For the building designer, the composite climate poses a challenge because elements
of a building that have been installed for one season may harm in another season. 

The western Uttar Pradesh region falls in what is termed the composite climatic zone.  The composite climate is one in which no single season predominates and at least three seasons are experienced - the hot dry summer, the warm humid monsoon, and the cold but largely dry winter.  There is a short cold humid spell within the winter.  Each of the seasons is sufficiently extreme so as to justify consideration when designing buildings, though short spells of moderate weather are possible.

For the building designer, the composite climate poses a challenge because elements of a building that have been installed for one season may harm in another season.

This article overviews some of the most important techniques for provision of better thermal comfort for building of this region, restricting the discussion to non air-conditioned buildings, and excluding dense urban buildings.  The techniques are listed and discussed in random order, the aim being only to familiarise the reader with the techniques.

Orientation, opening and shading devices  

With few exceptions, it can be said that the primary aim of buildings in this climate should be to maximise heat gain in the winter and minimise it in the summer, while maintaining the best cross ventilation in the monsoon. 

The maximum radiation incident any face of building in western U.P. in the winter is due solar south (more than the roof).  Therefore, it would seem desirable to orient buildings such that one long face is towards the south.  In fact, if buildings are not very deep and have well glazed south faces, the entire winter heating requirement can be eliminated in the region with one stroke.  This is due to the sunny and not too extreme nature of the winter.  Of course, one or two weeks of eating may still be required on the overcast of rainy winter days.

But is this orientation good for excluding summer heat?  With a few variations and care in the opening design, yes.  In the summer, it is no longer the south wall which receives the most solar radiation but the roof.  Therefore it is the roof which requires to be opaque, reflective, massive or insulated.  Whatever little direct sun streams in from the windows can be effectively cut off by a simple chujja (balcony).

If the south orientation with some sun protection for summer seems to work best for winter and summer, is it also appropriate for the monsoon?  This is a lot more difficult to say for the composite zone in general, but for western U.P. the prevailing south-easterly and north-westerly breezes can be comfortably tapped in the building.

The requirement for cross-ventilation does not predominate over the other considerations for a due south orientation because air movement is ephemeral, tending to be unreliable in direction and speed, changing from site to site, and can be tapped with a variety of other breeze catching methods anyway.  In western U.P. the winter heating requirement is sufficient to justify the due south orientation despite considerations of cross ventilation (though deviations of 20 degrees are acceptable).

Openings should be avoided or at least reduced in the west and east faces.  The openings in general should be based on considerations of light and glare on al faces except the south, where heating considerations may predominate.

Shading devices over openings can regulate the disadvantages of some faces to some extent.  The south facing chujja is of course the simplest and most successful. 

Insulation and thermal mass

Materials which resist heat flow are called insulating (still air, rock-wool, earth, to name a few in decreasing order of insulation per unit thickness).  These are used in buildings to store heat (or cool).

The use of insulation and mass can be very important to utilise the benefits of all other effects.  Insulation (especially of low thermal mass) is generally desirable in buildings which have a significant cooling source within, but is of lesser value in buildings which are not conditioned in any way.  Thermal mass can be generally thought of as a damping device which evens out the extreme fluctuations of diurnal conditions, and is generally useful in unconditioned buildings.  It is the primary  traditional technique for thermal comfort.

But it must be remembered that a well insulated roof shall impede the flow of summer daytime heat, but also resist the outflow of heat in the night.  Likewise, massive walls can create comfortable days in the summer, but overheat in the evenings and early part of the night. 

Surface

Just as smaller windows and shaded openings can reduce unwanted solar gain, reflective surfaces can do the same.   A fully reflective surface can be said to be as effective as putting the building in shade all the time.  Generally in this region, bright or white external surfaces are to be recommended, since the summer takes precedence over the winter in this regard.  But more important than the walls is the roof.  As far as possible, roofs should be either shaded (for example, with a pergola or veranda like space on tope, or even some creepers) or painted white.

A reflective metallic surface, despite it better reflective properties, is not as suitable as matt white finish due to its emission properties being low.  It will not be as efficient as the matter white surface would be in terms of shedding heat when required.

Movable devices

The composite climate zone is one where it would be ideal to change the properties of some of materials of the external skin of a building over the course of the day.  It would be good, for instance, if one could stay in a massive and insulated room in the day, and have a very lightweight in the night.

The barsati is just one example of such a device which provides a thermally unacceptable space during the day, when one can stay downstairs in the heavier rooms with few windows, while providing a very pleasant night space, when the spaces below are unbearably hot.  They also work very well all through the day and night for monsoons.

Wooden shuttered windows are another technique which is successfully employed by traditional buildings.  The only requirement is that the user be in a position to open the shutters when outside conditions are better than inside and vice-versa.

Ventilation and selective ventilation

Whenever there is a source of air which is cooler than the indoor air in the summer, it is desirable to ventilate.  This shall definitely happen in summer nights for unconditioned buildings, as also in the days if there is sufficient green area or water bodies around.  Ventilation is even more desirable in the monsoon to create comfort conditions by air flow across the skin alone, even if the breeze has the same temperature as the room (as is often the case).  The term selective ventilation is used to refer to systems which ventilate when conditions are favourable and do not when they are not.  The simplest traditional example is the shuttered window when operated by an intelligent user.  Selective ventilation can actually reduce indoor temperature on the whole, though rarely by more 3⁰C.

