The building's central system controls the rate of air flow into the cavity space.

None

Comments The unusually designed Double Skin Façade is intended to serve as an information carrier and act as an optical attraction. It also serves as protection against the external noise. The combination of window ventilation with additional mechanical support under extreme weather conditions allows a very high degree of thermal comfort to be achieved.

Single and Double Skin Glazed Office Buildings

The façade is used exclusively as a means of regulating thermal insulation for different weather conditions. The intake of air is at the foot of the building and extracted at roof level.

Air-intake and extract openings ensure a satisfactory supply of external air for the rooms when the inner façade is open.

Multi storey

Multi storey

Shaft box

Victoria Life Insurance Buildings Lee et al., (2002), Compagno, (2002) Victoria Ensemble Oesterle et al., (2001)

Gladbacher Bank Oesterle et al., (2001)

Ventilation strategy The extra air cavity acts as a thermal buffer, decreasing the rate of heat loss between outside and inside. Fresh air is supplied through the opening at the bottom and warm air is exhausted through the opening at the top of the façade. During extreme cold conditions, the windows are closed. Warm air is returned to the central plant via risers for heat recovery in the winter. The type of ventilation is diagonal. Fresh air is supplied at the bottom level and is extracted at 21 m height through poweroperated vents.

Façade type Box window

Building RWE AG Headquarters Lee et al., (2002), Kragh, (2000), Collins, (2000), Space modulator, Arons, (2000)

Openable dampers. A central control system keeps the flaps closed when external temperatures are low, ensuring maximum thermal insulation. When external temperatures rise, the flaps are opened to allow the ventilation of the cavity preventing overheating.

The cavity is 0.8m deep.

Construction Openable interior full-height, double-pane glass doors that can be opened 13.5 cm wide by the occupants (and wider for maintenance). The cavity is 0.5m deep, 3.6m high and 2m wide.

A single layer of reflecting, sun-screen glazing was inserted in the outer skin. Adjustable shading in the cavity.

The external skin consists of 15 mm laminated solar control glazing; the internal skin consists of solar control glazing. Aluminum 50mm deep louvres are integrated into the cavity. Continuous strips of flaps were installed around the entire building at the foot and the top of the façade to control temperatures.

Panes and shading devices The exterior layer is a 10-mm extra-white glass. The interior layer consists of full-height, double-pane glass doors. An anti-glare screen is positioned on the interior. Retractable venetian blinds are positioned just outside the face of the sliding glass doors within the cavity. Daylight, direct solar and glare can be controlled with blinds and an interior antiglare screen.

The Double Skin Façade was a part of a refurbishment project.

None

The main advantage of the double-skin façade system is the improvement in thermal comfort.

Comments The design of the RWE façade system was influenced by the clients’ desire for optimum use of daylight, natural ventilation, and solar protection.

Appendix A

351

352

Façade type Combination of boxwindow and corridor façade types

Box window

Building DB Cargo Building Oesterle et al., (2001)

Business Promotion Centre and the Technology Centre Compagno, (2002)

Ventilation strategy Natural ventilation. The construction of a double-skin façade made window ventilation possible, thereby overcoming the problem of a non-openable façade with inevitable air-conditioning of the adjoining rooms. A partial air-conditioning system was installed, providing a 2.2 fold hourly air change (ach). Air is injected at slightly higher than ambient pressure into the lower part of the cavity and the warming effect results in a natural stack effect.

The façade consists of 1.50 × 3.30 m toughened 12 mm thick panes suspended in vertical aluminum mullions. The inner façade skin consists of storey high

Construction The cavity is 0.23m deep.

Outside is a 6 mm float glass, inside is an 8 mm laminated glass with low-E and the cavity between is filled with argon gas. Perforated, computercontrolled aluminum louvres are incorporated into the cavity

Panes and shading devices Aluminum louvred blinds

Since the building went into operation, overheating problems have been reported in the top floors.

Comments Taking into account the savings made in the air-conditioning, the simple form of construction and the high degree of prefabrication of the façade resulted in an economical solution.

Single and Double Skin Glazed Office Buildings

Ventilation strategy The cavity is closed and can be vented by motoroperated vents at the top and bottom, which are controlled by thermostats.

No information given

Each floor has two service doors to the cavity. Ventilators are installed at the corners of the cavity area in order to move warm air through the corners. The windows of the inner envelope are fixed. However ventilation doors open to the intermediate space. The intermediate space has gravitational ventilation. No information given

Façade type Multi storey

Box window

Multi storey

Multi storey

Multi storey

Building Sanomatalo Uuttu, (2001)

SysOpen Tower Uuttu, (2001)

Martela Uuttu, (2001)

Itämerentori Uuttu, (2001)

Nokia Ruoholahti Uuttu, (2001)

No information given

The depth of the cavity is 0.925m

The depth of the cavity is 0.7m

The depth of the cavity is 0.55m

Construction The depth of the cavity is 0.7m The inner envelope consists of three glass layers, while the outer consists of two.

Inner: double insulating glass Outer: 6 mm tempered glass. The top of the cavity has an adjustable louvre, while the bottom is open.

The outer glazed skin consists of 6-8 mm toughened glass. The circular part of the building has laminated glass. Motorized solar shading blinds are placed outside the inner envelope’s windows.

Panes and shading devices inner glass: toughened and laminated 6 mm, middle glass: toughened 4 mm and outer glass: toughened and solar control 6 mm. The space: argon and krypton gas. The outer envelope: toughened and laminated 6+6 mm panes. Blinds exist inside the inner envelope. The inner envelope consists of 2k=2k418, 26 mm thick glass and the outer envelope consists of 1k=1k8 tempered, 8 mm thick glass. Automatic solar blinds are placed inside the cavity. Inner heat insulating glass, 4 mm + 4 mm laminated due to the rail requirements Outer 12 mm tempered glass

The double skin façade helps to restrict the excessive amount of solar heat and traffic noise.

None

The double-skin façade is totally separated from the main frame of the office building.

None

Comments A maintenance gondola fixed onto the girders of the roof enables outside maintenance.

Appendix A

Finland

353

Ventilation strategy The cavity formed is open at bottom and top.

No information given

The air in the cavity can be used for heating and cooling purposes.

The cavity is open from the bottom and each floor has vents, which can be opened.

Façade type Multi storey

Corridor façade

Multi storey

Multi storey

Building Sonera Uuttu, (2001)

High Tech Centre Uuttu, (2001)

354

Radiolinja Uuttu, (2001)

Nokia K2 Uuttu, (2001)

The depth of the cavity is 0.6m.

The depth of the cavity is 0.65m.

The depth of the cavity is 0.342m and is not accessible.

Construction No information given

Panes and shading devices Inner skin: green 6 mm glass (outer), selective 4 mm Ekoplus- glass (inner) argon gas 15 mm (in between) Outer envelope: 4+4 mm laminated glass (in between 0.76 mm opal sheet) elements. One of the glasses is clear and the other one is grey with a silk screenprinted pattern. The inner envelope consists of two different kinds of windows. The lower windows consist of: - float glass 6 mm - argon gas 18 mm - clear selective float glass 6mm and the upper windows consist of: - tempered float glass 6 mm - argon gas 18 mm - clear selective float glass 4 mm The outer glass skin consists of 10 mm tempered glass. Inner skin: 6 mm selective glass (inner), 4 mm float glass (middle) and 6 mm tempered glass (outer) The outer envelope: 12 mm thick tempered glass. Motorized solar shading blinds are placed in the cavity. Inner envelope: double insulating glass Outer envelope: 6 mm thick tempered glass. Solar blinds are installed in the cavity.

None

None

The inner envelope’s windows can be opened to perform cleaning inside the cavity. Outside cleaning is performed from a hoist.

