Is it better to blow hot air out or cooler air into a room?

Question

i have a room inside of a warehouse its a lot hotter in the room than out. I have one 3'door and a huge free standing fan. Would it be cooler in the room to blow the hot air in the room out or the cooler air in the warehouse in?

Answer 1

The answer to this straightforward question is complex. As one answer asked...what do you mean by better. But beyond that, the physics of heat transfer by convection is a difficult subject.

In southeast Asia, many of the buildings are built with very thick walls and wide open space up close to the ceilings. These spaces vent to the outside. Their purpose is to allow the hot air inside rise to the ceilings and escape.

This relatively simple design kept the offices where I worked in Saigon at 10 to 20 degrees cooler than the outside temperature. This meant the office temperatures were somewhere between 70 and 80 degrees F year around; comfortable even when outside reached the 90's.

And it did it without creating heat and by products from some sort of high tech cooling system...like air conditioners. So in the context that simple hot air venting was effective and more efficient that air conditioners, blowing hot air out (in this case just allowing the air to vent naturally) was better. Venting is more efficient because it takes no input energy at all to make it work.

But it did take a special designed building, which most of us in the Western world do not have. We are left with air conditioners. And, as one answer put it, air conditioners pump out hot air as they pump in cold air. They have to, because the heat extracted from the air to make it cold has to go somewhere. So there is no question of "better" here; it's a necessity to both pump in cold air and pump out hot air.

Which leaves us with fans...to exhaust the hot air. The deal here is, of course, when hot air is blown outside by a fan, outside air is brought into the building to replace what was exhausted. And if that outside air is hotter than the inside air, you are heating rather than cooling the inside of the building. Not only that, you are creating heat by that fan...you don't get something for nothing. Just feel that fan jacket, you will see how hot it is.

By the way, using fans to blow air directly on a person is also a way to cool off. But in this case, you are not cooling the air, which was the subject of your question I believe. In this case, you are accelerating the evaporation of your own sweat. And in evaporation, heat is lost and that lost heat results in cooler skin. And, to a point, if your skin is dry, there will be little cooling because there would be little to evaporate.

Answer 2

Depends on your objective.

If the ambient (the temperature of the environment outside) is warm and you want to cool a warm room, the best way is to blow cool air in. This is what air conditioners do. But cooling warm air takes energy and can cost money.

The same is true if you wish to warm a cool room with a cool ambient.

But if your objective is to lower costs, then blow warm out.... or just blow warm "around." Rather than an air conditioner, you merely have a fan. If the ambient is cooler than the room, it'll cool the room a little. If not, you'll just circulate warm air. If the ambient is warmer than the temperature of the room, just circulate what you have in the room already.

Just occurred to me... I'm presuming the room is not air-tight. If it were, forcing air out would remove breathable air from the room. Forcing air into a room would increase pressure and therefore warm the room. But neither is a problem in a standard house-type room. If you blow air out, it's replaced by air from elsewhere... probably from outside... or another room. If you blow air in, the air that's already there will go elsewhere. Air conditioners do both. They take air, usually from outside, cool it, and pump it inside while extracting the warm air and pumping it outside.

The problem is that people set the AC so low that it can't possibly cool the air to that temperature and so soon it's pumping cool air outside.

Answer 3

Make sure that where you place the fan is not the only opening in the warehouse. You must have another window or door open for new cold air to enter (if blowing hot air out) or the hot air to exit (if blowing cold air in). Otherwise, you will just cycle the air around the doorway.
With regard to which of the two choices to use, it's a matter of preference. If you blow cold air in, the area around the fan will be cooler, and the area around the opposite opening will be warmer. If you blow warm air out, the area around the fan will be warmer and the atrea around the opposite opening will be cooler.
The benefit of blowing warm air out, then, would be that you could make it cooler wherever you're working by opening a window there.

Answer 4

Most warehouses don't have an insulated roof. The best bet there is ventilation at the top of the warehouse, where the air is hottest. It need not even be powered ventilation. For a specific room, try to bring cool air into the bottom and take hot air out the top. If the fan in your room is on the floor, you have little choice. Try to get it to draw cooler air in from the floor outside your room. The air that escapes will be a little warmer than the air you draw in.

Answer 5

An air conditioner does both for you. It drives hot air out and cools some of that hot air and blows it in the room

Answer 6

Although such systems are very complicated and difficult to analyze - I would say that as a general rule blowing cooler air into the room would provide more efficient cooling.

The bigger question is whether you want the fan blowing on you or away from you - that may decide how you place the fan.

Answer 7

Blow Fan In Or Out

Answer 8

Open another window in the house where the exhaust from a fan blowing out hot air can draw cool air into the house, it is the best arrangement.

Answer 9

If you blow hot air out, what temp air will replace it, and it must be replaced. You will run the risk of replacing it with air that is just as hot......outside air maybe?

If you blow in cool air, it will push out the hotter air and you don't have to worry about what will replace it. This is the better choice.

Answer 10

Have the fan take the hot air out of the room. This way the heat generated by the fan motor will leave the room. If you bring cool air into the room, the heat from the fan motor adds to the heat of the room. The motor heat is the difference in the cooling efficiency of the room.