We talk a lot about the merits of an evaporative cooler over a standard air conditioner in terms of cost of installation, maintenance and operation, but it seems that not very many people understand how an evaporative cooler works. Also known as swamp coolers, evaporative coolers provide effective cooling by capitalizing on the natural process of water evaporation combined with a simple air-moving system. Keeping the interior of our desert buildings cool is a process that modern technology has made simple. But in the early 20th century, inventions such as air conditioning did not yet exist. People often stayed cool by sleeping outside on screened in porches during the summer. They would hang soaking-wet bedsheets and blankets on the screens and use fans to pull the night air through the moist cloth to provide a cool breeze to lower the room’s temperature.