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2.0 Green building characteristics
2.1 CLIMATIC RESPONSE
The Indian climatic zones
India’s climate varies drastically from region to region. This in turn demands that buildings
respond to regional climates through their design and construction. Essentially, the climatic
factors that must be considered are solar radiation, ambient temperature, humidity, rainfall and
wind. In total there are six distinct climatic zones encompassing the entire spectrum of climatic
conditions in India ; Hot and Dry, Warm and Humid, Moderate, Cold and Cloudy, Cold and Sunny,
Composite. Figure 2.0 maps India’s six climatic zones.
Hot and Dry: This zone lies in western and central India, effecting towns such as Jaisalmer,
Jodhpur and Sholapur. With typically flat terrain, the Hot and Dry region has rocky or sandy
ground conditions and sparse water resources. In summer maximum temperatures very between
45°C during the day with night time lows of 20-30°C. Winter temperatures vary between 5-25°C
and 0-10°C at night. Annual precipitation is generally less than 500 mm.
Warm and Humid: Covering the coastal parts of the country, the warm and humid zone
encompasses cities such as Mumbai, Chennai and Kolkata. High humidity encourages abundant
vegetation in these regions. Humidity runs at about 70-90% throughout the year with precipitation
at about 1200mm per year. Summer daytime temperatures vary between 30-35°C, with night
temperatures at 25-30°C. These vary between 25-30°C during the day and 20-25°C at night
during the winter months.
Moderate: Areas of moderate climate are generally located on hilly or high-plateau regions with
fairly abundant vegetation. Pune and Bangalore fall within this zone. With dry winters and rainfall
usually not exceeding 1100mm per year, the Moderate region is typified by low humidity in
winters and summers, with humidity varying between 20-55% and 55-90% during the monsoon
period. Summer daytime temperatures sit around 30–34 ºC and 17-24 ºC at night. In winter,
daytime temperatures vary between 27 to 33 ºC and 16 to 18 ºC at night.
Cold and Cloudy: Generally, the northern part of India experiences this type of climate. Most
cold and cloudy regions are situated at high altitudes. Shimla, Shillong, Ooty, Srinagar and
Mahabaleshwar are examples of places belonging to this climatic zone. These are generally
highland regions having abundant vegetation in summer. In summer, the maximum daytime
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Fig 2.0: Climatic map of India with the six distinct zones.
Capacity Building Series (2008-2009), June 2009, TARA Nirman Kendra, New Delhi
temperature ranges between 20–30 ºC and 17–27 ºC at night. Conversely, winter temperatures
sit between 4 and 8ºC during the day and from -3 to 4 ºC at night. With precipitation of about
1000mm per year, humidity runs between 70-80%.
Cold and Sunny: The cold and sunny type of climate is experienced in Leh (Ladakh). The region
is mountainous, has little vegetation, and is characterized by cold areas of desert. Typified by low
humidity of about 10-50% and low precipitation of 200mm per year. Summer temperatures vary
between 17-24ºC during the day and 4-11ºC at night. Winter daytime temperatures vary between
-7-8ºC during the day and -14-0 at night.
Composite: The area of composite climate is situated within central India. New Delhi, Kanpur
and Allahabad are a few cities within the composite zone. Variable landscape and seasonal
vegetation characterize this zone. Humidity is about 20–25 % in dry periods and 55-95 % in the
wet season. Summers range between daytime temperatures of 32–44 ºC, and night time values
are from 27 to 32 ºC. Daytime values of 10-25ºC during the day and 4 to 10 ºC at night can be
expected.
2.1.1 Microclimate
Climate is the average of the atmospheric conditions over an extended period of time over a large
region. Small scale patterns of climate resulting from the influence of topography, urban forms,
water bodies, vegetation, etc. are known as Microclimates. Microclimate refers to the climate of a
site or location. It implies to any local deviation from the climate of a large region or zone.
Elements like water bodies and vegetation can play a significant role in creating comfortable
ambient conditions. Water has a high heat storage capacity helps balance day and night
temperature variation. Vegetations absorb heat, but remain cool, due to the evaporation from the
leaves. Topography affects wind movement which can in turn affect the relative humidity of a
place in relation its temperature. (refer appendix 8.)
Human comfort level
Human comfort factors: Within all the climatic regions the basic function of a building is to
ensure human health and comfort, by moderating extreme external environment conditions to
within the comfort zone. It can be considered as the third skin, the second being our clothes.
Humans require thermal, visual and acoustic comfort conditions. Thermal comfort depends on
both environmental and physiological factors (figure 2.1). Environmental factors include air
temperature, humidity, temperature of surrounding surfaces 3easured as Mean Radiant
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Fig 2.1: Environmental and physiological factors
affecting human comfort in buildings
Subjective reactions to
air movement
<0.1 m/s
upto 0.2 m/s
upto 0.5 m/s
upto 1 m/s
upto 1.5 m/s
> 1.5 m/s
stuffy
unnoticed
pleasant
awareness
draughty
annoying
Capacity Building Series (2008-2009), June 2009, TARA Nirman Kendra, New Delhi
Temperature (MRT) and air velocity. Physiological factors include Metabolic rate, Clothing, state
of health and acclimatization.
Adaptive comfort
People can adapt to the most remarkable range of temperatures. This should be taken into
account when deciding upon the level of protection a building needs in a given climate. The Nicol
graph can be used for a general idea of comfort conditions required by building occupants (of a
non-air conditioned building) who have adapted to the local climate. The thermal comfort
tempperature can be calculated using the following expression -
TC = 0.315 (Tmean) + 17.82
where TC is Thermal Comfort and Tmean is the monthly mean outdoor temperature.
