Global Climate (Koenigsberger, et al, 1975)

Global climate can be understood with the help of following parameters :

(a) Heat

The earth receives almost all its energy from the sun in the form of radiation and thus the sun has the dominant influence on climate. This radiant energy is transmitted to earth as ultra-violet radiation (short waves) and infra-red radiation (long waves). Most of this energy is perceived as heat and only an insignificant part is visible as light.

Radiation Spectrum

The earth moves around the sun in a slightly elliptical orbit. One revolution is completed in 365 days, 5 hours and 48 minutes. The solar distance varies from 152 million kilometers to 147 million kilometers. The earth rotates around its own axis, every 24 hours, and the axis is tilted to the plane of the elliptical orbit at an angle of 23.5' w.r.t. the vertical. Due to this tilted position, the area receiving the maximum radiant intensity falls alternately to north and south between the tropic of Cancer (Latitude 23.5 N) and the tropic of Capricorn (latitude 23 S). This is the main cause of seasonal climatic changes.

The earth has an atmosphere which revolves along with it. As the earth rotates the length of the suns rays passing through the atmosphere changes and hence, the intensity of radiation, incident on earth surface, from the sun also changes.

Earth Revolving Around the Sun

Length of Sun's Rays Traversing Atmosphere

Fallowing figure illustrates the incoming radiation while below figure shows how the earths surface releases heat and thus, achieving a heat balance, each year. Buildings and the surrounding vegetation affect the heat balance and hence, the micro-climate of the site. Unless thermal balance is maintained, the temperature of the earth and its atmosphere.

Toht radiation amving (solar constant =100% )

Incoming Radiation thorough Atmosphere

would keep increasing and would soon cease to be favorable to most form of life. In fact we are concerned about global warming and ozone depletion these days. There are alarming indications of this imbalance which have arisen due to uncontrolled developmental activities and use of dangerous chemicals. 

Temperature is measured in degrees Celsius by a maximum-minimum thermometer. A simple sunshine recorder will register the duration of sunshine, expressed in number of hours per day. The temperature which is reported usually is called dry bulb temperature (DBT).

Heat Release from Ground Atmosphere

(b) Winds

Winds are basically convection currents in the atmosphere, tending to even out the differential heating of various zones. The pattern of movements is modified by the earth's rotation which has a speed of 27 km/min at the equator. At the maximum heating zone, which is somewhere between the tropics of Cancer and Capricorn, air is heated'by the hot surface of the earth, it expands and its pressure is reduced, and thus, it becomes lighter.

As a result, this air rises vertically and flows at a high level towards colder regions, parts of this air having cooled down at the higher level; and it descends to the surface in the sub-tropic regions from where the cooler, heavier air is drawn in towards the equator from both the Earth and south regions.

The area where the air rises, and these northerly and southerly winds meet and where the tropical calm ,is formed is called as the inter-tropical convergence zone. This area experiences either completely calm conditions or light breezes.

The atmospheric envelope rotates along with the earth. As it is light in weight and behaves like a fluid, it has a tendency to lag behind the earth at the equator, where the tangential speed of earth's surface is the largest. Thus, there is a slippage at the boundary layer between the earth and its atmosphere; and this is experienced as a wind blowing in a direction opposite to that of the earth's rotation, which gives rise to the north easterly and south easterly winds. These are known as trade winds (Koenigsbergar, et al, 1975).

Around 30' N and S, there are two bands of continuously high barometric pressure zones (descending air). Winds in these zones are typically light and variable. Between 30' N and 50' N and similarly in the south. strong westerly winds prevail, blowing in the same direction as the earth's rotation. The origin of these winds have been explained by the law of conservation of angular momentum of the earth-atmosphere system.

Further, down the poles form 60' N and S the air flow pattern is similar to that of the equator. Hence, the north easterly and south easterly polar winds.

Global Pressure Belts and Prevailing Winds

The prevailing wind direction is a major factor in selecting a site for a populated place and the allocation of functional zones. Account should be taken of the fact that the local topography has a significant influence; for example, in the daytime, the earth is heated faster than water and hence the air mass near the earth becomes less dense, creating a zone of low pressure. This gives rise to a wind that blows from the sea towards the shore.

At night, the temperature of water is higher than that of the air and this condition reverses the direction of the wind. Wind velocity is measured by a cup-type propeller known as anemometer, and its direction is measured by a wind-vane.