Comments None

Single and Double Skin Glazed Office Buildings

Ventilation strategy The cavity is not open at the top. The cavity is closed at its sides. The bottom of the cavity is closed with a laminated glass for sound insulation purposes. The cavity is open from the bottom and each floor has vents, which can be opened. The cavity is open from the bottom and each floor has vents, which can be opened.

In winter fresh air is taken from the southern side of the building and used in the HVAC system. In summer the fresh air is taken from the northern side.

Façade type Multi storey

Multi storey

Multi storey

Multi storey

Multi storey

Building Iso Omena mall Uuttu, (2001)

Kone Building Uuttu, (2001)

Nokia Keilalahti Uuttu, (2001)

Korona Uuttu, (2001)

JOT Automation Group Uuttu, (2001)

The depth of the cavity is 1m.

Part of the cavity is about 2 metes deep and another partly wider to form winter gardens.

The depth of the cavity is 0.69m.

The depth of the cavity is 0.58m.

Construction The depth of the cavity is 1m.

Inner envelope (triple): 6 mm antisun, green glass (outer), 4 mm clear glass (middle), 4 mm clear glass (inner) Outer envelope: 10 mm tempered, green sun protective glass panes.

Inner envelope: insulating glass Outer envelope: 8 mm tempered clear glass panes with a silk screen pattern. The inner envelope: 2k6-12 selective glass, argon gas in between The outer envelope: 6 mm tempered clear glass. Solar blinds are placed outside the inner envelope to restrict the excessive amount of solar heat. At the upper end of the intermediate space motorized louvres are placed. The windows in the inner envelope have a selective 2k insulating glass where the outer glass is K Glass and the inner glass is clear 4-6mm laminated glass. The outer envelope consists of clear, 6 mm thick float glass and partly also selective glass.

Panes and shading devices The inner envelope’s glass panes are float glass. The outer envelope has 8 mm thick tempered glass.

The cylindrical form of the building has an energy saving effect; the area of the envelope is small compared to the volume of the building.

None

Comments Two of the façades include a doubleskin façade. One of them is installed to reduce the traffic noise. None

Appendix A

355

356 Non-openable windows.

Motorized exhaust opening at roof level. 9.5 m long

Air enters at the bottom through the grating and leaves at the top through motorized controlled dampers

At the top and at the bottom there are automatically controlled dampers for controlling the airflow in the cavity.

Multi Storey

Multi Storey

Multi storey

Arlanda, Pir F, Sigtuna

ABB Business Center, Sollentuna

GlashusEtt

On-site erected steel construction. Nonopenable windows.

The depth of the cavity is 0.8m with gangways on each floor. Non-openable windows.

The depth of the cavity is 0.7m with gangways on each floor.

One-storey high cavity divided into five slits construction

Multi Storey

NOKIA House, Kista

Construction Prefabricated one-storey high aluminum construction Non-openable windows.

Ventilation strategy Diagonal ventilation.

Façade type Corridor façade

Building Kista Science Tower, Kista

Panes and shading devices Outer skin: 8/10 mm H, non-coloured Inner skin: double-pane sealed glazing units with LowE glass, non-coloured, 1.35m on centre Venetian blinds will be installed on the north side Outer skin: 10 mm Inner skin: Double pane sealed glazing unit with outer pane of soft coated LowE glass, 12 mm argon gas and inner pane of 300/30 clear glass for the wall below the window. Motorized venetian blinds, controlled by a pyranometer. Outer skin: 6 mm float glass. Lower big panes: 12 mm H Diamant Securit (iron free). Inner skin: 6 mm Planitherm Futur, 20mm argon, 6 mm clear float. Lower big panes: 8mm Planitherm Futur, 16 mm argon, 8.76 mm Contrasplit. Venetian blinds Aluminum frame construction with 8 mm H single panes in the outer skin and LowE glass in the inner skin (double pane sealed glazing unit) with Argon filling. Venetian blinds and with grating gangway on each floor. Inner curtains have been added for daylight control. Outer skin: 2×8 mm Planibel Top N. Sealed glazing units with argon. Same parts are laminated and hardened. Uvalue=1,1, and for the façade < 1,3. Inner skin: 8 mm single-pane hardened glass.

Daylight redirection with automatically controlled venetian blinds manually controlled for each façade and floor.

Calculations with double skin façade resulted in lower cooling demand than single skin facade. Sound proofing against the motorway E4.

None

Comments Two of the three facades (triangular floor construction: plan) are double skin facades, the third (to the north) is a single skin facade. Radiators and active cooling beams. District heating.

Single and Double Skin Glazed Office Buildings

Sweden

Appendix B

Appendix B Performance specifications for the reference building

The project team within the project “Glazed Office Buildings” developed performance specifications for the reference building, a typical office building of the nineties. The performance specifications were approved by a reference group.

Energy use For the entire building: Energy use, kWh/m2a District heating Electricity for pumps, fans etc. Electricity for lighting, PCs etc. Electricity for cooling Total use of electricity Total use of energy

Reference 80 20 50 30 100 180

m2 refers to non-residential/premises floor area (LOA see Swedish standard SS 021053 Area and volume of buildings) Energy use, kW/m3s Ventilation

Reference 2.5

Indoor environment The performance specifications below are valid for the whole building

357

Single and Double Skin Glazed Office Buildings

Air tightness Description Air tightness

Reference 44 dB (>40 dB for walls with door), to corridors > 30 dB

applicable during office hours.

reverberation time for open-plan < 0.4 s for cell-type office room < 0.5 s Light:

should be possible to shade against direct sun light. daylight factor min 1% and max 5%

Lighting:

Cell-type: 300 -500 lux, < 12 W/m2 electricity Corridors: > 100 lux, < 6 W/m2 electricity Open-plan: 300 - 600 lux, < 12 W/m2 colour rendering index (Ra-index) > 80 luminance distribution working material : nearest surrounding : surrounding areas 10 : 3 : 1 Luminance within the normal visual field < 1000 cd/m2 Outside the normal visual field < 2000 cd/m2

Internal gains:

from office equipment: < 20 W/m2 from PC + monitors: < 125 W i.e. < 5 W/m2 from office copier: < 400 W i.e. < 1 W/m2 from laser printer: 50 W i.e. < 2 W/m2 from persons: 4 W/m2 (100 W/person)

Ventilation:

> 0,35 l/sm2 + > 7 l/sperson, air change efficiency > 40%

IAQ:

< 1000 ppm CO2

Thermal comfort: air temperature minimumS 22°C and maximumS 24-26°C air velocityW < 0.15 m/s radiant temperature asymmetryW from vertical surfaces < 10 K vertical air temperature differenceW between 1,1 and 0.1 m < 3 K S

summer conditions where clothing of 0,6 clo is assumed winter conditions where clothing of 1 clo is assumed

W

358

Appendix C

Appendix C Architectural drawings

Figure C.1

Drawings of the cell type office plan.

359

Single and Double Skin Glazed Office Buildings

Figure C.2

360

Drawings of the open type office plan.

Appendix C

Figure C.3

Cross section of the reference building.

361

Single and Double Skin Glazed Office Buildings

Figure C.4

362

Gable elevation of the reference building.

Appendix C

Figure C.5

Front elevation of the reference building.

363

Single and Double Skin Glazed Office Buildings

364

Appendix D

Appendix D Geometry of the cell and open plan thermal zones

Cell Type: Geometry of the offices - thermal zones Corner office rooms Thermal zone type A1(1), A9(1), B1(4), B4(4), B6(4), B9(4), C1(1), C4(1), C6(1), C9(1). The office area is 15.1 m2 (including half internal wall a and half b). The numbers in the parenthesis show how many identical thermal zones are in the building. Typical corner office room is shown in Figure D.1. The total area of the all the corner office rooms is 331.8 m2.

b

4.19 m

a 3.6 m Figure D.1

Typical corner office.

