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If you've ever tested the wind by holding a wet finger in the air, you've used evaporate cooling. The same principle cools you off after a swim, and it also powers one of the oldest and simplest forms of air conditioning. Known in the U.S. as swamp coolers, modern evaporate coolers can trace their lineage to ancient Egypt. They're cheap, efficient and good for the environment, but they come with some limitations, so don't push your standard air conditioner out the window just yet.
The ancient Egyptians had a great need for air conditioning. They accomplished it by hanging wet blankets across the doors of their homes or, if they happened to be royalty, having servants fan them across jugs of water. When hot, dry air passes over water (or better yet, through it) the air cools off. Nowadays, we use electric fans instead of servants, but the principle of cooling the air by evaporation remains the same.
How Swamp Coolers Work
