Why is air cooler when blown by a fan, when essentially it is moving the same warm air around it?

Answer 1

Because the air intake is larger than the holes it blows it back out of, and air cools when it is compressed.

This may sound mad but try this - purse your lips like you're going to whislte and then blow onto the back of your hand. It's cool. Now open your mouth wide and do the same thing - it's warm.

See? Magic!

er... sorry, science.

Answer 2

The air is not cooler when blown by a fan. In fact the air can be a little bit warmer, since the heat of the motor driving the fan can raise the temperature of the air passingo over it little bit.

You feel cooler when the fan blows because it is causing moisture on the surface of your skin to evaporate. The process of evaporation draws heat from the surroundings, resulting in the surroundings cooling off a little.

Stick your head out of the window of a moving car hot summer day. The air temperature hasn't changed, but you will feel cooler for exactly the same reason.

Answer 3

I had a similar issue. It sounds like your AC is freezing up due to a shortage of freon in the system. You may have a slow leak that needs to be fixed. Once complete, they can add freon and you should be good to go. Here's an article I found on the web that trouble shoots the problem. The good news is you shouldn't be out a ton to get it fixed. Mine was $150ish to repair. Air conditioning coil icing and freezing is usually caused by a lack of refrigerant, due to a refrigerant leak --------------------------------------... I get lots and lots of inquiries about air conditioners and heat pumps icing up the indoor coils and the large line to the unit in the air conditioning mode. This is usually caused by a lack of refrigerant in the system due to a chronic leak. The reason that the coils form ice is that when the system is short on charge part of the coil runs very cold and ice starts to grow. Once the ice starts to grow it is in insulator and keeps on growing until the coil and the refrigerant lines are one block of ice. If this happens continuing to run the equipment will damage the compressor and not provide any cooling. If this was caused by running the system on a cold night, the best way to remove the ice is to leave the indoor fan on and let the ice melt (expect a mess). Refrigerant leaks will not go away and there is nothing that you can add to your system that will stop it. The only cure is to repair the leak. Usually when there is a refrigerant leak the oil that is mixed with the refrigerant will collect around the leak and attract dirt. Look for these stains and chances are good that is where the leak is (there can be more than one). We have seen many cases where a service company will keep adding refrigerant 22 (Freon) to a leaking system and claim that they cannot find the leak, but when the covers are removed the oil stains tell other wise. Other things that will cause or aggravate ice are clogged filters, bad fan motors, to many closed vents, dirty filters (never been changed), running the system when it is "too cold outside" (below 65 degrees F) with out modifying the system for cold weather operation, clogged capillaries or bad expansion valves. Somone recently wrote me complaining that their unit ices up when it rains allthough they blamed "humidity" the real cause was that the head pressure would drop to the point where the indoor coil would ice up. Do discount the possibillity that the outdoor unit was replaced by one that is larger without changing the indoor coil to a larger capacity. We have seen an epidemic of clogged capillaries on Rheem Ruud units on the indoor coil. The only fix is to replace the coil with one that has an expansion valve and watch the system work better than when it was new. We are currently working on a Rheem/Ruud unit that had a bad compressor and after replacing the compressor we found a bad reversing valve (hissing real bad with high suction pressure). We replaced the reversing valve only to find the the metering orifice is the wrong size or clogged inside (air conditioning mode). The system is running about 40 psi suction pressure which will ruin the compressor and reversing valve. The reason that we know this is we put a liquid line sight glass on the system and the sight glass is full but the indoor coil is freezing up. The hard part is going to be explaining to the home owner that this has been the cause of the problem all along. If they had just replaced the outdoor unit then the problem would have been worse and they would be out a few thousand dollars and still no cooling. We finally did repair the system after finding some crud caught in the orifice. We are recommending changing the system to thermostatic expansion valves because I am getting a foaming sight glass and 80 psi of suction pressure. Which means the system cannot be properly charged.

Answer 4

This question was asked yesterday.

When the air is still the air immediately around your body heats up to near body temperature. The fan blows this warm air away and replaces it with more room temperature air (which is cooler than you.).

Moving air also increases the amount of water that evaporates from your skin. Since it takes energy to turn liquid water into a gas (because it takes energy to break apart the bonds between water molecules), water evaporation drains energy (heat) from your body.


***Edit***

Regarding "frenziedmonkey" s response (above), air HEATS up when it is compressed. It cools when it expands. So his answer is the opposite of what it should be.

Answer 5

Read up on Newton's Law of Cooling. The level of humidity in the air combined with the speed of air movement gives rise to the Chill Factor, hence the cool feeling. If humidity were zero, you wouldn't notice the difference!

Answer 6

well maybe it could be that the air itself was being warmed by another source, say a heater in the middle of the room. when that air blows away cooler air replaces it.

Answer 7

Because the wind increases the rate of evaporation of the
sweat on your body..
The wind also blows "heat" off of your body faster than
still air, ( Wind Chill factor )
This fan can also work in reverse if the ambient temperature
is too high...Like a convection oven...

Answer 8

It is moving the air around. You are also most likely sweating a bit. When the fast moving air hits your sweat it cools you down. That is what you are feeling.
b

Answer 9

It isn't cooler, it feels cooler because it has a chill factor.

Answer 10

Its creating a small wind chill factor, it also helps to wick moisture away from you which all helps to cool you down.