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 Post subject: Top vs. bottom mount and which way up?
PostPosted: Thu Dec 06, 2012 7:27 am 
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I find myself in the position of having to consider a new casing, and looking at current designs, it seems bottom mounted PSUs are now quite popular. Most other places on the web cover top vs bottom mounting as a cooling issue, but I'm curious as to where the SPCR crowd stands on the issue from the silence perspective.

Google leads me to this tread and this article, though both are over a year old.

Seems to me that in the case of a passive PSU, we would have to mount it vent side up (as per the Seasonic passive X instructions) regardless of whether it's top or bottom mounted. The top mount position then requires a top blowhole, and it has the advantage of being a relatively "closed system" to the rest of the case. Bottom mounting it I suspect the issue is whether or not the case is running at a positive pressure.

With a fan-equipped PSU... well, I'm quite lost. At either top or bottom, if the PSU is fan side up, then I would think the fan would outweigh any convection. Bottom mounting the PSU and a positive pressure case would help here. But if there's a fairly hot GPU above it would that cause the PSU fan to ramp up early?

Fan side down - bottom mounting the PSU makes it a closed system. But there's the issue of ground clearance and dust intake. Top mounted the PSU then sees all the hot air rising in the case, again leading to the PSU fan ramping up. Would a case exhaust fan by the CPU help here?

And I haven't even considered whether a "normal" (CPU above GPU) or "flipped" (GPU above CPU) placement would have an effect on deciding where and how it'd be better to place the PSU. Admittedly, at that point this might be a better post for the Cases and Damping forum. Thoughts?


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 Post subject: Re: Top vs. bottom mount and which way up?
PostPosted: Thu Dec 06, 2012 8:09 am 
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Lucien wrote:
Google leads me to this tread and this article, though both are over a year old.

The physics of thermal and acoustic aspects around PC components haven't changed one iota in a year. :lol:

Seriously, the article about how to use a fanless PSU is perfectly uptodate. About the only thing you could add now is that with Platinum efficiency PSUs, you probably don't even need to think about the heat from a PSU till well over 200W load. The close proximity to case panels might allow just enough conduction of the heat to make it a non-issue.

IMO, the bottom mounted PSU case is the more versatile modern solution. It has been for nearly a decade.

The effect of dust on cooling in a quiet computer is way overrated, IMO. You have to let it get really bad -- choke the fan blades to the point where they have trouble turning -- before dust has a serious impact on cooling. I've vacuumed out horrific messes only to discover that the improvement in cooling was just a few degrees... but this is in systems which don't depend on any high speed fans for cooling. In typical gaming cases where lots of fans are going way over 1k rpm -- that's where those dust filters matter more.

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 Post subject: Re: Top vs. bottom mount and which way up?
PostPosted: Thu Dec 06, 2012 9:08 am 
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Joined: Mon Mar 17, 2008 1:49 pm
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Location: UK
Lucien wrote:
Seems to me that in the case of a passive PSU, we would have to mount it vent side up (as per the Seasonic passive X instructions) regardless of whether it's top or bottom mounted.

Not necessarily. If a bottom point position has a good intake vent underneath it then fitting the PSU upside down with natural convection taking air through fromt he underside fo the case out to the back will work fine. Plus you don't need to worry about dust filters as the speed and pressure of the convection currents won't be sufficient to deposit dust into the PSU. The heat impact on the PSU would be non-existent unless you happen to put the case on top of a brazier, barbecue, bonfine or similar.

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