[Physics] A fan in a hot room at what point does it put in more energy that it dissipates


If a fan that is using 50 watts is moving 1 m³/min of air. Lets say the walls are the same temperature as the air so there’s no heat dissipation there. How do I know if the fan is putting in more energy in to the room than its dissipating?

If the walls are 10 deg cooler than the air will this be sufficient for the molecules to dissipate the heat in to them. Where’s the point of balance.

Best Answer

Assuming no heat transfer from a cooler outside to a warmer inside, a fan always adds more energy than it dissipates (because it dissipates no energy). However, by introducing a breeze, it accelerates evaporation off your skin, which in turn cools you off. (This is related to the wind chill factor meteorologists talk about.) How much cooler you will feel will be a function of how much you are sweating. It's important to note that pets, who don't sweat from the majority of their skin like we do, thus aren't cooled as much by a fan as we are.

Another method by which a fan can cool (as mentioned by Mitchell) is to move hot air away from a hot object, thus reducing the air's insulatory nature. This is why fans help cool off CPUs even though they don't sweat.