When the humidity is low, the evaporation of water by a swamp cooler lowers the air temperature. These devices use a fan to pull air across wet pads to cause evaporation. The process lowers air temperature by 15 to 40 degrees Fahrenheit.
Swamp coolers are less expensive to install and operate than central air conditioning systems. They provide a 75 percent savings on power for cooling, according to the U.S. Department of Energy. While central air conditioning recirculates the air in a home, a swamp cooler provides a constant flow of cooled air while the stale air inside the house exits an open window.
When installing evaporative coolers, there are two options for distributing the cool air. The easiest is installing the cooler in a window. The second option is to distribute the air through a duct system. The duct system provides cooling for individual rooms while the window mount is better for a home with open space. Small portable units on wheels are also available, but because they do not provide the constant flow of air, their cooling effect is negligible.
Low relative humidity is essential to proper operation of a swamp cooler. If the humidity is high, water does not evaporate as well, making the cooling less effective. The additional humidity the cooler adds to the home under these conditions makes the occupants less comfortable than standard air conditioning.