[c-nsp] Data Center cooling

[jp]

On Thu, Jan 07, 2010 at 09:33:13AM -0700, Joel Snyder wrote:
> >   Has anyone looked at using outside air to provide data center
> > cooling during the winter season ?
> > I am aware of Google and Intel research into
> > this area but how about on a smaller scale ?
> > How about raising ambient
> > temperatures as well - do you keep your data centers at 65 or 80 ?
>
> We do this and we have had mixed success.  We have Liebert A/C units which 
> have something they call an "economizer."  Essentially, when the outside 
> temperature falls below a certain point as measured by a simple thermostat, 
> the A/C unit moves a damper and instead of sucking hot air from the room to 
> cool, it sucks cold air from the outside, filters it, and blows it in.  At 
> the same time, it turns off the compressor (because the air is, in theory, 
> already cold).

That's a good description of it. The compressor goes off so it will not 
ice up. If the coils are compressor-cooled AND taking in fresh damp air, 
it can ice up really good. We had the damper get stuck once and cause 
that. We have more than one A/C unit, so one damper failing and messing 
up the A/C isn't the end of the world. We have 2 A/C systems. The 
addition of the economizers meant two good sized insulated ducts going 
from the air handlers to vent grates on the end of the building about 
10' off the ground. There is also an exit louver in the hot section to 
allow efficient pumping of air without over-pressurization.

We use an economizer. 44N latitude in Maine. Saves us good cooling money 
from mid november till april by not running the compressors. We see it 
looking at the power bills year round. Your climate description doesn't 
sound like an ideal place to really see the benefits of it.

If you adjust the switchover temperature conservatively for the low 
side, you don't really have to worry about fiddling with it. It will of 
course vary for different locations, loads, building insulation, etc.. 
We have ours to switch at 48f, but could switch at a higher temp if we 
had a lesser load. We keep the space at 72f. We use 1-wire sensors to 
monitor temperature.

> In the sales presentations and talking to A/C gurus, it all sounded very 
> smart and economical, but we've found that the actual management of the 
> damper and the temperature that it shifts are very delicate settings. 
> Depending on the time of the day (i.e., is there sunlight on that side of 
> the building or not?) and the season of the year (i.e., is this just a 
> little cold snap or an extended period?), as well as the outside humidity 
> level (is it very different from the humidity in the room or not?), the 
> temperature has to be adjusted a bit in each direction.  Our units don't 
> have a computer control for that, so that means someone goes out every few 
> weeks with a screwdriver and manually fiddles the economizer thermostat 
> settings.
>
> We can compensate a bit on the computer control side by changing the the 
> system thermostat around a few degrees, but there is no direct linkage 
> between the economizer part of the system--it's completely independent, 
> essentially an add-on--and the rest of the cooling system.
>
> I honestly can't tell whether we are saving any money on this or not, but 
> for our latitude and climate, I would not recommend it to anyone else.  We 
> have had to replace the thermostats and damper controllers, and that eats 
> up $300 to $500 for every service call.  Plus, while we were learning about 
> it, we had some midnight room-got-too-hot moments, which also cost us.
>
> I think that if you lived someplace where it was in the 5C/40F range or 
> below day-round for weeks at a time, this would probably work (assuming 
> that you have physical ability to install this kind of unit).  In our 
> climate, where it is 5C/40F for 8 hours at night and 20C/70F the rest of 
> the day, for our 3 month winter, it was probably not the right decision.
>
> jms
>
> -- 
> Joel M Snyder, 1404 East Lind Road, Tucson, AZ, 85719
> Senior Partner, Opus One       Phone: +1 520 324 0494
> jms at Opus1.COM                http://www.opus1.com/jms
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