How to Design & Develop Efficient Buildings which Consume Less Energy

How to Design & Develop

Efficient Buildings which Consume Less Energy

                            

             Green building design is a practical and climate conscious approach to building design. Various factors, like geographical location, prevailing climatic conditions, use of locally available and low embodied energy materials and design parameters relevant to the type of usage of the building are normally taken into consideration. Such an approach ensures minimum harm to the environment, while constructing and using the building. A look at traditional building techniques clearly shows that the concept of green or sustainable buildings has existed in our country for a long time. These buildings were generally made of locally available materials like wood, mud and stone and dealt with the vagaries of weather without using a large amount of external energy to keep the inhabitants comfortable.

               Buildings are among the greatest consumers of energy. Combining cutting edge energy efficient technologies with adaptation of practices used in vernacular architecture which used more of locally available materials and resources is necessary, especially for countries like India where per ca pita energy consumption is rising rapidly due to high economic growth. This will reduce our dependence on the fossil fuels which have to be imported and are depleting at an alarming rate.A green building uses minimum amount of energy, consumes less water, conserves natural resources, generates less waste and creates space for healthy and comfortable living.

              When a number of green buildings are located in proximity, they would create a green zone, providing much healthier environment and minimise heat-island effect. The ultimate aim will then be to create many such areas, which would help the towns and cities and therefore the nation in reducing total energy requirement and also the overall global carbon footprint.

Hot and Dry Climate

Hot and dry climatic regions are characterised by very high radiation levels, ambient temperatures and relatively low humidity.

The design objectives in such a climate should be aimed at:

(A) Resisting heat gain:

Heat gain can be resisted by:

·                 Decreasing the surface of the building exposed to the outside.

·                 Using materials that take a longer time to heat up.

·                 Providing buffer spaces between the living areas and the outside.

·                 Decreasing ventilation during daytime in the summers.

·                 Providing adequate shading devices.

(B) Promoting heat loss:

Some measures to promote heat loss are:

·                 Providing for ventilation of various appliances used.

·                 Increasing ventilation during cooler parts of the day or night time.

·                 Providing for evaporated cooling (e.g. roof surface evaporated cooling).

·                 Using earth coupling systems like earth-air pipes. 

General recommendations for the climate are:

(1) Site

(a) Landforms:

·                 Regions in this zone are generally flat and heat up uniformly.

·                 In case of an undulating site, constructing on the leeward side of the slope is preferred.

This protects the building from direct impact of hot winds which can be quite uncomfortable.

·                 Building in a depression is preferable in cases where ventilation is assured.

 (b) Water bodies

·                 Water bodies like ponds and lakes act as heat sinks and can also be used for evaporated cooling. They humidify the air and make it comfortable inside.

·                 Fountains and water cascades in the vicinity of a building also aid in cooling.

 (c) Street width and orientation

Streets must be narrow so that they cause mutually shade the buildings. Streets need to be oriented in the north-south direction to block solar radiation.

(d) Open spaces and built form:

·                 Open spaces such as courtyards and atria promote ventilation.

·                 They can be provided with ponds and fountains for evaporated cooling.

·                 Courtyards act as heat sinks during the day and radiate the heat back at night.

·                 Grass can be used as ground cover to absorb solar radiation and aid evaporated cooling.

·                 Earth berming can help lower the temperature and also deflect hot summer winds.

(2) Orientation and plan form

·                 An east-west orientation is preferred in hot and dry climatic regions. 

·                 South and north facing walls are easier to shade than east and west walls. During summer, the south wall with significant exposure to solar radiation in most parts of India, leads to very high temperatures in south-west rooms. Hence, shading of the south wall is imperative.

·                 The surface to volume (S/V) ratio should be kept as minimum as possible to reduce heat gains.

·                 Cross-ventilation must be ensured at night as ambient temperatures during this period are low.

(3) Building Envelope

(a) Roof

·                 Flat roofs or vaulted roofs are ideal in this climate. Nonetheless, a vaulted roof provides a larger surface area for heat loss compared to a flat roof.

·                 The material of the roof should be massive; a reinforced cement concrete (RCC) slab is preferred to asbestos cement (AC) sheet roof.

·                 External insulation in the form of mud phuska with inverted earthen pots is also suitable.

·                 A false ceiling in rooms having exposed roofs is favourable as the space between the two acts as a heat buffer. Thermal insulation over false ceiling further increases the buffer action.

·                 Insulation of roofs makes the buildings more energy efficient than insulating the walls.

·                 Evaporative cooling of the roof surface and night time radiative cooling can also be employed.

