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DESIGN BEST PRACTICE METHODS TO
MINIMIZE THE IMPACT OF BUILDING
MATERIALS ON URBAN
MICROCLIMATE
D.Kannamma Dr.A.Meenatchi Sundaram
ABSTRACT
Urban spaces in tropical country like India have always been the focus of socio cultural activities. In
recent times these activities are stressed by increased urbanization. Among many factors that influence outdoor
ambient temperature (traffic, pollution, population density…) the building surface treatments have also
contributed in challenging the urban micro climate. Insufficient open spaces, diminished wind movement and
strong irradiation from the high rise densely packed built environment has very much reduced the quality of
urban outdoor life. Though there are many individual studies on the built form and building material influence
on urban micro climate, they seldom give comprehensive guidance to the city designers, essentially the planners
and the individual architects.
This paper investigates the influence of building materials on the micro climate of urban commercial
streets (pedestrian users) by comparing their thermal performances. The study also tries to explore possible
design interventions to minimize the impact of the building materials on the urban micro climate. Henceforth
the outcomes will create cognizance among the designers to evolve climate sensitive design and material
choice. Urban Micro Climate - Building Materials - Design Solution. The inferences in this paper will enable
the architects and planners to design buildings with the understanding of their response to the urban
microclimate and comfort of the pedestrian users.
KEY WORDS Urban Microclimate, Building Materials, Heat Transfer, and VASARI
INTRODUCTION
The phenomenon of city - induced environmental change has been known for many centuries. The
ancient Indian Architectural manual “Silpa Sastra”(translated by Acharya 1979) laid out rules for the siting of
villages, towns and forts based on prevailing wind directions and solar orientation.( Rohinton Emmanuel,2005).
The city design is basically composed of many elements like the buildings, open spaces, networks (roads,
streets, pathways, and bridges), traffic (vehicle & pedestrians), and vegetation. The inter relationship among
these elements influence the quality of the urban environment. Though there are many factors that define the
quality of urban life (environmental, functional, and aesthetic) this paper focuses on the environmental quality
of the cities.
Department of Architecture,
National Institute of Technology,
Tiruchirappalli, Tamil Nadu
India
Department of Architecture,
National Institute of Technology,
Tiruchirappalli, Tamil Nadu
India
30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad
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A large number of road users in India are pedestrians. (Gururaj G,2006)( Peden M, Scurfield R, Sleet
D, Mohan D, Hyder AA, Jarawan E, et al. ).The environmental comfort of the pedestrian users is seldom given
a thought by the planners, developers and designers. The factors that influence the outdoor thermal comfort of
the pedestrian users can be broadly classified as the Climatic Factors (Solar Radiation, cloud cover,
precipitation, wind speeds, Humidity, and air temperature) and the Physical Factors like (orientation, Aspect
Ratio, Vegetation, Sky View Factor (SVF), Building Materials) (Oke et al., 1987 and Santamouris, 2001). The
influence of the building materials on the urban microclimate focusing on to the pedestrian users and the
possible solution is a part that still needs to be explored by the planners and designers.
Hence the aim of this paper is to analyze the building material contribution on the urban microclimate,
specially focusing on the pedestrian users. The result of the analysis enable in arriving strategies to improve the
microclimatic condition as this will facilitate the architects and planners to design buildings with the
understanding of their response to the urban microclimate and comfort of the pedestrian users.
METHODOLOGY
To evaluate the influence of building materials on the urban microclimate of the pedestrian user’s two
commercial streets of the CBD (Central Business District) is chosen with different orientations. The surface
radiation in the streets were calculated for five different time periods. The climatic data was calibrated with an
Infrared Thermometer, air temperature and wind speed was calculated with hand held devices. The radiation of
the surfaces were calculated through the Stephen Boltzmann Constant. The radiation values were mapped. The
radiation values of the individual materials were analyzed for surfaces with different orientation and aspect
ratio. The result of the comparison enabled this study to derive strategies that would assist the designers and
planners to work on options so as to minimize building material influence on the microclimate the urban
pedestrian users. Since the study area is a CBD there was no scope for vegetation. Hence the impact of
vegetation on the microclimate of the study area is not considered.