Fig 2.2 – Sun path
diagram for 20o N
latitude
Adaptive comfort also takes into account certain behavioral traits of building occupants which can
determine the amount of artificial heating or cooling needed. Clothing provides thermal insulation
to body and is measured in terms of ‘Clo’ which means a U-value of 6.45 W/m2C. Shorts and
short-sleeved shirts give about 0.5 clo, whereas the heaviest type of Arctic clothing would be
some 3.5 clo.
2.2 CONFIGURATION
2.2.1 Orientation
A correctly oriented building can provide physical and psychological comfort to building
occupants. For example, in cold climates, a building must be oriented to receive maximum solar
radiation into the living areas for warmth, while keeping out prevailing cold winds. In hot regions,
solar radiation and hot dusty winds need to be avoided in summer, while cool winds must be
made to flow through the building. The ideal orientation enables a building to receive maximum
solar radiation in winter and minimum in summer. To decide on an optimum orientation, it is
essential to have an idea of the sun’s position on a daily as well as seasonal basis by using tools
such as the sun path diagram (figure 2.2). It is also necessary to consider the intensity of solar
radiation on various external surfaces of the building as well as the duration of sunshine. In areas
where comfort is acquired mainly by air movement, it is important to orient the building according
to prevailing winds.
MLA Hostel, Shimla (figure 2.3) – Cold and Cloudy region: Located in cold and cloudy Shimla,
individual blocks are orientated south (+- 15°) and integrate features like trombe wall (see
section…) to capture and store maximum sunlight. West and east walls remain solid with little
fenestration to minimize solar gain.
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Fig 2.3: MLA Hostel,
Shimla. Architect, Sanjay
Prakesh. Most windows
face due south for
maximum solar gain.
Capacity Building Series (2008-2009), June 2009, TARA Nirman Kendra, New Delhi
West Bengal Pollution Control Board, Kolkata (fig 2.4) - Warm and Humid region: Although
having to deal with a difficult site, through manipulating the buildings form by ‘stepping’ the facade
key spaces are orientated North/South to optimize daylighting and ventilation potential.
Guidelines - orientation




Cold climates: An orientation slightly east of south is ideal (15° east of south is
favoured). This exposes the building to more morning than afternoon sun and helps the
building to heat up early in the day. Windows should preferably face south to encourage
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.
Hot and dry climate: East-west orientation (longer axis running along east-west) is
preferred, because south and north facing walls are easier to shade than east and west
walls. During summer, the north wall gets significant exposure to solar radiation in many
parts of India. This in turn leads to very high temperatures in north-west rooms. In
Jodhpur, for example, rooms facing north-west can reach temperatures of 38 ºC.
Warm and humid climate: As temperatures are not hugely excessive, ‘free’ plans can
evolve as long as the house is reasonably shaded. An unobstructed air path through the
interiors is important. In this climate buildings should ideally be long and narrow to allow
cross-ventilation.
Moderate climate: Ideally buildings are to be oriented north-south; bedrooms may be
located on the eastern side, with an open porch on the south/southeast side. The western
side should be well-shaded. Humidity producing areas must be isolated. Sunlight is
desirable except in summer, so the depth of the interiors should not be excessive.
Fig 2.4: West Bengal Pollution Control Board, Kolkata.
Architects, Ghosh and Bose & Associates. Most windows face
due south for maximum solar gain.
2.2.2 Built form & open spaces
The surface area to volume (S/V) ratio of a building is an important factor determining heat loss
and gain. The greater the surface area the more the heat gain/ loss through it. The cube is the
most compact orthogonal building form but, it places a large portion of the floor area far from
perimeter daylighting. To optimize daylighting and ventilation, the building mass would be
elongated so that more of the building area is closer to the perimeter. While this may appear to
compromise the thermal performance of the building, the electrical load and cooling load savings
achieved by a well-designed daylighting system will more than compensate for the increased
fabric losses. Small S/V ratios imply minimum heat gain and minimum heat loss and are
appropriate for hot-dry and cold-dry climates. When heat production of the buildings is low, such
as in traditional settlements, compact planning minimizes heat gain and is desirable. However, in
urban centres buildings produce much heat of their own, in which case heat loss becomes
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Fig 2.5: Incident solar radiation in different
orientations for a typical hot-dry climate
Capacity Building Series (2008-2009), June 2009, TARA Nirman Kendra, New Delhi
important. In cold climates open spaces should be small and surfaces should be hard and
absorptive to store maximum warmth from the sun. In warm-humid climates, open spaces should
be oriented with respect to wind patterns. The prime concern is creating spaces with maximum air
flow through them, which increases the S/V ratio.
2.3 THE BUILT ENVELOPE
A building can be considered as a thermal system, with a series of heat inputs and outputs. The
environment and a building interact through peripheral elements such as walls, windows,
projections and roofs that together create the building envelope. The built envelope acts as a
thermal shell, which controls the flow of heat between the inside and outside in order to create an
internal temperature that is comfortable for occupants. The change in heat stored in a building is
a result of –
Fig 2.6: Examples of heat resistance of construction
layers of the built envelope
(1) admitting solar heat gain – this is the most significant energy input into the building
(2) Conduction heat gain or loss primarily through construction materials,
(3) Ventilation heat gain or loss because of natural airflow through the building to meet fresh air
requirements or through requirements of fresh air,
(4) Internal heat gain through people, equipments, machines and re-radiation from interior
surfaces and
(5) Evaporative heat loss.