(c) Humidity

The air in the lowly layers of the atmosphere always contains a certain amount of water vapor resulting from evaporation of water on and in the earth's surface. The rate of evaporation depends primarily on temperature and wind. It has been estimated that the surface of the ocean, in the tropics, evaporates in a year a layer of water up to 3 meters in depth. This must be replenished by rainfall and run-off from the rivers. The ability of air to absorb and retain the maximum amount of water vapor is directly related to temperature.

Absolute Humidity is defied as the amount of water vapor in moist air at any given time and is expressed in gm/m3 of air.

Relative Humidity (RH) is defied as the ratio of water vapor in moist air to water vapor in saturated air, expressed in percentage. For example, if the absolute humidity of air, for any given temperature is equal to 7gm/m3, and saturated air (at the same temperature) contains 10 gm/m3, the ratio 7 : 10, expressed as a percentage will be the I relative humidity.

 RH= 7/10 x100=70%

Humidity is usually measured by wet- and dry-bulb hygrometer.

(d) Precipitation (Rainfall) 

Precipitation is the collective term used for rain, snow, hail, dew and frost, i.e. all forms of water precipiated from the atmosphere. It is measured by rain gauges and snow gauges and is expressed in millimeters per day or month.

(e) Climate Data 

It is important to note that climate at a global/regional level is best described by measured data, over a period of time, such as sunshine (hours per day), radiant heat (watts per meter square per day), wind velocity (meter/sec) and wind direction (N, NE, E, SE, S, SW, W and NW), rainfall (mm per month), relative humidity (percentage) and temperature (maximum and minimum in degrees Celsius).

It is not easy to understand the nature of a particular climate by merely looking at the vast i amount of data collected by the nearest meteorological station. It is necessary to sort, summarize and simplify the available data with reference to the objectives of site-selection exercise. This is the best accomplished by adopting a standardized method of graphical representation. Fallowing figure illustrates a graphical method that was developed for describing the climate of any location.

Graphical Representation of Meteorological Data

Below figure shows how wind speeds and directions are recorded for a specified period. Based on such climatic data certain zones and belts of approximately uniform climates, have been identified and described as under (Koenigsberger, et al, 1975).

(f) Clssification of Climates

Climates can be classified, broadly, as given below :

(i) Warm-Humid Climate

Warm-humid climates are found in a belt near the equator extending to 15' N and 15's. There is very little seasonal variation except for the occurrence periods of more or less rain.

Monthly Wind Frequency Graph

Air temperature is 27' to 35OC during the day and 21' to 27' C in the night. Relative humidity remains high at about 75%; but it may vary from 55 to almost 100%. Rainfall is high throughout the year. Annual rainfall can vary from 2000 mm to 5000 mm and monthly rainfall may exceed 500 mm. During severe storms the down pour may be also as high as 100 mm/hr.

Wind velocities are low, calm periods are frequent but strong winds exceeding 30 m/s can occur during rain squalls. There are usually one or two dominant directions of wind.

Special characteristics of this region are that the high humidity accelerates mould and algae growth, rusting and rotting. Organic building materials teild to decay rapidly. Mosquitoes and other insects abound. The thunder-storms are accompanied by frequent air-to-air electric discharges. The subsoil water table is usually high and the ground may be water-logged.

(ii) Hot Dry Climate

This type of climate occurs in two belts at latitudes between 15' and 30' north and south of the equator. Two marked seasons occur, a hot and a somewhat cooler period.

Air temperature during day time may reach a maximum of 43' to 49' C in the summer. The night temperature will range from 27' to 32'C during summer. During the cool season the day time temperature

reaches 27' to 32" C. Night time temperature may vary from.O' to 18' C. The relative humidity varies from 10 to 55 percent. Rainfall is slight and variable throughout the year from 50 mm to 150 mm per annum. Flash storms may occur over limited areas with 50 mm rain in a few hours.

Winds are usually local and whirlwinds are often created. Winds are hot, carrying dust and sand, and often develop into dust-storms.

The soil is usually dusty and very dry. The sub-soil water table is very low. The high day time temperatures and rapid cooling at night may cause materials to crack and break up since the daily temperature variation reaches 17' to 22'C.

(iii) Monsoon Climate

Monsoon climate occurs over large land masses near the tropics of Cancer and Capricorn, which are sufficiently far from the equator to experience marked seasonal changes in solar radiation and wind directions. Our capital, New Delhi is subject to such a climate.

Approximately one-third to two-thirds of the year is hot and dry and the other third may be warm and humid or cool and dry as the latitude increases from the tropics; day-time temperatures in the hot and dry seasons will vary from 32' to 43OC. Night time temperatures may be 21" to 27'C. During the cool and

dry seasons the day time temperature may dip down to 4' to 10°C. Relative humidity during dry period
rises from 55 to 95%. Rainfall varies from 500 to 1300 mm per year with 200 to 250 mm in the wettest month; there is little or no rain during the dry season.

