Evaporative Cooler

An evaporative cooler, also called a swamp cooler or desert cooler, lowers air temperature by evaporating water rather than by running a mechanical refrigeration cycle. As liquid water turns to vapor it draws sensible heat from the surrounding air, which is what produces the drop in air temperature; a typical mechanical unit uses a fan to draw ambient air through pads kept moist with water, cooling the air as it passes through before sending it into the building through vents or ducts, while also raising the humidity of that air. The technology performs best in dry climates, where the surrounding air can absorb the extra moisture the process adds, with its effectiveness governed by the wet bulb depression, the gap between the air dry bulb and wet bulb temperatures; in humid climates, where the air already holds substantial moisture, the achievable cooling drops sharply.