Glass fibre
insulation 0.1m
If thoughtlessly constructed, energy leaks through its elements can place an excessive load on
heating and cooling requirements of the building. While the opaque (solid) portions of the
envelope are fixed controls, the dynamic elements like openable windows, shading devices and
insulating shutters are a function of the degree of operational control.Key concepts that govern an
envelopes thermal efficiency include Thermal mass, Time lag, thermal conductance - U-value,
and Resistance – R value. The thermal efficiency of a building envelope in a given external
environment, principally depends on
Resistivity, r, of construction material or combined resistivity of layers of materials, commonly
observed in wall construction
Thickness, t, of the material/s – thicker the material, greater is the resistance to heat flow
Resistance to heat flow, R-value = r x t
While resistance is important to reduce heat escaping from the building, conductance is useful in
quantifying the heat that is lost through the envelope.
Conductance is better known as U-value. Mathematically, U value can be expressed as
U = 1 / R, where R is resistance
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0.1m
brick
Conductivity
Conductance, U
Value
0.84
(0.84 x 0.1)
= 0.084
0.1m
brick
0.035
(0.035 x 0.1)
= 0.00345
0.84
(0.84 x 0.1)
= 0.084
The total U-value for the structure can be found by adding the
U value of each layer.
U-value of wall = 0.084 + 0.00345 + 0.084 = 0.171 W/ m 2°C.
Capacity Building Series (2008-2009), June 2009, TARA Nirman Kendra, New Delhi
This is the amount of heat (energy) that flows in 1 second through a 1m2 section of wall when the
temperature difference between the two sides is 1ºC.
Based on the above, the heat loss or gain through a built envelope, Q, can be expressed as
Q = A x U x (t i – t o) , t i and t o are building interior and exterior temperatures.
The time delay between peak outside and inside temperature due to the thermal mass is the time
lag of a particular envelope. Correspondingly, the ratio of the two temperatures is the decrement
factor. The thicker and more resistive the material, the longer it will take for heat to pass through.
The U-value indicates the total amount of heat transmitted from outdoor air to indoor air through a
given wall or roof per unit area per unit time. The lower the value of U, the higher is the insulating
value of the element. Thus, the U-value can be used for comparing the insulating values of
various building elements1.
Appendix 1 describes the thermal loadings (in MWh) for individual elements within a building
envelope for a four story structure within four different cities. Walls clearly show the greatest
loading.
Fig 2.7: Time Lag and Decrement factor
2.3.1 Wall
Walls usually form a large part of the building envelope and consequently receive a large amount
of solar radiation. The thickness and material composition of a wall can be varied to control heat
gain, depending on whether climatic conditions predominantly require heating or cooling of the
building . The heat flow through wall is primarily governed by the Specific heat2, density,
thickness and thermal conductivity of wall materials which ultimately determine the resistance,
absorption and transmittance of heat.
Most commonly, the design and construction of walls in India ignores their role and potential as
moderators of temperature inside a building. This ought to be achieved through designing for the
desired thermal storage, time lag and decrement factor of the wall, depending on climatic
requirements. Increasing the thermal storage capacity of a wall is largely determined by the wall’s
thickness, type of material and the colour of the external surface. These factors allow a wall to
absorb and store heat within itself, becoming a thermal reservoir which can release heat in the
1
J.K. Nayak & J.A. Prajapati. Handbook on Energy Conscious Buildings (IIT Bombay/MNES India, May
2006). Chapter 4, page 12.
2
Specific Heat is the measure of the heat energy required to increase the temperature of a unit quantity of a
substance by a certain temperature interval.
9
Fig 2.8: A rammed earth wall uses its mass as insulation and for
thermal storage. Project photo from Bangalore construction site,
Chitra Vishwanath Architects.
Capacity Building Series (2008-2009), June 2009, TARA Nirman Kendra, New Delhi
later and mostly cooler hours of the day. Even simple cost effective measures like a whitewash or
light coloured distemper on the building exterior can reduce solar heat gain by reflecting heat.
Trombe walls can be constructed to significantly enhance heat storage of walls, particularly for
cold and sunny climates. The system uses glazing which is installed on the wall exterior to create
around 10cm air gap between wall and glazing. This column of air is circulated directly into the
living space by top and bottom vents in the wall. The outer surface of the wall is generally a dark
colour in the form of a selective coating for maximum heat absorption. This feature is prominently
used along the length and height of the south façade of the LEDeg Trainees’ Hostel, Leh (figure
2.8).Thick walls to west, east and north elevations provide insulation through their mass. In ideal
conditions the internal temperature can be maintained at 15°C with the external temperature as
low as -11°C.
A composite wall construction which combine more than one material can also form a thermally
efficient envelope. For example, simple and effective wall compositions could be granite blocks
cladded to a base wall made of bricks or a cavity wall with infill insulation. In cavity walls, the
property of the air gap can be varied by opting for a ventilated or unventilated air cavity, and
adjusting its thickness. On the other hand, there are more sophisticated composite walls such
curtain walls, often using an aluminium skin sandwiched over foam insulation to create a ready to
use component that can be craned into position. The final decision should preferably be based
on, to the extent possible, materials available locally and minimum transportation.
Fig 2.9 LEDeG Trainees’ Hostel, Leh. Architect, Sanjay
Prakash.