Winds are hot and dusty during the dry period. Wind changes direction in the beginning of the warm-humid seasons, but monsoon winds are fairly strong and steady.

There is a risk of soil erosion during monsoons. In the dry season. strong ground glare is experienced. Seasonal changes in relative humidity cause rapid weakening of building materials. Dust and sand storms may occur. Termites are common.

(iv) Other Climates

Mountain regions and plateaus, more than 900 to 1200 meters above sea level experience special climates as also the coastal regions and islands. Site selection and orientation of buildings, and the selection of building designs will have to be suitably adjusted to suit such climates.

Climatic Considerations

Climate has a considerable influence on the life of man and his economic activity. The , climate of a particular site is determined, first and foremost by its location on the globe. Hence global climatic considerations will have to be taken into account first. Secondly, local site conditions also affect the climate and hence the site-climatic considerations will have to be studied next. It is possible to control the specific climate of a particular building by structural design and/or mechanical devices. 

It is important to realize that the increasing tempo of the developmental activities of man has started affecting the global environment itself (in an adverse manner) and many national and international agencies are demanding the imposition of controls on development at national, regional and local levels. However, this is a topic beyond the scope of this text.

A study of the physical parameters that influence the climate will help us to choose locations properly and site our buildings in the most effective manner, and to design our buildings and services to take advantage of the natural climatic conditions and also to mitigate the negative impact of such building activities on the environment.

Climate is defined as that state of atmospheric environment that results from the combined processes of the elements of weather, averaged at any given place, over a period of years. Climate is dependent on the geographical latitude, elevation above sea level, the physical state of the atmosphere such as its temperature, humidity, rainfall, wind conditions and the terrain of the place.

Let us now proceed to study the various physical aspects of climate at the global and local levels respectively.

Criteria for Location and Site Selection

Selection of the best site available for putting up a structure (or groups of buildings) to serve a particular function is very important. Appropriate location has a direct effect on :

(a) Cost of the project

(b) Accessibility

(c) Structural techniques required

(d) Extent and nature of site preparation needed

Basic Requirements

Certain basic needs form the basis for judging the suitability of a site for all types of buildings :

(a) Availability of physical resources such as good water supply, power supply and material supply

(b) Climatic considerations such as temperature, humidity, solar radiation, rainfall, wind etc.

(c) Physical factors such as the contour of the site and nature and condition of the soil.

Zoning and Other Factors

Political factors and land use restrictions by local authorities have to be considered while choosing locations. Usually a city or regional governmental agency divides its area into certain zones. This process sets aside land in an orderly fashion for residential, commercial and industrial use. It places industrial and commercial activities in areas, where they will not interfere with the residential areas or affect the properly values. Zoning facilitates transportation planning, location of railway lines and yards and in segregating hazardous and noisy buildings from those which need safe, dust and pollution free atmosphere and quintuplet. Location is influenced also by its nearness to highways and railway lines where this factor is important to the project under consideration.

The extent of local taxes, such as property tax, sales tax and income tax must be considered in the selection of location. Central government offers certain tax concessions including a tax holiday for locating industries in certain not-so-well developed locations.

Community acceptance is another important factor.

Building bylaws of municipalities and development control rules of various government authorities govern most of the building activities.

Environmental Impact Study (EIS)

Every developmental activity of man has some positive and some negative impacts upon the environment, and site developers should consider the following factors right from the very early stages of planning 

(a) Air quality

(b) Water quality ,and quantity

(c) Solid wastes

(d) Noise

(e) Radiation from nearby radio-active sources

(0 Hazardous situations

(g) Energy supply and natural resources depletion

(h) Protection of environmental critical areas - flood plains, wet-lands, beaches and dunes, unstable soil, steep slopes, aquifer recharge areas,

(i) Land use in coastal areas

(j) Redevelopment in built-up areas

(k) Density and congestion mitigation

(l) Neighborhood character and continuity.

Need for Expertise in Site Selection

Site selection is a serious professional task and should not be left to the whims and fancies of the uninitiated. The need for experts to analyse and evaluate specific requirements exists in greater urgency today than in earlier times. Because of urban growth, corporate relocation between urban centers, as well as legislations regarding new zoning limitations and building restrictions together with growing environmental considerations, the evaluation of appropriate locations and sites has become a very crucial aspect of development. 

