Heat rises. When the heat is on, a fan should pull air from below to mix cooler air near the floor with warmer air near the ceiling and force the mixed air back down the walls to the floor. When the AC is on, pushing air toward occupants promotes evaporation and a cooling sensation.
Stu's Views is Education and Fun. What do YOU want to VIEW today? MathLandia High school mathematics learning fun. Both Stu's Views and MathLandia are free websites that do not sell anything. Saving energy is not always free. Be a world saver.
Please don't PM with questions that can be asked in a forum.
I always love discussions of this type! One fact of nature... Heat rises cool air falls, We seem to agree. So if all your heat is rising (collecting at the ceiling) You would think you would want to Push the hot air back down.. (opposite on the consensus here)
Lets look at it from a different approach, Is the goal to mix the air for it to be uniform in temp? If this is the case then you need to look at the efficiency of the fan. can it move more air pushing down or pulling up? Generally considering all the aerodynamics I would say it moves more air pushing down. I say this based on the exit effect of the ceiling when pulling up and the entrainment effect when pushing down.
So If you are staying warm and pushing the air down (humor me) you are pushing a lighter mass air against a more dense air (cold) so you would think it would not move very well up the wall.. BUT you are adding energy / momentum from the fan to give it added velocity so it may do well in stiring the mass to a more uniform temp. At least the immediate effect is to push the warmer air to you! . And at the least it will be pushing the air horizontally and perhaps out the window cracks and door jams from which it came in in the first place.
Ok now consider pulling air up. Now you are trying to suck the cold air up (that wants to stay at the floor) to the fan to mix with the warm air at the ceiling. Warm air still rises so why doesn't it stay at the ceiling? And since you are sucking from the floor why aren't you sucking in more cold air in from the windows and door jams.
Did I convince anyone that snow falls up Charlie Brown. It comes out of the ground a swirls around so It only looks like it is falling!
the best way to keep the room feeling cool is to open the window and put a Ceiling fan or pedestal fan in it facing the interior. The cooler air from outside would be blowing onto sweaty bodies, helping them evaporate sweat even faster.
And what to do when it's hot inside and hotter outside? When the heat really goes off the rails, a fan just ends up blowing hot air on you, unless it's a super powerful pedestal fan, then it's difficult to tolerate.
Fans just move whatever air is already in the room--which means recirculating bad/hot air. Air conditioner air purifier combo is the way to go because it purifies hot air and circulates cool air simultaneously
Ceiling Fans
Posted - 07/27/2013 : 07:37:07 AM
