most parts from www.wikipedia.com
windcatchers were used mostly in the central part of Iran for natural ventilation in buildings. The towns in the central part of Iran have dry and hot climates, so the houses and other buildings were constructed closely together with high walls and ceilings, maximizing shade at ground level. Function wise, we have two types of windcatchers. Here we don’t bore you with the scientific names but just tell you how they function. In the first type, there exist tall, one-side-open towers on the roof of the building, one facing the air flow and the other facing away from the direction of the prevailing wind. This open side faces the prevailing wind, thus “catching” it, and brings it down the tower into the heart of the building to maintain airflow, thus cooling the building interior. It does not necessarily cool the air itself, but rather relies on the rate of airflow to provide a cooling effect. Windcatchers have been employed in this manner for thousands of years.
In the second type, the cooling effect happens with the help of qanats. In this method, the open side of the tower faces away from the direction of the prevailing wind (the tower’s orientation can be adjusted by directional ports at the top). By keeping only this tower open, air is drawn upwards using the Coandă effect.