365

Single and Double Skin Glazed Office Buildings

Typical double office rooms Thermal zone type A2(8), A6(5), B2(28), B8(28), C2(7), C8(7). The office area is 15.3 m2 (including whole internal wall b and the half a). The numbers in the parenthesis show how many identical thermal zones are in the building. Typical double office room is shown in Figure D.2. The total area of the typical double office rooms is 1272.8 m2.

b

4.19 m

a 3.66 m Figure D.2

Typical double office room.

Typical single office rooms Thermal zone type A3(4), A7(12), B3(56), B7(56), C3(14), C7(14). The office area is 10.05 m2 (including whole internal wall b and half a). The numbers in the parenthesis show how many identical thermal zones are in the building. Typical single office room is shown in Figure D.3. The total area of the typical single office rooms is 1568 m2.

366

Appendix D

b

4.19 m

a 2.4 m Figure D.3

Typical single office room.

Typical meeting rooms Thermal zone type A10(1), B5(4), B10(4), C5(1), C10(1). The office area is 12.96 m2 (including whole internal wall b and half a). The numbers in the parenthesis show how many identical thermal zones are in the building. Typical meeting room is shown in Figure D.4. The total area of the typical meeting rooms is 142.56 m2.

3.6 m

a

b 3.6 m Figure D.4

Typical meeting room.

367

Single and Double Skin Glazed Office Buildings

Meeting room (12 persons) Thermal zone type A4(3). The office area is 25.14 m2 (including half internal wall b and whole a). The numbers in the parenthesis show how many identical thermal zones are in the building. A 12 persons meeting room is shown in Figure D.5. The total area of the meeting rooms (12p) is 75.42 m2.

4.19 m

a

b

6.0 m Figure D.5

Meeting room for 12 persons.

Meeting room (8 persons) Thermal zone type A8(1). The office area is 20.2 m2 (including half internal wall b and whole a). The numbers in the parenthesis show how many identical thermal zones are in the building. An 8 persons meeting room is shown in Figure D.6. The total area of the meeting room (8p) is 20.2 m2.

368

Appendix D

4.19 m

a

b

4.82 m Figure D.6

8 persons meeting room.

Storage room (1st floor) Thermal zone type A5(1). The room area is 56.2 m2 (including half b). The numbers in the parenthesis show how many identical thermal zones are in the building. . The storage room is shown in Figure D.7. The total area of the storage room is 56.2 m2.

369

Single and Double Skin Glazed Office Buildings

b

15.6 m

3.6 m Figure D.7

370

Storage room.

HVAC

Construct.

Occupants

Equipment

Lights

Area

Average emitted heat per unit Number of units Rated input per unit (12W/m2) Luminous efficacy* Convective fraction Units desks (d), chairs (c), bookshelves (b) Construction

Clothing (s: during summer, w: during winter) Activity level (sitting, reading) Number of units PC: 125W, PR: printer : 30W, Fax : 30W Schedule

External wall without windows Number of occupants Occupant’s schedule

External wall with windows

Water radiator (Pmax = 1000W/unit) Cooling Beams (number of units, design air flow)

1 clo (w), 0.6 clo (s)

1 met

2 PCs

Equipment’s schedule 125W 1 175 W 41.67 lm/W 0.3

2 (d), (c), (b)

Default furniture 10 m2

1 clo (w), 0.6 clo (s)

1 met

1 PC, 1 printer 1 fax

Equipment’s schedule 61.67W 1 175 W 41.67 lm/W 0.3

1 (d), (c), (b)

Default furniture 10 m2

Short external facade 1 Schedule for offices

Long external facade Short ext. facade 1 Schedule for offices

1 unit d.a.f.= 15 l/s

1 unit d.a.f.= 15 l/s

Long external facade

1 unit

1 unit

Double office room

Default furniture 7 m2

1 (d), (c), (b)

Equipment’s schedule 125W 1 113 W 41.67 lm/W 0.3

1 PC

1 met

1 clo (w), 0.6 clo (s)

1 Schedule for offices

-

Long external facade

1 unit d.a.f.= 10 l/s

1 unit

Single office room

-

-

Default furniture 15 m2

1 (d), 6 (c)

1 148 W 41.67 lm/W 0.3

1 met

1 clo (w), 0.6 clo (s)

6 Schedule for meeting rooms

-

-

-

-

-

Default furniture

20 m2

25 m2

1 (d), 8 (c)

1 233 W 41.67 lm/W 0.3

1 met

1 clo (w), 0.6 clo (s)

8 Schedule for meeting rooms

-

Long external facade

2 units d.a.f.= 28 l/s (each)

2 units

Meeting room (8 persons)

Default furniture

1 (d), 12 (c)

1 291 W 41.67 lm/W 0.3

1 met

1 clo (w), 0.6 clo (s)

12 Schedule for meeting rooms

-

Long external facade

3 units d.a.f.= 28 l/s (each)

2 units d.a.f.= 21 l/s (each)

Short external facade

2 units

Meeting room (12 persons)

1 unit

Typical meeting room

Default furniture 50 m2

shelves

1 233 W 41.67 lm/W 0.3

-

-

-

-

-

-

-

-

-

4 units

Storage room

Table D.1

Furniture

Corner office room

Appendix D

Properties of the cell type offices.

371

Single and Double Skin Glazed Office Buildings

Corridor for the ground floor Since the corridors and the common spaces are (almost) internal thermal zones, they are not so interesting for the energy and thermal comfort simulations. Thus, they were considered as one thermal zone as shown below. Thermal zone type A11(1). The corridor area (including the reception and 1 meeting room is) 470 m2. The numbers in the parenthesis show how many identical thermal zones are in the building. The total area of the corridor of the ground floor is 470 m2 (Figure D.8).

Figure D.8.

Corridor of the ground floor.

Corridors for the 1st-5th floor Thermal zone type B11(4), C11. The corridor area (including the reception and 1 meeting room is) 444.8 m2. The numbers in the parenthesis show how many identical thermal zones are in the building. The total area of the corridors is 2224 m2 (Figure D.9).

Figure D.9

372

Corridor of the 1st-5th floor.

Appendix D Table D.2.

HVAC

Construct.

Occupants

Equipment

Lights

Furniture

Properties of the cell type corridors.

Water radiator (Pmax = 1000W/unit) Cooling Beams (number of units, design air flow) External wall with windows External wall without windows Number of occupants Occupant’s schedule Clothing (s: during summer, w: during winter) Activity level (sitting, reading) Number of units Copy machines: 500W PR: printer : 50W, Fax : 30W Schedule Average emitted heat per unit Number of units Rated input per unit (6W/m2) Luminous efficacy* Convective fraction Units desks (d), chairs (c), bookshelves (b) Construction Area

Corridor (ground floor)

Corridor (1st-5th floor)

2 units

4 units

-

Short external facade Long external facade -

-

Short external facade Long external facade 0 -

-

-

-

-

4 Printers, 4 Copy machines, 2 Faxes

4 Printers, 4 Copy machines, 2 Faxes

Equipment’s schedule 226W 1 2796 W 41.67 lm/W 0.3

Equipment’s schedule 226W 1 2460 W 41.67 lm/W 0.3

Chairs, etc

Chairs, etc

Default furniture 100 m2

Default furniture 80 m2

Open Plan Type: Geometry of the offices - thermal zones Typical corner zones Thermal zone type A1(1), B1(4), B4(4), C1(1), C4(1). The zone area is 258.7 m2 (including half internal wall a and half b). The numbers in the parenthesis show how many identical thermal zones are in the building. Typical corner zone is shown in Figure D.10. The total area of the corner office rooms is 2846 m2.

373

Single and Double Skin Glazed Office Buildings

b

a

Figure D.10

Typical corner zone.

