report on passive solar design

7/28/2019 Report on Passive Solar Design

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PASSIVE SOLAR DESIGN .Ar. Vaishali Muneshwar

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PASSIVE SOLAR DESIGN.

What is PASSIVE Design? is based upon climate 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 to use of suns energy for heating and cooling of living spaces.In this approach, building itself or some element takes advantage of natural energycharacteristics in materials and air created by exposure to sun. passive systems, have fewmoving parts, require minimal maintenance and require no mechanical systems.

Operable windows, thermal mass and chimneys are elements of passive design. Operable

windows- windows that can be opened. Thermal-mass- materials such as masonry andwater that store heat energy for extended time. Prevents rapid temperature fluctuations.Thermal chimneys create or reinforce effect hot air rising to induce air movement for coolingpurpose.

Passive design practiced throughout world and has been shown to produce buildings withlow energy costs, reduce maintenance and superior comfort. Key aspects include solarorientation, use of thermal mass and appropriate ventilation and window placement. Mosteffective 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 used in passive solar energy are thermal energy flowsassociated with radiation, conduction and natural convection. Sunlight striking on building,building materials reflect, transmit or absorb solar radiation, heat produced by sun causesair movement that can be predictable in designed spaces. Passive solar energy means thatmechanical 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


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

Strategies should be project specific

Passive solar systems rules of thumb:

Building should be elongated on an east-west axis. Buildings south face should receivesunlight between hours of 9.00 a.m. and 3.00p.m. (suntime) during heating season, Interiorspaces requiring most light and heating and cooling should be along the south face ofbuilding. Less used spaces should be located on the north. An open floor plan optimizespassive 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 gain, indirect gain and isolated gain.Goal of all passive solar heating systems is to capture suns heat within buildings elementsand release heat during periods when sun is not shining.


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DIRECT GAIN

In this system, actual living space is a solar collector, heat absorber and distribution system.South facing glass admits solar energy into house- strikes directly and indirectly thermalmass materials- such as masonry floors and walls.Direct gain systems utilize 60-75% of suns energy striking windows. Thermal mass floorsand 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.


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The direct gain system makes overt use of solar geometry to ensure that sun reaches thethermal mass in the winter, and that shading devices prevent solar access during the monthswhere cooling is the dominant issue.

INDIRECT GAIN

In indirect gain system, thermal mass is located between sun and living space. Thermalmass absorb sunlight and transfer it to living.space by conduction. Indirect gain systemutilize 30-45% of suns energy striking the glass adjoining thermal mass.

There are two types of indirect gain systems:1. Thermal storage wall systems (Trombe walls)2. Roof pond systems.

Thermal storage wall systems (Trombe Walls)

Thermal mass is located behind south glass in system. Operable vents at top and bottom ofthermal storage wall permit heat to convect from between the wall and glass into living

space.


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Trombe Wall with Vents


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


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Roof pond systems

Six to twelve inches of water contained on a flat roof. This system best for cooling in lowhumidity climates but modified to work in high humidity climates,

Water stored in large plastic or fibre glass containers covered by glazing and space below iswarmed 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 tosupport dead load.


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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 inhouse. Utilizes 15-30% of sunlight striking glazing toward heating adjoining living areas.

Sunrooms employ combination of direct and indirect gain system features. Sunlight enteringsunroom retained in thermal mass and air of the room. Sunlight brought into house byconduction through shared mass wall in rear of sunroom or vents that permit air betweensunroom and living space.

Use of south facing air collector to naturally convect air into storage area. These are passivecollectors. Collective air collectors located lower than storage areas so heated air generatedin collector rises into storage area and replaced by air from lower cooler section. Heat canbe released from storage area either by opening vents access storage by mechanicalmeans, or by conduction if storage is built into house. Sunroom provide additional usablespace to house and plants can be grown effectively.

Convective air collector are more complex. Drawback in this area, where space heating isless of a concern than in colder regions where system used longer.

SUNSPACE


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What is a Convective Air Loop??

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


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Hybrid System -- A predominantly passive solar heating system which utilizes an activecomponent, such as a fan, to force heat from one location to another.