2.3.2 Insulation
While thermal mass provides ‘capacitive’ insulation, conductance of building envelope is also
reduced by ‘resistive’ insulation, such as mineral wool, cellulose fibre, polystyrene (also known as
thermocol) which are available as ‘bulk’ products. The more insulation in a buildings exterior
envelope, the less heat transferred into or out of the building due to temperature difference
between the interior and exterior. Insulation also controls the interior mean radiant temperature
(MRT) by isolating the interior surfaces from the influence of the exterior conditions.
Made from a variety of materials, insulation falls into the following categories:
(1) Rigid or semi rigid blocks or boards- high compressive strength, suitable for insulating
beneath heavy objects
(2) Boards with impact- or weather resistant surfaces, attached to exterior surfaces or below
grade,
(3) Blankets, felts, or sheets, which are either attached to vertical surfaces or laid flat on
horizontal ones - Usually consisting of glass fibre or mineral wool, it is manufactured in standard
widths of 400mm – 600m and is typically 75 to 175mm thick.
10
Fig 2.10
Development
Alternative
heafdquarters in
Delhi, designed by
Ashok Lall has a
cavity wall with fly
ash bricks and mud
bricks as exterior
and interior leaves
along with 75mm of
thermocol insulation
Capacity Building Series (2008-2009), June 2009, TARA Nirman Kendra, New Delhi
(4) Loose-fill, commonly cellulose, vermiculite, wood shavings - poured or blown into cavities or
onto flat surfaces such as ceilings,
(5) Foams and dry spray types which can be pneumatically applied - Properly applied, this
material can be shaped into almost any form and has considerable structural support. It is
applicable to odd-shaped structures, but needs a weather-protective membrane for protection.
(6) Reflective insulation - Reflective aluminium foil / radiant barrier (figure 2.12.) can be fixed to
the underside of roofs, ensures that heat gain through a roof is minimized. Usually a tarp-like
material with aluminium foil on both sides, in hot and humid climates the radiant barrier should be
perforated to ensure the passage of moisture.
The key principle of insulation is that of thermal resistance (R value), and is a standard
measurement in the construction industry. Essentially the larger the R value, the better the
insulation effectiveness. Appendix 5 demonstrates R values for a selection of insulation materials.
Insulation along with infiltration control is important for reducing heating and cooling loads in skinload-dominated buildings such as residences (internal load dominated buildings are typically
offices). Increased insulation levels in internal load-dominated buildings, may cause an increase
in energy usage for cooling when the outside is cooler than the inside, unless natural ventilation
or an economizer cycle on the HVAC system is available. In hot climates insulation should be
placed on the external face of a wall. This ensures that the thermal mass of the wall is weakly
coupled with the external source and strongly coupled with the interior.
Himurja office building, Shimla (figure 2.11): 50mm thick glass wool insulation has been used
over RCC diaphragm walls which creates good insulation in conjunction with passive heat gain
systems ensures a comfortable internal winter environment for all users.
Fig 2.11: Himurja office building, Shimla:
50mm insulation to the Northern
elevation helps prevent heat loss.
It is important to choose the right insulation for a given building. For instance, if the insulation is to
be used internally, then fire resistance is essential. If it is to be placed in well sealed cavity walls,
then fire resistance may not be an issue. Similarly, micro-location i.e whether it is an exposed or a
sheltered wall will decide appropriate construction details for water proofing. The estimated
energy savings from a given insulation is also a useful criteria. To decide how much insulation to
use, practical details of mounting and fixing insulation are often more critical than economic ones.
Given the fact that many regions of India have predominantly hot climates, insulation will
undoubtedly help in reducing the electrical energy demand of buildings, particularly for
commercial buildings with large air-conditioning loads. Roofs receive the highest intensity of solar
radiation and therefore conduct a large part of the heat inside the building. A combination of
resistive and reflective insulation for roofs (such as broken china mosaic which can be sourced as
waste) can be instrumental in keeping internal temperatures within comfort levels.
11
Fig 2.12: Reflective foil installed to the underside of a
warehouse roof for India Yarn by Macmillans Insulations
India.
Capacity Building Series (2008-2009), June 2009, TARA Nirman Kendra, New Delhi
2.3.3 Fenestration and glazing systems
Fenestration is provided for the purposes of heat gain, daylighting and ventilation. Their pattern
and configuration form an important aspect of building design and its energy requirement.
Appropriate design of openings and shading devices helps to minimize the effects of sun and
wind or allow them into a building. Ventilation lets fresh air in and hot air out, resulting in cooling.
Glazing is generally transparent to solar radiation but opaque to long wave radiation. This
characteristic can be used to heat a buildings interior by promoting heat gain. This is desirable in
winter, but may cause overheating in summer. This overheating through large aesthetic-driven
areas of exposed glass is commonly observed in commercial buildings in India today and in turn
results in excessive loads on air conditioning systems. For reducing solar gain during summer,
window size should be kept minimum in the hot and dry regions. For example, in Ahmadabad, the
number of uncomfortable hours in a year can be reduced by as much as 35% if glazing is taken
as 10% of the floor area instead of, say, 20% 3.
The amount of light entering a building needs to be effectively controlled to maintain a suitable
level of comfort. This can be achieved through proprietary systems such as openable shutters
and movable covers like curtains or Venetian blinds. Tinted glazing with surface coatings can also
be used to control solar transmission, absorption and reflection. Surface coatings can reduce the
transmission of solar radiation through a piece of 6mm thick absorbing glass by about 45%.
Reflective glass is usually achieved by a layer of reflective material or a low emittance layer.
Glazing of these types can reduce heat gain without obstructing views from the building. They are
usually used for windows which cannot be shaded externally.
