Report on Passive Solar Design

PASSIVE SOLAR DESIGN. What is PASSIVE Design? is based upon upon climate climate considerations considerations attempts to control comfort (heating and cooling) without consuming fuels uses the orientation of the building to control heat gain and heat loss uses the shape of the building (plan, section) to control air flow uses materials to control heat maximizes use of free solar energy for heating and lighting maximizes use of free ventilation for cooling uses shade (natural or architectural) to control heat gain • • • • • • • •

Passive solar design refers refers to use of sun’s energy for heating and cooling of living spaces. In this approach, building itself or some element takes advantage of natural energy characteristics in materials materials and air created created by exposure to sun. passive systems, have few moving parts, require minimal maintenance and require no mechanical systems. Operable windows, windows, thermal thermal mass and chimneys are elements of of passive design. design. Operable windowswindows- windows windows that can be opene opened. d. ThermalThermal-massmass- material materials s such such as mason masonry ry and and water that store heat heat energy for extended time. Prevents rapid temperature temperature fluctuations. Thermal chimneys create or reinforce reinforce effect hot hot air rising to induce air movement for cooling purpose. Passive design practiced throughout throughout world and and has been shown shown to produce buildings with with low energy costs, reduce maintenance and superior comfort. Key aspects aspects include include solar  solar  orientation, use of thermal mass and appropriate ventilation and window placement. Most effective designs based on specific understanding of buildings sites wind patterns, terrain, vegetation, solar exposures and other factors. Passive Solar Design: Introduction: Solar Energy is a radiant heat source causes natural processes upon which all life depends. Basic natural processes that are are used in passive solar solar energy are thermal energy flows flows associated with radiation, radiation, conduction and natural natural convection. Sunlight striking on building, building, building materials reflect, reflect, transmit or absorb solar radiation, radiation, heat produced produced by sun causes air movement that can be be predictable in designed designed spaces. Passive solar energy means means that mechanical means are not employed to utilise solar energy. Basic Design Strategies • • • • • • • • • • • •

Insulation Infiltration Control Shading Glazing Ventilation Lighting Lighting Controls Day Lighting Evaporative Cooling Thermal Mass Surface condition Passive Solar Heating

PASSIVE SOLAR DESIGN ………………………………………….Ar. ………………………………………….Ar. Vaishali Muneshwar  Muneshwar 

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Don’t assume a strategy is right for every building  A nightclub will not benefit fro m daylighting Buildings located along the expressway may not want natural ventilation Evaporative Evaporative cooling is not effective effective in the south Shading is not important in areas areas dominated dominated by overcast skies • • • •

Strategies should be project specific

Passive solar systems rules of thumb: Building should should be elongated on an east-west east-west axis. Buildings Buildings south face should should receive sunlight between between hours of 9.00 a.m. and and 3.00p.m. (suntime) (suntime) during during heating season, season, Interior  Interior  spaces requiring most light and heating and cooling should be along the south face of  building. Less used spaces should be located on the north. An open floor plan optimizes passive system operation. Use shading to prevent summer sun entering the interior.

PASSIVE SOLAR HEATING:

Two primary elements of passive solar heating are required: south facing glass thermal mass to absorb, store and distribute heat. • •

Three approaches to passives systems –Direct –Direct gain, indirect gain and isolated gain. Goal of all passive solar heating systems is to capture sun’s heat within building’s elements and release heat during periods when sun is not shining.

DIRECT GAIN In this system, actual living space is a solar collector, heat absorber and distribution system. South facing glass admits admits solar energy into into house- strikes directly directly and indirectly indirectly thermal thermal mass materialsmaterials- such as masonry floors floors and walls. Direct gain gain systems systems utilize utilize 60-75% 60-75% of sun’s sun’s energy striking striking windows. windows. Thermal Thermal mass floors floors and walls are functional parts. Also possible to use water containers inside to store heat. There must be an expanse of south-facing glass and enough thermal mass, strategically located in a space for heat absorption and storage.

The direct gain system makes overt use of solar geometry to ensure that sun reaches the thermal mass in the winter, and that shading devices prevent solar access during the months where cooling is the dominant issue. INDIRECT GAIN In indirect gain system, thermal mass is located between between sun and living space. Thermal mass absorb sunlight and transfer it to living.space by cond uction. Indirect gain system utilize 30-45% of sun’s energy striking the glass adjoining thermal mass. There are two types of indirect gain systems: 1. Therma Thermall storage storage wall wall system systems s (Trombe (Trombe walls) walls) 2. Roof Roof pond pond syst system ems. s. Thermal storage storage wall systems systems (Trombe (Trombe Walls) Walls) Thermal mass is located behind south glass in system. Operable vents at top and bottom of  thermal storage wall permit heat to convect from between the wall and glass into living space.

