How to Properly Ventilate Racks - AVS Forum
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post #1 of 16 Old 12-30-2011, 09:25 AM - Thread Starter
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How to Properly Ventilate Racks
By Frank Federman
Should rack fans blow in cool air or push out hot air? Should some fans in a rack be pushing while others are pulling?

Is it better to push cool air into a cabinet or pull the hot air out? Should all rack fans push or pull, or should you use half for each function?

There are a couple of fundamentals to remember when you're planning to ventilate a cabinet, closet, video projector enclosure, etc.



Check Air Movement
In a situation where air can move freely with little or no resistance, multiple fans should either all be used for intake of fresh air or exhaust of hot air. If air can move freely, ventilation probably isn't much of a problem.

This is called placing the fans in parallel. In the real world, you'd probably use all of the fans to exhaust hot air high and out the rear of the cabinet, but they would work just as well pushing fresh air in low in the front of the cabinet.

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post #2 of 16 Old 12-31-2011, 12:55 PM
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I'm going to differ in my opinion a bit on this based on my experience building larger servers and tower PCs. Studies have shown that the most effective cooling is achieved by focusing on evacuating hot air from the enclosure and providing adequate venting for the inflow of fresh air to replace it. This results in creating negative pressure inside the case and the most direct flows of air through the enclosure. Forcing air into the case can create confused airflows that actually decrease cooling efficiency.
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post #3 of 16 Old 01-01-2012, 12:29 AM
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Quote:
Originally Posted by Ironlight View Post

I'm going to differ in my opinion a bit on this based on my experience building larger servers and tower PCs. Studies have shown that the most effective cooling is achieved by focusing on evacuating hot air from the enclosure and providing adequate venting for the inflow of fresh air to replace it. This results in creating negative pressure inside the case and the most direct flows of air through the enclosure. Forcing air into the case can create confused airflows that actually decrease cooling efficiency.

I have to agree with what you stated Ironlight. Always better to remove the hot air and allow cool air to replace it.

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post #4 of 16 Old 01-01-2012, 04:25 AM
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Another +1 with Ironlight.
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post #5 of 16 Old 01-01-2012, 11:44 AM
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How does posting these junk articles from CePro benefit the community?
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post #6 of 16 Old 01-01-2012, 01:11 PM
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it pays the bills of the www. community server ?
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post #7 of 16 Old 01-02-2012, 09:19 AM
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From my experience building PCs, this advice is false. You need a balance of intake and exhaust air. Too much exhaust means cold air is sucked in through all of the openings, not intake itself. Too much intake creates hot and cold spots in the case, with no way to pull the hot air out.

I would never configure a PC with this type of cooling.
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post #8 of 16 Old 01-02-2012, 08:26 PM
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The author has a Bsee degree but specializes in selling computer case fans to cool audio equipment. He does have some interesting ways to cool a projector, it looks as if he may have stopped at a local vacuum shop and picked up some hoses cheep.
http://www.activethermal.com/page33.html

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post #9 of 16 Old 01-03-2012, 07:31 AM
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Every time I see a competitor's rack with no blank rack panels between their amps or signal processing equipment, I slap my company sticker on it, as I know there's going to be an expensive service call forthcoming when overheated equipment fails a couple of years after the warranty expires.
My stickers never fail me.

Want to see some bad installations with no concern given to cooling? Go look at any old back issue of Audio Video Interiors...

www.curtpalme.com - CRT tech info

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post #10 of 16 Old 01-03-2012, 07:38 AM
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Quote:
Originally Posted by lawrence99 View Post

The author has a Bose degree but ...

Fixed!

www.curtpalme.com - CRT tech info

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post #11 of 16 Old 01-04-2012, 04:23 AM
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I disagree with Ironlight, and with the article.

First of all: Negative pressure is a bad idea for both computers, and for media rack systems. The reason is, negative pressure means the computer case, or rack system will attempt to draw air into it through any crack that will allow air through it. This means you have no control over dust entering the case or rack. Unless you are constantly swapping equipment in and out of the rack, or components in and out of the computer, you will spend an excessive amount of time chasing all of the dust out. A computer case or media rack should ALWAYS run positive pressure (More intake pressure than exhaust) so that you can put filters on the intake, and capture all of the dust entering the enclosure. This will prevent a LOT more thermal failures down the line due to dust insulating the components, and clogging up fan bearings causing them to fail. It would take a VERY poor design to cause a thermal failure in a rack that had any sort of ventilation, as long as all the components are kept free of dust.

Second: Don't confuse computer cooling for media rack cooling. The two are very different animals. Computers have gotten to a point where they stick a lot more strictly to standards, which allow for simpler and cheaper solutions in a rack environment. For the most part, any rack-based computer system is built to draw cold air in from the front, and exhaust out the rear. Media systems do not stick so strictly to standards, so from one component to the next, you can not be assured where it will draw in cold air, or where it will exhaust hot air. The good news, is that media systems are typically not as sensitive to heat as computers. As long as you give them some sort of ventilation, not just locking them in a hot box, they will manage on their own.

As far as hot spots are concerned; the goal is not to avoid having ANY hot spots in a computer case or rack. The goal is keeping the hot spots from collecting around sensitive components. The way you do this, is by exhausting from as close to the component as possible. If the top of your rack has no equipment in it, who cares if there is a pocket of hot air sticking around up there ? If the 5-1/4" drive bays have no components in them,who cares if there is a pocket of hot air swirling in there ? As long as your active components are kept cool, the pockets don't matter. Once you find a component that generates a lot of heat, find a way to exhaust that hot air directly outside of the case or rack. As long as you are bringing cold air into the rack, that exhaust will draw that cold air right to your component. That is all there is to it.

I would never run a rack that had ONLY intake OR exhaust fans. There always needs to be something to guide the airflow. So either you seal the rack to be air-tight other than your intake and exhaust fans, or you run positive pressure with at least one decent exhaust fan to get the airflow moving in the right direction. The most efficient systems will always draw just slightly more air into the case or rack, than it expels through the exhaust. When you have a component that generates a lot of heat, make sure your design keeps it's hot air from blowing by the cold air intake of another component. The easiest way is by ducting from that spot, directly to the exhaust fans.

Ultimately, the biggest thing that will cause thermal failure in a media rack is dust buildup. The second is just letting one component cook the next component. If you manage those two things well, the ventilation part becomes much less important.
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post #12 of 16 Old 01-04-2012, 06:09 PM
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I remember modifying a piece of equipment that the power supply was getting so hot that you could not hold it in your hand right after it was turned off and we had lots of failure on those unit.

I just reverse the fan and the after the modification the power supply was barely warm and I never had to fix power supply on those unit after that modification
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post #13 of 16 Old 01-05-2012, 06:41 AM
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My preferred method for ventilating racks is by motorboating them.
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post #14 of 16 Old 01-06-2012, 03:41 PM
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This article provides a fairly good tutorial on cooling electronics enclosures with fans.

Pretty much what 3Z3VH says.
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post #15 of 16 Old 01-07-2012, 06:39 AM
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Quote:
Originally Posted by Beantown Bronco View Post

My preferred method for ventilating racks is by motorboating them.

Thank you. I was going to post something very similar. Glad to see that somebody has my level of humor.

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post #16 of 16 Old 01-08-2012, 06:23 PM
 
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Quote:
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thank you. I was going to post something very similar. Glad to see that somebody has my level of humor.

+2!!! :d
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