[mythtv-users] Quiet fans

[Darrin]

On Tue, Oct 21, 2008 at 9:40 AM, Mike Perkins
<mikep at randomtraveller.org.uk>wrote:

> [...]
>
> If you are planning on using external sensors, rather than the ones on the
> motherboard, where do you expect to site them? I would naturally expect
> them to
> be somewhere near the items being monitored. If so, then there will be a
> certain
> level of decoupling from the fans which you are controlling, given that
> most
> fans are in the front, back or occasionally sides of the case, and not next
> to
> the items being cooled. How do you plan to handle the feedback delay? And
> how do
> you determine that the big fan you screwed into the back of the box is,
> actually, contributing to the cooling of the particular component you are
> monitoring? Airflow is not an exact science, after all[1].
>
> These questions are not intended as criticisms, rather just to satisfy my
> curiosity.
>
> --
>
> Mike Perkins
>

You are correct - it's not an exact science and what makes matters even
worse is the fact that most computer cases control air flow like a sieve.

I had planned to monitor only the exhaust air temperature.  Cooling the rest
is a matter of controlling how air enters the case from the outside... which
means I have to figure out some way to plug a lot of holes.

As for individual components, the best we can do is to figure out an
acceptable difference between the temperature of the component and the
temperature of the ambient air that is cooling that component.  I think the
exhaust air would be a good indicator of just how much heat we are creating
since we know that the result is room temperature + component heat
contribution.

Yes this does ignore the temperature of the air entering the case, but we
would still compensate for variances in room temperature if we are trying to
regulate the exhaust air to some fixed value.  Room temperature air plus
some added heat from the components would yield a higher exhaust temperature
if the room is warmer.  Therefore, the speed of the fan would have to
increase to compensate.

Of course, we can always add passive heat sinks where necessary to further
improve heat transfer to the air, if required.

--Darrin
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