Intermediate zones Thermal zone type A8(1), B(8), C8(1). The zone area is 430 m2 (including half internal wall a and half b). The numbers in the parenthesis show how many identical thermal zones are in the building. Typical corner zone is shown in Figure D.11. The total area of the intermediate zones is 2577 m2.

Figure D.11

374

Typical intermediate zone.

Appendix D

Reduced corner zone Thermal zone type A4 (1). The zone area is 203 m2 (including half internal wall a and half b). The numbers in the parenthesis show how many identical thermal zones are in the building. Typical corner zone is shown in Figure D.12. The total area of the reduced corner zone is 203 m2.

Figure D.12

Reduced corner zone.

Meeting rooms and Storage room These two zones are completely identical with the meeting room for 8 persons (cell type) and the storage room (cell type) correspondently.

375

Single and Double Skin Glazed Office Buildings Table D.3

Properties of the open plan type zones.

Construct.

HVAC

Typical corner zone

Water radiator (Pmax = 5000W/unit) Cooling Beams (number of units, design air flow)

External walls (a)

External walls (b)

Furniture

Lights

Equipment

Occupants

Number of occupants

Occupant’s schedule

Clothing (s: during summer, w: during winter) Activity level (sitting, reading) Number of units PC: 125W, PR: printer : 30 or 50W, fax : 30W, copy machines: 500W

Schedule

Average emitted heat per unit Number of units Rated input per unit (12W/m2) Luminous efficacy* Convective fraction Units desks (d), chairs (c), bookshelves (b), Common furniture (cf)

Construction

Area

376

Intermediate zones

Reduced corner zone

Meeting room (8 persons)

4 units

Storage room

2 units

2 units

2 units

2 units

1 unit d.a.f.= 131 l/s

1 unit d.a.f.= 202 l/s

2 units d.a.f.= 28 l/s (each)

-

Long external facade

Long external facade

Long external facade

-

-

-

-

-

-

12 Schedule for meeting rooms

3 units d.a.f.= 28 l/s (each) Long external facade

Short external facade 16

24

Schedule for offices

Schedule for offices

1 clo (w), 0.6 clo (s)

1 clo (w), 0.6 clo (s)

1 clo (w), 0.6 clo (s)

-

1 clo (w), 0.6 clo (s)

1 met

1 met

1 met

-

1 met

16 PCs 4 PR (30W), 4 faxes

24 PCs 4 PR (50W), 4 c.m.

-

-

-

Equipment’s schedule

Equipment’s schedule

-

-

-

93.4 W

159.3W

1

1

1

1

1

3104 W

5148 W

233 W

233 W

291 W

41.67 lm/W 0.3

41.67 lm/W 0.3

41.67 lm/W 0.3

41.67 lm/W 0.3

41.67 lm/W 0.3

16 (d), (c), (b), (cf)

24 (d), (c), (b), (cf)

1 (d), 8 (c)

shelves

1 (d), 12 (c)

Default furniture 160 m2

Default furniture 260 m2

Default furniture 20 m2

Default furniture 50 m2

Default furniture 25 m2

8 Schedule for meeting rooms

-

-

-

-

Appendix E

Appendix E Corrected theoretical U-values (including thermal bridges)

The thermal bridges caused by the steel columns and the wooden studs were calculated using the two-dimensional software Heat 2 (version 6). Due to the fact that when defining a thermal zone in IDA ICE 3.0 one has to insert the loss factor for thermal bridges (W/°C) for each thermal zone type (depending on the geometry of the zone) we decided to calculate the U-value of the external wall including the thermal bridges (using Heat 2) and then design an equivalent new wall in IDA ICE 3.0 assuming that the loss factor = 0. The 4 steps followed are: 1. We defined wall structure without the steel columns and the material properties in IDA ICE 3.0 (heat conductivity, density and specific heat). IDA ICE 3.0 calculated the U-value of the external wall (=0.2201Wm-2K-1) as show in Figure E.1.

Figure E.1

U-value (without the columns) calculated by IDA ICE 3.0.

377

Single and Double Skin Glazed Office Buildings

2. We built the same model in Heat 2 and calculated the U-value. Since the minimum material properties and thickness (minimum thickness 10mm) were not exactly the same, we tuned the model in order to get the same U-value with the one calculated by IDA ICE 3.0 (step 1) as shown in Figure E.2.

Figure E.2

U-value (without columns) calculated by Heat 2.

The construction was: • • • • •

120mm facing bricks 40mm air gap 10mmgypsum 150mm insulation 10mm gypsum

The properties of the materials were the same with the IDA ICE 3.0 model The boundary conditions assumed were: • Inside temperature: 1°C • Outside temperature: 0°C (temperature difference 1°C in order to get the Wm-2K-1) • Heat flow from both sides q=0 Wm-1, i.e. sideways in the wall The U value calculated was 0.2027 Wm-2K-1. The calculations were steady state.

378

Appendix E

3. We added the columns in the Heat 2 model as shown in Figure E.3. The distance between the centres of the steel columns is 2.4m, between the centres of studs 0.6m and between centres of the floors 3.5m.

Figure E.3

External wall construction (with columns).

Using the same assumptions as in step 2, we simulated the new model (Figure E.4). The new U-value calculated was 0.27 Wm-2K-1.

Figure E.4

Simulation with the steel columns (Heat 2).

4. We assumed an equivalent external wall (with the same U-value) in IDA ICE 3.0 by reducing the insulation from 0.137m to 0.1125m as shown in Figure E.5.

379

Single and Double Skin Glazed Office Buildings

Figure E.5

380

Final model of the external wall in IDA ICE 3.0 (reduced thermal insulation).

Appendix F

Appendix F AHU- Ventilation rates

AHU for Cell type For the cell type air the air exchange with the outdoor environment takes place in 4 different ways: o Supply air to the offices and meeting rooms during the working hours (mechanical ventilation) o Infiltration to all the zones always (natural ventilation) o Exhaust air from the corridors during the working hours (mechanical ventilation) o Exfiltration from all the zones always (natural ventilation) In all the offices and the total ingoing air is due to mechanically supplied air and the infiltration and the total outgoing air is due to exfiltration. The supplied air to the offices is extracted though leakages to the corridor and exhausted from there through the AHU. The infiltration and exfiltration are assumed to be 0.1ach for all the zones. In the meeting rooms all the air supplied is also exhausted. The reason for that is that if the supplied air (VAV CO2 control) was extracted to the corridors the total exhaust air would be unknown. This means that any mistake in the estimation of the VAV supplied air would destroy the balance of the total supply – exhaust air influencing the AHU efficiency. However, the VAV CO2 control applied in the meeting rooms caused 2 problems for the simulations: o Infiltration (increase the mechanical ventilation) could not be added since the rooms were supplied with the necessary air so we had to add this infiltration to the offices. o The supplied air was not known so it was not possible to know how much the efficiency of the AHU should be decreased. In order to solve the problem the airflow was estimated

381

Single and Double Skin Glazed Office Buildings

The Table E.1 below shows the ventilation rates of each zone as inserted in IDA ICE 3.0. o The Supplied air per zone (mech. ventilation) shows the air that is provided by the AHU as mechanical ventilation. In the corridors there is not any supplied air and in the meeting rooms is shown the estimation we made. o The supplied air per zone (mech. ventilation) is increased in the offices (natural ventilation in the offices, corridor and meeting rooms). In the meeting rooms the airflow is the same since infiltration was added to the offices. o The Total Exhaust air (l/s) per floor shows in each zone the exhaust air. There is not any exhaust air in the meeting rooms since they do not contribute in the total exhaust air from the corridors. However in reality it should be considered in order to find the proper amount of total airflows which will give the correct decrease of the AHU efficiency.

