Daylight Design Formulae and Their Implimentation

DAYLIGHT DESIGN FORMULAE AND THEIR IMPLIMENTATION “Architecture is the masterly, correct, and magnificent play of masses brought together in light. Our eyes are made to see forms in light; light and shade reveal these forms." Le Corbusier  SUBMITTED BY SUMITABH CHOWDHURY B.ARCH,3RD YEAR,6 TH SEM MITS,GWALIOR

Separate evaluation of: Different conditions regarding daylight

Bad daylighting design with DFs .Entrance of daylight is from rare side Because of that the presentation board shines thus reflects back to the viewers eyes Due improper daylight electricity is used to light the room, hence energy consumption

Reasons for the success of the Daylight approach: • •If the natural lighting is sufficient on an overcast day, it is likely to be more than adequate adequate when the sun is shining. • •But ... a daylight factor optimized building admits as much light as possible, therefore the ideally daylight building would be fully glazed! This is clearly in contrast with comfort requirements. • •A densely overcast sky looks the same whichever direction one faces -North, South, East or West.  Therefore the effect of the orientation vanishes from the calculation. • •But ... the simplification introduced with the use of  the daylight factor does not account for building location and orientation, season, time of day, direct solar penetration, variability of sky conditions. It is not possible to predict glare.

Lighting exposure on windows

Architect’s intentions • Let daylight in • Modulate daylight through translucent materials (alabaster, paper,fibre glass) • previously this technique was used in churches

Use of daylight using skylights • By using skylight we can use the sunlight to light the room • Performance indicator: light exposure

a ow an e ect on Analysis •

Shadows cast on a dwelling by eaves and trees

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Shadows cast in a stadium from stand and lighting towers Reflection study showing reflections from building onto street and adjacent buildings

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Description For a given mean daylight factor this method calculates from 1. the reflectance of the room surfaces, 2. the room dimensions, 3. the glazing parameters (transmission, framing factor, and dirt-on-glazing factor), 4. and the type of rooflight with the geometric parameters of the light wells the necessary total rooflight area.

solar light factor SF2 as function of  distance from the window and window percentage (of  facade)

Properties of materials • Properties of  different materials which are used in buildings •  Their scattering property •  Their thickness ,reflection,perm eability,absorpt

Heating requirement and sunshine duration

Heating requirement and global radiation are inversely propertional to each other 

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ay g t actor approach

•  The DF is the standard recognised daylighting metric in any place in the World where there is an interest in daylighting.

• Reasons for the success of the DF approach: • •

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If the natural lighting is sufficient on an overcast day, it is likely to be more than adequate ade quate when the sun is shining. But ... a daylight factor optimised building admits as much light as possible, therefore the ideally daylit building would be fully glazed! This is clearly in contrast c ontrast with comfort requirements. A densely overcast sky looks the same whichever wh ichever direction one faces -North, South, East or West. Therefore the effect of the orientation vanishes from the calculation. But ... the simplification introduced with the use of the daylight factor does not account for building location and orientation, season, time of day, direct solar penetration,

mate ase ynam c lighting simulation • •

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Input: 1) weather data, 2) 3D model, 3) sensor points Pre-process: calculation of daylight coefficients to save time. If dynamic daylighting systems are used, such as movable blinds, sun tracking systems, electrochromic glazing, etc., different sets of daylight coefficients need to be calculated. Simulation: coupling of daylight coefficients with climate data over the chosen time basis and occupancy profile. For dynamic systems, a control algorithm triggers the use of  the different set of daylight coefficients. Results: time series of illuminance and/or luminance (annual, seasonal, daily, etc ...) Post-process: time series can be plotted, and other indicators can be calculated (daylight autonomy,

Windows options

Static diffusing fabric blinds

Seasonally adjusted blinds, manual control

Automatic open/close roller  blinds

Automatic venetian blinds

Light level control -three luxlevel control that allows the slats to adjust to maintain light levels within a selected band width.

Fixed interstitial louvres

 Average Daylight Factor  •

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 The average daylight factor is the ratio between the mean illuminance in a space and that from an unobstructed sky externally expressed as a percentage. In calculation terms the sky is generally assumed to be the CIE overcast sky. It is measured or predicted on the working plane that for domestic buildings is assumed at 0.85m. There are two formulae that give an average daylight factor, Sumpner’s and the BRE average daylight factor formulae. Both are based on a ratio of the window area to the surface area of the room, with corrections for any obstructions, glass transmission and room reflectance.

BRE formula : DF = θTW/A ( 1-R2) Sumpner’s formula: DF = θTW/2A(1-R) θ is the angle of obstruction measured from the mid-point of the window T is the light transmission of glazing W is the window area A is the area of all the surfaces of the room

• Alternatively the average daylight factor can be calculated using a variety of computer programs which determine the daylight factor on predefined grid and take the average. It is clear that the latter method will give a more accurate result, but the former is particularly useful at an early design stage.