Fig 2.13 DFL Gateway Tower, Gurgaon. Huge areas
of exposed glass are a common approach in today’s
commercial building design
The following definitions are the most commonly used in assessing the performance of windows;
U-value (U factor): measures the rate at which heat transfer takes place through glazing
and window assemblies. The lower the U value the better the window’s insulation value
and its ability to resist heat flow.
Solar Heat Gain Co-efficient (SHGC): The SHGC measures how well a product blocks
heat from the sun. The co-efficient is the fraction of incident solar radiation admitted
through a window, both directly transmitted, and absorbed and subsequently re-released
inward. The lower the SHGC value, the less solar heat it transmits.
3
J.K. Nayak & J.A. Prajapati. Handbook on Energy Conscious Buildings (IIT Bombay/MNES India, May
2006). Chapter 3, page 15.
12
Fig 2.14 Transmission properties of reflecting
glass (6mm thick).
Capacity Building Series (2008-2009), June 2009, TARA Nirman Kendra, New Delhi
Visible transmittance (VT): measures how much light comes in through glass. It is an
optical property that indicates the amount of visible light transmitted. VT is expressed as
a number between 0 and 1. The higher the number, the more light is transmitted.
There are various approaches to glazing system design which have evolved within the
marketplace. A few of these systems are discussed here;
Single Clear Glazing: Relative to all other glazing options, single-glazed with clear glass allows
the highest conductive transfer (i.e. heat loss or heat gain) while permitting the highest solar heat
gain and daylight transmission.
Spectrally selective glazing (low E glazing): This glazing permits some portions of the solar
spectrum to enter while blocking others; this is sometimes known as Low Emissivity or Low-E
glazing. It admits as much daylight as possible while preventing transmission of as much solar
heat as possible. Spectrally selective glazing has the advantage of being more transparent than
tinted glazing and offering better night views than reflective and dark tinted glazing.
Angular selective solar control: Frit is the most common angle-selective coating. It consists of
a ceramic coating, either translucent or opaque, which is screen printed in small patterns on a
glass surface. The pattern used controls the light based on its angle of incidence. The colour of
frit controls reflection or absorption, the view and/or visual privacy4.
Smart windows: Smart windows have the ability to control the ingress of light as well as solar
radiation through a thin photochromic, thermochromic or electrochromic film which gets activated
by light, heat and electricity respectively.
Fig 2.15 Transport Corporation of India, Gurgaon.
Window details.
Appendix 6 shows information regarding various types of glazing and their properties.
Transport Corporation of India Ltd, Gurgaon (figure 2.16)- Situated in the ‘composite’ climate
of Gurgaon, the external façade was envisaged as a solid, insulated wall with minimal
fenestration. Areas of glazing are kept to a minimum, utilizing a composite double glazing and
Venetian blind windows for solar control to all facades. Because the windows are set deeply into
the façade, shading naturally occurs to reduce heat gain. Windows that face the internal
courtyard are single glazed, allowing the cooling effects of the courtyard fountain to transfer to the
interior of the building.
4
J.K. Nayak & J.A. Prajapati. Handbook on Energy Conscious Buildings (IIT Bombay/MNES India, May
2006). Chapter 3, page 18.
13
Fig 2.16: Transport Corporation of India, Gurgaon. Architect,
A.B. Lall. Considered fenestration layout to minimum solar
gain.
Capacity Building Series (2008-2009), June 2009, TARA Nirman Kendra, New Delhi
Guidelines:







Donot make unshaded windows too large to prevent over-heating inside the building.
Minimizing the area of glazing in hot/dry and moderate climates to be 10% of internal
floor area can give good reductions in heat gain.
Shade all windows in summer through chhajjas, adjustable shading devices, etc. Only in
colder climates should the sun be allowed to penetrate into the house in summer.
Within warm/humid climates smaller windows can be placed on the windward side, while
the corresponding openings/windows on the leeward side may be bigger for facilitating a
plume effect for natural ventilation.
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 year5, within the hot/dry
and moderate climate ranges.
Take into account highly reflective pavements outside the windows that will bounce light
back into the room, as will glass walls
Fenestration should allow proper ventilation and air circulation; openings at higher levels
would naturally aid in venting the hot air out.
Glazing should provide natural lighting without drastically compromising the insulating
properties of the building envelope. It should be ensured that windows are similar in
thermal performance to the adjacent walls, so that they donot attract condensation.
Fig 2.17 The use of a high level light shelf enables light to
be distributed deep within a space – the principle used on
the WBREDA building.
2.3.3.1 Daylighting
Traditionally, artificial means have been the predominant lighting source in commercial buildings,
mainly because the cost effectiveness of integrating passive measures is not appreciated by
architects and clients. Commonly, energy wastage occurs through over-illumination and where
natural lighting is ignored. Daylighting-conscious design and can significantly reduce lighting
energy requirements in a building. Since most buildings are largely used during the daytime,
effective daylighting makes economic sense. Unless dealing with a space where natural light is
inappropriate (eg secure facilities, archives, computer facilities), designers should therefore seek
to provide natural light. Building occupants will typically express a strong preference for spaces
that have a daylit appearance during the daytime. The benefits accrue not only through reduced
lighting energy consumption, but also in increased productivity. Studies have shown that within
the commercial context, spaces that are redesigned to make more effective use of daylight can
produce productivity increase in the order of 20%.
5
J.K. Nayak & J.A. Prajapati. Handbook on Energy Conscious Buildings (IIT Bombay/MNES India, May
2006). Chapter 5, page 16.