Rockbed -- a heat storage component consisting of an enclosed volute of rocks (fist-sized)with a plenum at each end. During the charging cycle, warm air from the solar collector iscirculated through the rocks, warming them. During the discharge cycle, cool room air iscirculated through the rocks where it is heated and returned to the room.


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PASSIVE SOLAR COOLING

Passive cooling is the counterpart of passive heating. While passive heating is driven only bythe sun, passive cooling can use various heat sinks and climate influences to decrease heat.

1. Ventilative Cooling2. Dehumidification3. Evaporative Cooling4. Radiative Cooling5. Mass effect Cooling


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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 CoolingVENTILATION AND AIR MOVEMENT

Functions of ventilation: Natural ventilation and air movement could be considered underheading of structural controls as it does not rely on any form of energy supply ormechanical installation.It has 3 different functions

Supply of fresh air

Convective cooling Physiological cooling

Radial difference in form of provisions of 1,2 and 3. First 2 functions as ventilation but lastone as air movement.

SUPPLY OF FRESH AIR:

Requirement of fresh air supply governed by type of occupancy, number and activity ofoccupants and by nature of any processes carried out in space. Requirement may bestipulated by building regulations and advisory codes or in number of air changes per hour,but applicable only to mechanical installations. Can be taken as useful guides for naturalventilation faced and solutions less and not workable. Provision of permanent ventilators i.e.

of openings which cannot be closed, compulsory with grills or air-bricks built in wall orincorporated with windows.

Size of openable windows on floor area/ volume of room. Aim of these rules to ensureventilation but rigid application often inadequate to ensure satisfactory performace principleinvolved must be understood.

You have to not only provide openings but also, locate them correctly, make sure theyare large enough, for this to work properly!!

CONVECTIVE COOLING

Exchange of indoor air with fresh air out-door provide cooling, if latter at lower temperaturethan indoor air. Moving air acts as heat carrying medium. Useful in moderate or coldclimates.

PROVISION FOR VENTS; STACK EFFECT.

Ventilation, i.e., both supply of fresh air and convective cooling, involves slow movement ofair and can be either thermal or dynamic wind. Stack Effect relies on thermal forces, set upby difference between indoor and outdoor air. When air is still it can occur through an open


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window, warmer and lighter indoor air will flow out at top and cooler, denser out-door air willflow in at bottom. Special provision made for it in form of ventilating shafts.

Higher the shaft, more is cross-sectional area with greater temperature difference, moremotive force, therefore more air will be moved.

Motive force is stack pressure x cross sectional area (force-Newtons, area- m),Ps = Stack pressure

Therefore Ps = 0.042 x h x T

Where Ps= stack pressure in N/m

h = height of stack in m.T = difference in temperature in C.

0.042 = constant in N/m,C.

Such shafts used for baths, toilets, etc. most satisfactory under winter conditions whentemperature difference enough to generate air flow.

PHYSIOLOGICAL COOLING:

Movement of air past skin surface accelerate heat dissipation in 2 ways:Increasing convective heat lossAccelerating evaporation.

For this to take place, higher temperature tolerated with air velocity are required. In lowhumidities (below 30%) this cooling not great, as restricted evaporation even with very lessair 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 neededwhere 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 air movements. Only natural force canbe relied on is dynamic effect wind. When creation of air movements indoor is the aim,designer should capture as much of wind available as possible.

Negative control- when wind is too much, easy is window and openings can be shut.Local conditions can change wind patterns on micro-climatic scale. In same way as wind isgenerated by pressure difference so an air flow through building is result of a pressuredifference between 2 sides.

Air although light has a mass (1.2kg/m) and as it moves, has momentum- product of massand its velocity (kgm/s). this is vector quantity, which can be changed in direction or inmagnitude only by other force. Moving air on striking an obstacle (building), will slow downair flow but will exert pressure on obstructing surface.