382

Appendix F

Table F.1 Room type

Ventilation rates for cell type. Zone

Supplied air per zone (mech. vent.) (l/s)

Supplied air per zone (total) (l/s)

Total Exhaust air (l/s) per zone

Supply air/ Exhaust air

Input for IDA

Corner office rooms

B1 B4 B6 B9 C1 C4 C6 C9 A1 A9

15 15 15 15 15 15 15 15 15 15

17.01 17.01 17.01 17.01 17.01 17.01 17.01 17.01 17.01 17.01

0 0 0 0 0 0 0 0 0 0

1000 1000 1000 1000 1000 1000 1000 1000 1000 1000

0.017008 0.017008 0.017008 0.017008 0.017008 0.017008 0.017008 0.017008 0.017008 0.017008

Double office rooms

A2 A6 B2 B8 C2 C8

20 20 20 20 20 20

22.04 22.04 22.04 22.04 22.04 22.04

0 0 0 0 0 0

1000 1000 1000 1000 1000 1000

0.022042 0.022042 0.022042 0.022042 0.022042 0.022042

Single office rooms

B3 B7 C3 C7 A3 A7

10 10 10 10 10 10

11.34 11.34 11.34 11.34 11.34 11.34

0 0 0 0 0 0

1000 1000 1000 1000 1000 1000

0.011339 0.011339 0.011339 0.011339 0.011339 0.011339

Meeting rooms (6p)

B5 B10 C5 C10 A10

21 21 21 21 21

21 21 21 21 21

0 0 0 0 0

1000 1000 1000 1000 1000

0.022726 0.022726 0.022726 0.022726 0.022726

Meeting rooms (8p)

A8

28

28

0

1000

0.03069

Meeting rooms (12p)

A4

42

42

0

1000

0.045349

Storage room (1st floor)

A5

62

70.58

0

1000

0.070576

Corridor (1st floor)

A11

0

0

577.10

0.001

577.10

Corridor (2-6 floors)

B11 C11

0 0

0 0

699.67 699.67

0.001 0.001

699.67 699.67

Natural Ventilation (not including the corridors and the meeting rooms) Natural Ventilation ( including the corridors and the meeting rooms) Weighted Natural Ventilation) Total Weighted Natural Ventilation Total Mechanical Ventilation Recovered heat (60%) Equivalent percentage for recovered (%) AHU on Value AHU off Value Weekends off value (=50% mechanical ventilation +100% natural ventilation)

242.5 462.9 462.9 4075.4 3612 2398.2 53.773 1 0.1038 0.551

383

Single and Double Skin Glazed Office Buildings

AHU for Open plan type For the open plan type the calculations were much simpler since both supply and exhaust air were provided in all the thermal zones. However, the meeting rooms were treated exactly in the same way as the cell type office building. In Table F.2 are shown the airflows of the building.

Table F.2

Ventilation rates for open plan type.

Room type

Zone

Supplied air per zone (mech. vent.) (l/s)

Natural ventilation per zone (l/sec)

Ventilation per zone (l/s)

Supply air/ Exhaust air

Input for IDA

Typical corner zones

B1 B4 C1 C4 A1

112 112 112 112 112

19.4 19.4 19.4 19.4 19.4

131.4 131.4 131.4 131.4 131.4

1 1 1 1 1

133.0366 133.0366 133.0366 133.0366 133.0366

Reduced corner zone

A4

84

15.2

99.2

1

100.4822

Intermediate zones

A8 B8 C8

168 168 168

32.22 32.22 32.22

200.22 200.22 200.22

1 1 1

202.938 202.938 202.938

Meeting Rooms

A2 A5 B2 B5 C2 C5

0 0 0 0 0 0

1.5 1.5 1.5 1.5 1.5 1.5

29.5 29.5 29.5 29.5 29.5 29.5

1 1 1 1 1 1

0 0 0 0 0 0

Storage room (1st floor)

A9

62

4.83

66.83

1

67.23745

Natural Ventilation (not including the meeting rooms) Natural Ventilation ( including the meeting rooms) Weighted Natural Ventilation (the natural ventilation of the meeting rooms is added as nat. vent. In the offices) Total Weighted Natural Ventilation (the natural ventilation of the meeting rooms is added as nat. vent. In the offices) Total Mechanical Ventilation Recovered heat (60%) Equivalent percentage for recovered (%) AHU on Value AHU off Value Weekends off value (=50% mechanical ventilation +100% natural ventilation)

384

426.75 462.75 462.75 3520.75 3074 1844.4 52.387 1 0.1314 0.5679

Appendix G

Appendix G Frame Construction for the single skin glazed alternatives

The “improved” frame constructions were suggested by Schüco International. For the first to sixth 60% glazed alternatives the frames used are the Royal FW 50+ Hi and FW 60+ Hi as shown in Figure G.1 and G.2.

Insulation thickness (mm)

Glass thickness (mm)

Frame depth (mm)

Glass thickness (mm)

Frame depth (mm)

Glass thickness (mm)

Figure G.1

System FW 50+ Hi.

385

Single and Double Skin Glazed Office Buildings

Glass thickness (mm)

Glass thickness (mm)

Glass thickness (mm)

Figure G.2

System FW 60+ Hi.

The Uframe depends on the frame depth. As shown in Figure F.3

Figure G.3

386

Relationship between Uframe and frame depth.

Appendix H

Appendix H Pane properties for the glazing used for the double skin façade alternatives

Table H.1

Glazing Unit

Pane properties for the glazing used for the double skin façade alternatives. Thickness (mm)

Corrected emissivity indoor outdoor

Reflectance

Direct solar transmittance

indoor

outdoor

0.078 (s) 0.082 (v) 0.074 (s) 0.081 (v) 0.207 (s) 0.059 (v) 0.053 (s) 0.067 (v)

0.078 (s) 0.082 (v) 0.074 (s) 0.081 (v) 0.179 (s) 0.064 (v) 0.053 (s) 0.067 (v)

0.820 (s) 0.893 (v) 0.742 (s) 0.870 (v) 0.666 (s) 0.865 (v) 0.460 (s) 0.751 (v)

Clear pane

4

0.837

0.837

Clear pane

8

0.837

0.837

Low E coated

4

0.837

0.092

Optigreen (s. c. tinted) (OpGrn6 pgl) Optigreen (s. c. tinted) (OpGrn8 pgl) Solar control + low E (soft coated) (galaxy6gvb) Solar control + low E (soft coated) (galaxy8gvb) Solar control + low E (hard coated) (sunnycl8 gvb) Low E (hard coated) (Kglass6pgl)

6

0.837

0.837

8

0.837

0.837

0.053 (s) 0.067 (v)

0.053 (s) 0.067 (v)

0.389 (s) 0.703 (v)

6

0.837

0.042

0.293 (s) 0.146 (v)

0.412 (s) 0.134 (v)

0.201 (s) 0.440 (v)

8

0.837

0.042

0.268 (s) 0.143 (v)

0.412 (s) 0.133 (v)

0.198 (s) 0.435 (v)

8

0.298

0.837

0.102 (s) 0.101 (v)

0.088 (s) 0.085 (v)

0.520 (s) 0.669(v)

8

0.170

0.837

0.108 (s) 0.109 (v)

0.090 (s) 0.098(v)

0.677 (s) 0.822 (v)

(s) = solar (v) = visual

387

Single and Double Skin Glazed Office Buildings

388

Appendix I

Appendix I Optical and thermal properties of the double skin façade alternatives

Table I.1

Glazing properties for the “standard” double façade mode (closed cavity).