SITE DESCRIPTION
The study was conducted in Tiruchirappalli City (Tamil Nadu , India) located at 10° 48' North and
78° 41' East. The city is at the altitude of 88 m above sea level. The climate of Tiruchirappalli is Hot Humid.
The state of Tamil Nadu has a clear climate change scenario. The study was done in the month of April - 2013,
based on the IMD report April month has recorded the highest. (State Level Climate Change Trends in India,
Meteorological Monograph No. ESSO/IMD/EMRC/02/2013).
Traffic Pattern
The commercial streets (NSB Road, Big Bazaar Street) of the CBD (Central Business District) of
Tiruchirappalli City was chosen for the study. The streets are both high density and high rise in character with
no scope for vegetation. These streets are significant because they are mostly used by the pedestrians. At the
time of festivals like Deepavali and Pongal the streets are completely pedestrianized.
Figure1: Shows the traffic pattern in
(a) NSB Road,(b) Big Bazaar Street.
(Source: Tiruchirappalli city Traffic
Police)
30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad
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The buildings of both the NSB road as well as the Big Bazaar Street are of different heights and different surface
treatments. The common material used on the building skin are the Aluminum composite panel, Structural glazing
(both doubly as well as single glazed layer) and Cement plastered wall with paint. The road surface is made of asphalt.
Solar Access
The urban microclimate is influenced by many anthropogenic induced factors like Pollution, High
density construction that cause less wind (A.M. Papadopoulos 2001, B. Givoni 1998) , building material choice
(H.Taha,1997),Orientation of buildings,streets (M. Santamouris, N. Papanikolaou ,2001),Lack Of Shading(L.
Barring et.al ,1958),Canyon Geometry (S. Yamshita , 1986). The incident solar radiation influences
significantly on these anthropogenic factors. Unlike the western countries the right to solar radiation has to be
controlled in Tropical country like India to achieve an ambient urban microclimate. The incident solar radiation
contributes significantly to the heat transfer phenomenon of the building materials (C. Conner, 1985).
The urban canyon is a more useful city unit for the study of the microclimate of urban environment.
The energy balance of the ‘Earth surface’s – ambient air’ system in the urban environment is governed
by the energy gains and losses as well as by the energy stored in the opaque elements of the city, mainly
buildings and streets.(M.Santamouris,2001)
NSB
BIG BAZAAR
Figure2: Shows the character of NSB Road
Figure 3: Shows (a) NSB Road (East-West), (b) Big Bazaar
Street (North- South) orientation(Ecotect 2011)
Figure 4: Shows the character of Big Bazaar
Street
30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad
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Energy gains = Energy losses + Energy Storage (1)
Incident solar radiation values are based on two primary components: Direct Radiation from the sun
(direct bean radiation = Ib which is always measured perpendicular to the sun’s rays. Diffuse radiation that is
both scattered by the clouds and atmosphere (diffuse sky radiation = Id) and the ground in front of the surface
(Ir).This is always measured on a horizontal surface.
i.e Incident Solar Radiation = (Ib * FShading * Cos ø ) + (Id + FSky) + Ir (2)
Where: Ib = direct bean radiation
Id = diffuse sky radiation
Ir = radiation reflected from the ground
FShading = Shading factor (1 if a point is not shaded, 0 if a point is shaded, a percentage if
measured on a surface)
FSky = Visible sky factor (a percentage based on the shading mask)
Ø = angle of incidence between the sun and the face being analyzed.
