They're also called "evaporative coolers"- - - - -they have a reservoir of water and it's pumped through a horsehair-like material as air blows across it. The water evaporates and cools the air- - - - -a little. They work best in very low humidity areas- - - -southwest deserts, California, Arizona, etc. If the air is too humid to evaporate much water, they just blow hot, wet air!
Jerry