14
Fig 2.18 South façade of the WBREDA building with
horizontal light shelves depicted.
Capacity Building Series (2008-2009), June 2009, TARA Nirman Kendra, New Delhi
West Bengal Renewable Energy Agency, Kalkata (figure 2.18): Entry of daylight into work
areas is maximized through the use of light shelves to windows. This bounces light deep into a
space and is ideally suited when daylighting is required to reach deep into floor plates.
Daylight Factor: This is a good measure for designing daylit spaces. Light levels achieved will
vary throughout the year due to the position of the sun and changes in cloud cover, etc. What is
required is some measure of the penetration of daylight into a space that is independent of the
actual levels prevailing outside. Although, overcast sky illuminance, measured in ‘Lux’ may vary
between wide limits, the ratio between illuminance at a point indoors to that outdoors remains
constant. Target Daylight Factors are related to the use of a space and as a general rule do not
need to be particularly high (refer appendix 7 for daylight factors in relation to building types and
their specific functions).
Daylight factor =
Daylight Factor
Less than 2%
illuminance received from the sky at any point of interest inside your building
horizontal illuminance outdoors from an unobstructed hemisphere of the same
sky
Quality of lighting within space



Between 2% and
5%


More than 5%



Room looks gloomy under daylight alone
Full electric lighting will usually be required during
daytime
Electric lighting dominates daytime appearance, ie, the
space does not appear daylit
Windows give a predominantly daylit appearance but
some supplementary electric lighting will be needed
Best balance between daylighting and overall energy use
Room appears strongly daylit
Daytime electric lighting is rarely needed
Can be major thermal problems from large windows
Because external light levels tend to be very high, only relatively low daylight factors are required
to make an internal space serviceable. A room can have a daylit appearance if the area of glazing
is at least 1/25th of the total room area. This rule of thumb is based on achieving an average
daylight factor of 2% at table-top level in the room.
15
Fig 2…: Solar Energy Centre, Gaul Pahari, Gurgaon.
High level windows ensure diffuse lighting deep
into the floor plate.
Fig 2.17 Light reflected from external
surfaces provides valuable diffuse lighting
within a building.
Fig 2.19 Solar Energy Centre, Gaul Pahari, Gurgaon.
Light is reflected off roof areas and bounced off
internal ceilings.
Capacity Building Series (2008-2009), June 2009, TARA Nirman Kendra, New Delhi
Daytime electric lighting is usually required for a bright room appearance when the average
daylight factor is less than 5%. It should supplement the daylight and not swamp its natural
variation. The amount needed depends on the type of task and hence the illuminance required.
Where activities permit, good value is given by local task lighting instead of overall workplace
illumination. For most buildings the graph of lifetime energy costs against window size is Ushaped (refer figure 2.20) the optimum is found where daylight and electric light complement
each other during daytime hoursError! Bookmark not defined.. Choices of internal materials
and m\finishes are also important in determining the lighting gradient inside a building. User
control of lighting is always preferable to avoid wastage of lighting where its not needed or where
daylighting can create sufficient illuminance for the intended task. (figure 2.21)
Fig 2.20 Window size and energy costs.
2.3.3.2 Shading
Shading is an extremely effective means for reducing solar gain through windows and
subsequently the air-conditioning loads. Common external shading devices include fixed and
adjustable overhangs, trellis, awnings, louvers (horizontal or vertical, fixed or adjustable), and
wing walls (refer figure….). Common interior shading devices include roller shades, blinds,
drapes, and movable panels. Interior shading devices, while often not as thermally effective as
exterior devices, are generally easier to operate and maintain for the user.
The effectiveness of all shading devices is measured in terms of Shade factor, which is defined
as the ratio of the solar heat gain from the fenestration under consideration, to the solar heat gain
through a 3 mm plain glass sheet. The buildings form can also provide effective shading utilizing
simple ‘H’ or ‘L’ forms. Using a chajja of just 0.76m deep can reduce the maximum room
temperature by 4.6°C within a single story building in Ahmadabad. Shading can also be
increased through the use of side fins; ideally these are permeable so as not to completely
obscure views.
Fig 2.21 Control of electric lighting.
The reduction in yearly beam radiation incident on a typical window of size 1.2m X 1.2m having
different external shading devices (horizontal and vertical) in some cities of India is presented in
figure 2.21 The figure shows that providing a horizontal chajja can reduce the incident beam
radiation falling on the window in various orientations considerably. The shading can be further
enhanced by providing vertical fins6.
6
J.K. Nayak & J.A. Prajapati. Handbook on Energy Conscious Buildings (IIT Bombay/MNES India, May
2006). Chapter 3, page 6.
16
Fig 2.21 Effect of shading devices – window 1.2mx 1.2m
shaded by 0.6m chajja and full fins – the black bands indicate
the reduced solar radiation on the window.
Capacity Building Series (2008-2009), June 2009, TARA Nirman Kendra, New Delhi
Indian Institute of Health Management Research, Jaipur (figure 2.22) - Large chajja
overhangs provide appropriate shading to the main windows. Vertical Jali fins to windows also
provide shading and allow air movement. These ensure only diffuse light enters the office space.
Office building for Anarde Foundation in Guragaon by A.B. Lall: Custom designed with the
aid of computer simulation, the main building façade takes advantage of canvas shading devices
for individual windows.