This pressure is proportionate to air velocity, as expressed by:

Pw = 0.612 V

Where Pw = wind pressure in N/m


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V = wind velocity in m/s

0.612 = constant = Ns/m

This slowing down process effects a roughly wedge-shaped mass of air on windward side ofbuilding, which in turn diverts rest of air flow upward and sideways. A separation layer isformed between stagnant air and building on one hand and laminar air flow on other.Laminae air flow itself may be accelerated at obstacle, as area available for flow is narrowedby obstacle. At separation layer, due to friction, upper surface of stagnant air is movedforward, turbulence or vortex is developed.

A stagnant mass of air is formed on leeward side, but is at reduced pressure. It is notstagnant: a vortex is formed, movement is light and variable and after referred as windshadow. If building has an opening facing high pressure sone and another low pressurezone 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 onbasis of empirical values derived from measurements in actual buildings/ in wind tunnelstudies. Such empirical rules five useful guide to designwe in critical cases.


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Following factors can be isolated which effect indoor air flow:

a. Orientationb. External featuresc. Cross-ventilationd. Position of openingse. Size of openingsf. Controls of openings.

a) ORIENTATION: greatest pressure on windward side of building is generated whenelevation at right angles to wind direction, so greatest indoor air velocity received in thiscase.

Wind flow incident at 45 reduce pressure by 50% thus, designer must ascertain prevailingwind direction from wind frequency charts of wind roses and must orient his building to getlargest openings facing wind direction.

Wind shadow is less if building is perpendicular to wind flow and is greatest when building is

more than 45 to wind flow.


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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) EXTERNAL FEATURES: external features of building strongly influence pressure

build-up, eg: if air flow is at 45 to an elevation, a wing at down wind end or a projecting wind

of a L-shaped building can more than double the pressure created.

Funnelling effect (Venturi effect) can be created by upward projecting eaves. Any extensionof elevational area facing wind will increase pressure build up. If gap between 2 buildings isclosed by a solid walss, similar effect produced. Air velocity between free -standing trunks oftrees with large crowns can be quite substantially.

a b b


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WING WALLS

c) CROSS VENTILATION: In absence of an outlet opening or with a full partition therecan be no effective air movement through a building when in case of strong winds. With awindward opening and no outlet, a pressure similar to that of front of building will e builtindoors, make conditions even worse, increase discomfort. In some cases, oscillatingpressures changes, buffering, can occur, produced by opening on leeward sid e with noinlet.


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d) POSITION OF OPENING: Air movement must be directed at body surface. Means,that air movement ensured through space mostly used by occupants: through living zone,(upto 2m high). Difference in position of inlet openings create a more difference in flow of airthrough room.

e) SIZE OF OPENINGS: best arrangement in full openings on both sides, withadjustable sashes or closing devices which assist in channelling air flow in requireddirection, following change of wind.

f) CONTROLS OF OPENINGS: Sashes, canopies, louvers and other elementscontrolling openings, also influence indoor air flow pattern. Mosquito nets, fly screens, etc.reduce velocity of air. The percent of reduction in velocity may depend on material of there

screens.

AIR MOVEMENT AND RAIN: Exclusion of rain not a different task and making provision forair movement does not create any particular difficulties, between 2 together andsimultaneously is no means easy.

Opening of windows during periods off wind driven rain admit rain and spray; while closingwindows create intolerance conditions indoors. Conventional tilted louvre blades areunsatisfactory:


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1) Strong wind will drive rain in, even upwards through louvers.2) Air movement will be directed upwards from living zone.

Verandah and large roof overhands are perhaps best traditional methods of protection.

AIR FLOW AROUND BUILDINGS:

Effect of tall blocks mixed development has been examined in experiments conducted byBuilding Research Station at Garston. Air stream separates on face of a tall block, part of itmoving up and over roof part of it down, form a large vortex, leading to very high pressurebuild-up. An increased velocity found at ground level at sides of tall block could serve asuseful purpose in climates, if tall block not fully closed but permeable to wind-effect would bereduced.

a) If in rural setting in open country, single storey buildings placed rows in a grid-ironpattern, stagnant air zones leeward from first row overlap with second. Spacing ofsix times of building height is necessary to ensure adequate air movement for secondrow. Five times height rule for spacing not satisfactory.

b) In similar setting, buildings are staggered in a checker-board pattern, flow field is

much more uniform, stagnant air zones almost eliminated.

