Equipment closet cooling

So I have an equipment closet that is roughly 3' X 7'. As you can imagine it has several computers and other gear in it and gets rather warm, especially during the summer months. I just recently installed a bathroom exhaust fan, 50CFM, and louvers into the bottoms of the closet door. The thinking here was that the exhaust fan would kick on, pulling air from the top of the closet, which would in turn pull cool air through the louvers and cause an overall cooling effect on the closet. This has not worked out as planned. I shut the doors for a few hours yesterday and the temp built up to around 90 degrees. I then kicked the fan on, expecting air flow, circulation and cooling, but an hour later the temp was the EXACT same! I tested the fan to be sure it is actually moving air by placing toilet paper across it and yes, it is working as it should. I even got into the attic to check the other end and there is air being pushed out.

My thought here is that what is happening is that the cool air is being brought in and sucked into the updraft from the fan and not circulating throughout the closet, so no cooling is actually happening. My next thought is to put a small desk fan into the closet near the louvers to get the air circulating lower in the closet so that the updraft from the fan does not just suck the cold air up (As it appears to be doing now).

I am a little at a loss here, because the theory behind what I did should be sound. Hot air rises and so on.

Any thoughts here?

I would think 50 CFM would be enough to provide some measurable difference. Can you measure the intake and output temperatures?

To get an estimate of the heating you should be seeing you need to estimate or measure the power going to all the equipment. It all becomes heat. For example take 200W.

To raise 1 cu. ft. of air 1 degree F takes 0.02 BTU.
1 W = 3.41 BTU/hr

So 200 watts = 680 BTU/hour

In 1 hour at 50 CFM you move 50 x 60 = 3000 cu ft of air.

0.02 x 3000 = 60 BTUs for 1 degree rise

Temp rise is 680/60 = 11 degrees F.

You could measure the temperature in several places in the closet to see if the cooling air is bypassing the equipment. If so a fan in the closet may help. Better would be to duct the input of the exhaust fan to be near the equipment so it is removing the hottest air.

Right now there are 2 computers a monitor and 2 routers/switches in there that run at an average load of 250 - 300W total. Eventually I want to put my A/V gear in there as well, which would be a lot more load in there, but it would only be periodic and not on all the time like the load in the room now.

Ducting the exhaust fan towards the back end of the computers is not a bad idea since they are front to back cooled and I could easily put something in to try that out.

Venting to the attic tends to not work well; that's best suited for removing moisture from a bathroom. What you're doing will affect the equalization of air in the house (if you're pushing indoor air out, what's replacing it? It's best to recirculate that air!

For equipment closets, it's best to bring in air from the house, pass it by the equipment, then return the "hotter" air back to the house to be diluted and conditioned as the rest of the place. Or better yet, dedicated A/C - but that's far less likely.

Maybe you could strap some dryer hoses to the exhausts of your PCs and run them to a junction that is hooked up to the bathroom fan?

Why don't you do what all of the rest of the rooms in your house do, add a duct from your AC unit.

Do you have your AC units in the attic? If so, just get yourself a 6in flex duct and a 6in starter collar and run a vent into the room. Since you have louvers on the door you shouldn't need a return air vent.

Ducting from your AC may work ok in the summer when the rest of the house needs cooling. Even then I doubt the cooling will be consistent - no cooling except when the rest of the house needs cooling. And in the winter you don't have cooling. You could shut the vent to prevent heating but that gets you back to where you are now.

Where does the exhaust fan vent to? I agree with Work2play that venting to the attic is not the thing to do.

Lou Apo said:

Do you have your AC units in the attic? If so, just get yourself a 6in flex duct and a 6in starter collar and run a vent into the room. Since you have louvers on the door you shouldn't need a return air vent.

Click to expand...

I would try the opposite....since you have louvers in the door add a return duct to draw air out. This will mix the closet with the rest of the house and will work whenever there is a heat/cool cycle.

Also, what are these 2 computers doing 24hrs/day to produce that much heat?

In my previous home I had an AC duct into the closet, the issue is that with the closet doors closed that does not really do anything because since it cannot recirculate then you only get a small burst of cooling before the back pressure stops that vent from pushing any more air into the room.

I understand what you guys are saying about the exhaust fan, and that is in essence what I am seeing. The exhaust fan is pulling some of the hot air out, but the air is not coming off the top or mixing so I am not getting the net effect I was looking for, which was a circulation.