West Bengal Pollution Control Board, Kolkata (figure 2.23): Angled fixed louvers specific for
different elevations help reduce thermal load and control glare. Vertical louvers screen windows
facing North, South facing windows have horizontal louvers. Windows facing East and West have
vertical louvers set with 30° angle towards South. This lets in early morning winter sun and cuts
out all day summer sun.
Guidelines:




Fig 2.22 Shading devices used in Indian Institute of
Health Management Jaipur and office of Anarde
Foundation NCR.
Within hot/dry and hot and humid climates all openings should be protected by Chajja and
side fins. Integrate shading systems at early stage within the design process. Use them to
cut down excessive light and glare.
Moderate climates should take advantage of movable shades should to prevent over heating
in summers. Shades can then be adjusted in winter months to promote heat gain.
East and West fenestrations require large overhangs for protection. Porticos or verandahs
can be used for this purpose.
Consider both internal controls such as blinds and curtains as well as external devices. Be
aware that curtains and blinds can diminish airflow when ventilation is needed in humid and
warm climates.
2.3.2 Roof
The roof of a building receives a significant amount of solar radiation and has a key role in heat
gain and loss, daylighting and ventilation. Depending on varying climatic needs, proper roof
treatment is essential to maintaining internal comfort within a building. Preventing heat flow
through the roof either by enhancing its thermal mass or by installing insulation makes sense in a
tropical climate of India where daytime sun is directly overhead in many cases. Roof areas using
lighter construction methods will require secondary insulation to be applied such as Vermiculite
concrete screeds or internally laid loose-fill type insulation. The pitch of a roof is also important
with steeper angles receiving less gain.
17
Fig 2.23 Fixed angled louvers as shading devices in the
WBREDA building in Kolkata
Capacity Building Series (2008-2009), June 2009, TARA Nirman Kendra, New Delhi
Insulation may be applied externally or internally to the roofs. For external application, material
needs to be protected by appropriate waterproofing. For internal use, false ceilings can hide
insulation material and provide an air gap between the internal space and roof.
Integrated Rural Energy Programme Training Centre, Delh (figure 2.24)i. Architect
Manmohan Dayal. The entire roof has been covered in densely packed inverted earthen pots laid
in mud phuska. This is a traditional cost effective system that provides an insulation cover of still
air over the roof trapped within the pots, impeding heat flow through to the building.
Redevelopment of property at Civil Lines, Delhi (figure 2.25): The courtyard roof/skylight uses
evaporative cooling by running water over its surface. A Chic to the exterior of the roof can be
rolled down to retain heat in winter months and internal Razai (quilts) can seal off the skylights
and provide insulation when needed.
Guidelines:

 Shiny and reflective material (e.g. glazed china mosaic) may be laid on top of the roof for
reflection of incident radiation.
 The use of inverted earthen pots for trapped air insulation provides a traditional, cost effective
solution.
 Vermiculite lightweight concrete can be used as an insulative screed layer over the top of
roofing structure.
 Use plant cover with deciduous plants and creepers to create a ‘green’ insulative layer as an
option.
 White washing of the roof can be done before the onset of each summer. To maximize the
roofs reflective efficiency, all surfaces should be kept clean and free of dust.
 Ventilation devices through roof vents can greatly aid air movement within a building.
Carefully consider the orientation of these to suite prevailing wind directions. These are can
effectively increase comfort levels in hot/humid climates.
 In hot/dry regions, consider the use of flat roofs. These can be used for sleeping in summer
and winter daytime activities. Materials chosen should have adequate mass such as
reinforced concrete, with possible external insulation. This region would also benefit from
evaporative cooling of the roof surfaces and night-time radiative cooling.
 Cold/cloudy and cold sunny climates benefit from having sloped roofs to promote drainage of
water and snow. Insulation must be used to ensure heat retention. Aluminum foil to the
underside of the roof further reduces heat loss.
18
Fig 2.24 Roof details showing inverted earthen pots for
insulation.
Fig 2.25 A rural school building in hot and dry Tehri
region with a roof garden
Fig 2.26 Property at Civil Lines, Delhi. Roof with
integrated systems for insulation and cooling.
Capacity Building Series (2008-2009), June 2009, TARA Nirman Kendra, New Delhi
Ground floors
Of primary concern within the colder regions of India is heat loss through ground level floors. Heat
is transferred by conduction from the building through the ground floor where the structure makes
direct contact with the soil. The transfer of heat between ground and floor primarily occurs around
the perimeter of a building, with less transmission through the center of a ground floor. In warmer
climates heat loss is desirable and in cold climates it needs to be minimized through the use of
insulation. Factors such as the moisture content and temperatures alter the effectiveness of
insulation under a slab. In these situations the perimeter should be insulated with 50mm x 600mm
wide strips of insulation. To improve this, the entire underside of the slab can be insulated.
2.4 PASSIVE SYSTEMS
Passive systems regulate a building’s heating and cooling load without any mechanical means.
To meet heating needs, passive methods store, control and distribute thermal energy flow
through the natural principles of heat transfer7. For cooling needs, which are more significant in
the context of India’s tropical climate, passive methods usually involve a combination of
minimized heat gain through an efficient building envelope, ventilation for heat dissipation and,
commonly, natural techniques based on evaporative cooling.
2.4.1 Passive cooling and ventilation
The essential principle of passive cooling is to prevent heat from entering the building, or remove
heat once it has entered. The main methods employed within the Indian context are ventilation
cooling, evaporative cooling, nocturnal radiation cooling, desiccant cooling and earth coupling.
The success of these concepts depends greatly depends upon localized climatic conditions.