Case

DSF A

DSF B

DSF C

DSF D

DSF E

DSF F

DSF G

U-value g-value (total solar energy transmittance) solar direct transmittance solar direct reflectance outdoor solar direct reflectance indoor light transmittance reflectance outdoor reflectance indoor

1.93 0.627

1.15 0.551

1.85 0.516

1.85 0.404

1.15 0.354

1.04 0.301

1.14 0.443

0.53

0.447

0.326

0.297

0.264

0.151

0.335

0.153

0.188

0.123

0.0848

0.0867

0.327

0.15

0.169

0.248

0.132

0.159

0.241

0.422

0.25

0.708 0.194 0.201

0.683 0.18 0.174

0.594 0.168 0.173

0.571 0.141 0.191

0.551 0.132 0.166

0.416 0.395 0.311

0.526 0.16 0.177

Table I.2

DSF Case A D E F

Properties of the inner and outer skin of the “standard” double façade mode (closed cavity). U value Outer skin Inner skin 5.79 5.79 5.79 5.79

2.9 2.74 1.46 1.31

g value Outer skin Inner skin 0.789 0.532 0.532 0.789

0.746 0.746 0.655 0.215

Tsol Outer skin Inner skin 0.742 0.389 0.389 0.742

0.685 0.685 0.565 0.179

389

Single and Double Skin Glazed Office Buildings

Table I.3

Glazing properties for the Airflow window mode (closed cavity).

Case

AW A

AW B

AW C

AW D

AW E

AW F

AW G

U-value g-value (total solar energy transmittance) solar direct transmittance solar direct reflectance outdoor solar direct reflectance indoor light transmittance reflectance outdoor reflectance indoor

1.93 0.627

1.15 0.561

1.83 0.529

1.85 0.404

1.15 0.354

1.04 0.195

0.824 0.191

0.53

0.447

0.326

0.297

0.264

0.157

0.149

0.153

0.201

0.123

0.0848

0.0861

0.279

0.278

0.169

0.224

0.132

0.159

0.216

0.311

0.322

0.708 0.194 0.201

0.683 0.173 0.182

0.594 0.168 0.173

0.571 0.141 0.191

0.551 0.128 0.174

0.357 0.172 0.238

0.344 0.169 0.208

Table I.4

AW Case A D E F G

390

Properties of the inner and outer skin of the airflow window mode (closed cavity). U value Outer skin Inner skin 2.87 2.71 1.45 1.30 1.31

5.92 5.92 5.92 5.92 5.66

g value Outer skin Inner skin 0.688 0.419 0.369 0.213 0.214

0.846 0.846 0.846 0.846 0.738

Tsol Outer skin Inner skin 0.624 0.338 0.299 0.169 0.176

0.82 0.82 0.82 0.82 0.677

Appendix J

Appendix J Description of the opening areas for the box window and multi-storey double skin façade

Cavity Depth, m

Cavity Width, m

Damper free area, m²

Discharge coeff. top (Cdtop)

Discharge coeff. bottom (Cdbottom)

Damper Copen

Bottom leak, m²

Upper leak, m²

Leak in between floors, m²

Leak in between rest floors²

ELA1 Multi storey

Description of the opening areas for the box window and multistorey high cavities.

Zone type

Table J.1

Corner offices (short façade) Corner offices (long façade) Double office rooms (long façade) Double office rooms (short façade) Single office rooms Corridor

0.80

4.19

0.87

0.65

0.55

2.94

1.84

2.18

2.35

3.35

1.60

0.80

3.60

0.87

0.65

0.55

2.52

1.58

1.87

2.02

2.88

1.38

0.80

4.19

0.87

0.65

0.55

2.94

1.84

2.18

2.35

3.35

1.60

0.80

3.60

0.87

0.65

0.55

2.52

1.58

1.87

2.02

2.88

1.38

0.80

2.40

0.87

0.65

0.55

1.68

1.06

1.25

1.34

1.92

0.92

0.80

1.60

0.87

0.65

0.55

1.12

0.70

0.83

0.90

1.28

0.61

1:

ELA: Equivalent Leakage Area

391

Single and Double Skin Glazed Office Buildings

392

Appendix K

Appendix K Shading properties for the double skin façade alternatives

Table K.1

Properties of the venetian blinds. White venetian Dark venetian blinds blinds

Diffuse reflectance (shortwave radiation, front and back) Absorbtance (shortwave rad., front and back) Diffuse reflectance (longwave rad., front and back) Emitance (longwave rad., front and back) Width of slat Slat spacing Slat angle

67% 33% 10% 90% 28 mm 22 mm 45°

19% 81% 10% 90% 28 mm 22 mm 45°

393

Single and Double Skin Glazed Office Buildings

Table K.2

Case

DSF A,F

Multipliers for the shading devices for the “standard” double façade alternatives. Orientation north northeast east southeast south southwest west northwest

north northeast east DSF D,E southeast south southwest west northwest

394

White venetian blinds U value g value Tsol

0.923

0.923

0.6144 0.6102 0.6012 0.5936 0.5938 0.5964 0.604 0.61

0.2554 0.2332 0.2058 0.1962 0.1996 0.1952 0.2032 0.2294

0.7218 0.7198 0.7144 0.7148 0.7192 0.7208 0.7212 0.7208

0.2512 0.236 0.2004 0.192 0.1962 0.1912 0.198 0.2252

Blue venetian blinds U value g value Tsol

0.923

0.923

0.7524 0.762 0.7726 0.7732 0.773 0.777 0.7768 0.7642

0.153 0.1294 0.1016 0.0968 0.1032 0.0954 0.0982 0.1248

0.803 0.809 0.8176 0.821 0.8236 0.8264 0.8242 0.8122

0.1524 0.1282 0.0998 0.0962 0.1032 0.0948 0.0966 0.1236

Appendix K

Table K.3

Case

AW A

AW D

AW E

AW F,G

Multipliers for the shading devices for the airflow window alternatives. Orientation north northeast east southeast south southwest west northwest north northeast east southeast south southwest west northwest north northeast east southeast south southwest west northwest north northeast east southeast south southwest west northwest

White venetian blinds U value g value Tsol

0.955

0.952

0.951

0.954

0.6852 0.6836 0.6804 0.6762 0.6764 0.6792 0.6844 0.6856

0.2692 0.2468 0.2196 0.2106 0.2146 0.21 0.217 0.2432

0.7454 0.7442 0.7426 0.7414 0.7442 0.7452 0.747 0.7466

0.2668 0.2442 0.216 0.2082 0.213 0.2072 0.2134 0.2406

0.7874 0.7876 0.788 0.7882 0.7916 0.7922 0.792 0.79

0.2832 0.2612 0.2334 0.2266 0.232 0.2258 0.231 0.2576

0.7926 0.7926 0.793 0.793 0.7966 0.7978 0.7972 0.795

0.2806 0.2584 0.2314 0.2234 0.2276 0.2224 0.229 0.2548

Blue venetian blinds U value g value Tsol

0.955

0.952

0.951

0.954

0.8134 0.8242 0.8388 0.8406 0.84 0.8444 0.8434 0.8284

0.1566 0.1322 0.1038 0.0998 0.1068 0.0986 0.1008 0.1276

0.8424 0.8514 0.8662 0.8662 0.8638 0.8698 0.8668 0.8554

0.1562 0.1314 0.099 0.099 0.1018 0.0982 0.107 0.1266

0.859 0.8678 0.8798 0.8824 0.883 0.8858 0.884 0.8714

0.159 0.1344 0.1048 0.102 0.1106 0.1012 0.1018 0.1292

0.8618 0.8694 0.8808 0.8834 0.885 0.8876 0.885 0.8728

0.159 0.1342 0.1058 0.102 0.1092 0.1008 0.1026 0.1296

395

Single and Double Skin Glazed Office Buildings

396

Appendix L

Appendix L Energy use

Use of electricity for lighting (kWh/am2)

Use of electricity for equipment (kWh/am2)

Use of electricity for pumps, fans (kWh/am2)

Use of electricity for server rooms (kWh/am2)

Energy use for cooling server rooms (kWh/am2)

Total (kWh/am2)

SS-30%-Cell-NS-strict SS-30%-Cell-NS-normal SS-30%-Cell-NS-poor SS-30%-Cell-NS45-strict SS-30%-Cell-NS45-normal SS-30%-Cell-NS45-poor SS-30%-Cell-EW-strict SS-30%-Cell-EW-normal SS-30%-Cell-EW-poor SS-30%-Open-NS-strict SS-30%-Open-NS-normal SS-30%-Open-NS-poor SS-30%-Open-NS45-strict SS-30%-Open-NS45-normal SS-30%-Open-NS45-poor SS-30%-Open-EW-strict SS-30%-Open-EW-normal SS-30%-Open-EW-poor

Energy use for cooling (kWh/am2)

Energy use for the reference building alternatives.

