Wind towers are generally used in Hot Dry climates for cooling purposes. A pre- requisite for using wind tower is that the site should experience winds with a fairly good and consistent velocity. A wind tower is operates in various ways, according to the time of day, and the presence and absence of wind. The cardinal principle behind its operation lies in changing the temperature and thereby density of the air in and around the tower. The difference in density creates a draft, pulling air either upwards or downwards, through the tower.
The tower area is so designed that the top part provides large heat storage
capacity, and at the same time has a large surface area for heat transfer. The
tower walls and the internal walls of the air flow passages absorb heat during
the day, and release it at night, warming the cool night air in the tower. Warm
air moves up creating and upward draft and is exhausted through the openings.
The pressure difference thus created pulls the cool night air though the doors
and windows into the building. In the absence of wind, the tower acts as a
chimney. The nocturnal radiation through the roof and the external walls brings
about further cooling.
In the presence of wind, the cool night time air enters the tower and forces itself down into the structure. Though it is warmed slightly during the process, sufficient cooling can be achieved due to forced circulation.
The hot ambient air coming in contact with the cool part of the tower is cooled. It becomes cold and dense, and sinks through the tower and into the living spaces, replacing the hot air. In the presence of wind, the air is cooled more effectively and flows faster down the tower and into the living area. It must be noted that the temperature of the tower soon reaches that of the ambient air and hence, in the absence of wind, the downward flow ceases. The tower then begins to act like a chimney. Operation of the tower depends greatly on the ambient fluctuations like the wind velocity, air, temperature changes, etc. However, wind towers are more effective than evaporative/ desert coolers.
Due to small storage capacity, the sensible cooling may stop after several hours of operation on hot summer days. In order to improve the efficiency of it operation, evaporative cooling is used. The air flowing down the tower is first sensibly cooled and then further cooled evaporatively. This is achieved by providing evaporative cooling system in the tower. The reduction in the temperature of air can be as much as 10 to 15°C in arid climates.