VENTILATION AND OPERABLE WINDOWS.

Primary strategy for cooling buildings without mechanical assistance (passive cooling) in hothumid climates to employ natural ventilation.

In Austin area, prevailing summer breezes are from south and southeast. This matches withincreased glazing on south side needed for passive heating, making it possible to achievehelpful solar gain and ventilation with following strategies.

Place operable window on south exposure

Casement windows offer best air will be directed to ceiling. Awing windows offer best

rain protection and perform better than double hung windows, If a room can have windows on only one side, use two widely spaced windows

instead of one.

Wing Walls: Wing walls-vertical solid panels placed along side of window perpendicular towall on windward side of house.Wind walls accelerate natural wind speed due to pressure difference created by wind wall.

Thermal chimney (Stack ventilation): A thermal chimney employs convective currents todraw air out of a building. By creating warm or hot zone within exterior exhaust outlet, aircan be drawn into house ventilating structure.

Sunrooms designed to perform this function. Excessive heat generated in south facing

sunrooms during summer can be vented at top. With connecting lower vents to living spaceopen along with windows on north side, air is drawn through living space to be exhaustedthrough sunroom upper vent.

Thermal chimney constructed in a narrow configuration with heated black metal absorber oninside behind a glazed front that can reach high temperature and be insulated from house.Chimney must terminate above roof level. A rotating metal scoop at top opens opposite thewind will allow heated air to exhaust without being overcome by prevailing wind. Thermalchimneys effects can be integrated into house with open stairwells and atria.


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Other Ventilation strategies:

Make outlet openings slightly larger than the inlet openingsPlace the inlets at low to medium heights to provide airflow at occupant levels in room inletclose to wall result in air washing along the wall. Centrally located inlets for air movementin centre areas of room.Window insect screen decrease velocity of slow breezes more than stronger breezes.Screening a porch will not reduce air speeds.

Night ventilation done at rate of 30 air changes per hour or greater.Mechanical ventilation required to achieve this. High mass houses cooled with nightventilation providing fabric furnishings minimum. Keep high mass house closed during dayand opened at night.

Stack Effect (i.e. warm air rises):


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COURTYARD EFFECT

Due to incident solar radiation in a courtyard, the air gets warmer and rises. Cool air from the ground level flows through the louvered openings of rooms

surrounding a courtyard, thus producing air flow.At night, the warm roof surfaces get cooled by convection and radiation.

If this heat exchange reduces roof surface temperature to wet bulb temperature ofair, condensation of atmospheric moisture occurs on the roof and the gain due tocondensation limits further cooling.


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If the roof surfaces are sloped towards the internal courtyard, the cooled air sinks into thecourt and enters the living space through low-level openings, gets warmed up, andleaves the room through higher-level openings.However, care should be taken that the courtyard does not receive intense solarradiation, which would lead to conduction and radiation heat gains into the building.

DEHUMIDIFICATION: HUMIDITY CONTROL

Dehumidification only possible by mechanical means without this, in warm-humid climates,some relief is provided by air movement.

In hot-dry climates humidification of air may be necessary, associated with evaporativecooling. In these climates, buildings normally closed to preserve cooler air retained withinstructure of high thermal capacity, exclude sand and dust carries by winds. Some form of airsupply to building interior is necessary.

All these functions:

Controlled air supply

Filtering out sand supply: Evaporative cooling.

Humidification.

are served by a device wind scoop.Large intake openings capture air movement above roofs in densely built up areas. Waterseeping through porous pottery jars evaporates, some drips down onto charcoal placed on agrating, through which air is filtered. Cooled air assists downward movement, reversedstack effect.

In India, curtain made of cascas grass is hung in front of windows on windward side, this iswetted by throwing a bucket of water against it. Grass is highly absorptive and retainsmoisture for long time. Wind passing through loose textured mat curtain is cooled and

humidified. The desert cooler developed is a cube shaped frame, of 500 to 600 mm sides.Top and bottom are shallow tanks. Sides are covered with cascas mats. Top of whichimmersed in upper tank. Water seeps down through mat and collected in lower tank. Insidebox is an ordinary table fan, which blows air through cascas mat, cooling and humidifying it.

