Evaporative coolers (also calle swamp, desert, or air coolers) are devices that cool air through the simple evaporation of water. They differ from refrigeration or absorption air conditioning, which use the vapor-compression or absorption refrigeration cycles. In the United States, small-scale evaporative coolers are called swamp coolers by some users due to the humid air conditions produced. The name sump cooler is also used. Air washers and wet cooling towers utilize the same principles as evaporative coolers, but are optimized for purposes other than air cooling.