Energy use for heating (kWh/am2)

Table L.1

56 52 47 56 52 47 56 52 47 50 45 38 50 45 38 51 45 38

21 11 7 20 11 7 19 10 7 29 18 11 29 17 10 28 16 9

14.7 14.4 14.2 14.7 14.4 14.2 14.7 14.4 14.2 19 19 19 19 19 19 19 19 19

22 22 22 22 22 22 22 22 22 21 21 21 21 21 21 21 21 21

8 8 8 8 8 8 8 8 8 6 6 6 6 6 6 6 6 6

10 10 10 10 10 10 10 10 10 13 13 13 13 13 13 13 13 13

5 5 5 5 5 5 5 5 5 6 6 6 6 6 6 6 6 6

137 123 114 136 123 114 136 122 113 144 127 114 144 127 113 143 126 112

397

Single and Double Skin Glazed Office Buildings

398

Use of electricity for lighting (kWh/am2)

Use of electricity for equipment (kWh/am2)

Use of electricity for pumps, fans (kWh/am2)

Use of electricity for server rooms (kWh/am2)

Energy use for cooling server rooms (kWh/am2)

Total (kWh/am2)

SS-60%-Cell-NS45-strict (1) SS-60%-Cell-NS45-strict (2) SS-60%-Cell-NS45-strict (3) SS-60%-Cell-NS45-strict (4) SS-60%-Cell-NS45-strict (5) SS-60%-Cell-NS45-strict (6) SS-60%-Cell-NS45-strict (7) SS-60%-Cell-NS45-normal (1) SS-60%-Cell-NS45-normal (2) SS-60%-Cell-NS45-normal (3) SS-60%-Cell-NS45-normal (4) SS-60%-Cell-NS45-normal (5) SS-60%-Cell-NS45-normal (6) SS-60%-Cell-NS45-normal (7) SS-60%-Cell-NS45-poor (1) SS-60%-Cell-NS45-poor (2) SS-60%-Cell-NS45-poor (3) SS-60%-Cell-NS45-poor (4) SS-60%-Cell-NS45-poor (5) SS-60%-Cell-NS45-poor (6) SS-60%-Cell-NS45-poor (7)

Energy use for cooling (kWh/am2)

Energy usefor the 60% glazed alternatives (cell plan type).

Energy use for heating (kWh/am2)

Table L.2

76 54 58 59 53 58 62 72 50 54 55 48 54 59 66 44 48 50 43 48 53

31 36 28 22 48 27 14 20 24 18 13 36 16 7 14 17 12 9 28 12 5

14.7 14.7 14.7 14.7 14.7 14.7 14.7 13.4 13.8 14.2 14.4 13.8 14.2 14.4 13.2 13.7 14.1 14.3 13.6 14.2 14.4

22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22

8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8

10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10

5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5

167 150 146 142 161 145 137 151 133 131 129 143 130 126 138 120 120 118 130 119 118

Appendix L

Use of electricity for server rooms (kWh/am2)

Energy use for cooling server rooms (kWh/am2)

Total (kWh/am2)

19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19

Use of electricity for pumps, fans (kWh/am2)

38 44 34 29 54 33 21 26 31 22 17 41 21 10 18 22 17 10 31 15 6

Use of electricity for lighting (kWh/am2)

70 49 52 53 47 52 56 65 43 46 48 42 47 50 57 36 39 41 35 39 43

Use of electricity for equipment (kWh/am2)

SS-60%-Open-NS45-strict (1) SS-60%-Open-NS45-strict (2) SS-60%-Open-NS45-strict (3) SS-60%-Open-NS45-strict (4) SS-60%-Open-NS45-strict (5) SS-60%-Open-NS45-strict (6) SS-60%-Open-NS45-strict (7) SS-60%-Open-NS45-normal (1) SS-60%-Open-NS45-normal (2) SS-60%-Open-NS45-normal (3) SS-60%-Open-NS45-normal (4) SS-60%-Open-NS45-normal (5) SS-60%-Open-NS45-normal (6) SS-60%-Open-NS45-normal (7) SS-60%-Open-NS45-poor (1) SS-60%-Open-NS45-poor (2) SS-60%-Open-NS45-poor (3) SS-60%-Open-NS45-poor (4) SS-60%-Open-NS45-poor (5) SS-60%-Open-NS45-poor (6) SS-60%-Open-NS45-poor (7)

Energy use for cooling (kWh/am2)

Energy use for the 60% glazed alternatives (open plan type).

Energy use for heating (kWh/am2)

Table L.3

21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21

6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6

13 13 13 13 13 13 13 13 13 13 13 13 13 13 13 13 13 13 13 13 13

6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6

172 157 151 147 166 150 142 156 139 133 130 148 132 125 139 123 120 116 131 119 113

399

Single and Double Skin Glazed Office Buildings

400

Use of electricity for lighting (kWh/am2)

Use of electricity for equipment (kWh/am2)

Use of electricity for pumps, fans (kWh/am2)

Use of electricity for server rooms (kWh/am2)

Energy use for cooling server rooms (kWh/am2)

Total (kWh/am2)

SS-100%-Cell-NS45-strict (1) SS-100%-Cell-NS45-strict (2) SS-100%-Cell-NS45-strict (3) SS-100%-Cell-NS-strict (3) SS-100%-Cell-EW-strict (3) SS-100%-Cell-NS45-strict (4) SS-100%-Cell-NS45-strict (5) SS-100%-Cell-NS45-strict (6) SS-100%-Cell-NS45-strict (7) SS-100%-Cell-NS45-normal (1) SS-100%-Cell-NS45-normal (2) SS-100%-Cell-NS45-normal (3) SS-100%-Cell-NS-normal (3) SS-100%-Cell-EW-normal (3) SS-100%-Cell-NS45-normal (4) SS-100%-Cell-NS45-normal (5) SS-100%-Cell-NS45-normal (6) SS-100%-Cell-NS45-normal (7) SS-100%-Cell-NS45-poor (1) SS-100%-Cell-NS45-poor (2) SS-100%-Cell-NS45-poor (3) SS-100%-Cell-NS45-poor (4) SS-100%-Cell-NS45-poor (5) SS-100%-Cell-NS45-poor (6) SS-100%-Cell-NS45-poor (7)

Energy use for cooling (kWh/am2)

Energy use for the 100% glazed alternatives (cell plan type).

