Coming from the humid east coast, one of the first things you notice upon arrival in the southwestern United States is how dry the air is. Dew points are often in the 40s while the air temperature soars into the 80s and 90s during the summer. This is why swamp coolers are popular in the region.
A swamp cooler is an evaporative cooling device. It takes hot, dry outside air and blows it across water soaked pads. This allows the process of evaporation – the transition of liquid water to water vapor – to cool the air that is pumped into a building. It also adds some moisture to the inside air, making it more comfortable.
While the U.S. Energy Department says swamp coolers cost about one-half as much to install as central air conditioners and use about one-quarter as much energy, they do not work well everywhere. In hot, muggy climates, for example, the high relative humidity would significantly reduce the rate of evaporation. Moreover, adding extra water vapor to the air would not be considered a bonus in an already uncomfortably humid environment.
For this reason, only 3% of homes nationwide utilize swamp coolers, according to a report from the Energy Information Administration. In the arid Rocky Mountain region, however, they are found in more than 26% of all households.