Here's a current debate in our house:
If a fan is on in a room and there's no one around to feel it, does it cool the air?
We know keeping cool with fans (instead of air conditioners) is a green way to beat the heat. But whether or not to keep a fan on when no one is around is a common question…
The reason fans are great for cooling is because blowing air across the skin increases evaporation, which creates a cooling effect on the body. So… if nobody's there to feel the air blown from the fan, than no body is getting cooler.
However, a window fan can help bring in outside fresh cool air, a floor mounted fan can push up low cooler air and ceiling fans can help circulate stale air. But again, this is only useful if the room is occupied, or will be occupied shortly after the fan is turned on.
So to end the debate: keeping cool by a fan is merely a sensation, as a fan does not literally cool the ambient temperature of a space. Only air conditioners can do that. Turning on fans to stay cool is easy, but don't forget to turn them off to save electricity.