Trombe Wall with Vents

Whether or not a wall has flaps, and flaps that automatically close off when the air direction reverses, becomes a critical issue in making sure that preheating of the room occurs in the morning hours.

Roof pond systems Six to twelve inches of water water contained on a flat roof. This system best for cooling in low humidity climates but modified to work in high humidity climates, Water stored in large plastic or fibre glass containers containers covered by glazing and space below is warmed by radiant heat from warm water above, require elaborate drainage systems, movable insulation to cover and uncover water at appropriate times and structural sys tem to support dead load.

ISOLATED GAIN Isolated gain system has integral parts separate from main living area of a house, Examples: sunroom and a convective loop through an air collector to a storage system in house. Utilizes 15-30% of sunlight striking glazing toward heating adjoining living areas. Sunrooms employ employ combination combination of of direct and indirect gain system system features. Sunlight Sunlight entering entering sunroom retained in thermal mass and air of the room. Sunlight brought into house by conduction through shared mass wall in rear of sunroom or vents that permit air between sunroom and living space. Use of south facing air collector to naturally convect air into storage area. These are passive collectors. Collective air collectors located lower lower than storage areas so heated air generated in collector collector rises into storage storage area and and replaced replaced by air from from lower lower cooler section. section. Heat c an be released from storage area either by opening vents –access storage by mechanical means, or by conduction conduction if storage storage is built into into house. Sunroom – provide provide additional additional usable usable space to house and plants can be grown effecti effectively. vely. Convective air collector are more complex. Drawback in this area, where where space heating is less of a concern than in colder regions where system used longer. SUNSPACE

What is a Convective Air Loop?? Convective Convective Air Loop -- a passive solar heating heating system that consists consists of a solar collector and a thermal storage mass (usually a rockbed) isolated from the living spaces. Air is used to transfer heat from the collector to the storage and the living spaces.

Hybrid System -- A predominantly passive solar heating system which which utilizes an active component, such as a fan, to force heat from one location to another. Rockbed -- a heat storage component component consisting of an enclosed volute volute of rocks (fist-sized) with a plenum at each end. During the charging cycle, warm air from the solar collector is circulated through the rocks, warming them. During the discharge cycle, cool room air is circulated through the rocks where it is heated and returned to the room.

PASSIVE SOLAR COOLING

Passive cooling is the counterpart of passive heating. While passive heating is driven only by the sun, passive cooling can use various heat sinks and climate influences to decrease heat. 1. Venti Ventila lati tive ve Cooli Cooling ng 2. Dehu Dehum midif idifiicati cation on 3. Evap Evapora orati tive ve Cool Cooling ing 4. Radi Radiat ativ ive e Cool Coolin ing g 5. Mass Mass effec effectt Cool Coolin ing g

These design strategies reduce heat gains to internal spaces. • • • • • • • •

Natural Ventilation Shading Wind Towers Courtyard Effect Earth Air Tunnels -Evaporative Cooling Passive Down Draught Cooling Roof Sprays

Ventilative Cooling VENTILATION AND AIR MOVEMENT Functions of ventilation: Natural ventilation and and air movement could be considered under  under  heading of ‘structural controls’ as it does not rely on any form of energy supply or  mechanical installation. It has 3 different different functio functions ns Supply of fresh air  Convective cooling Physiological cooling • • •

Radial difference in form of provisions provisions of 1,2 and 3. First 2 functions as ‘ventilation’ but last one as ‘air movement’. SUPPLY OF FRESH AIR: Requirement of fresh air supply governed by type of occupancy, number and activity of  occupants and by nature nature of of any processes processes carried carried out in space. Requirement Requirement may be stipulated by building regulations regulations and advisory codes or in number number of air changes per hour, but applicable only to mechanical mechanical installations. Can be taken as useful guides guides for natural ventilation faced and solutions less and not workable. workable. Provision of permanent ventilators ventilators i.e. of openings which cannot be closed, compulsory with grills or ‘air-bricks’ built in wall or  incorporated with windows. Size of openable windows windows on on floor area/ volume volume of room. Aim of these rules to ensure ventilation but rigid application often inadequate to ensure satisfactory performace principle involved must be understood.  You have to not only provide provide openings but also, also, locate them correctly, correctly, make sure they are large enough, for this to work properly!! CONVECTIVE COOLING Exchange of indoor air with fresh air out-door provide cooling, if latter at lower temperature than indoor air. Moving air acts as heat carrying carrying medium. medium. Useful in moderate or cold climates. PROVISION FOR VENTS; STACK EFFECT. Ventilation, i.e., both supply of fresh air and convective cooling, involves slow movement of  air and can be either either thermal thermal or dynamic wind. wind. Stack Effect relies on thermal forces, set up by difference between between indoor and outdoor air. When air is still it can occur through through an open

