An evaporative cooler is a device that relies on the principle of evaporation to cool air in a room. Air is blown over water in an internal reservoir or wick, and as the water evaporates into the air, heat energy is absorbed. This cools the air, reducing its temperature.
Evaporative coolers are sometimes called swamp coolers, because while they cool the air, they also distinctly increase its humidity. Swamp coolers are most effective in extremely dry climates, since hot, dry air can absorb more water than humid air. The more water the air absorbs, the more energy is expended and the cooler the air becomes.
An evaporative cooler requires a steady supply of water to cool the air effectively. Most coolers use a reservoir of water that is pumped to moisten a pad or wick inside the unit, producing a thin layer of water to help it evaporate more completely and quickly into the air.
Since moisture levels are high in evaporative cooling, these units are prone to mold and mildew and must be cleaned regularly to prevent problems. In addition, the high humidity levels produced by a swamp cooler can cause condensation on room surfaces, possibly leading to moisture damage to walls and furnishings.