What is Evaporative Cooling?:

The exchange of sensible heat in the air for the latent heat of water droplets of wettedsurfaces. It may be used to:

cool the building (where wetted surfaces are cooled by evaporation), building air (cooled directly by evaporation or indirectly by contact with a surface

previously cooled by evaporation), or the occupants (where evaporation of perspiration cools the skin surface.)

Sensible heat is the dry heat in the air.Latent heat is the wet heat released into the air as water changes from liquid to vapour byevaporation or boiling.

Evaporative cooling lowers indoor air temperature by evaporating water. It is effective in hot and dry climate where the atmospheric humidity is low. In evaporative cooling, the sensible heat of air is used to evaporate water, thereby

cooling the air, which, in turn, cools the living space of the building. Increase in contact between water and air increases the rate of evaporation.


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The presence of a water body such as a pond, lake, and sea near the building or afountain in a courtyard can provide a cooling effect.

1. Ground cover2. Water sprinkler3. Insulated roof4. Shading trees5. Water trough

PASSIVE DOWN DRAUGHT COOLING Evaporative cooling has been used for many centuries in parts of the middle east,

notably Iran and turkey. In this system, wind catchers guide outside air over water-filled pots, inducing

evaporation and causing a significant drop in temperature before the air enters theinterior.

Such wind catchers become primary elements of the architectural form also.

Passive downdraught evaporative cooling is particularly effective in hot and dryclimates. It has been used to effectively cool the Torrent Research Centre inAhmedabad.


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WIND TOWER

In a wind tower, the hot air enters the tower through the openings in the tower, getscooled, and thus becomes heavier and sinks down.

The inlet and outlet of rooms induce cool air movement. In the presence of wind, air is cooled more effectively and flows faster down the

tower and into the living area. After a whole day of air exchanges, the tower becomes warm in the evenings. During the night, cooler ambient air comes in contact with the bottom of the tower

through the rooms. The tower walls absorb heat during daytime and release it at night, warming the cool

night air in the tower. Warm air moves up, creating an upward draft, and draws cool night air through the

doors and windows into the building. The system works effectively in hot and dry climates where fluctuations are high. A wind tower works well for individual units not for multi -storeyed apartments.

In dense urban areas, the wind tower has to be long enough to be able to catchenough air. Also protection from driving rain is difficult.

EARTH AIR TUNNELS Daily and annual temperature fluctuations decrease with the increase in depth below

the ground surface.


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At a depth of about 4 m below ground, the temperature inside the earth remainsnearly constant round the year and is nearly equal to the annual averagetemperature of the place.

A tunnel in the form of a pipe or otherwise embedded at a depth of about 4 m belowthe ground will acquire the same temperature as the surrounding earth at its surface.

Therefore, the ambient air ventilated through this tunnel will get cooled in summerand warmed in winter and this air can be used for cooling in summer and heating inwinter.

This technique has been used in the composite climate of Gurgaon in RETREATbuilding.

The living quarters (the south block of RETREAT) are maintained at comfortabletemperatures (approx. 20-30 degree Celsius) round the year by the earth air tunnelsystem, supplemented, whenever required, with a system of absorption chillerspowered by liquefied natural gas during monsoons and with an air washer during drysummer.

However, the cooler air underground needs to be circulated in the living space. Eachroom in the south block has a 'solar chimney; warm air rises and escapes throughthe chimney, which creates an air current for the cooler air from the undergroundtunnels to replace the warm air.

Two blowers installed in the tunnels speed up the process. The same mechanismsupplies warm air from the tunnel during winter.


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PASSIVE SPACE CONDITIONING USING EARTH AIR TUNNEL SYSTEM

What is Radiative Cooling?:

Transfer of heat from warmer surface to cooler surrounding surface (or outer space). It maybe used to cool the building (where warm building surfaces radiate heat to the sky) or to coolthe people (where the warm skin radiates heat to the cooler building surfaces -- to the coolwalls of an underground building, for example.

