RE: [datacenter] peak capacity planning for power vs. cooling

```Depends if you have 100 bodies using those 100 units.

Make sure you don't forget people and the losses to the surrounding
environment. If you are talking about just supplemental cooling, the math
looks ok.

DJ

> -----Original Message-----
> From: Ofer Inbar [mailto:[email protected]]
> Sent: Wednesday, January 15, 2003 1:14 PM
> To: datacenter
> Subject: [datacenter] peak capacity planning for power vs. cooling
>
>
> Is this a reasonable statement to make:
>
> When planning power capacity for a machine room, you need to base it
> on the peak power consumption of the machines, usually when they are
> powering up / booting, because it is possible that they will all power
> up simulataneously.  However, when planning cooling, you can plan
> based on average load, with some headroom, because even if everything
> will be at peak heat output simultaneously, it will be a brief event,
> and cooling averages out naturally over time.
>
> -----
>
> For example, say I've got a lab that will host 100 units.  Based on
> measurements, I know that each unit peaks at just under 0.8 amps
> briefly when powering on.  When running under load with disks active,
> it draws about 0.45 amps.  When up and idle, 0.3 amps.
>
> For power, I must not exceed 20 units per 20 amp circuit (0.8 amps +
> 20%), and should only put 16 units per circuit.  For 100 units, I
> should have 120 amps or more of capacity feeding the lab.
>
> For cooling,
>  peak: 100 x 0.8a x 120v x 3.41 BTU/h per watt = ~2 3/4 tons
>  normal high load: 100 x 0.45a x 120v x 3.41 BTU/h per watt = ~1 1/2 tons
>
> Two tons of cooling for this lab should be theoretically sufficient.
> It is possible for heat output to exceed this amount substantially,
> but only for a very brief period.  That's not okay when it comes to
> power, but it is not a problem when talking about cooling.
>
> Does this reasoning make sense?
>
> --
>   --  Cos (Ofer Inbar)  --     [email protected]  781-273-2380
>   --  Permabit, Inc.    --  [email protected]  617-252-9600
>
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