Q: Building a small machine room? Materials/costs/etc.

Michael Stein mas at ucla.edu
Wed Sep 17 14:53:42 EDT 2003

>   a) Thermal kill switch.  You may well want the room to be equipped
> with one.  This is a thermostatted switch that kills all room power if
> the ambient temperature exceeds some threshold, e.g. 90F.  The idea is
> that if AC fails and you don't get down there to shut down nodes fast
> enough, the kill switch kills power all at once rather than permit the
> nodes to overheat to where they physically break (as they will if they
> get hot enough).
> Remember, at 10 KW/rack, four racks is 40 KW all being released in your
> itty bitty 15x25' room.  The room will go from ambient cool to meltdown
> in a matter of minutes if AC fails, and (Murphy's law being what it is)
> it WILL FAIL sooner or later.

At that size/power a lot less than minutes.

1 1U machine might output about 30 CFM of 99 F air.  4 racks full of
them (42 * 4) would be about 5000 CFM of 99 F air.

You have 15 x 25 x 8? so about 3000 cubic feet of 75 F air to start.
At 5000 CFM through the machines the whole room will be 99 F in about
36 seconds.   After that it gets interesting (the machines are now taking
in 99 F air)...

And this assumes uniform/perfect air flow (no hot/cold spots).   
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