PASSIVE SOLAR DESIGN ………………………………………….Ar. ………………………………………….Ar. Vaishali Muneshwar  Muneshwar 

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window, warmer and lighter indoor air will flow out at top and cooler, denser out-door air will flow in at bottom. bottom. Special provision made for it in form of ventilating shafts. Higher the shaft, more is cross-sectional area with greater temperature difference, more motive force, therefore more air will be moved. Motive force is ‘stack pressure’ x cross cross sectional area (force-Newtons, (force-Newtons, area- m ²), Ps = Stack pressure Therefore Ps = 0.042 x h x • T Where Ps= stack pressure in N/m ² h = height height of stack stack in m. m. • T = difference in temperature in °C. 0.042 = constant in N/m ²,°C. Such shafts used for for baths, toilets, etc. most satisfactory under winter conditions when when temperature difference enough to generate air flow. PHYSIOLOGICAL COOLING: Movement of air past skin surface accelerate heat dissipation in 2 ways: Increasing convective heat loss  Accelerating evaporation. evaporation. For this to take place, higher temperature temperature tolerated with with air velocity are required. required. In low humidities (below 30%) this cooling cooling not great, as restricted evaporation evaporation even even with with very less air movement. In high pressure (> 85%) cooling effect is restricted as higher pressure prevents evaporation, but greater velocities (> 1.5 to 2m/s) have some effect. Most significiant in medium humidities (35-60%) cooling by air movement is most needed where there are no other forms of heat dissipation available, when air as warm as skin, surrounding surface also at similar temperature. PROVISION FOR AIR MOVEMENT: WIND EFFECTS Thermal forces rarely sufficient to create appreciate appreciate air movements. Only ‘natural’ force can be relied on is dynamic effect wind. wind. When creation of air air movements indoor is the aim, designer should capture as much of wind available as possible. Negative control- when wind wind is too much, much, easy is window and openings openings can be shut. Local conditions can change wind wind patterns on micro-climatic scale. In same way as wind is generated by pressure difference so an air flow through building is result of a pressure difference between 2 sides.  Air although light has a mass (1.2kg/m³) and as it moves, has momentummomentum- product of mass mass and its velocity (kgm/s). this is vector quantity, which which can be changed changed in direction or or in magnitude only by other force. force. Moving air on striking an obstacle (building), will will slow down air flow but will exert pressure on obstructing surf ace. This pressure is proportionate to air velocity, as expressed by: Pw = 0.61 0.612 2 V² Where Pw = wind pressure in N/m ²

PASSIVE SOLAR DESIGN ………………………………………….Ar. ………………………………………….Ar. Vaishali Muneshwar  Muneshwar 

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V = wind velocity in m/s 0.612 = constant = Ns²/m• This slowing slowing down process effects effects a roughly wedge-shaped mass of air on windward windward side of  building, which which in turn turn diverts rest of air air flow upward and sidew sideways. ays. A separation separation layer layer is formed between between stagnant air and building building on one hand and laminar laminar air flow on other. Laminae air flow itself may be accelerated at obstacle, as area available for flow is narrowed by obstacle. At separation layer, due to friction, upper surface of stagnant air is moved forward, turbulence or vortex is developed.  A stagnant mass of air is formed on leeward side, but is at reduced pressure. It is not stagnant: a vortex is formed, movement is light and variable and after referred as ‘wind shadow’. shadow’. If building building has an opening facing facing high pressure sone sone and another another low pressure zone air movement will be generated through building.

AIR FLOW THROUGH BUILDINGS:  As no satisfactory and complete theory is available, air flow patterns can be predicted on basis of empirical values derived from measurements in actual buildings/ in wind tunnel studies. Such empirical rules five useful guide to designwe designwe in critical cases.

Following factors can be isolated which effect indoor air flow: a. b. c. d. e. f.

Orie Orient ntat atio ion n Exte Extern rnal al fea featu ture res s Cros Crosss-ve vent ntil ilat atio ion n Posi Positi tion on of of open openin ings gs Size Size of of open openin ings gs Cont Contro rols ls of open openin ings gs..

a) ORIENTATION: ORIENTATION: greatest pressure on windward side of building is generated generat ed when when elevation at right angles to wind direction, so greatest indoor air velocity received in this case. Wind flow flow incident incident at 45 45° reduce pressure by 50% thus, designer must ascertain prevailing wind direction from wind frequency charts of wind roses and must orient his building to get largest openings facing wind direction. Wind shadow is less if building building is perpendicular perpendicular to wind wind flow and is greatest when when building is is more than 45° to wind flow.

It may happen that optimum solar radiation and optimum orientation for wind do not coincide. In equatorial regions a N-S orientation would be preferred for sun but wind is east oriented. These may resolve contradictory requirements.

a

b

b

a