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1.INTRODUCTION

1.1 BACKGROUND

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In India,
33% of the total energy consumption happens in the building sector (1) and
primarily due to the cooling load requirements of summer season which add up to
environmental pollution, resulting in global warming and ozone depletion.

It has
become need of the hour to promote passive cooling techniques, to achieve the
thermal comfort, thus reducing the air conditioning requirement and for the
period for which it is generally used.

Productivity
and satisfaction of indoor building occupants is greatly influenced by the
thermal comfort. The interactions between people and thermal environment are
studied through various factors which vary independently of each other.
Fanger,P.O, has developed a concept combining thermal effect of all physical
factors which create thermal comfort. By means of this comfort equation, it is
possible, for any activity level and any clothing, to calculate air
temperature, air velocity and humidity values which create thermal comfort.
(Fanger,P.O, 1970,P 244).

This
paper aims to study the heating and cooling loads of an 80 sqm library space in
Mumbai, India, known to have a warm and humid climate and work out a design
solution to comparatively a balanced interior solution.To carry
out a solution for thermally comfortable indoor space, it is very important to
understand the climatic conditions of the site and its impact on the any space.
This paper analyses the most crucial factor, i.e.  the climatic conditions with respect to the
thermal comfort and approaches the space with improvements of an energy
conservation design strategy.

 Mumbai (Latitude: 19.12° N, Longitude:
72.85 ° E, Elevation: 14 MASL)

Figure1
India map on Koppen climate classification
Image source: Köppen-Geiger,2006
 
 

 

Figure 2
Image source: meteoblu,2017
 

 

The climate in
Mumbai is predominantly warm and humid. Although temperatures are not very high
in summer, conditions are uncomfortable due to the high humidity.

 

Mumbai has a tropical climate. When compared with winter, the
summers have much more rainfall. According to Köppen and Geiger, this climate
is classified as a tropical savanna climate (Aw) (Figure 1)

Figure 3
Image source: meteoblu,2017
 

 

It can be best described as moderately hot with high level of
humidity. The average annual temperature is 26.8 °C in Mumbai. In a year, the
average rainfall is 2386 mm.1
May is the hottest month with the monthly average daily maximum temperature
reaching as high as 38 °C, coupled with a humidity of about 60% during daytime.
(Figure 2,3).

Hence, reducing heat gain and promoting heat loss becomes
essential to maintain a thermally comfort environment in a space with warm and
humid environment.
Further calculations for heat load are carried out in this paper to analyse the
range of heat gain and thus, provide better alternatives for designing an
efficient and thermally comfortable space.

3. BUILDING AND OCCUPANTS

(Base-case
model)

The work in
this essay aims to investigate the energy consumption and thermal comfort in a
small space. It focuses on 80 sq.mt library room in Mumbai, India, built inside
a residential building. (Figure 5). The space dimension is broadly 8m façade by
10m depth with a height of 4m. The density of occupants is 5sq.mt per person
(Neufert,2012). The occupants clothing coefficient is 0.6 clo for summer season
and 1 clo for winter, while their metabolic rate is set to 1.3 met and 1.4 met
for the summer and winter season respectively (CIBSE 2015; Building Directorate
2013).The weather was data was found on the govt official
sites and from the epw file from EnergyPlus.
This was later used in the climate consultant.
Heat balance equation (Welsh School of Architecture, 2017), is used to
investigate the energy balance and thermal comfort of the library in steady
state where the thermal mass of the space structure is omitted.

The equation states:HEAT BALANCE EQUATION  From the calculations it can be noted that
annually there is a heat gain of 242.38KW and thus, cooling is required
throughout the year.DISCUSSIONFrom the
calculations above it is safe to infer, annually the worst case of heat gain is
the solar heat gain through single pane reflected coated glass frames (78%) and through ventilation and infiltration
(13%) (figure 8). These are the crucial points which in this paper are further
worked upon after getting an understanding from the typical practices and
techniques worked in this area to achieve comfort. 

