On Thursday, July 24, 2014 2:13:39 PM UTC-4, Ralph Mowery wrote:
"trader_4" wrote in message

...

Not really, because again most of the energy from the motor is

not resulting in heat. I made that mistake myself, suggesting that

you could measure the wattage using a Kill-a-Watt. You can measure it,

but you can't then say because it's pulling 50W that it's generating

50W of heat in the room.



I understand your thinking, but all the power a fan is using in a closed up

room is going to generating heat.



Part of the power to turn the motor is being used in the wiring, part is

lost in the bearings of the motor, and whatever is left over is moving the

air. When the air is moving, that movement is being converted back to heat.



If it was being used to blow air out of the room, then much of the enegry

used to move the air would be dissapated as heat outside the room.



OK, I agree with your analysis. As long as the air stays within
the room, then the increased energy of the air that the motor transfers to
it has to go somewhere and I agree it would result as heat in the room.
From what I can see, these fans are typically ~75W. From a heat standpoint,
just pushing the hot air from the ceiling down is going to have a bigger
effect than the 75W ever will. For example, when I turn one of my fans
on I can feel the hotter air moving down suddenly. Once it evens out,
the breeze makes the room feel more comfortable. But from an energy
standpoint, I would bet that the fan constantly moving hot air from higher
levels instead of just leaving it be, raises the temp of the lower levels
of the room a couple orders of magnitude more than the 75W of the fan
generated heat. You also have to wonder on it's effect of using more
AC. Two scenarios. One is leave the air stratified, so the hottest air
is up high where no one is. Or use the fan to bring the hot air down,
where the AC has to deal with it. I guess if you leave the AC slightly
higher because you now have a breeze, it could make up for it. Otherwise,
with the hot air being pushed down, I'd expect the AC is going to have to
run more.








Just plucking out numbers from the air, say the fan draws 100 watts from the

AC line. All 100 watts will be heating the room unless you blow air out of

the room. The fan may only use 25 watts to heat up the motor due to

electrical and mechanical losses. The other 75 watts will be converted to

heat when the air molicules rub against each other and slow down. Just like

rubbing your hands together.



Same as a light bulb. So much goes to generating the light, and whatever

the light hits heats up. So unless there is a window that lets a few photons

out, all the power of a light bulb of any kind will go to heating up the

room. Some types of bulbs are just more efficiant in making light than

others so you can get an equivilent ammount of light with less wattage and

het.