[mythtv-users] Cooling data centres (Was: raid array spin down possible?)

[Simon Hobson]

Ronald Frazier wrote:
>On Tue, Sep 27, 2011 at 7:38 AM, Simon Hobson <linux at thehobsons.co.uk> wrote:
>>  Where huge savings can be made is by not "cooling" the datacentre at
>>  all - but instead just use outside air at whatever temperature it
>>  comes in at. In relative terms, blowing outside air in (through
>>  filters) is very cheap compared with active cooling.
>
>Data centers aren't air conditioned...they are climate controlled. The
>problem with piping in outside air is that you have no control over
>its humidity. If the humidity is too high, you can get condensation
>inside your systems.

You won't ever get condensation, or at least it's fairly unlikely. To 
do that means getting 100% RH and that means you will have to draw in 
saturated air and not heat it, or draw in less than saturated air and 
cool it. Bear in mind that you're doing this to remove heat from a 
bank of fan heaters ! Also, you are going to be directing the 
incoming air through a fan and ducting, and ideally a filter, which 
will cause water droplets to get removed and reduce saturated air to 
just below saturation.

The only way you could get condensation would be to draw in cold air, 
and then have that air change suddenly to warm and humid - the change 
being faster than the equipment warms up. I suppose if your climate 
is prone to such changes then it's a possibility to be aware of, but 
in the years I've been at my current place we've had no problem - 
even when the building has been completely enveloped by fog.
You can, of course, avoid the problem by tempering the intake air a 
little using waste heat from the exhaust - that could be our secret, 
unless the sensors are lying, I think our unlagged ductwork adds a 
degree or two to the intake air.

>Too low and you have static problems.

Adding humidity is trivial - "just" a matter of a bit of water spray 
in the intake. If the air is that dry, the spray will evaporate 
rapidly. This is very common in office ventilation systems.

Richard Morton wrote:

>Agreed re humidity but was it ms or google who have done this 
>recently, piping in air from outside to save a bundle.

Not just Google - I've seen quite a few announcements, including on 
in somewhere hot (Arizona comes to mind but I'm not sure of that). In 
at least one case, I think they basically talked of making the sides 
of the building into shutters - when the outside air is cool enough 
they turn off the chillers and open the shutters, when the air is too 
warm then they turn the chillers back on and close the shutters.


All in all, given the rising cost of electricity, and the PR issues 
around big datacentres, there's no really insurmountable problem for 
a lot of people in temperate climates.

-- 
Simon Hobson

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