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From: kony on 20 Dec 2009 17:31
On Sun, 20 Dec 2009 08:42:35 +0800, "Dave C."
<noway(a)nohow.never> wrote:

>
>> >I think it is wrong to put the power supply in the bottom of an ATX
>> >case. It's just plain stupid to design a box that most customers
>> >will have a problem with. -Dave
>>
>> Wrong... Why? Other then the cable length issue, what's your
>> objection?
>
>You need a shitload of extra fans (adding extra noise) to
>counter-balance the fact that much of your cool intake air is going in
>the wrong direction to cool anything. -Dave


Cases these days, at least anything decent besides this
factor, tend to have more than enough fan mounts... unless
someone is building a higher end gaming system.

Regardless of where the PSU exhausts, as long as there is
one low RPM 120mm fan at the top rear it is enough for the
typical PC.

That is, beyond where the PSU is, the same arrangement as
any other case. Only other fan needed might be right
across from the video card if someone has particularly hot
running (esp. overclocked) card(s), unless the system is in
a particularly hot environment in which case another fan
would be prudent no matter where the PSU is located.


From: kony on 20 Dec 2009 17:35
On Sun, 20 Dec 2009 08:40:38 +0800, "Dave C."
<noway(a)nohow.never> wrote:

>
>> I'm not sure if there was any specific reasoning as to why they
>> started off putting them on top in the first place, but *that*
>> decision seems a little odd.
>
>Many computers were cooled with only one cooling fan. That is the one
>that was mounted on the back of the power supply. Air would be pulled
>through the case, then through the power supply, then exhausted out the
>back of the power supply. Therefore it made sense for the bottom/back
>of the PSU to be mounted as high as possible in the case. That's the
>direction all the hot air was going anyway, so it made cooling more
>efficient to have the PSU way up top.
>
>The PSU still assists somewhat in cooling the case...and more
>importantly the components in the case. The only advantage to having
>the PSU bottom mounted is that the PSU fan will be drawing more cool
>air into the PSU itself. In turn, this means you need a shitload of
>airflow to cool the case (and components like the northbridge, CPU and
>GPU in particular), because much of your cool intake air is now going
>down low where it's not cooling a damned thing. -Dave


If you consider a single 120mm fan at low RPM a shitload,
then yes.

Modern systems aren't THAT hard to cool. When you wrote
about old systems that had only the PSU fan as an exhaust,
those were typically about 60W, cooled solely by a single
80mm fan. Today with both the PSU fan (No matter where it
is, so long as it exhausts) and a 120mm fan moving more air
than the 80mm PSU fans did, you have an increase in airflow
correspondent to the increase in heat produced.
From: Paul on 20 Dec 2009 17:48
Dave C. wrote:
>> I'm not sure if there was any specific reasoning as to why they
>> started off putting them on top in the first place, but *that*
>> decision seems a little odd.
>
> Many computers were cooled with only one cooling fan. That is the one
> that was mounted on the back of the power supply. Air would be pulled
> through the case, then through the power supply, then exhausted out the
> back of the power supply. Therefore it made sense for the bottom/back
> of the PSU to be mounted as high as possible in the case. That's the
> direction all the hot air was going anyway, so it made cooling more
> efficient to have the PSU way up top.
>
> The PSU still assists somewhat in cooling the case...and more
> importantly the components in the case. The only advantage to having
> the PSU bottom mounted is that the PSU fan will be drawing more cool
> air into the PSU itself. In turn, this means you need a shitload of
> airflow to cool the case (and components like the northbridge, CPU and
> GPU in particular), because much of your cool intake air is now going
> down low where it's not cooling a damned thing. -Dave
>

There is an equation, to work out what a shitload is.

CFM = 3.16 x Watts / Delta_T_degrees_F [ Formula for case cooling ]

If the entire contents of the computer case dissipated 200W
(components and PSU waste heat), and you wanted to meet the
"well cooled" criterion of 7C difference between case and
ambient (7C = 10F), then the equation gives you

CFM = 3.16 * 200 / 10 = 63.2 CFM

That amount of air can be moved by a single fan.

If you allow a larger delta_T, it means the components in the case
will have a hotter environment to work in, your hard drive gets
warmer and so on. You don't have to shoot for 7C if you don't want to.

Paul
From: Ken Maltby on 20 Dec 2009 20:37

"kony" <spam(a)spam.com> wrote in message
news:r59ti510a75fq3fanoevmgqg8u9ukg9ijg(a)4ax.com...
> On Sun, 20 Dec 2009 08:42:35 +0800, "Dave C."
> <noway(a)nohow.never> wrote:
>
>>
>>> >I think it is wrong to put the power supply in the bottom of an ATX
>>> >case. It's just plain stupid to design a box that most customers
>>> >will have a problem with. -Dave
>>>
>>> Wrong... Why? Other then the cable length issue, what's your
>>> objection?
>>
>>You need a shitload of extra fans (adding extra noise) to
>>counter-balance the fact that much of your cool intake air is going in
>>the wrong direction to cool anything. -Dave
>
>
> Cases these days, at least anything decent besides this
> factor, tend to have more than enough fan mounts... unless
> someone is building a higher end gaming system.
>
> Regardless of where the PSU exhausts, as long as there is
> one low RPM 120mm fan at the top rear it is enough for the
> typical PC.
>
> That is, beyond where the PSU is, the same arrangement as
> any other case. Only other fan needed might be right
> across from the video card if someone has particularly hot
> running (esp. overclocked) card(s), unless the system is in
> a particularly hot environment in which case another fan
> would be prudent no matter where the PSU is located.
>
>

The one exception I might take to that is where an intake
fan might be needed to overcome the resistance of a filter
and still supply a good flow of air for cooling hard drives.
This will usually only be a factor in extreme/dusty
environments.

Luck;
Ken


From: DevilsPGD on 21 Dec 2009 12:20
In message <20091220084235.8bfcdaef.noway(a)nohow.never> "Dave C."
<noway(a)nohow.never> was claimed to have wrote:

>
>> >I think it is wrong to put the power supply in the bottom of an ATX
>> >case. It's just plain stupid to design a box that most customers
>> >will have a problem with. -Dave
>>
>> Wrong... Why? Other then the cable length issue, what's your
>> objection?
>
>You need a shitload of extra fans (adding extra noise) to
>counter-balance the fact that much of your cool intake air is going in
>the wrong direction to cool anything. -Dave

A "shitload"? One 120mm fan will push more air then a 80mm (or even
120mm) which needs to push air through the PSU.

In addition, you get lower average temperatures, so your fans (both on
the PSU if it's temperature regulated) and the one you install at the
top of your case can run at lower RPMs.
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