Earth Berming used to cool buildings


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Green roof on the Vancouver Public Library


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ROOF SPRAYS

What is Mass Effect Cooling?:

The use of thermal storage to absorb heat during the warmest part of the day and release itduring a cooler part. Night flushing, where cooler air is drawn through a building to exhaustheat stored during the day in massive floors and walls is an example of daily-cycle-mass-effect-cooling.A good strategy to couple with direct gain passive solar systems that will t end to absorb heatfrom its thermal mass component during the day of hot cycles.


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PASSIVE SOLAR STRATEGIES : LIGHTING

Lighting or illumination deliberate application of light to achieve practical or aesthetic effect.Lighting includes artificial light sources such as lamps and light fixtures as well as naturalillumination by capturing daylight.

Daylighting (windows, skylights or light shelves)used as main source of light during daytimein buildings. This can save energy compared with artificial lighting, represents majorcomponent of energy consumption in buildings.

Proper lighting can enhance task performance,improve appearance of an area and havepositive physiological effects on occupants.

Lighting Strategy General lighting

Use low levels of illumination for the general areaUse efficient fixtureUse affective control system

Task lightingUse higher levels of illumination at work stations

The combined strategies results in a much lower watts / sq.ft. figure.

Daylighting

Daylighting practise of placing windows or other openings and reflective surfaces so thatduring the day natural light provides effective internal lighting.Artificial lighting energy use can be reduced by installing fewer electric lights becausedaylight is present or switching electric lights automatically in response to presence of

daylight- process known as Daylight Harvesting.

Amount of daylight received in an internal space can be analysed by undertaking a daylightfactor calculation. Use of computers and proprietary industry software such as Radianceallow architects or engineer to quickly undertake complex calculations to review benefit of aparticular design.

DaylightingThe Challenges:

1. Using sunlight without over heating2. Getting light to the interior of the space

Window

Windows most common way to admit daylight into space. Vertical orientation that theyselectively admit sunlight and diffuse daylight at different times of day and year.Windows on multiple orientations combined to produce right mix of light for building,depending on climate and latitude. These are three ways to improve amount of lightavailable from a window.

Place window close to a light coloured wall


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Slant sides of window openings so inner opening is larger than outer opening

Use a large light coloured window sill to project light into room

Different types and grades of glass and different window treatments can also effect amountof light transmission through the windows.

Glazing Glazing properties

U value pertains only to conduction has not affect on direct radiation SHGC percentage of solar energy allowed through the glass

Glazing options Clear single pane high SHGC .90 Clear insulated glass high SHGC .85 Heat absorbing (tinted) moderate SHGC .60 Reflective glass low SHGC .35

Clear Heat absorbing

Reflective


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South facing glass must: limit the quantity of light to avoid over heating. Avoid direct beam radiation reaching the building interior. Diffuse the light.

CLERESTORY WINDOWS

Another important element is creating daylighting is use of clerestory windows. These arehigh, vertically-placed windows, used to increased direct solar gain when oriented towardsequator. Case of a passive solar house, clerestories may provide a directly light path topolar-side rooms that would otherwise be not illuminated. Clerestories can be used to admitdiffuse daylight that illuminates a space such as a classroom or office, walls placed so as toreflect indirect light to interior areas where it is needed. Method has advantage of reducingdirectionality of light to make it softer and more diffuse, reducing shadows.


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SKYLIGHTS

Skylight is any horizontal window, placed at roof of building, often used for daylighting whitetranslucent acrylic is a Lambertian Diffuser transmitted light transmitted light is perfectlydiffused and distributed evenly over affected areas.

Skylights admit more light per unit area than windows and distribute more evenly over aspace.

Optimal area of skylights varies according to climate, latitude and characteristics of skylight,but is 4-8% of floor area. Thermal performance of skylight is affected by stratification i.e.tendency of warm air to collect skylight wells, which in cold climates increases rate of heatloss.

Poorly constructed or installed skylights may have leaking problems and single panedskylights may weep with condensation. Using modern designs with proper installation willeliminate issues with leaks and provide greater energy efficiency.

