Here we are in the middle of air conditioning season. So why don’t we chop down some myths and misconceptions about ceiling fans?
What got me on to this topic was a video of a fan with blades that hide on top of the fan when the fan is turned off. Sounds clever, but it’s a ridiculous idea.
Anyway, here are seven things about ceiling fans that a lot of people seem not to know.
1. Ceiling fans heat the room
Yes, a ceiling fan is a cooling device. (See point number 2 below.) But its effect on the room it’s in is to add heat. Why? Because electric motors are devices that turn electrical energy into mechanical energy, most of which ends up as heat. The infrared photo reproduced as Image #2 (below) shows a ceiling fan motor that’s hotter than the room it’s in. From the second law of thermodynamics, we know where that heat is going — into the cooler room.
The net result of running a ceiling fan is that you’re adding heat to the room.
2. Ceiling fans cool people
Ceiling fans are useful for cooling only when they move air over skin. They cool our bodies two ways: by aiding evaporative cooling and by aiding convective cooling. If the air movement created by a ceiling fan isn’t hitting anyone’s skin, it’s just making the space warmer with no cooling benefit.
3. A fan’s efficacy tells you how well it moves air
Every new ceiling fan being sold in the US these days is labeled with its efficacy. (Efficacy is an efficiency rating where the output and input quantities have different units.) For fans, the measure of efficacy is how much air flow you get…
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