homepage Forums Technology Hardware & Software - PC Is PSU in bottom of the case better than the top?

I see some cases put the PSU at the bottom of the case now instead of the top. Hot air rises so having the PSU at the top seems like a more logical place to put it as it can help exhaust heat. How does putting it at the bottom of the case make it better for heat management?

That's the new form factor I believe. I think it started with the Antec P180 last year.

Intel has a white paper on the new design about a year or two ago.

My case:

http://www.arctic-cooling.com/pc_case2.php?idx=4&data=1&disc=

It's called BTX isn't it?

Not necessarily - there are ATX cases with the PSUs at the bottom too & then there is also reversed ATX & ....

Yea, I thought they were BTX at first too but a case like the Antec P180 is actually ATX, they just put the PSU at the bottom. From what I have read it is supposed to isolate the PSU from the rest of the case which is supposed to provide better cooling. The thing is I don't buy that theory and need to see hard data that proves it is better. Seems to me like the Intel spec for cases with a side duct that never cooled better in practice. I know the side duct design isn't better because I bought one of those cases and it is much worse for cooling than my Antec Lanboy which uses a front and rear 120mm fan design.

Those designs isolate the heat of the PSU and usually HDDs giving them a separate intake fan and exit fan (the PSUs) from the heat of the motherboard, CPU, and cards.

In theory less heat hits your processor and video cards. It's not about convection it's about thermal mass.

Having said that I agree with Gatticus, I'd like to see test results first.

Is the power supply's heat even much of a factor compared to "hot plate" vid cards?

Currently, I'm leaning towards a 120mm fan that blows over my HDD's and into my PSU on one side of my case.

Then I'll have another 120mm intake fan for Mobo and Vid card, with a side exhaust fan.

Lots of "quiet" fans around it seems.

The only advantage I can see of having the PSU at the bottom is if cooling the PSU is a primary concern. With the PSU in the top hotter air is entering the PSU, reducing its effective capacity and/or increasing its fan speed (noise) to keep it at the same temp.

The BTX form factor looked a mess to me back when I read about it. It was geared toward making Intel's hot CPU's to work at the expense of everything else.

I've designed quite a few industrial heat exchange systems and fixed problems in others' designs. In comparing my process industry work to PC building I've not been too impressed by most case designs over the years. Years ago I couldn't find decent cases for ATX systems except for the Antec midtower. Before that I bought and modified an old Enlight to make a nice performer of it.

The simple guidelines that AMD and others were giving back in the early days of Athlons made the most sense (cold air in the front and low, hot air out the back and high, balance your intake and outlet fans) but case manufacturers were ignoring it. I'm skeptical of designs that require work to undo what nature is trying to do--especially when they could instead work with it. Don't fight the natural convection from rising hot air unless you have to. (Hell, I've redesigned huge industrial reactors to fix just those sorts of old design mistakes as well.)

P.S.
I don't see how "thermal mass" would impact this unless there was insufficient air flow or *reversed* flow. You would have to be talking about radiant heat transfer...while that is a function of T to the 4th the temperature differences in a PC case are small and the radiant constant is tiny so I doubt it would have any measurable impact.

Thermal mass is a factor in the response time to a *change* in conditions. It is not relevant to a steady state case. Steady state will be dependent on: air flow, temps, effective heat transfer coefficient, heat exchange area, and duty.

You sir are correct and I was using the term incorrectly as a way of illustration. The way I used it was illustrative of T not Delta T.

Most cases rely on convection, yet create vortexes, and eddies, that when taking in total create "hot spots" (i.e CPU fans blow down, relying on the wash to cool adjacent capacitors, etc. yet directly over the CPU most side fans blow in the opposition. add to this GPUs that intake near the CPU base then vent directly out the rear. It's a mess, a chocolate mess.

Most designs also inadequately cool the HDDs and I empirically know that is a primary cause of failure, so giving them their own chamber "seems" to make sense, especially if you use big slow quiet fans.

Having stated your expertise, I respect your opinions ABOVE any marketing ploys. I will need to look at a number of cases before I buy my next one.

Jake,

Eddies and dead zones are indeed a problem. This has always seemed most evident to me in vid cards and other cards. aIt was about two to three years ago that vid card coolers began taking up an extra slot to expel the hot vid card air out the rear.

The old Antec midtower case I use has a spot for an 3rd intake cooler to blow across the hard drives. I haven't really needed it as the case layout has proper vents included for that fan in the front bezel while the three rear facing fans (2 case, 1 PSU) plus vid card fan seem to create enough effective draw since the front has only two fans drawing.

The CPU fan indeed impacts the eddies and local air distribution. I can see differences in "motherboard" temps from varying the CPU fan speed and without knowing where the sensor is the results would seem counterintuitive.

Dell had a slick semi-passive CPU cooling design for years that relied on a plastic ductwork/cover from the CPU slot to the rear case fan. With low thermal loads it was effective and quiet.

My older system still using the Enlight case had one fundamental flaw that I recognized before I bought it--but I knew it would be easy to fix whereas other cases had bigger problems at the time. It had an effective hole area in the front bezel of ~8% of the front fan's swept area. It was badly choked and I could see it in case temperatures. Fortunately the front bezel was a clean design so I bored out the few small holes to larger diameter, doubled the number of holes, drilled holes in an empty drive bay cover, and cut a slot in a hidden indentation at the bottom of the bezel. This increased the hole area many fold and testing proved that it greatly cooled the case and the CPU as well, and it looks stock rather than like some Frankenstein home project.

some Frankenstein home project

Hey I resemble that statement!

What do you guys think of this as far as effective airflow and cooling.

1. A horizontal (flat) case for a desktop
2. Facing it, you have a two 120mm intake fans, one left of center that blows onto the mobo the other far right of center.
3. the left rear of the case has the mobo, the right rear has the PSU.
4. 2 HDD's mounted in the right side of the case, the right side intake fan blows over them and into the PSU.
5. The left fan blows over the mobo and vid card.
The left side rear of the case as a side exhausting 90mm fan, to evacuate hot air from the Vid card and mobo.

Functional??

I am no engineer, just curious.