In this example of an evaporative cooler, a small motor (top) drives a large fan (center) which blows air out the bottom and into your home. The fan sucks air in through the louvers around the box, which are covered with water-saturated absorbent material.
In low-humidity areas, evaporating water into the air provides a natural and energy-efficient means of cooling. Evaporative coolers, also called swamp coolers, rely on this principal, cooling outdoor air by passing it over water-saturated pads, causing the water to evaporate into it. The 15°–40°F-cooler air is then directed into the home, and pushes warmer air out through windows.
When operating an evaporative cooler, windows are opened part way to allow warm indoor air to escape as it is replaced by cooled air. Unlike central air conditioning systems that recirculate the same air, evaporative coolers provide a steady stream of fresh air into the house.
Evaporative coolers cost about one-half as much to install as central air conditioners and use about one-quarter as much energy. However, they require more frequent maintenance than refrigerated air conditioners and they're suitable only for areas with low humidity.