lecture 5 eea- sap, chennai

8/11/2019 Lecture 5 EEA- SAP, Chennai

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School of Architecture and Planning, Anna University Campus, Chennai

SOLAR PASSIVE DESIGNMETHODS

AD9022 ENERGY EFFICIENT ARCHITECTURE


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PASSIVE SHADINGDESIGN



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The most important characteristic of solar position is its seasonal

variation.

During summer the sun rises much earlier and sets much later and is in

completely different positions than in winter.

The aim of good shading design is to utilise these characteristic to

maximum advantage -typically to exclude as much solar radiation as

possible in summer whilst letting as much through as possible during

winter.



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The hourly path of the Sun through the sky in summer and Winter.



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The requirement for solar protection and/or solar gain will be determined

by the climate you are designing the building for.

In very cold or very warm climates, shading decisions are really

quite easy -you either want solar penetration or you don't.

In moderate mid-latitude climates however, there will be times

when solar radiation is of significant benefit as a heat source and

times when it could be a problematic due to glare and overheating.



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3.Look up Sun Position: (Use solar tables or a sun-path diagram toobtain the azimuth and altitude of the sun at each time on the cut-

off date.)

4.Calculate the Shadow Angles:(calculate the HSA and VSA at

each time).

5. Calculate Required Depth and Width:(using the Shadow Angle

methods, calculate the depth and width of the required shade on

each side of the window.)



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Reduction in yearly

beam radiation

incident on windows

due to shading.



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Of all elements in the building envelope, windows and other glazed areasare most vulnerable to heat gain or losses.

Proper location ,sizing and detailing of windows and shading form an

important part of the Bio-climatic design.

The important components of a window that govern these are glazing

systems and shading devices.



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Heat gain through window is determined by the overall heat loss co-efficient U- value (W/ m2 K).

Shading devices for windows thus moderate heat gains into the building.

In a low-rise residential building in Ahmedabad (hot and dry climate),

shading a window by 0.76 m horizontal deep chajja, can reduce the

maximum temperature by 4.6 deg C (47.7 to 43.1 deg C).

Moreover in the same climate this shading device can reduce the number

of uncomfortable hours in a year by 14%.



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Shading devices are of various types:

1. Moveable opaque (roller blind curtains, etc.) can be effective in

reducing solar gains but eliminate view and impede air movement.



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2. Louvres (adjustable or fixed) affect the view and air movement tosome degree.



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3. Fixed overhangs



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Relative Advantages and disadvantages of these shading devices:

Movable blinds or Curtains:

Block the transmission of solar radiation through glazed windows

especially on the east and west walls.

In the hot and dry climate the ambient air is hotter than the room air,

they help to reduce convective heat gain.

In warm, humid climates, where the airflow is desirable they impede

ventilation.

For air-conditioned buildings, where the flow of outside air is to be

blocked, they can reduce cooling load.



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Overhangs and Louvres:

Block that part of the sky through which sunlight passes.

Overhangs on south-oriented windows provide effective shading from

the high altitude sun.

An extended roof shades the entire north or south wall from the noon

sun.

East and West openings need much bigger overhangs, which may not bepossible and can be achieved by porticos or verandahs on these sides or

specially designed louvres to suit the building requirements.



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INSULATION



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Heat always flows from a hotter to a colder state, and it cannot be created or

destroyed.

In our homes we merely change the state of energy, or degrade it, when we burn

wood or heat a kettle.

Heat is a form of energy that is measured in the same units as any other type of

energy, in Joules



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Thermal insulation:

Insulation is of great value when a building requires mechanical heating or

cooling insulation helps reduce space conditioning loads.

Location of insulation and its optimum thickness are important.



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In hot climates, insulation is placed on the outer face (facing exterior) of the wallso that thermal mass of the wall is weakly coupled with the external source and

strongly coupled with the interior.



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Use of 40 mm thick expanded polystyrene insulation on walls and vermiculite

concrete insulation on the roof has brought down spaceconditioning loads of

the retreat building by about 15%.



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There are three different ways in which a wall can be insulated:

Resistive insulation.

This is what most of us think of as insulation. These are the bulk insulation

products, which include mineral wools, strawboard, wood-wool slabs, glass

Fibre products, kapok, wool and cellulose fibre. They also include

expanded and extruded polystyrene, polyurethane, urea formaldehyde,

vemiculite and perlite.

Used in Colder climates to maintain heat within the building.



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Reflective insulation.

This requires a highly reflective material, aluminium foil, to face a cavity across

which high levels of radiant heat are being transmitted. The foil reflects the radiant

energy back across the cavity, rather than absorbing it. This type of insulation will

not work if the face of the foil is touching the opposite wall.



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WALLS

Walls are a major part of the building envelope and receive large amounts of solar

radiation.

The heat storage capacity and heat conduction property of the walls are key to

meeting desired thermal comfort conditions.

The wall insulation methods can be based on the heating and cooling needs.

Appropriate thermal insulation and air cavities in walls can reduce heat

transmission into building, which is the primary aim in a hot region.



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AIR CAVITIES IN WALLS

Ventilated air does not reduce radiative heat transfer from roof to ceiling.

The radiative component of heat transfer may be reduced by using low emissivityor high reflective coating like aluminium foil on either surface facing the cavity.



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ROOF COOLINGTECHNIQUES



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The roof receives significant solar radiation and plays an important role in heat

gain/ losses, day lighting and ventilation.

Depending on the climatic needs, proper roof treatment is essential.

In a hot region, the roof should have enough insulating properties to minimizeheat gains



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Roof cooling techniques can help exploit ambient heat sinks selectively, so as to

contribute further, or more directly, to the cooling of buildings.

DESIGN GUIDELINES:

1.Green Roof.

2.Radiativecooling.

3.Reflective roofs.



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Roof cooling techniques can help exploit ambient heat sinks selectively, so as to

contribute further, or more directly, to the cooling of buildings.

1.Green Roof.



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Green Roof.



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2. Radiative Cooling .



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Other methods of roof Cooling:

Broken China mosaic can be used as top most layer in the roof for reflection of

incident radiation.



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A cover of deciduous plants or creepers can be provided . Evaporation from the

leaf surfaces will keep the spaces below cool.



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The entire roof surface can be covered with inverted earthen pots. It is also an

insulating cover of still air over the roof.



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Effective roof insulation can be provided by using vermiculite concrete. Eg.

RETREAT building at Gual Pahari, which has reduced roof conduction by 60%



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The roofs can be given effective insulation also by having vents and skylights.



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Any Questions?


lecture 5 eea- sap, chennai

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