[Beowulf] cooling question: cfm per rack?

[John Bushnell]

A few comments below...

On Fri, 11 Feb 2005, David Mathog wrote:

> Mike,
> 
> I've been trying to pick the brains of other folks on the
> beowulf list who have computer rooms with modern equipment.
> 
> One problem with the existing air, with regards to future
> expansion, is apparently the total amount of air that the
> current A/C can move.  This is all horrendously complicated
> and needs to be looked at carefully by a HVAC consultant.
> Pretty sure we have enough tons and flow for now, meaning
> my rack and Deshaies and everything else I know is going in there
> in a couple of months.  More and more convinced that we don't
> have enough to handle multiple full racks of the next generation
> of computers.

  We learned about this after putting in a big new A/C (adding to an
old but still functioning one) in our server room.  The problem was
mitigated by having the vents on the old AC replaced with flanges
attached to large flexible vents.  They hang near the top/front of
two racks, and this has helped quite a bit.  Air flow is important!
 
> Jim Lux from JPL answered my questions as attached after
> my signature.

  Thanks go out to Jim for the useful numbers.

> Darryl did say something interesting though, he said that for
> some units the A/C people can increase the capacity by changing
> the pulleys around.  Apparently this blows more air, and the
> cold water isn't limiting, so it effectively upgrades the unit
> without changing very much.  Darryl said that this was done
> at some point for Mayo's computer room in the subbasement
> of the BI.

  Sounds like a pretty cheap upgrade.  It would certainly be nice
if we could do that here, as we've been running on the edge in terms
of cooling for some time now.

  Our industial chilled water loop runs at around 16C, so obviously
the chilled water is simply acting as a resevoir for dumping heat
from a compressor rather than being the direct source of cooling.
So the limiting factor is likely the compressor/fluid/heat exchanger
with the chilled water, rather than the chilled water itself.  I
wonder what "changing pulleys around" is really doing?

    Stay cool  -  John