Traditionally, the courtyard was an important means of reducing external surface area of buildings by tight clustering while allowing just sufficient light into the interior.  Its major advantage, however, is considered to be ventilation.  It is possible to design courtyards that heat or ones that cool.

The entire field of scientific courtyard design is not fully studied, and the only guideline possible at present is to keep courtyard as small as architecturally acceptable to keep out the summer sun and dust.

Evaporative cooling

The use of the phenomenon of cooling produced by evaporation can potentially provide temperatures as low as 22⁰C in the summer, though it would rarely go below 25⁰C in the monsoon due to the highly humid heat prevailing at that time.

The commonest traditional form of this cooling used to be khas mats which were kept wet around the house.  The development of the desert cooler which included a tank, recirculating pump, and a fan allowed the use of smaller pad areas at the expense of a small amount of energy.  The technology is viable option provided it is not used in the wet mode during the monsoon when better cross-ventilation of ambient air only may suffice for reasonable comfort.  It is also possible to duct the air various rooms much like an air-conditioning system.

In recent years, studies have been undertaken of the traditional wind towers and wind scoops of the middle east.  The thermal mass of the tower cools the air before entry to the house.  However, many designs incorporated water in some from to make the air cool and heavier in order to sink into the house.

Another interesting recent development, largely derived from the original khas concept, is roof top evaporation.  The idea is to keep a moist surface above the roof which is the source of the maximum heat in the summer, thereby converting the roof from a heating element to a cooling element.  The concept has the potential to be applied with a direct head of water available, or with pumps and sprinklers.  The idea should only be to discover a combination which provides effective cooling with minimum water use.  Naturally it must be ensured that the roof is moisture resistant.  It is also desirable with this method working that the roof be thin.  Since humidity is not added directly in the space, the method has certain advantages over desert cooling otherwise.

The presence of water bodies and vegetation in the landscape or even within the house has also been used traditionally and can be thought of as form of evaporative cooling.

Ground cooling

The temperature of the earth at some depth remains more or less constant throughout the year and this average depends upon the climate of the location.  In many western U.P. locations, this temperatue is as low as 22⁰ C to 24⁰C.  Therefore this can be source of cooling in the summer and heating in the winter.  Also, not requiring evaporation to make it work, this method can be fairly effective in the monsoon also.

Earth contact is the commonest and traditional form of making use of ground temperatures.  Underground of subterranean architecture, basements for living in, earth bermed walls, earth covered roofs, are all ideas that immediately come to mind.  In all these, a large portion of the space is in direct contact with the earth.  One has to be careful about daylight provision and water proofing.

In recent years, earth air tunnels have been made to channel the air though the ground (ideally about 4 m deep in the western U.P. region).  The air is then fed to the building.  These systems normally require sufficient fan power to allow them to work.

The role of the landscape

Suburban and rural buildings can gain tremendously from proper vegetation and environmental treatment around them.  The first advantage of good vegetation would be a tempering of the micro-climate.

Heating

The role of the south orientation has already been stressed.  Glazing on openings crates what is termed the greenhouse effect.  This effect is simply that the tradition passing through glass is absorbed by objects and surfaces in the space and re-radiated at a changed wavelength.  Since glass is relatively more opaque for these wavelengths, heat accumulates inside the space.

With a judicious use of thermal mass, the heat form the south can be used in the winter nights.  For western U.P. plains, it would be sufficient to provide a dark coloured floor or rug on which the south sun falls through the day, and a solid sub-floor.  The stored heat shall continue to warm the room through the night.

If greater sophistication is desired, Trombe walls which consist of thermal masses placed behind south glazing, can absorb the radiation in the day to emit it to the space at night.  Greenhouse or sunspaces work on a similar principle.  However, unless these spaces and features have functional uses, such sophisticated heating concepts have not much application value in western U.P. plains. 

The sky as a sink

A significant amount of heat can be lost by a building to the night sky.  The maximum theoretical gain of this technique works out to be about 6⁰C, which is quite dramatic.  But the potential advantage drops quickly in the presence of clouds, dust haze, pollutants, and objects which shade the building from the dome of the sky, such as neighbouring taller buildings, trees, and the like.

The application of the technique involves ensuring significant emission from a thermal mass in the night and insulated storage of the same in the day, to release the cooling into the space.

Aspects of daylighting

Closing up a building too much in order to reduce heat gain may work only upto a point.  If there is too little light, there will be a tendency to switch on electric light during the day to work.  Daylight is the coolest source of light known to man.  In the summer and monsoon, artificial lights add both to the electricity cost as well as the heat gain.  This can be avoided by providing a just adequately lit interior  however, care must be taken to avoid glare by providing a good distribution of this light, otherwise curtains shall be drawn and artificial lights shall be used. 

However people in the area do not use too much energy (compared with international standards) to heat or cool the house.   The techniques described above may have only a minimal effect on energy consumption, but they can help in providing better thermal comfort in buildings which do not have any conditioning systems or those with only fans.  They can also help retard the increasing and often unnecessary demand for full air-conditioning in buildings.

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