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Green Business Directory Green Buildings

Buildings as they are designed andused today, symbolise unrestrainedconsumption of energy and other natural

resources with its consequent negative

environmental impact. In India, the

residential and commercial sector

consumes 25% of the total electricity

usage of the country and a major portion

of this is utilised in buildings. Designing &

developing new buildings based on sound

concepts of sustainability and applying

suitable retrofit options to existing

buildings could substantially improve the

energy use efficiency in the building sector

with an associated reduction in both local

as well as global emissions. An integrated

approach to building design involves

judicious use and application of:

Efficient materials and construction

practices

Bio-climatic/solar passive architectural

principles

Efficient systems and equipment

Renewable sources of energy

Efficient waste and water management

practices

Incorporating the above features in a

holistic manner would result in buildings

that would impose a minimal impact on

the environment while enhancing user

comfort and productivity.

About the author: Mili Majumdar,B.Arch, M.Tech (IIT, Chennai), architectwith specialisation in buildingtech-nologies and development ofsustainable habitats has beenworking in the field of energy efficiencyin buildings for the past 10 years.

She has been involved in design,detailing and execution of energyefficient buildings, design of energyefficient lighting schemes for new andexisting buildings. She also hasexperience in integration of energyefficient and renewable energy

technologies into building design.

She is proficient in simulation of

building envelope using Doe 2.1e,SUNCODE-PC, TSBI3, Lumen micro2000 etc. She is adept in use of variouslighting design/retrofit tools which helpin designing of efficient lightingschemes, integrate natural lighting and

control strategies into lighting design,and in retrofitting of existing schemeswith more efficient ones. She has lectured at variousworkshops, seminars and conferencesrelated to energy efficient andsustainable architecture and building

systems.

Mili MajumdarFellow, The Energy and

Resources Institute,

Habitat Place, Lodhi Road,

New Delhi 110 003

Energy is used in various forms in a

building e.g electrical energy is used to

power various appliances and equipment

and thermal energy is used for cooking.

Typically electricity accounts for the major

share in a buildings energy consumption.

The primary end uses in a building that

use electricity are air conditioning

equipment, lights, fans, and office/

household appliances or machines. In a

typical unconditioned building in India,

lighting accounts for maximum energy

consumption, and in an air-conditioned

building, 40-50% of the total electricity

consumption is accounted for by HVAC

system, followed by lighting system

(20%). Other loads (pumps, equipment,

etc.) contribute to balance 20 - 30%.

An unconditioned green building

would be designed to maximise thermal

comfort and avoid use of air-conditioners/

air-coolers/heaters for maximum part of

the year. It would also have appropriate

daylighting to reduce lighting energy

consumption. This is done through

judicious use of passive solar principles

conducive to the climate in which the

building is located e.g. in TERI-Bangalore

office building located in moderate climate

of Bangalore, south facing dark coloured

solar chimneys create draft for exit of hotair, in turn drawing in cool air from the open

Energy efficiency in green buildings - An integrated approach

to building design

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The thermal storage capacity of the

earth being high, the daily and annual

temperature fluctuations keep

decreasing with increasing depth of

the earth. At a depth of about 4m below

the ground the temperature remains

constant round the year and is equal

to the annual average temperature of

a place. For instance in Delhi this

temperature is between 25-26 C.

The principle of the tunnel is to take

advantage of constancy in temperature

throughout the year at a certain depth below

ground. So if air is passed through such

earth before funneling it to a room, we can

expect it to be cool in the summer and

warm in the winter. An earth air tunnel is a

system in which air is forced through

underground pipes or tunnels and then

circulated in the room. This system hasbeen used to precool the fresh air input to

windows on north, ensuring adequate airflow at body level to provide thermal

comfort. Thermal performance of solar

passive buildings varies with changing

outdoor conditions and in largely

dependent on weather conditions.

On the other hand, air-conditioned

green buildings with maintained uniform

thermal conditions round the year are

designed to minimise load on conventional

HVAC system. This is done by adopting

appropriate passive solar design strategiese.g. orientation, fenestration sizing and

shading, landscaping, day-lighting; and by

using appropriate building materials and

finishes, e.g. thermal insulation, insulating

glass units, heat reflecting paints, etc.

A recently concluded study by TERI has

shown that for an institutional designed ina composite climate, the cooling load could

be reduced by 40% from the initial

estimated load (fig 1). The measures

which resulted in this load reduction, were:

Use of over deck roof insulation using

expanded polystyrene slabs/spray

applied polyurethane foam topped by

reflective broken china mosaic flooring.