Heat Transfer
The heat transfer phenomenon between the buildings and the environment is very complex (R. Priyadarsini
and N.H. Wong, 2005). This phenomenon can be defined on the basis of three basic parameters
( A.M. Papadopoulos,2001):
1. The insolation of the buildings, which is a direct function of the orientation, the morphology of the
building and the shading factor due to opposite buildings and the existing shading devices;
2. The wind flow in the street canyon that depends on the road’s orientation in relation to the prevailing
wind direction, the geometric characteristics of the canyon and the temperature conditions on the
surfaces of the buildings and the road; and
3. The additional heat emission from local points like the air conditioning systems and the road traffic.
Temperature and Radiation
The three main methods of heat transfer resulting in change of temperature are conduction, convection
and radiation. All bodies with a temperature greater than absolute zero radiate energy. Absolute zero is the
temperature at which there is no molecular or atomic random motion. It’s denoted by 0 Kelvin
degrees, which is equivalent to -273.15° C or -459.67° F. Late in the nineteenth century, Stefan experimentally
and Boltzmann theoretically developed a relationship between the temperature of a body and the amount of
power it radiates.:
To determine outgoing radiation power, we utilize the Stefan-Boltzmann Law
P = A ε Ϭ T 4 (3)
Where P (watts) is the radiated power from a body of area A (m2) at temperature T (K).
ε is emissivity
σ is the Stefan-Boltzmann constant, 5.67x10-8 Wm-2T-4
T is the body temperature in Kelvin.
Hence the radiation emitted by buildings, streets and all emitting surfaces in the canopy layer can be
calculated through the Stefan-Boltzmann Law (M. Santamouris ,et al. , 2001)
30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad
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Material Map
The materials of the streets are mapped and the area for the individual materials are calculated, the surface
temperature of the materials are measured for five different time period (7.00 am,11.00am,13.30 pm,15.00 pm,17.00
pm).
Observation
The documentation of the building in
NSB Road and the Big Bazaar Street resulted
in thirteen different materials. (Table 1).
When the radiation of the materials
were calculated using Stephen Boltzmann
Law, it was observed that due to more
emissivity value and substantial percentage of
usage in the surfaces, concrete and asphalt
contribute significant radiation for all the five
time periods analyzed. The radiation value of concrete range between
0.0841W to 0.0878 W and that of asphalt range between 0.042 W to
0.046 W (Figure 6).
S.no Material Area
1 Concrete 5727.3
2 Glass 1477.14
3 Plastic Board 626.1
4 Flex 674.8
5 Metal 142
6 Granite 9.9
7 Asphalt 2722.9
8 ACP - white 286
9 ACP - Red 87.3
10 ACP – Grey 1391.3
11 ACP - Gold 186.2
12 Gypsum – White
20.3
13
3 Gypsum - Gold 39.7
Figure 5: Shows the materials map on the
building façade - the streets in elevation.
Figure 6: Shows the radiation value of the materials
NSB ROAD - NORTH
NSB ROAD - SOUTH
Table 1: Shows the materials and the area on the
building façade.
BIG BAZAAR STREET - EAST
STREET - SOUTH
BIG BAZAAR STREET
STREET - SOUTH
BIG BAZAAR STREET - WEST
STREET - SOUTH
30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad
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The surface temperature value of the materials in the NSB Road (East – West orientation) was 3° C
more in comparison with that of Big Bazaar Street (North – South Orientation) and this difference was more
significant in the early evening time (15.00 pm) when the materials start reradiating the incident radiation.
Hence it was evident that the materials in particular, concrete and asphalt influence the microclimate of both
the streets.
Street Geometry – Materials – Urban Microclimate
This study further explored the relationship between urban canyon and urban microclimate. There were
very interesting relationships observed.
The open space between the buildings in the Urban Canyons along the East - West orientation streets
experienced more radiation on the base surface (roads) compared to that of the vertical surfaces
(building façade). This phenomenon was opposite in the urban canyons of the North - South
orientation. (Figure 7).
