Evaporative Cooler

A swamp cooler (more formally called an evaporative cooler) is essentially a large box-like frame containing a big fan and walled in by water-wetted pads, usually made of cedar shavings or cellulose. The fan whooshes the hot outside air through the dripping pads (which are continually soaked by a water pump), cooling the air by about 20 ºF as the air evaporates water molecules from the pads. The fan then blows the water-cooled air through the house and out a deliberate vent.

Wet the back of your hand -- then blow on it. Your skin surface feels cooler. That's evaporative cooling.

Swamp coolers are popular in the southwest because they are relatively inexpensive, use a quarter as much electricity as a refrigerated unit, are easy to maintain by the average do-it-yourselfer, and add a comfortable level of humidity to the dry desert air. The smell of fresh cedar pads on the first hot days of summer is delightful.