Evaporative cooling is one of the most ancient and one of the most energy-efficient methods of cooling a home. It long has been regarded as environmentally "safe," since the process typically uses no ozone-depleting chemicals, and demands one-fourth as much energy as refrigeration during the peak cooling months of the year. In dry climates, evaporative cooling, even the relatively inefficient "swamp box" household cooler, can be used to inexpensively cool large homes.
The effect is similar to the coolness one feels when you are wet after swimming or bathing and a breeze causes you to feel chilled.
Direct evaporative cooling adds moisture to the air. When humidity rises during the rainy season the efficiency is diminished, and it feels stickier although it stills cools.
The most common form of residential evaporative cooling uses a vertical pad of cellulose fiber, a system for delivering water to the top of the pad, and a fan to draw air through the porous pad as the water runs down the medium and is absorbed. As dry air moves over the wet pad, water evaporates, and the air gives up its heat. The air moving from the wet pad into the home is cooler than the outdoor air.
It is always best to leave a window or door open a small amount to allow the hot air to escape and increase the cooling effect.
In Tucson there are more homes using evap cooling then homes using A/C.