Figure 8 (From the calculation above)

 

 

 

5. TYPICAL PRACTICES This part will talk about three
buildings. –1.     
Kohinoor
Hospital, Mumbai (first LEED Platinum rated project in Asia) (Figure 9)2.     
Computer
Maintainance Corporation building, Mumbai (Daylight intergration factor)(_)3.     
Observations for
RTI building, Mumbai (with respect to ECBC requirements)(_)5.1. Kohinoor Hospital, MumbaiKohinoor hospital
is 227000 sqft with 150 bed health case facility housing 2 basements,
ground  +5storey structure. It is a
multispeciality hospital implementing a range of energy efficient measures to
reduce energy consumption, decreasing green house gas emission and improving
the quality of patient care.Energy Analysis-·       
Gross window to
wall ratio is approx 27% ·       
Considers
ASHRAE/IESNA 90.1(2004) baseline.Fenestration·       

Fenestration detail
 

 

Capacity to retain and reflect
heat·       
Double glazed
units with high performance reflective glass of 1.2U value.Envelope·       
WALL : External
brickwall 230mm
Airgap: 650mm
Extruded Polystyrene: 75mm
Brickwall:100mm·       
Roof: 200mm thk
RCC with 75mm extruded insulation entirely above deckLighting ·       

Double glazed window
 

 

Efficient and intelligent
lighting system with LED/CFL combination·       
LED for cove
lighting·       
Activitywise
distribution to achieve optimum lux level·       
Occupany sensors
in public toilets·       
Careful
circuiting for efficient lighting stategyAchieved overall
LPD of 0.54W/sqft.

5.2 Computer
Maintainance Corporation building, MumbaiIt is a cubical
form office complex of 25mx25m with height of 30m.This building is a good
example for integration of day lighting system.·       
Windows on
periphery are unable to transmit day light into the working areas.·       
To introduce
daylight on all floors, a central atrium with circulation routes around the
atrium is designed.·       
Double glazed
peripheral windows are split in two parts
to serve different purposes : upper half for day lighting and lower half for
view.·       
Upper window
incorporates light shelves which respond which repond to the angle of incidence
of sunlight on different faces of the building.·       
Motorized louvers
automatically adjust to reflect sunlight on white ceiling.The net effect of
this daylight integration factor succeeds in achieving dayligh without any
artificial lighting during day light hours.  5.3 Observations
for RTI building, MumbaiThe RTI building,
Mumbai is a air conditioned building in an area of 4972sqm. 
The observation for this building with respect to ECBC is carried out by Teri,
The energy and resource insitute for the PWD(public work department) .
The table (9) shows energy consumption by a running building while following
the ECBC requirements.                         6.BEST PRACTICEIndia’s
Energy Conservation Building Code(ECBC) currently provides guidance which has potential
to reduce energy loads in a convention building by 40% to 60%, as stated by the
Ministry of Power, Govt of India,2007. But this guidance isn’t compulsory to
follow as of yet.Bioclimatic chart of Mumbai shows May to be the hottest month with
average daily maximum temperature as high as 32? with a humidity of 60% during daytime. Thereby suggesting mechanical
air conditioning from April to October during these days. The months of
January, February, November and December are comparatively comfortable.Due to high
Relative humidity, cross ventilation is both
desirable and essential to protect the building envelope from direct solar
radiation through shading.In order to
produce an efficient design, it is important to resist heat gain by decreasing
exposed surface area, increasing thermal resistance, increasing buffer space
and increasing shading; and to promote heat losses through ventilation of
appliances, increase air exchange rate throughout the day and decreasing
humidity levels. Recommended design parameters for the base
case:  1.     
Glazing TypeDouble
glazing with reflective coated glass has higher performance in contrast to the single pane
reflective coated glass (base case). This is because single pane clear glass
increases the load by 9.3%, whereas the double glazing with reflective coating
decreases the load by 2.2%. (Handbook of
energy conscious design,2006 pg. 239)2.     
Window
SizeThe base case of window size 2.8X2.8 m
intakes huge amount of solar gain. Reduction of glazing size to 1.2m height has
potential to reduce the annual load by 6.5% (Handbook of energy conscious
design,2006 pg. 397) 3.     
ShadingAnother way of reducing the solar gain Is
to provide windows with external shading by means of external shading by means
of external shading by means of external projections like chajjas. If 50% of
window areas are shaded, then annually there can be a load reduction of 8.5%
(base case: no shades)4.     
Wall
Type Having an autoclaved cellular concrete
block over concrete wall (base case) can reduce the heating load by 2.4%,
because of its lower U value.5.     
Colour
of external wallDark colour over white colour for the
external surfaces can increase the load by 4% annually. Hence, is avoided.6.     
Air
ExchangesLowering the air exchange rate to 0.5ach
from 5ach(base case) reduces the annual load by 1.7%.               7. CONCLUSION

The combination of all design parameters is
taken into account will reduce 25.3% of the heating load. Hence, succeeding in optimising
the energy balance/comfort for the library of 80sqm in Mumbai,India.

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