Fig 2.27: Induced ventilation principles and variations.
Natural ventilation and airflow utilize breezes to create air movement through a building and the
resultant cooling. Effective ventilation requires openings to be in opposite pressure zones. If the
inlet and outlet are placed at different heights, air flows from the inlet to the outlet due to the
density difference created by the upward movement of warm air. Ventilation requirements of
different seasons and for different types of occupancies should be determined early on in the
design process to create an effective passive system with minimized dependence on mechanical
means.
7
J.K. Nayak & J.A. Prajapati. Handbook on Energy Conscious Buildings (IIT Bombay/MNES India, May
2006) Chapter 3, page 2.
Fig 2.28 The basic rule of thumb for cross
ventilation.
19
Capacity Building Series (2008-2009), June 2009, TARA Nirman Kendra, New Delhi
A key area in ventilation design is the principle of air changes per hour referred to as ‘ACH’. This
is essentially the capacity of a space to dissipate heat. With key data of air density, ventilation
rates, specific heat of the air, and the internal and external temperature differences optimal air
change rates can be calculated for different spaces. Figure 8 states a selection of air-change
rates per hour for different types spaces.
Torrent Research Centre, Ahmedabad (figures 2.29 and 2.30) This project has successfully
incorporated passive down draft towers to cool the building. Monitoring the building performance
during the summer of 1997 revealed an internal temperature stayed at 29-30°C when the outside
temperature reached 43-44°C.
Following are some passive cooling and ventilation systems:

Cross ventilation: When a building is cross ventilated during the day, the temperature of the
indoor air is similar the ambient temperature (refer figure 2.28) for the basic cross ventilation
rule of thumb). Cross ventilation is an absolute must for warm and humid climates to remove
the excess heat input from the external environment.

Stack effect: A lot of air movement indoors is created through the stack effect and wind
pressure. Stack effect can be created by differences in temperature or humidity. For example,
a duct with an elevated vent above the terrace level is effective in inducing air movement
inside the building through the stack effect. Such an arrangement expels hot air which is
replaced by incoming air from other openings and is called a solar chimney.

Wind towers: Similarly, wind towers use wind pressure for cooling. The change of
temperature and thereby the density of the air in and around the tower creates a draft, pulling
air either upwards or downwards through the tower.

Evaporative cooling: The outdoor air is cooled by evaporating water before it enters a
building. A water body such as a pond, lake or sea near the building, or even a fountain can
provide a cooling effect. This is a highly effective technique for predominantly hot and dry
climates and can be greatly enhanced by system design which integrates high quality cooling
surfaces or pads with the required air flow rate for the given building.
A variant of the system is Passive downdraft evaporative cooling which consist of a downdraft
tower with wetted cellulose pads at the top of the tower. These cool the air flowing over them,
causing air to sink into the body of the house and hot air to rise up.
20
Fig 2.29: Photograph showing the large inlet
shafts and tall, narrow outlet shafts.
Fig 2.30: Typical Cross section of the Torrent Research
Centre with inlet shafts.
Capacity Building Series (2008-2009), June 2009, TARA Nirman Kendra, New Delhi

Nocturnal cooling: This occurs if the ambient air is cooler than the room air. The interior mass
of the building is cooled and on the next day the cooled mass reduces the rate of indoor
temperature rise providing a cooling effect.

Earth Coupling: Utilizing the earth as a massive heat sink this method is for both heating and
cooling. At a depth of 4-5m below ground, seasonal variations of temperature within soil
remain fairly constant. Ambient air is blown through a section of buried pipe and is cooled in
summer and heated in summer (figure 2.31) for a typical earth coupling section.
Fig2.32 Sun space passive heating system cross section.
2.4.2
Passive Heating
Direct gain is a passive heating technique that is generally used in cold climates and is the most
common, simple, cheap and effective heating approach. In this technique, sunlight is admitted
into the living spaces directly through openings or glazed windows. The sunlight heats the walls
and floors, which then store and transmits the heat to the indoor environment.
Sun spaces are a common approach to passive heating, usually in the form of an attached glazed
room or solar greenhouse (refer figure 2.32 for a typical cross section). The sun space acts as a
solar collector, admitting solar radiation and storing it within interior surfaces such as a mass wall.
Some of the heat is rapidly transferred by natural convection to the sunspace air and some of it
flows into massive elements within the sunspace (floor, walls and water containers) to be
returned later. The sunspace is, thus, a direct gain space in which heat is used directly to
maintain a temperature suitable for its function, such as a secondary living space. This may be by
conduction through a masonry common wall, by natural convection through openings (doors,
windows, or special vents) in the common wall 8.
The main requirements of a direct gain system are large glazed windows to receive maximum
solar radiation and thermal storage mass. Direct gain can result in overheating, glare and
degradation of building materials due to ultraviolet radiation are some of its disadvantages.During
the day, the affected part of the building tends to get very hot, and hence, thermal storage mass
is provided in the form of bare massive walls or floors to absorb and store heat.
This also prevents overheating of the room. The stored heat is released at night when needed
most for space heating.
Examples of indirect heat gain include Trombe and water storage walls (refer figures 2.33 and
2.34 for Trombe wall).
Fig 2.31 Cross section of an earth coupling system.
Active systems are discussed in the next section on Energy in buildings
8
Sue Roaf, Manuel Fuentes and Stephanie Thomas. Ecohouse, A Design Guide. (Architectural Press 2001).
Page 157.
21
Fig 2.33 Trombe wall facing south, winter condition:
heating by radiation and convection.