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# Need ball park power and cooling requirements

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Jim Meyer purp at acm.org
Tue Oct 1 11:59:18 PDT 2002

```On Mon, 2002-09-30 at 14:17, Timothy H. Keitt wrote:
> I'm setting up lab space and plan to build a small (8-16 node) cluster
> of dual Xeon nodes (Dell 2650 or equivalent). I need to give the
> engineers the power and cooling needed in the 6'x8' server room that
> will house the cluster. Any rules-of-thumb for what's required? Thanks.

A good friend of mine gave me three magic formulas when I was asked for
the same information for a new data center to hold ~1600 CPUs worth of a
render farm. That good friend is now a VERY good friend as it enabled us
to immediately spot that the contractors proposals were underpowered and
undercooled. =]

I must confess that I've used these without fully understanding what
they represent. I'll add my deductions beneath each formula and invite
some of the (many) people here who do fully understand them to comment.

Rough KVA at 3 phase = ((Amps * Volts) * 1.73) / 1000
The 1.73 is an approximation of the square root of 3. I don't
know why it's there, though, other than a blind guess that
it's related to 3-phase power.

Rough BTU/hr cooling = (((Amps * Volts) * 0.8) / 1000) * 3413
The 0.8 is something called "power factor" I think, and largely
relates to how efficiently the power is converted and used. I
believe the 3413 is just a conversion factor; it takes 3413 BTUs/hr
to cool a constant load of 1250VA at 0.8 power factor. I think. =]

Rough AC Tonnage     = BTUs per hour/12000

Hope that helps!

--j
--
Jim Meyer, Geek At Large                                    purp at acm.org
Jim Meyer, Geek At Large                              purp at wildbrain.com

```