We all appreciate cool breeze inside the house, but for this to happen, air should be able to flow around the house freely. It is important that on the windward side the air blows with some force or energy so that it can not only enter the house but also absorb and carry the heat to the outside on the leeward side of building. Air can only flow easily provided we have lots of open space in the way of its entry and some space on the other side for its easy exit as well. `Lots’ of open space in an urban context can be about 10 feet and in a metropolitan city like Bangalore, even 5 feet will ensure quite a bit of natural ventilation.
A big house does not mean much if we don't have open space around the house, especially on the windward side. In fact it is better to plan houses in such a way that the open space around the house becomes part of the house, and extend the house outward visually so that we can feel the house getting extended to the open space.
This can be done by taking the outside inside, by bringing the open space inside and make it part and parcel of the house. If we build from one end of the site to the other, covering more or less completely, then we are sure to feel cramped and suffer from lack of light and air. Natural light can be to a certain extent, compensated by artificial lighting, but natural ventilation is something that is not compensated by any amount of fan churning the same stale air or air conditioners that merely cool the air, recirculating a part of the stale air to reduce the load on the system.
We all know that the air blows from an area of higher pressure to that of lower pressure. On the windward side the air pressure is higher, on the leeward side the pressure is similarly lower. We need to keep bigger windows on the windward side and even small windows will do on the leeward side to exhaust the stale air.
Wind will have positive pressure on the south and west during the summer monsoon months and similarly there will be negative air pressure on the north and east during this season. Air not only flows when we can feel it as a stream passing by our body but also flows rather slowly most of the time, even if we don't exactly feel it. This is due to the pressure differential between the two sides of a building, either adjacent or opposite sides. Even this slow movement of wind brings many air changes per hour and provide the much needed relief from heat.
Air exchange
Apart from this, there will be air exchanges happening even when there is absolutely no movement of air that is during `still air’ conditions. Even in this case, there will be gaseous movement due to air diffusion, which is nothing but gaseous exchange from a higher level of concentration to lower level. Usually carbon monoxide, carbon dioxide, body odour, cigaret smoke, etc, which is being generated inside the house will be exchanged to the fresh air from outside, carrying in the much needed oxygen to the  inside. This exchange happens in a passive way, but for this too we need sufficiently big windows to the outside.
Trees can be useful in directing and cooling the breeze into the house.
Trees with a large canopy will not only cool the house and the incoming breeze, but will also guide the breeze inside the house through the windows. Similarly shrubs and bushes can be strategically planted to guide useful breeze to the inside of the house and filter hot rays of sun.
The windward side
Houses are constructed so close to each other that we can expect little fresh air from our neighbours’ site. We can only depend on the open space that we have around the house to allow fresh air to come inside. For this to happen, we need to keep more open space on the side from where we want the summer cool breeze to enter the house. This can be ensured by keeping more open space on the south and west. South side open space is more useful because the sun will be at high angle on this side and it is easy to control the sun by providing minimum projections. Even though we get good breeze from the west too, because of the low angle of the sun from this direction in the afternoon, it is comparatively difficult to control sunlight penetrating the house.
However, we can keep large projections like portico and pergola covered gardens in the open space on the west and filter the sun light considerably, while allowing easy access to summer breeze
Planning
We have very little control over the open spaces around our site. Therefore it is all the more important to leave sufficient open space around the building within our site. Since every inch of space cost hundreds of rupees in urban areas, we have to leave it where it really adds to the quality of living in the house and most importantly, open space has to be left taking into consideration the summer wind directions.

The author is an architect and can be contacted on phone no 98441 32826.
or at No 67, 3rd Main, Income Tax Layout, Vijaynagar,
Bangalore 560 040.