Windcatcher: The Predecessor to the Evaporative Cooler

Evaporative coolers are the more environmental counterparts to portable air conditioners. The technology behind them seems really simple. They add moisture to the air to help with cooling. The idea of using moisture to cool has been around for ages. Proof of this is evident in the device called the windcatcher.

Windcatchers were Persian architectural devices used for natural ventilation of buildings. In the country of Iraq, there is a big difference in temperatures from day to night. During the day it can be extremely hot and at night it can be quite cool. Also, the towns were packed closely together with high walls and ceilings. How did they cool their buildings without using power?

The windcatcher is topped with four directional ports. All of the ports would be closed except for the one facing away from the incoming wind. Because of this air is drawn upward. This creates significant cooling ventilation with the structure below the windcatcher. This alone was not enough to bring the temperature down below ambient because it simply draws hot air through any cracks or windows in the structure below.

To get colder temperatures, a few conditions must be in place:

-There had to be very few cracks at the base of the structure below.

-The structure had to be very thick.

-There was a sort of well with water below the structure called a qanat. There was a space between the water and structure to promote evaporative cooling of air.

-The qanat is completely shaded from the sun so it draws the cooler night air. This cool air, that is being even more cooled by evaporation, is drawn through the structure.

If there is no wind and no water, the windcatcher works as a stack effect aggregator of hot air. There is a pressure gradient that makes the less dense hot air travel up and escape out the top of the windcatcher.

The windcatcher was so effective in Persian architecture that is has been used as a refrigeration device for ages. It still can be seen in many countries today. Just like the evaporative coolers of today, the windcatchers were best used in hot and dry conditions. It's amazing what a little evaporation can do.