Lower winter angles = less light

Higher summer angles = more heat

LIGHT SHELVES

Light shelves are an effective way to enhance lighting from window, this effect beingobtained by placing a white or reflective metal light shelf outside the window. Usuallywindow protected from direct summer season sun by a projecting eave. The light shelfprojects beyond shadow created by eave and reflects sunlight upward to illuminate the

ceiling. This reflected light can contain little heat content and reflective illumination fromceiling will typically reduce deep shadows, reducing need for general illumination.Light shelves made of an extruded aluminium chasis system and aluminium composite panelsurfaces. Extruded components can be painted or anodized and they are all field fabricatedand assembled from stock lengths.


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Light shelves used in high-rise and low rise office buildings, as well as institutional buildings.

LIGHT TUBES

Light tubes also called solar tube which is placed into a roof and admits light to a focussedarea of interior. Resemble recessed ceiling light fixtures. Do not allow as much heattransfer as skylights because they have less surface area.

TUBULAR DAYLIGHTING DEVICES (TDDs)

Use modern technology to transmit visible light through opaque walls and roofs. Tube ispassive component consisting of reflective interior coating or a light conducting fibre opticbundle. It is frequently capped with a transparent, roof -mounted dome light collector andterminated with a diffuser assembly that admits daylights into interior spaces and distributesavailable light energy evenly.It is more energy efficient than skylight since less energy escapes from interior due to lesssurface area.


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ATRIA / LIGHT WELLS

SAWTOOTH ROOF

Another roof-angled glass is a saw tooth roof sawtooth roof have vertical roof glass facingaway from equator side of building to capture diffused light. Angled portion of glass-supportstructure is opaque and well insulated with cool roof and radiant barrier. Sawtooth roofslighting concept partially reduces summer solar furnace skylight problem, with significantundesirable heat transfer.


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HELIOSTATS

Use of heliostats, mirrors which are moved automatically to reflect sunlight in a constantdirection as sun moves across sky, is gaining popularity as an energy-efficient method oflighting. Heliostat used to shine sunlight directly through a window or into any arrangementof optical elements, that distribute light where it is needed.


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SMART GLASS

Glass of materials that can be switched between a transparent, reflective or retro-reflective.Switching is done by applying an electric voltage to material or by performing somemechanical operations.4 types of glazing are studies for their dynamic performance (glare, solar control andvisibility)

ELECTROCHROMIC GLASS

Is glazing that changes its opacity depending on amount of sunlight being received. This istested for its light and heat control.

PHOTOVOLTAIC GLASS

Has dual function of providing shading and generating power at same time. This is beingtested for its efficiency, impact on view, shading, heat absorption and re-radiation.

DOUBLE GLAZED UNIT (DGU)

With internal operable glass is studied for its impact on view, shading and heat absorption.

These consist of blinds between glass which can be turned up during strong sunlight.Doubling of glazing used in all air-conditioned areas. Single glazing used in classrooms andschool halls.

FIBRE OPTIC CONCRETE WALLS

Another way to make secure structural concrete well translucent is to embed optical fibre cables in it. Daylight can then pass directly through solid-concrete wall. LiTraCon trademarkfor translucent concrete building material. Light Transmitting Concrete ( Li Trs Con).


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Technical data sheet from manufacturer says the material is made of 96% concrete and 4%by weight of optical fibres. Developed in 2001 by Architect Aron Lononczi.

SOLARIUMIn well designed isolated solar gain building with solarium, sunroom, greenhouse, etc. thereis glass on southern side. A large area of glass can be added between sunroom and interiorliving quarters.Low-cost high-volume product ratio door safely glass inexpensive way to accomplish thisgoal. Doors used to enter a room, should be opposite sunroom interior glass. Hallsminimised with open spaces used instead. Drapes over interior glass used to controllighting. They can be automated with sensor-based electric motor control -aware ofoccupancy, daylight, interior temperature and time of day.

To help distribute sunroom daylight to the sides of rooms that are farthest from the sun side,inexpensive ceiling-to-floor mirrors can be used.


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DAYLIGHTING CONCEPTS

It is important for daylighting design process to involve integration of many disciplinesincluding mechanical, electrical and lighting.Design team members needed to be brought into process early to ensure daylightingconcepts and ideas carried throughout the project.

report on passive solar design

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