·                 In case of evaporative cooling, it is better to use a roof having high thermal transmittance.

(b) Walls

·                 In multi-storied buildings, walls and glazing account for most of the heat gain.

·                 The control of heat gain through the walls by shading, thus, becomes an important design consideration.

·                 A wall that transmits less heat is hence feasible.

(c) Fenestration

·                 In hot and dry climates, reducing the window area leads to lower indoor temperatures.

·                 More windows should be provided in the north facade of the building as compared to the east, west and south as it receives lesser radiation throughout the year

·                 All openings should be protected from the sun by using external shading devices such as chhajjas and fins.

·                 Moveable shading devices such as curtains and venetian blinds can also be used.

·                 Ventilators are preferred at higher levels as they help in throwing out the hot air.

·                 Since daytime temperatures are high during summer, the windows should be kept closed to keep the hot air out and opened during night-time to admit cooler air.

·                 The use of 'jaalis'(lattice work) made of wood, stone or RCC may be considered as it they allow ventilation while blocking solar radiation. Scheduling air changes (i.e. high ventilation rate at night and during cooler periods of the day, and lower ones during daytime) can significantly help in reducing the discomfort.

·                 The heat gain through windows can be reduced by using glass with low transmissivity.

(D) Colour and textures

·                 Change of colour is a cheap and effective technique for lowering indoor temperatures.

·                 Colours that absorb less heat should be used to paint the external surface.

·                 Darker shades should be avoided for surfaces exposed to direct solar radiation.

·                 The surface of the roof can be of white broken glazed tiles.

·                 The surface of the wall should preferably be textured to facilitate self shading.

Remarks

·                 As the winters in this region are uncomfortably cold, windows should be designed such that they encourage direct gain during this period.

·                 Deciduous trees can be used to shade the building during summer and admit sunlight during winter.

·                 Well-insulated and very thick walls give a good thermal performance if the glazing is kept to a minimum and windows are well-shaded.

·               In case of non-conditioned buildings, a combination of insulated walls and high percentage of glazing will lead to very uncomfortable indoor conditions as the building will tend to act like a green house with the insulated walls preventing the radiation from the windows from escaping into the environment.

·                 Indoor plants can be provided near the window, as they help in evaporative cooling and in absorbing solar radiation.

·                 Evaporative cooling and earth air pipe systems can be used effectively in this climate.

·                 Desert coolers are extensively used in this climate, and if properly sized, they can help in achieving comfort levels

Hot and Humid Climate

In hot and humid climatic regions, high temperatures are accompanied by very high humidity levels leading to immense discomfort. Cross ventilation is hence very essential here. Adequate shading measures are also necessary to protect the building from direct solar radiation.

The main design objectives should be:

(A) Resisting heat gain

Measures that are convenient to resist unwanted heat gain are:

(a) Decreasing surface area of the building exposed to the outside.

(b) Using materials that take a longer time to heat up.

(c) Providing buffer spaces between the outside and the inside.

(d) Increasing shading of the building in general.

(e) Using materials that reflect heat.

(B) Promoting heat loss

To promote heat lost it is essential to ensure:

(a) Appliances used are well ventilated.

(b) Proper ventilation occurs throughout the day.

(c) Humidity levels are reduced as much as possible.

General recommendations for building design in warm and humid climate are:

(1) Site

(a) Land form

·                 For flat sites, design considerations for the land form is immaterial.

·                 In case of slopes and depressions, the building should be located on the windward side or crest to take advantage of cool breezes.

(b) Water bodies

·                 Water bodies are not essential as they would tend to further increase the humidity.

(c) Open spaces and built form

·                 Buildings should be spread out with large open spaces in between for unrestricted air movement.

·                 In cities, buildings on stilts can promote ventilation and cause cooling at the ground level.

(d) Street width and orientation

·                 Major streets should be oriented parallel to or within 30 of the prevailing wind direction during summer months to encourage ventilation in warm and humid regions.

·                 A north-south direction is ideal from the point of view of blocking solar radiation.

·                 The width of the streets should be such that the intense solar radiation during late morning and early afternoon is avoided during the summers.

(2) Orientation and Plan form

·                 As temperatures are not very high, free plans can be evolved as long as the house is under protective shade.

·                 An unobstructed air path through the interiors is important to ensure proper ventilation.

·                 The buildings could be long and narrow to allow cross-ventilation. For example, a singly loaded corridor plan (i.e. one with rooms on one side only) is preferable over a doubly loaded one.

·                 Heat and moisture producing areas like toilets and kitchens must be ventilated and separated from the rest of the structure.

