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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

[email protected]

Department of Architecture,

National Institute of Technology,

Tiruchirappalli, Tamil Nadu

India

[email protected]

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)


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http://www.sciencedirect.com/science/article/pii/S0169204614000607#bib0150

http://www.sciencedirect.com/science/article/pii/S0169204614000607#bib0170

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


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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)


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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


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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)


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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


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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

1. Acharya,P.K (1979),Indian Architecture According to Manasara Silpasastra,Patna,India:Indian India.

2. A.M. Papadopoulos, “The influence of street canyons on the cooling load of buildings and the

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)

4. C. Conner, “The effect of exterior surface absorptivity and emissivity on energy use in residential

buildings”, Unpublished report, Lawrence Berkeley Laboratory (1985)

5. Gururaj G. Road traffic injury prevention in India. Bangalore: National Institute of Mental Health and

Neuro Sciences; 2006.

6. H. Taha, “Urban climates and heat islands: albedo, evapotranspiration and anthropogenic heat”, Energy

and Buildings, Vol. 25, pp. 99-103 (1997)

7. www.imd.gov.in - Indian Meteorological Department, Ministry of Earth Sciences, Government of

India.(IMD)

8. L. Barring, J.O. Mattsson and S. Lindovist, “Canyon geometry, street temperatures and urban heat

island in Malmo, Sweden”, Journal of Climatology, Vol. 5, pp. 433-444 (1985).

9. Energy and Climate in the Urban Built Environment , M.Santamouris,(2001)

10. M. Santamouris, N. Papanikolaou, I. Livada, I. Koronakis, C. Georgakis, A. Argiriou, and D.N.

Assimakopoulos, “On the impact of urban climate on the energy consumption of buildings”, Solar

Energy, Vol. 70, pp. 201-216 (2001).

11. Oke, T. R. (1987). Boundary layer climates. Cambridge: University Press.

12. Peden M, Scurfield R, Sleet D, Mohan D, Hyder AA, Jarawan E, et al. World report on road traffic

injury prevention. Geneva: WHO; 2004.

13. R. Priyadarsini and N.H. Wong Parametric Studies On Urban Geometry, Air Flow And Temperature ,

International Journal on Architectural Science, Volume 6, Number 3, p.114-132, 2005 ).

14. Rohinton Emmanuel, An urban approach to climate sensitive Design strategies for the Tropics(2005-

pp21).

15. S. Yamshita, K. Sekine, M. Shoda, K. Yamashita and Y. Hara, “On the relationship between Heat

island and sky view factor in the cities of Tama river basin, Japan”, Atmospheric Environment, Vol.

20, No. 4, pp. 681-686 (1986)


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