Fan mail from some experts who explain how fans make us feel cooler.

Before air conditioning became common, fans were often used to keep the air moving, which cools people by evaporating sweat. I thought that was all they did, which is why I have quoted Green Curmudgeon Carl Seville, who says Ceiling fans are evil. He wrote in Green Building Advisor:

I am surprised at how few people understand the basic concept of fans — that they make you feel cool due to the movement of air across your skin. The same way a breeze cools you off, a ceiling fan can make you feel cooler, but only if you are close enough to it to feel the air blowing on you. If you can’t feel it, it isn’t doing any good.

That’s why it is pointless to have a fan on when nobody is in the room; then it is just generating heat from the motor, which is why they are evil- they are heating when you want cooling.

Those are two points from Carl, but TreeHugger is also a big fan of Energy Vanguard’s Allison Bailes, who makes 7 points you may not know about ceiling fans. He points out that beside evaporative cooling, fans also aid in “convective cooling.” I had to ask what this means:

Lloyd, convective cooling is moving warmer air out and cooler air in. When a breeze aids in evaporative cooling, it's moving humid air away and replacing it with drier air. The former is sensible cooling since it lowers dry bulb temperature. The latter is a form of latent cooling since it lowers the vapor pressure of the air near the skin, thereby allowing more water to evaporate from the skin.

I wanted to argue this point, because heat rises, so I thought that the air moved by a ceiling fan was likely warmer than the air down where the person is, but Alison is a PhD in Physics and I’m just an architect.

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