The idea of putting a small air return into the top of the closet is probably the best I have heard honestly, I could put a 4" duct with a return and splice that into my return line, which is right on the other side of the wall from my closet, and then anytime the AC kicks on it would suck that air through and perform heavy circulation, without changing the overall air equalization in the house. Not to mention the added benefit that I would get in that the closet I am using is in a back office on the upstairs, so this would very possibly INCREASE the air equalization in the upstairs of the house.

Video321, it is 2 computers running 24 hours a day in a 3' X 7' closet. They do not have to do much to create enough heat to warm that small of an area. The whole closet is roughly 170 cubic feet.

For now I have put a small desk fan into the closet to recirculate the air in there, but I will look into adding the return duct.

It doesn't take much equipment to build up heat - in my closet I just have a MediaSmart WHS, the Elk, and a router and switch - and I can't close the doors. There is an HVAC vent in there that I have to close in the winter to keep the heat out; I'll likely add an exhaust fan soon as well. This is a 7x13 closet.

Agreed Work2Play, but if I keep the doors open my office gets uncomfortably warm, and since I spend a fair amount of time working from home I do not want to have my office be the hottest room in the house.

Another thought I had was too tee off a 4" vent and put it near the floor of the closet to push cool air across the front of the equipment and then in the ceiling at the other end of the closet tee into the air return. That way I get cool air pushing in and a return to suck the hot air off and pull additional air in through the louvers.

Work2Play said:

It doesn't take much equipment to build up heat - in my closet I just have a MediaSmart WHS, the Elk, and a router and switch - and I can't close the doors. There is an HVAC vent in there that I have to close in the winter to keep the heat out; I'll likely add an exhaust fan soon as well. This is a 7x13 closet.

Click to expand...

Hmmm...I guess I just don't see the same heat issue as you with my closet, which actually is a closet.
The closet itself is a standard dual sliding door type that is 8'x2'. It is built out into the room so one side is viewable and I took that side, opened it up and put in a custom wood shelving system and a louvered door. The equipment rack comes right to the opening of one of the sliding doors and I put in a partition to keep the other half blocked off (it is the kid's toy room so guess what's in the other half...) This allows full access to the back of the equipment.

I have (2) receivers, a 24/7 PC (HTPC/Server), CCTV DVR, Cable TV DVR, VoIP box, matrix switcher, a couple switches, router, cable modem, WDTV Live, and numerous other devices like powered VGA splitters and such and never had a heat issue. It probably helps that 2' away on the adjacent wall from the louvered door is the HVAC return.

chewie said:

Video321, it is 2 computers running 24 hours a day in a 3' X 7' closet. They do not have to do much to create enough heat to warm that small of an area. The whole closet is roughly 170 cubic feet.

Click to expand...

I was asking what they're actually doing because if they're older computers doing simple automation tasks then you would be seeing the type of heat generated along with a high electric bill. You might be able to save yourself a lot of work by building more efficient computers and using "green" drives too. A newer computer would be faster with less heat generated - the power supply would be the biggest culprit.

video321 said:

I was asking what they're actually doing because if they're older computers doing simple automation tasks then you would be seeing the type of heat generated along with a high electric bill. You might be able to save yourself a lot of work by building more efficient computers and using "green" drives too. A newer computer would be faster with less heat generated - the power supply would be the biggest culprit.

Click to expand...

Video321 has a very good point. The best thing to do is cut down the heat to start with - it helps solve the heat issue, lowers your electric bill and lowers the cooling load (which lowers your electric bill some more). 200 watts on 24 x 7 at $0.10/kWh (your rate is probably higher) is $175/year and this doesn't count the extra cooling needed.

There are much smaller PCs available depending on what you need to do. If you can do it with Linux you can run quite a bit on a 5 - 10 watt router by loading dd-wrt or Tomato. I just picked up an Asus WL520GU and am getting a WL500GPV2 for just that. Both were under $50.

Those are both very valid points. I do not need a tremendous amount of compute power (Homeseer automation software, file sharing and 4 or 5 IP cams that I plan to record using either Vitamin-D or something like that) and the systems I am using are very powerful (Quad core CPU's with 8GB of Memory)with a lot of hard drive space (2 X 2TB drives mirrored) so I could probably drop one of them entirely and potentially even sell both of these machines and use a more power efficient machine like an Atom which only really sits and draws about 40 watts.

What I want to do is move all my AV gear (Which is only on usually between 1-3 hours a day) into this closet, but I have to get my computer and heat situations under control first.

I really appreciate all the suggestions you guys are throwing out here, they are all very helpful.