Here's a picture of one. They are also called evaporatoive coolers. You keep the sides wet where the pads are and it cools the air going into the house. You can have downdraft, sidedraft, or window units, and I think they actually make freestanding units now. They don't work very well when the humidity is high, but they are great for places like Colorado and West Texas. When I was growing up, one of my jobs was keeping the pads wet, but now they have a water line system that distributes the water to the pads. More than you wanted to know, eh?