What About Ceiling Fans?
Long used in tropical climates to circulate the hot air, ceiling fans have found their usage in the modern home. This note explores how they may be used effectively in managing your energy use.
The Typical Fan
Usually, the home fan has five wide blades that can be set to rotate at one of three speeds and in either direction. Their motors are fairly efficient, and at the lower speeds they don’t use a lot of electricity – about the same amount as one medium-size light bulb. The high speed is useful for clearing the air and rapid cooling in the summer whereas the medium and low speeds are good for air circulation without causing nuisance air drafts (especially in the winter.)
Fan Direction
Most home fans push air downward when rotating counter-clockwise and pull air upward when rotating clockwise. They can do this because the blades are tilted; one edge is lower than the other. If the low edge leads, air is pushed up. If the low edge trails, air is pushed down.
In the winter, you want the hot air that is close to the ceiling to be moved down toward the floor, but you don’t want the air drafts from the fan to blow on you (this would increase evaporation from your skin and cool you off). So you need to make the direction of the fan’s rotation to be clockwise. Air pushed upward by the fan causes the hot air at the ceiling to move downward along the walls to the floor. Using the low speed prevents this air from cooling you through increased evaporation. If you have a very high ceiling, you may want to use the medium speed.
In the summer, you want to move air toward you to raise the rate of evaporation from your skin. That means you need to have the fan rotate counter-clockwise. Use the medium speed (or high speed if the ceiling is very high) to move the air rapidly.
Air from the fan doesn’t actually cool the room; it just cools your skin, so you should turn off the fan whenever you leave the room and save the electricity.
Summary
Winter: blades rotate clockwise; use lower speeds
Summer: blades rotate counter-clockwise; use higher speeds
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