PSU positioning relating to cooling

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PSU positioning relating to cooling

Postposted on Mon Mar 10, 2014 6:43 pm

I got asked a interesting question today. It relates to the PSU and the trend in newer cases that allow you to position it to draw air from outside of the case.

In the past every PSU drew air from inside the case and exhausted it out the back, thus helping remove heat from the case. In the last few years several cases have allowed you to turn the PSU over and draw cooler air from outside the case. Supposedly this will help the PSU last longer by keeping temps lower. Does it really make a difference in the life span of the PSU or would the system as a whole benefit more by using the PSU as an additional air exhaust by drawing air from inside the case?
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Re: PSU positioning relating to cooling

Postposted on Mon Mar 10, 2014 6:50 pm

There's probably no easy answer here. It will depend on how good the ventilation of your case is (aside from the PSU fan).

As a very rough rule of thumb, I'd say if you are routinely pushing the PSU hard there's probably some benefit to drawing the PSU intake air from outside the case. But only if the case isn't sitting on the floor; if it is on the floor the PSU will suck up too much dust.

One of my systems here at work (the one that was a DIY build, as opposed to the corporate-issue Dell) has a bottom mount PSU, but I mounted it upside down because the system is on a carpeted floor. It has been working well for about a year and a half so far; the only issue I've had is I dropped a screw into the PSU once while installing an expansion card. Getting it out was a PITA. Now I cover the PSU fan intake with a piece of cardboard whenever I'm working inside the case.
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Re: PSU positioning relating to cooling

Postposted on Mon Mar 10, 2014 7:14 pm

The system that brought on the question sits on a desk so the dirt/dust from the floor isn't an issue. It's in a Corsair case with a 200mm air intake fan in the front of the case, a 200mm exhaust at the top of the case, and a 120mm exhaust fan in the back. The system in question is going to be getting two to three more GPU's, which model of GPU is still up for debate, added in to run a distributed computing project similar to Folding@Home. The GPU's will be EVGA and the debate is over getting cards with reference coolers or with EVGA's ACX coolers that dump heat inside the case.

Water cooling has been ruled out for various reasons. Aside from replacing each of the 200mm fans with two 120mm fans, the only other option to provide more cooling was the using the PSU as another exhaust source.

I have the same case which is why I was the one asked the question.
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Re: PSU positioning relating to cooling

Postposted on Mon Mar 10, 2014 7:17 pm

Cooler PSUs also tend to be more power efficient. Most cases with the ability to draw outside air for the PSU are 'higher end' and will generally have more cooling options like extra fan mount points and 120/140mm fan mounts. In those cases - pun intended - cooling won't be harmed so long as you have a couple of fans which most high end cases come with these days anyway.

Since most PSU fans are at a 90 degree angle to the exhaust and it has to pass a lot of components the rate of airflow is significantly smaller than a fan pointing directly out of the case with nothing in it's path on either side.
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Re: PSU positioning relating to cooling

Postposted on Mon Mar 10, 2014 7:36 pm

just brew it! wrote:As a very rough rule of thumb, I'd say if you are routinely pushing the PSU hard there's probably some benefit to drawing the PSU intake air from outside the case.

This. Since you're going to be running 2-3 GPUs, then there is probably some benefit to not drawing in the heat that the GPUs are pumping out. Many cases also have filters on the bottom, which helps with the dust problem.


just brew it! wrote:...the only issue I've had is I dropped a screw into the PSU once while installing an expansion card. Getting it out was a PITA. Now I cover the PSU fan intake with a piece of cardboard whenever I'm working inside the case.

Yikes. Several years back I was messing around with a disposable camera flash and accidentally touched my knuckle to the uncovered back of the (charged) capacitor. Once I recovered, I think I knelt down and did the sign of the cross. I have alot of respect for capacitors now. I'd hate to think of what a much larger PSU cap could do. :o
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Re: PSU positioning relating to cooling

Postposted on Mon Mar 10, 2014 9:13 pm

The Egg wrote:
just brew it! wrote:As a very rough rule of thumb, I'd say if you are routinely pushing the PSU hard there's probably some benefit to drawing the PSU intake air from outside the case.

This. Since you're going to be running 2-3 GPUs, then there is probably some benefit to not drawing in the heat that the GPUs are pumping out. Many cases also have filters on the bottom, which helps with the dust problem.

...until you forget to clean the filter and it blocks the intake.

The Egg wrote:
just brew it! wrote:...the only issue I've had is I dropped a screw into the PSU once while installing an expansion card. Getting it out was a PITA. Now I cover the PSU fan intake with a piece of cardboard whenever I'm working inside the case.

Yikes. Several years back I was messing around with a disposable camera flash and accidentally touched my knuckle to the uncovered back of the (charged) capacitor. Once I recovered, I think I knelt down and did the sign of the cross. I have alot of respect for capacitors now. I'd hate to think of what a much larger PSU cap could do. :o

I unbolted it, flipped it over and shook the screw out, so no risk to life and limb. (I *have* taken PSUs apart before, and know what to watch out for... that wasn't necessary in this case though!)
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Re: PSU positioning relating to cooling

Postposted on Tue Mar 11, 2014 11:04 am

It's normally a question of balancing what you want to cool most.
If you have the PSU drawing warm air from inside the case and exhausting it, you are making the PSU fan work harder and under hotter conditions, but improving exhaust airflow from your case.

Personally I find that keeping graphics cards cool and quiet is the hardest task in a PC case. If the PSU can significantly contribute to the case cooling for your graphics cards, it's often worth the disadvantages of having it suck warm air from inside the case. If you already have a pair of 200mm fans in your case, I doubt the PSU can help much, in which case it's best to isolate it.

Khali wrote:the debate is over getting cards with reference coolers or with EVGA's ACX coolers that dump heat inside the case.


Exhausting reference coolers for SLI/Crossfire, unless your case is vast/has hurricane-like airflow.
I've done many a dual-GPU rig and you don't want the hot air from one card going straight into another card - get it out the back ASAP.
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