Energy use for heating (kWh/am2)

Table L.4

95 63 69 69 69 71 75 92 59 65 68 58 66 72 84 53 59 61 52 59 66 95 63 69 71

43 50 37 38 34 29 16 30 37 27 19 54 24 9 22 28 20 13 44 17 6 43 50 37 29

14.7 14.7 14.7 14.7 14.7 14.7 14.7 12.9 13.5 14.0 14.2 13.4 13.9 14.3 12.7 13.3 13.8 14.1 13.2 13.7 14.2 14.7 14.7 14.7 14.7

22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22 22

8 8 8 8 8 8 8 8 8 8 8 8 8 8 30 8 8 8 8 8 8 8 8 8 8

10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10

5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5

198 173 166 168 164 160 151 180 155 151 147 170 149 141 186 140 138 134 154 136 131 198 173 166 160

Appendix L

Use of electricity for server rooms (kWh/am2)

Energy use for cooling server rooms (kWh/am2)

Total (kWh/am2)

19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19

Use of electricity for pumps, fans (kWh/am2)

48 56 41 33 71 39 21 36 44 30 22 58 27 11 27 34 21 15 47 19 6

Use of electricity for lighting (kWh/am2)

86 58 63 64 56 63 68 82 53 58 59 51 58 63 75 45 51 52 44 51 56

Use of electricity for equipment (kWh/am2)

SS-100%-Open-NS45-strict (1) SS-100%-Open-NS45-strict (2) SS-100%-Open-NS45-strict (3) SS-100%-Open-NS45-strict (4) SS-100%-Open-NS45-strict (5) SS-100%-Open-NS45-strict (6) SS-100%-Open-NS45-strict (7) SS-100%-Open-NS45-normal (1) SS-100%-Open-NS45-normal (2) SS-100%-Open-NS45-normal (3) SS-100%-Open-NS45-normal (4) SS-100%-Open-NS45-normal (5) SS-100%-Open-NS45-normal (6) SS-100%-Open-NS45-normal (7) SS-100%-Open-NS45-poor (1) SS-100%-Open-NS45-poor (2) SS-100%-Open-NS45-poor (3) SS-100%-Open-NS45-poor (4) SS-100%-Open-NS45-poor (5) SS-100%-Open-NS45-poor (6) SS-100%-Open-NS45-poor (7)

Energy use for cooling (kWh/am2)

Energy use for the 100% glazed alternatives (open plan type).

Energy use for heating (kWh/am2)

Table L.5

21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21

6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6

13 13 13 13 13 13 13 13 13 13 13 13 13 13 13 13 13 13 13 13 13

6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6

199 179 169 162 193 167 154 183 161 152 146 174 150 140 167 144 136 132 157 135 127

401

Single and Double Skin Glazed Office Buildings

402

Use of electricity for lighting (kWh/am2)

Use of electricity for equipment (kWh/am2)

Use of electricity for pumps, fans (kWh/am2)

Use of electricity for server rooms (kWh/am2)

Energy use for cooling server rooms (kWh/am2)

Total (kWh/am2)

SS-100%-Cell-NS45-strict (1-cor) SS-100%-Cell-NS45-normal (1-cor) SS-100%-Cell-NS45-poor (1-cor) SS-100%-Open-NS45-strict (1-cor) SS-100%-Open-NS45-normal (1-cor) SS-100%-Open-NS45-poor (1-cor) SS-100%-Cell-NS45-strict (5-cor) SS-100%-Cell-NS45-normal (5-cor) SS-100%-Cell-NS45-poor (5-cor)

Energy use for cooling (kWh/am2)

Energy use for the 1st and 5th (cell type) 100% glazed alternatives (increased heating and cooling capacity).

Energy use for heating (kWh/am2)

Table L.6

99

43

14.7

22

8

10

5

202

95

31

12.9

22

8

10

5

184

87

22

12.7

22

30

10

5

189

90

48

19.2

21

6

13

6

203

85

36

19.2

21

6

13

6

186

77

27

19.2

21

6

13

6

168

62

68

14.7

22

8

10

5

190

58

55

13.4

22

8

10

5

171

52

45

13.2

22

8

10

5

155

Appendix M

Appendix M Number of working hours with PPD values lower than 10% and 15% for the 90% of the working hours

Table M.1

Percentage of working of hours with PPD below 10% and 15% for the cell type alternatives. Cell type plan Open type plan 30% glazed 60% glazed 100% glazed 30% glazed 60% glazed 100% glazed PPD PPD PPD PPD PPD PPD PPD PPD PPD PPD PPD PPD 10% 15% 10% 15% 10% 15% 10% 15% 10% 15% 10% 15%

strict(1) normal(1) poor (1) strict(2) normal(2) poor (2) strict(3) normal(3) poor(3) strict(4) normal(4) poor (4) strict(5) normal(5) poor (5) strict(6) normal(6) poor(6) strict(7) normal(7) poor (7)

66 73 39

93 93 63

61 57 27 72 70 31 68 70 34 66 71 38 71 65 30 68 70 33 68 71 33

83 82 45 94 94 52 93 93 57 92 93 61 93 90 49 93 93 57 93 92 57

46 31 15 68 55 27 62 57 27 60 59 30 64 50 25 62 58 27 57 60 40

65 60 30 87 84 42 84 82 45 83 83 49 84 78 40 84 83 45 82 83 58

63 84 44

97 97 64

69 65 27 81 73 32 78 79 32 77 82 34 82 68 31 78 80 32 78 80 78

90 90 42 97 96 49 96 97 51 96 97 56 97 93 46 96 97 51 96 97 96

50 36 19 75 60 34 70 67 34 69 71 35 72 56 32 70 69 34 66 77 46

70 64 34 92 87 49 91 90 52 90 91 56 92 80 47 91 91 53 90 91 71

403

Single and Double Skin Glazed Office Buildings

4th alt. 5th alt. 6th alt. 7th alt.

404

Corner office (northeast)

Single office (northeast)

Double office (northeast)

Meeting room (southeast)

53 96 66 62 59 68 57 69 65 60 59 67 54 70

64 100 81 19 74 22 73 21 66 29 75 21 70 23

Percentage of working of hours with PPD below 10% and 15% for the cell type alternatives (normal set points, zone level).

PPD 10% PPD 15% PPD 10% PPD 15% PPD 10% PPD 15% PPD 10% PPD 15% PPD 10% PPD 15% PPD 10% PPD 15% PPD 10% PPD 15%

Meeting room (southeast)

3rd alt.

53 93 66 85 59 87 57 87 66 75 59 87 54 88

Double office (northeast)

2nd alt.

39 90 48 100 44 100 41 100 46 87 44 100 33 100

Single office (northeast)

1st alt.

56 88 71 100 64 100 61 100 70 88 64 100 57 100

Corner office (northeast)

Figure M.3

Meeting room (northwest)

7th alt.

59 86 72 97 68 97 65 97 67 91 67 97 62 97

Meeting room (northwest)

6th alt.

Single office (southwest)

5th alt.

57 80 71 95 65 93 64 93 62 87 66 93 62 93

Single office (southwest)

4th alt.

Double office (southwest)

3rd alt.

37 74 49 90 42 87 46 87 34 82 46 88 44 86

Double office (southwest)

2nd alt.

PPD 10% PPD 15% PPD 10% PPD 15% PPD 10% PPD 15% PPD 10% PPD 15% PPD 10% PPD 15% PPD 10% PPD 15% PPD 10% PPD 15%

Corner office (southwest) 1st alt.

Percentage of working of hours with PPD below 10% and 15% for the cell type alternatives (strict set points, zone level).

Corner office (southwest)

Figure M.2

24 70 32 85 30 82 33 85 25 75 31 85 42 87

47 77 59 92 59 89 62 92 53 80 61 92 68 93

48 83 60 95 59 94 61 96 53 85 60 96 65 97

40 88 51 98 57 97 58 100 50 82 57 100 59 100

24 90 30 99 34 97 36 100 27 80 35 100 34 100

44 85 55 89 59 87 59 89 52 71 59 89 56 87

43 78 54 71 59 73 61 72 51 57 60 72 59 69

39 56 51 29 49 32 53 25 43 31 51 26 67 22

Appendix M

405

Single and Double Skin Glazed Office Buildings

406

ISSN 1671-8136 ISBN 978-91-85147-23-6