An evaporation cooler (also swamp cooler, desert cooler and wet air cooler) is a device that cools air through the evaporation of water. Evaporation cooling differs from typical air conditioning systems which use vapor-compression or absorption refrigeration cycles. Evaporation cooling works by employing water’s large enthalpy of vaporization. The temperature of dry air can be dropped significantly through the phase transition of liquid water to water vapor (evaporation), which can cool air using much less energy than refrigeration. In extremely dry climates, evaporation cooling of air has the added benefit of conditioning the air with more moisture for the comfort of building occupants.

Air washers and wet cooling towers use the same principles as evaporation coolers but are designed for purposes other than directly cooling the air inside a building. For example, an evaporation cooler may be designed to cool the coils of a large air conditioning or refrigeration system to increase its efficiency.