Types of Buildings

Buildings are generally classified on the basis of occupancy and type of construction. Since Development Control Rules and Building Bylaws are based on occupancy criteria, such a classification is essential for planning and design. The National Building Code of India (NBC,1983) has classified buildings as outlined below :

Group A : Residential Buildings

Residential buildings include any building in which sleeping accommodation is provided f a normal residential purposes, with or without cooking or dining or bathing facilities.

subgroups have been identified as follows :

(A1) Lodging or rooming houses

(A2) One- or two- family private dwellings

(A3) Dormitories

(A4) Apartment houses (flats)

(A5) Hotels

Group B : Educational Buildings

These buildings include any building used for a school, college or day-care purposes, involving assembly for instruction, education and recreation.

Group C : Institutional Buildings

These buildings shall include any building which is used for medical treatment or care of persons suffering from physical or mental illness, disease or infirmity, care of infants, convalescents or aged persons and for penal or correctional detention. Institutional Buildings ordinarily provide sleeping accommodation for its occupants. Sub-groups are as follows :

(Cl) Hospitals and Sanatorium

(C2) Custodial institutions.

(C3) Penal and mental institutions

Group D : Assembly Buildings 

This group shall include any building where groups of people congregate or gather for amusement, recreation, social, religious, civil, travel and similar purposes;

examples are theaters, motion-picture houses, assembly halls, auditoriums, exhibition halls, museums, skating rinks, gymnasiums, restaurants, places of worship, club-rooms, passenger stations and terminals of air, surface and marine transportation services, recreation halls and stadiums.

Group E : Business Building

Such buildings are used for transaction of business, for keeping of accounts and records, professional establishments, service facilities etc. Examples of this group are city halls, town halls, court houses and public libraries. Business buildings shall be further subdivided as under :

(El) Offices, banks, professional offices of architects, engineers, doctors, lawyers and other consultants etc.

(E2) Laboratories, research establishments and test houses (E3) Computer installations

Group F : Mercantile Buildings

These shall include buildings which are used as shops, stores, markets for display and sale of merchandise, either wholesale or retail. Sub-groups are as follows :

(Fl) Shops, stores, a market with an area upto 500 m2

(F2) ,Underground shopping centers, departmental stores with areas more than Group C; : Industrial Building

These are buildings in which products or materials of all kinds and properties, excepting those which are hazardous, are fabricated, assembled, manufactured or processed; 

examples under this category are assembly plants, laboratories, dry-cleaning plants, power plants, pumping stations, laundries, gas plants, refineries, dairies and saw-mills.

Group H : Storage Buildings

Such buildings are primarily used for the storage or sheltering (including servicing, processing or repairs, incidental to storage) of goods, wares or merchandise, vehicles, or animals; examples are warehouses, cold storage \s, freight depots, transit sheds, store houses, truck and marine terminals, garages, hangers (other than aircraft repair hangers), grain elevators, bars and stables. Storage buildings are characterized by the presence of relatively small number of persons in proportion to the area.

Group J : Hazardous Buildings 

These shall include ally building or part of a building which is used for the storage, handling, manufacture or processing of highly combustible or explosive materials or products which are liable to burn with extreme rapidity and/or which may produce poisonous fumes or explosions; for storage, handling, manufacturing or processing which involves highly corrosive, toxic or noxious alkalis, acids, or other liquids or chemicals producing flame, fumes, and explosive, poisonous, irritant or corrosive gases; and for the storage, handling or processing of materials producing explosive mixtures of dust which results in the further division of matter into fine particles subject to spontaneous ignition.

Other Classifications While the above classification is based on the nature of occupancy, which is important for the functional design of buildings, it is also necessary to have sub-classifications on the basis of fire-resistance characteristics.

The selection of site for a particular building depends not only on its functional use and fire-rating but also on climate (global and local), topography, and the developmental needs of the site. In addition, socio-political aspects may also have to be considered. In the various sections that follow, you will learn about the relevant rules and/or requirements.

Location and Site Selection

The first arid most important part of the decision regarding a building project is about its location. With increasing demand for land for a variety of developmental activities, locations which would be ideal for different types of buildings, are becoming scarce. The criteria for the selection of a suitable location are becoming more and more complex, due to developmental control rules imposed by National, State and Local governments.

Climatic considerations are equally important not only for functional efficiency, but also because of the adverse impact of large scale building constructions on the environment. In addition to the local topographic considerations, the engineer will have to consider the above mentioned aspects at the very initial stages of a building project. Such a detailed study is bound to help the engineer to choose an economical and appropriate location in order to avoid costly rectification expenditure at a later stage.

In these discussions, the term location is used with respect to a relatively large area, such as a district, taluk or town. The term site will refer to the specific land, within such a location. where a building or a project will be constructed.