Science Questions

Does waving a fan really cool you down?

Tue, 21st Apr 2015

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Stephen Flesch asked:

It seems to me that when people fan themselves in hot weather that the energy expended in waving the fan negates the cooling effect of the air movement ? Is it not better to sit still ?


We put this question to Naked Scientist Ginny Smith...Hand fan

Ginny - I have used fans before. It certainly feels like itís cooling you down. I imagine itís helping your sweat to evaporate which is going to cause a cooling effect. I mean if you're holding one of those huge fans when you're fanning a queen, you know, those giant ones, I imagine that takes quite a lot of energy. But if itís a little sort of handheld foldout thing, I wouldnít have thought it takes too much energy to fan.

Chris - There is going to be an energy cost to moving the fan as you say. Muscles are only about 20 per cent efficient. So, of all the energy you use, actually moving the fan, 80 per cent of it is being wasted and turning into heat, exactly as Steven is suggesting. So, youíve actually got to fan a bit harder and sweat a bit more to compensate for the fanning effect, but it will still cool you down because of evaporation. So, I think there's still a net benefit Steven, but itís going to be a modest one.

Kat - Absolutely fascinating stuff.


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