·                 Semi open spaces such as balconies, verandas and porches can be used advantageously for daytime activities as well as give protection from rainfall.

·                 In multistoreyed buildings a central courtyard can be provided with vents at higher levels to draw away the rising hot air.

(3) Building Envelope

(a) Roof

·                 In addition to providing shelter from rain and heat, the form of the roof should be planned to promote air flow.

·                 Vents at the rooftop effectively induce ventilation and draw hot air out.

·                 Insulation does not provide any additional benefit for a normal RCC roof in a non-conditioned building.

·                 However, very thin roofs having low thermal mass, such as AC sheet roofing, require insulation as they tend to rapidly radiate heat into the interiors during daytime.

·                 A double roof with a ventilated space in between can also be used to promote air flow. The space in between can also act as a heat buffer.

(b) Walls:

·                 The walls must also be designed to promote air flow so as to counter the prevalent humidity.

·                 Baffle walls, both inside and outside the building can help to divert the flow of wind inside.

·                 They should be protected from the heavy rainfall prevalent in such areas.

·                 If adequately sheltered, exposed brick walls and mud plastered walls work very well by absorbing the humidity and helping the building to breathe.

(c) Fenestration

·                 Cross-ventilation is of utmost importance in warm and humid climatic regions.

·                 All doors and windows should preferably be kept open for maximum ventilation for most of the year.

·                 These must be provided with venetian blinds or louvers to shelter the rooms from the sun and rain, as well as for the control of air movement.

·                 Openings of a comparatively smaller size can be placed on the windward side, while the corresponding openings on the leeward side should be bigger for facilitating a plume effect for natural ventilation

.

·                 The openings should be shaded by external overhangs.

·                 Outlets at higher levels serve to vent hot air.

Examples illustrating how the air movement within a room can be better distributed

(d) Colour and texture

·                 The walls should be painted with light pastel shades or whitewashed, while the surface of the roof can be of broken glazed tile (china mosaic flooring) to reflect the sunlight back to the environment, and hence reduce heat gain of the building.

·                 The use of appropriate colours and surface finishes is a cheap and very effective technique to lower indoor temperatures.

·                 The surface finish should be protected from/ resistant to the effects of moisture.

Remarks

·                 Ceiling fans are effective in reducing the level of discomfort in this type of climate.

·                 Desiccant cooling techniques can also be employed as they reduce the humidity level.

·                 Careful water proofing and drainage of water are essential considerations of building design due to heavy rainfall.

·                 In case of air conditioned buildings, dehumidification plays a significant role in the design of the plant.

Moderate Climate

In regions with a moderate climate, prevalent temperatures are neither too high nor too low. Techniques such as shading, cross ventilation, orientation, reflective glazing, etc. need to be incorporated into buildings so as to maximise their energy efficiency. The thermal resistance and heat capacity of walls and roofs need not be very high as the prevalent temperatures are generally within human comfort levels.

The main objectives while designing buildings in this zone should be:

(A) Resisting heat gain

To resist heat gain the measures that can be adopted are:
(a) The exposed surface area of the building be reduced.

(b) Using materials that absorb heat slowly.

(c) Adequately shading the building.

(B) Promoting heat loss

Heat loss can be promoted through 
(a) Proper ventilation of appliances used.
(b) Increasing the rate of ventilation in the building.

In this region, the general recommendations are:

(1) Site

(a) Landforms

·                 Building the structure on the windward slopes is preferable for getting cool breeze

 (b) Open spaces and built form

·                 An open and free layout of the buildings is preferred.

·                 Large open spaces in the form of lawns can be provided to reduce reflected radiation.

(2) Orientation and Plan form

·                 It is preferable to have a building oriented in the north-south direction.

·                 Living areas like bedrooms may be located on the eastern side to allow for heat penetration in the mornings, and an open porch on the south south east side allows heat gain in the winters while providing for shade in the summers. The western side should ideally be well-shaded.

·                 Humidity producing areas must be isolated.

·                 Sunlight is desirable except in summer, so the depth of the interiors need not be excessive.

(3) Building Envelope

(a) Roof

·                 Insulating the roof does not make much of a difference in the moderate climate.

(b) Walls

·                 Insulation of walls does not give significant improvement in the thermal performance of a building.

(c) Fenestration

·                 The arrangement of windows is important for reducing heat gain.

·                 Windows can be larger in the north, while those on the east, west and south should be smaller.

·                 All the windows should be shaded with chajjas of appropriate lengths.

·                 Glazing of low transmissivity should be used.

(d) Colour and texture

·                 Pale colours are preferable; dark colours may be used only in recessed places protected from the summer sun.

