Climatic Design of Buildings

7/27/2019 Climatic Design of Buildings

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: CLIMATIC DESIGN OF BUILDINGS:

(Prof.A.J.Sanyal, B-Arch;M.T.P;AIIA;AITP)

Basic needs of man are (a) food, (b) shelter & (c) clothing. Architects are concerned with the design of

comfortable building. Design subject is the backbone of architecture course & it starts from 1st

semester

till retirement from service/practice. Climatic factors in the design of buildings are very important in

proper comfortable design of buildings so as to reduce the dependence on conventional energy sources

e.g. electricity, diesel, fossil fuel etc.

Basic concepts: Weather is the set of atmospheric conditions prevailing at given place and time.

Climate can be defined as the integration in time of weather conditions, characteristic of a certain

geographical location. At global level climates are formed by the differential solar heat input & the

uniform heat emission over the earths surface. The movement of air masses & of moisture bearing

clouds is driven by temperature differentials & strongly influenced by the Coriolis force.

Classification of climate: Classification climate for the purposes of building design can be done based onthe nature of the thermal problem in particular location is often used & it is as under:

1. Cold climate: Main problem is lack of heat or excessive heat dissipation for all or most parts ofyear.

2. Temperate climate: Where there is a seasonal variation between under heating & over heating,but neither is very severe.

3. Hot & dry (Arid) climate: Where main problem is overheating, but air is dry, so evaporativecooling of the body is not restricted, There is large diurnal (day-night) temperature variation.

4. Warm humid climate: Where overheating is not as great as in hot-dry areas, but it is aggravatedby very high humidity, restricting evaporation potential. The diurnal temperature is small.

The general climate (macro-climate) is influenced by the topography, the vegetation & nature of the

environment on a regional scale (meso-climate) or at a local level within the site itself (micro-climate).

Importance of climatic design: Climate has a major effect on building performance & energy

consumption. The process of identifying, understanding & controlling climatic influences on the building

site is perhaps the most critical part of building design. The key objectives of climatic design include:

To reduce energy cost of a building. To use natural energy instead of conventional energy sources. To provide comfortable & healthy environment for people.

Climatic data & Climatic information: The main climatic elements, regularly measured by

meteorological stations, and published in summary form are as under:

Temperature: Dry bulb temperature-monthly mean of daily maxima (deg. C), monthly mean ofdaily minima (deg. C), standard deviation of distribution.


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Humidity: Expressed as R.H; or absolute humidity, or as the WBT or dew point temperature maybe stated, from which the humidity can be calculated-early morning R.H. (in %); early afternoon

R.H. (in %)

Air movement: Both wind speed & direction is indicated-prevailing wind sped & direction. Precipitation: The total amount of rain, hail, snow, dew, measured in rain gauges & expressed in

mm per unit time (day, month, year etc.)-monthly total (in mm).

Cloud cover: Based on visual observation & expressed as a fraction of the sky hemisphere(tenths, or Octas-eighth) covered by cloud.

Sunshine duration: The period of clear sunshine (when a sharp shadow is cast), measured by asunshine recorder, which chars a trace on a paper strip, expressed as hours per day or month.

Solar radiation: Measured by pyranometer, on an unobstructed horizontal surface & recordedeither as the continuously varying irradiance (W/m2) or through an electronic integrator as

irradiance over the hour or day-monthly mean daily total (in MJ/M2

or Wh/M2)

Factors affecting climatic design:

(A)Site related factors are as under:

a) Site factors: Topography-elevation, slopes, hills & valleys & ground surfaces.b) Vegetation: Height, mass, silhouette, texture, location, growth patterns.c) Built forms: Nearby buildings, surface conditions etc.

(B) Major thermal design factors are as under:

a) Solar heat gain.b) Conduction heat flow &c) Ventilation

(C) The design variables in architectural expression that are important will include:

a) Shape- surface to volume ratio; orientation; building height.b) Building fabric- materials & construction; thermal insulation; surface qualities; shading & sun

control.

c) Fenestration- the size, position & orientation of windows; window glass material; external andinternal shading devices.

d) Ventilation- air tightness; outdoor fresh air, cross ventilation & natural ventilation.Indices of human comforts: There are mainly four factors responsible for the comforts of occupants

Air temperature. Air movement-speed & direction. Relative humidity & Purity of air.


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Principles & strategies of climatic design: The objective of the design of a structure that responds to the

environment should be to maximize solar gain in winter & minimize heat gain in summer. This can be

achieved by:

1. Manipulating microclimate & site design.2. Manipulating building design.3. Manipulating building envelope.4. Manipulating orientation with respect to sun & wind.5. Manipulating fenestration.6. Manipulating building material & construction techniques.7. Manipulating with finishes.

Microclimate & site design: Elements of site design that can be used for efficient natural cooling include

landscaping, orientation with respect to sun & wind, building shape & planning & natural ventilation.

Building design-shape & planning: In general compact planning will have a relatively small exposed

surface. This can offer advantages for the control of heat gain through the buildings skin without conflict

between design priorities for winter & summer months. Other options are court planning, use of wing

wall, construction on pillars etc.

Building envelope: Design strategies for building envelope includes-design of openings, solar control &

shading systems, thermal insulation & air tightness.

Orientation to sun & wind: The major openings in building envelope should be on the North while the

south face shall be adequately protected from sun. Prevailing wind direction should be taken into

consideration while deciding the position & size of the opening to ensure proper cross ventilation.

Building materials & construction techniques: The material used for walls & roofs have following

selection criteria for deciding which material is most suitable for given climatic conditions & they are :

1. Specific heat capacity of the material.2. Density of material.3. Time lag &4. Decremental factor.

In hot & cold climate walls & roofs should have a low transmittance value, while in warm-humid climate

it should have a low thermal capacity & roof should be light with high U values. Various building

materials are in use e.g. mud, brick, concrete, timber, steel etc. in conjunction with constructiontechnique will dictate the amount of heat gain or heat loss in buildings through walls/roofs.

References:

1. http:/www.arch.hku.hk2. Climate Responsive Architecture-A Design Handbook for Energy Efficient Buildings by A. Krishan

& others;Pub:Tata McGraw-Hill Pub. Co. Ltd;New Delhi.

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Climatic Design of Buildings