VARIOUS TEST ROOMS • Not only numerical but also visual information is included. This gives a fast understanding of the visual perception of daylight in rooms. A powerful simulation tool has been used to show the strong impact of simple modifications of basic daylighting design parameters like window size and placement. The study is not suited for thorough numerical analysis; it should rather be understood as design guide for architects and building designers in the early conception of a building. The study has been performed for Swiss conditions, thus some of the provided information is restriced to Swiss latitudes, climates, and regulations.

Application Example

Daylight performance at the lower floors of high-rise residential development was very poor. VDF of  approximately 6% to 8% were recorded. The room average daylight factor for habitable rooms was typically in the order of 0.2%, whilst kitchens located at the rear end of a deep re-entrant recorded close to 0.0% - hardly ha rdly any light at all. (F

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Daylight performance of  a typical residential unit in high density sites in Hong Kong. Daylight Factor at the rear of the space is about 0.2%

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(Right), the window facing into a narrow space and obstructed by an opposing building is allowed by the building regulations. (Left), the window facing directly a high block but with an open aspect on its left is not permitted.

Some key problem areas were identified. Whilst satisfying the building regulations, these windows do not provide adequate daylight to their respective interior spaces. (A) Windows placed inside deep re-entrant (local term for deep recesses from the main façade). (B) Windows facing into narrow streets where no height restriction in force. (C) Windows placed in the ‘large’ light well formed by surrounding building blocks. (D) The misuse of the regulatory Rectangular Horizontal Plane (RHP). This results in tight spaces being formed between building blocks. (E) Windows not properly positioned in the space.

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simulated daylight performance At the same time, daylight performances of around 6000 windows of the 12 housing estates were computed using simulated results (Figure 5). Lightscape was used as it has been noted previously that it could cope with high-density conditions reasonably well. From the computed results, daylight availability of the windows of  each of the residential unit that were user surveyed was identified and coded into the survey forms. The performance data of each of the space and the associated user responses

User satisfaction vs. simulated daylight performance

 TOWARDS A NEW DESIGN AND REGULATORY METHOD •

How to formulate a simple method for f or daylight design and building regulations is the next task. It is important to strike for “simplicity” and “reasonable accuracy” at the same time. • A method based on a two-dimensiona t wo-dimensionall “the visible area /volume in front of the window” was first speculated – on a napkin during a dinner session! It was considered very similar in spirit to the existing regulatory Rectangular Horizontal Plan (RHP) requirements. The method was based on modifications a more accurate three-dimensional sky component overlay method developed by Tregenza. •  The new method, dubbed the Unobstructed Vision Area Method (UVA) is a simple method suitable for high-rise, h igh-rise, high-density development. The method is not fundamentally new. R G Hopkinson proposed similar offering before. The Unobstructed Vision Area (A) is

• [Take a cone of light φL+φR=100° φL+φ R=100° from the window, given a vertical obstruction angle of  θL=71°, the mathematical formula relating the horizontal area in front of the window (A) and the Height of the building (H) can be given here, k is a constant relating A with H2. ]

Ray-Tracing Techniques •  The ray-tracing technique determines the visibility of  surfaces by tracing imaginary rays of light from a viewer’s eye to the objects of a rendered scene. A centre of  projection (the viewer’s eye) and an arbitrary view plane are selected to render the scene on a picture plane. Thanks to the power of novel computer algorithms and processors, millions of light rays can be traced to achieve a highresolution rendered picture. • Originally developed for imaging purposes, some raytracing programmes (e.g., RADIANCE, GENELUX, and PASSPORT) were adapted and optimised for calculation of  daylighting within building spaces [Ward and Rubinstein 1988]. In this case, light rays are traced t raced until they reach the main daylight source, which is usually the sun position (clear and intermediate skies) or the sky vault (cloudy skies). Figure 6-3 illustrates the principle of ray tracing,

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Most daylighting and electric lighting calculation programmes currently use this backward ray-tracing technique (from the viewpoint to the source). A slightly different technique is used by some software to improve daylighting calculations, especially for clear sky conditions (with sun). A forward rather than backward ray-tracing technique is used by the GENELUX programme to follow rays from the light source to a scene.

 The principal features of the ray-tracing technique for all types of light calculations are the following: • the method accounts for every optical phenomenon that can be analytically expressed by physical equations; e quations; • the method can consider specular materials, like window panes and glossy surfaces;

Sky Simulators

View of the EPFL scanning sky simulator 

the BRE mirror sky (UK),

conclusion • Required setbacks should be given in highrise buildings • Proper planning should be done so as to get sufficient amount of daylight • Where it is not possible to give windows or any other opening we must provide skylight if possible • Openings should be sufficient to light the room • At hot regions we should provide proper arrangements at the openings so as to

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