Cold Climate

Regions that fall under the cold climate experience very cold winters. As such, trapping the sun’s heat whenever possible is a major design concern. At the same time, the buildings in such regions need to be properly insulated so that the internal heat is retained with minimum loss to the environment. Exposure to cold winds should also be minimised.

The main objectives of building design in these zones are:

(A) Resisting heat loss

To resist heat loss, the following measures may be taken into consideration:

(a) Decrease the exposed surface area of the building.

·                 (b) Using materials that heat up fast but release heat slowly.

·                 (c) Providing buffer spaces between the living area and the outside.

·                 (d) Decreasing the rate of ventilation inside the building.

(B) Promoting heat gain

Heat gain can be promoted by

·                 (a) Avoiding excessive shading.

·                 (b) Utilising the heat from appliances.

·                 (c) Trapping the heat of the sun.

The general recommendations for these climatic regions are

(1) Site

(a) Land form

·                 In cold climates, heat gain is desirable. Hence, buildings should be located on the south slope of a hill or mountain for better access to solar radiation.

·                 Exposure to cold winds can be minimised by locating the building on the leeward side. In case the southern side is the windward side. The building should be glazed in such a manner that minimum wind enters the building.

·                 Parts of the site which offer natural wind barrier can be chosen for constructing a building.

(b) Open spaces and built forms

·                 Buildings can be clustered together to minimise exposure to cold winds.

·                 Open spaces between buildings must be such that they allow maximum solar rays to be incident on the building.

·                 They should be treated with a halt and reflective surface so that day reflect solar radiation onto the building.

 (c) Street width and orientation

·                 In cold climates, the street orientation should be east-west to allow for maximum south sun to enter the building.

·                 The street should be wide enough to ensure that the buildings on one side do not shade those on the other side (i.e. solar access should be ensured)

 (2) Orientation and Plan form

·                 Buildings must be compact with small surface to volume ratios to reduce heat loss.

·                 Windows should face south to facilitate direct gain.

·                 The north side of the building should be well-insulated.

·                 Living areas can be located on the southern side while utility areas such as stores can be on the northern side.

·                 Air-lock lobbies at the entrance and exit points of the building reduce heat loss.

·                 Heat generated by appliances in rooms such as kitchens may be used to heat the other parts of the building.

(3) Building Envelope

(a) Roof

·                 False ceilings with internal insulation such as polyurethane foam (PUF), thermocol, wood wool, etc. are feasible for houses in cold climates.

·                 Aluminium foil is generally used between the insulation layer and the roof to reduce heat loss to the exterior.

·                 A sufficiently sloping roof enables quick drainage of rain water and snow.

·                 A solar air collector can be incorporated on the south facing slope of the roof and hot air from it can be used for space heating purposes.

·                 Skylights on the roofs admit heat as well as light in winters.

·                 Skylights can be provided with shutters to avoid over heating in summers.

(b) Walls

·                 Walls should be made of materials that lose heat slowly.

·                 The south-facing walls (exposed to solar radiation) could be of high thermal capacity (such as Trombe wall) to store day time heat for later used.

·                 The walls should also be insulated.

·                 The insulation should have sufficient vapour barrier (such as two coats of bitumen, 300 to 600 gauge polyethylene sheet or aluminium foil) on the warm side to avoid condensation.

·                 Hollow and lightweight concrete blocks are also quite suitable.

·                 Skylights can be provided with shutters to avoid over heating in summers.

·                 On the windward or north side, a cavity wall type of construction may be adopted.

(c) Fenestration

·                 It is advisable to have the maximum window area on the southern side of the building to facilitate direct heat gain.

·                 They should be sealed and preferably double glazed to avoid heat losses during winter nights.

·                 Condensation in the air space between the panes should be prevented,

·                 Movable shades should be provided to prevent overheating in summers.

(d) Colour and texture

·                 The external surfaces of the walls should be dark in colour so that day absorb heat from the sun.

Composite Climate

Regions having a composite climate display characteristics of hot and dry, warm and humid as well as cold climates. Design of buildings here should be guided by longer prevailing climatic conditions. Uncomfortable periods in each season need to be prioritised to generate the necessary guidelines for design.

The objectives of building design should be:

(A) Resisting heat gain

Unwanted heat gain can be reduced by

·                 Decreasing the surface area of the building exposed to the outside.

·                 Using materials that absorb heat slowly.

·                 Providing buffer spaces.

·                 Providing adequate shading devices.

(B) Promoting heat loss

To promote heat loss, the following measures need to be undertaken:

·                 Ventilating appliances used.