The urban canyons with Aspect Ratios (2 – 5) in both the NSB Road and the Big Bazaar Street had air
temperature values less compared to that of the urban canyons with Aspect ratios (0.3 – 0.5). But when
the PET (Physiological Equivalent temperature) values were calculated using RAYMAN software for
the five different time periods, the values were above the normal comfort range. The PET values (22° C
min. - 43° C max), which is much above than the normal range of comfort. (When the comfort range
for Tiruchirappalli City was calculated using the weather tool of Ecotect 2011 the range was found to
be 26° C - 31° C). The reason behind this discomfort range even in canyons with more aspect ratio is
because of very poor wind speed (range between 0.27m/s – 0.54 m/s) due to the high density. When the
study area was simulated using the Autodesk Vasari software it was found that practically no wind
movement at the height of 2.8m from the ground surface, which is almost the height of the space used
by the pedestrians (Figure 8).
Figure 7: Shows the solar irradiation value of surfaces in NSB Road and Big Bazaar Street. (Simulated Using Autodesk VASARI)
NSB Road
Big Bazaar Street
Figure 8: Shows the wind movement along NSB Road and Big Bazaar Street. (Simulated Using Autodesk VASARI)
Aspect Ratio (2-5)
Aspect Ratio (0.3-0.5)
30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad
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Since Tiruchirappalli belongs to hot
humid climatic zone, the problem of
humidity was also felt in certain
canyons with poor wind movement.
Increased air temperature (almost 42°
C) and humidity as high as 63%
further deteriorated the outdoor
comfort condition of the pedestrian
users.
Autodesk Vasari, Ecotect and
RAYMAN were all validated with
the questionnaire survey. The
Percentage of people Dissatisfied
were more in NSB Road (East -
West) compared to the users of Big
Bazaar Street (North – South) for all the
five time period (Figure 9).
Design Best Practice Methods
After careful study and analysis of the urban canyon and urban microclimate interactions following
design best practice methods were derived (Figure 10):
The choice of building material used on the surface of all planes of urban elements (Base plane – floor,
Vertical Plane – walls, Overhead Plane – Building Projections) should be more environment friendly,
in radiating heat.
The street orientation has to be considered while deciding on the material choice for roads. (In the case
of NSB road maximum radiation was from the asphalt used on road).
As how the built space - open space ratios are worked out in 2 – D plans of individual building designs,
similar structure has to be considered for the city planning to enable and enhance wind movement. But
in areas of high density and high rise buildings like the study area (CBD), outdoor microclimate can be
resolved only by providing shading, as wind movement is restricted.
In order to enhance wind movement among high density built spaces, regulations can be formulated to
design buildings with solid and void volumes.
Figure 9: PPD of NSB Road and Big Bazaar Street
Figure 9: Shows the PPD value for NSB Road and Big Bazaar
Street
Figure 10: Design best practice methods
30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad
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The planning of cities should also consider the 3 - D of the built volumes, since aspects like SVF can
be resolved. The canyons can be designed with surface projections and overhanging to reduce the
impact of surface radiation of the materials as well they can provide shading for the pedestrian users.
Since there is less scope of vegetating spaces near buildings , greening of roofs and walls can be done
to minimize the impact of radiation.
Conclusion
In a Tropical country like India, where more activity is extended outdoors, climatic comfort of
pedestrians is inevitable in the design of urban spaces. Though there are many climatic factors that control
urban microclimate, the most important of them is the air temperature, since it directly influences the PET
(Physiological Equivalent Temperature). From the study of the commercial streets in the Tiruchirappalli city it
was obvious that the air temperature value can be controlled with the help of canyon geometry as well as by
enhancing the movement of wind. The increase in wind also offers important role in minimizing the impact of
excess humidity in air. These design best practice methods has to be executed right from the level of individual
building design to the scale of city design in coherence with the climatic factors. Because the physical factors of
the urban canyon and the city climatic factors mutually interact and influence one other. This influence has to
be made positive to achieve better comfort condition for the urban pedestrian user.
REFERENCE
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performance of air conditioning systems”, Energy and Buildings, Vol. 33, pp. 601-607 (2001).
3. B. Givoni, Climate considerations in building and urban design, John Wiley & Sons Inc. (1998)
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30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad
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