[Beowulf] 'liquid cooled' racks

Mark Hahn hahn at physics.mcmaster.ca
Mon Dec 4 09:57:26 PST 2006

> For my next cluster room, I am hoping to use 'liquid cooled' racks make by 
> Knurr (CoolTherm, http://www.thermalmanagement.de/).  The scale is 67 racks x 
> 7.5kW heat removal per rack (36 U usable per rack).

7.5 KW/rack isn't much; are you designing low-power nodes?

> The racks have front and back doors that close, and contains fans in the back 
> which circulate air through a heat exchanger located in the bottom of the 
> rack.  The heat exchanger transfers the heat into chilled water.

APC has something similar with the cooling on the side.

> The advantages of this are that it is quiet, and that you don't need vertical 
> height for underfloor ducting or overhead hot air removal. Disadvantages are 
> cost, potential difficulty of working within the rack. and loss of one rack 
> of cooling capacity if you open both the front and back doors.

I'm pretty skeptical of the sealed-pod approach, since it seems to 
multiply the number of parts, create access issues, doesn't seem to 
actually save on space, etc.  I've also been burned by cold water cooling,
so to speak (assuming you don't have your own, well-controlled CW plant.)
I would definitely consider a normal big-chillers approach _with_
back-of-rack CW boosters (heat exchangers).  and I'd definitely consider
creative layouts of racks and chillers (for instance, I'm not crazy
about the hot/cold-aisle approach - something W-shaped would be better
for my ~50-rack machineroom.  or even just lining all the hot racks up
against the chillers along one wall.)

> (In this case I have access to 'building' funds that can not be used to buy 
> more cpus, so the cost issue is not important.)

are you sure you can't just be clever about laying out normal 
front-to-back racks?  possibly with back-of-rack heat-exchangers?

regards, mark hahn.

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