·                 Providing evaporated cooling systems like roof surface evaporated cooling.

·                 Using earth coupling systems like earth air pipe system.

(C) Promoting ventilation

·                 Increasing the rate of ventilation during cooler parts of the day or night-time and during the humid periods is a necessity in composite climatic areas.

General recommendations for the climate are:

(1) Site

(a) Land form

·                 Regions in this zone are generally flat and heat up uniformly.

(b) Water bodies

·                 Water bodies like ponds and lakes act as heat sinks and can also be used for evaporative cooling.

·                 Fountains and water cascades in the vicinity of a building also aid in cooling.

·                 However, it has to be ensured that these water bodies do not increase the relative humidity during the humid seasons.

(c) Street width and orientation

·                 Streets must be narrow so that buildings mutually shade each other. They need to be oriented in the north-south direction to block solar radiation.

(d) Open spaces and built form

·                 Open spaces such as courtyards and atria promote ventilation.

·                 They can be provided with ponds and fountains for evaporative cooling.

·                 Courtyards act as heat sinks during the day and radiate the heat back at night.

·                 Grass can be used as ground cover to absorb solar radiation and aid evaporative cooling.

·                 Earth berming can help lower the temperature and also deflect hot summer winds.

 (2) Orientation and Plan form

·                 An east-west orientation is preferred as northern and southern walls are easier to shade.

·                 During summer, the south wall which gets significant exposure to solar radiation in most parts of India, leads to very high temperatures in south-west rooms. Hence, shading of the south wall is imperative.

·                 The surface to volume ratio should be kept as minimum as possible to reduce heat gains.

·                 Cross-ventilation must be ensured at night as ambient temperatures during this period are low.

(3) Building Envelope

(a) Roof

·                 Flat roofs may be used in this climate.

·                 A massive roof structure like a reinforced cement concrete RCC slab is preferable over an asbestos cement AC sheet roof.

·                 External insulation in the form of mud phuska with inverted earthen pots is quite suitable.

·                 A false ceiling in rooms having exposed roofs can help in reducing the discomfort level.

·                 Provision of roof insulation yields greater life cycle savings compared to walls in this climate.

·                 Evaporated cooling of the roof surface and night-time radiative cooling are measures that can also be employed to improve comfort levels.

·                 In case the former is used, it is better to have a roof that will cool down fast.

(b) Walls

·                 In multi-storied buildings, walls and glazing account for most of the heat gain. So, the control of heat gain through the walls by shading is an important consideration in building design.

·                 A wall that takes a longer time to heat up reduces the heat gain.

(c) Fenestration

·                 Minimising the window area leads to lower indoor temperatures.

·                 More windows should be provided in the north facade of the building as compared to the east, west and south as it receives lesser radiation during the year.

·                 All openings should be protected from the sun by using external shading devices such as chhajjas and fins.

·                 Move able shading devices such as curtains and venetian blinds can also be used.

·                 Since daytime temperatures are high during summer, the windows should be kept closed to keep the hot air out and opened during night time to admit cooler air.

·                 The use of 'jaalis'(lattice work) made of wood, stone or RCC may be considered as they allow ventilation while blocking solar radiation. Measures to control ventilation of the building as and when required makes it more comfortable indoors.

·                 The heat gain through windows can be reduced by using glass with low transmissive.

(d) Colour and texture

·                 Change of colour is a cheap and effective technique for lowering indoor temperatures.

·                 Colours having low absorptivity should be used to paint the external surface.

·                 Darker shades should be avoided for surfaces exposed to direct solar radiation.

·                 The surface of the roof can be of white broken glazed tiles.

·                 The surface of the wall should preferably be textured to facilitate self shading.

Remarks

·                 As the winters in this region are uncomfortably cold, windows should be designed such that they encourage direct gain of solar heat during this period.

·                 Deciduous trees can be used to shade the building during summer and admit sunlight during winter.

·                 Well-insulated and very thick walls give a good thermal performance if the glazing is kept to a minimum and windows are well shaded.

·                 In case of non-conditioned buildings, a combination of insulated walls and high percentage of glazing will lead to very uncomfortable indoor conditions.

·                 Indoor plants can be provided near the window, as they help in evaporative cooling and in absorbing solar radiation.

·                 Evaporative cooling and earth air pipe systems can be used effectively in this climate.

·                 Desert coolers are extensively used in this climate, and if properly sized, they can help in achieving comfort levels.

This article on Urban Residential Design development is written by

Ms. Vinita  Mathur ,

Head of the Interior Design Department,

Dezyne E’cole College ,Ajmer
Rajasthan