Use of double glazed windows with

spectrally selective coating.

Use of cavity wall construction withinsulation infill.

Use of energy efficient lighting.

Use of underground earth air tunnel

(EAT) to supply pre-cooled air to the air

handling units.

Fig 1: Reduction in cooling load for an institutional building by

incorporation of energy efficiency measures

Base load as

per initial

estimate

Roof insulation

using EPS

Roof insulation

+ efficient

windows

Wall and roof

insulation +

efficient

windows

Puf insulation

on roof

(rest same

as in run 4)

Efficient

lighting with

all measures

EAT for

precooling

Energy saving options

for building envelope

Tons of refrigeration (TR) % savings

120.0

99.0

87.1 82.0

1827

32 32

81.5

35

78.472.1

40

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the air handling units thus reducing loadon the AHUs.

The excess investment incurred to

incorporate the above mentioned

measures was estimated to payback in a

years time from savings in initial system

costs and reduced energy consumption.

Thermal modelling and simulation tools

(Visdoe 3.1 and HAP 4.0) were used to

accurately calculate the load reduction and

energy savings.

While building and system design

interventions help downsize HVAC

(Heating, Ventilation and Air-conditioning)

systems, use of appropriate controls help

to reduce consumption of the optimised

systems.

Lighting forms the major load centre in

unconditioned buildings and next to HVAC

systems in conditioned buildings. Energy

efficient lighting provides for right quality

and quantity of light with minimal energy

requirement. To accomplish this step, the

designer designs a lighting scheme for a

specific application based on illumination

levels recommended by BIS or IESNA

standards. The aim of the designers should

be to use efficient lamp and luminaire

combination to achieve the required

illumination level (lux or foot-candle level).

This helps the designer in ensuring that

the lighting power density (w/sq.ft) for a

particular space is not exceeding the

prescribed limits. The ASHRAE 90.1-2001standards specify the lighting power

densities for different space categories.

Lighting simulation tools (e.g. lumen micro,

etc) could be used to design lighting

schemes for a given power density.

Lighting schemes are normally

designed for providing desired lux levels

for night- time condit ions, i.e . without

considering presence of daylight. Suitable

control strategies are then devised e.g. use

of day-linked, occupancy sensors, timeswitches, etc. to switch off or dim lights

during daytime or when an area isunoccupied. Design for day lighting further

requires in-depth analysis of glare, visible

light transmission of glazing, sill level,

window position and height, orientation,

outdoor obstruction, indoor reflectance etc:

e.g. heat reflective glasses used in

buildings to reduce solar heat gain (to lower

cooling load) typically have low visible light

transmission, thus reducing daylight into

spaces. In a predominantly hot climate like

ours, glass with low shading co-efficient

and high visible transmittance should be

selected to reduce solar gains and increase

visible light transmission.

Efficient design of building envelope

and lighting is the foremost step in the

integrated design approach which helps to

minimise space-conditioning loads. The

task of the designer is then to use efficient

space conditioning equipment and controls

to further reduce energy consumption. In

an air-conditioned building use of efficient

space-conditioning equipment and

controls e.g. use of efficient chillers, air

handling units, pumps and cooling towers;

use of variable speed drives at AHU fan

motors, at cooling tower fan motors and

secondary chilled water pumps; use of low

leakage dampers, enthalpy control, dry

bulb economiser are some of many energy

conservation techniques possible for

HVAC systems.

Use of natural cooling systems e.g wind

towers, earth air tunnels etc., can be

integrated with conventional air

conditioning systems to save energy.

Judicious building and system design

can reduce energy consumption in a

building by 30-40% over conventionally

designed buildings. After maximising

energy saving opportunities in a building,

a designer may consider use of renewable

forms of energy to meet a part of the

buildings energy requirements e.g. use of

solar assisted water heating system, solar

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photovoltaic system can reducedependence on conventional/non-

renewable forms of energy.

Conclusions

With increasing energy prices,

diminishing reserves of conventional

forms of energy, and increasing GHG

emissions, green buildings are the need

of the hour. Globally speaking, in 1990, the

residential, commercial, and institutional

building sector consumed 31% of global

energy and emitted 1900 mega tonnes ofcarbon and by 2050 its share would rise to

38% and 3800 mega tonnes respectively

(IPCC, Nov.1996). On the brighter side,

energy efficiency measures with paybacks

in five years or less can reduce global

emissions by 40% by 2050. With

increasing threat on our planet earth caused

by depleting resources and increasing

emissions it is absolutely pertinent that all

our future buildings should be designed to

function as green buildings.