Fans and air conditioning - staples of summertime. Both keep you cool, but they do so in very different ways.

Fans don't cool the air, they just make your skin feel cooler. Wind speeds up the evaporation of water on your skin - that is, your perspiration. It takes energy to evaporate water, and some of that energy comes from your skin. So you feel cooler when air blows past your body. Another reason fans cool you is that there's always a very thin layer of air right next to your skin that's been warmed by your body. Fans whisk away that thin layer of body-warmed air.

Air conditioners actually chill the air. Indoor air cools as it passes across a refrigerant coil. The chilled air is pumped inside, while the heat that was removed warms other air that's blown outside. The cooling process has another byproduct that you may have noticed dripping from your air conditioning system - water droplets form as water vapor in the air condenses when the air is cooled. By the way, for every 1^oF you turn your thermostat up, your air conditioner will use about 3% less energy.