IP: Re: computer and telecom centers get undeserved black eye for power usage

[David Farber <dave () farber net>]

> Date: Mon, 09 Apr 2001 07:24:04 -0700
> To: farber () cis upenn edu, ip-sub-1 () majordomo pobox com
> From: "Joseph C. Pistritto" <jcp () jcphome com>
> Subject: Re: IP: computer and telecom centers get undeserved black eye
>   for power usage
>
> I just got done ordering our data center setup at Zaplet Inc. where I used 
> to work.  The datacenter is at Equinix.
>
> We provisioned it at 2 20amp 120V circuits per rack (42U units of 
> equipment).  That's not enough for 42U of "1U" servers, but then you have 
> a huge cooling problem as well if you dump that much power into that small 
> a space.  The reason we used 2 20amp circuits was for redundency, but i 
> can see someone actually *using* that much power if they really fill up 
> the rack space (in which case you'd need to provision additional circuits 
> but not additional current draw for redundency).
>
> So assuming 20amps @ 120v = approx 2.5KW per "rack" and lets say it takes 
> *another* 2.5KW to air condition that space (which is overkill, air 
> conditioning is more efficient than resistive heating, which is 
> essentially what computers are...), that means approximately a 4 sq. foot 
> area would have 5KW of draw.  (not including corridors and such).  Or 
> 2.5KW per square foot (high estimate).
>
> So that works out to:
>   1.25KW per sq. foot (high estimate for densely packed areas)
>
> We know this is high because people usually quote "available power" in the 
> 200-300 watts/sq. foot range (inclusive of hallways etc.).  275watts/sq. 
> ft. is a common metric used here for power availability for 
> instance.  (your lesser dataccenters dont even have that much 
> available).  (thats direct power draw, not including airconditioning, so 
> doubling that would be approximately 0.5 KW/sq. ft.  So we can tell my 
> estimate above from our racks is high, but irrationally so for actual 
> worst case).
>
> It seems reasonable that a datacenter (aka "server farm") would ask for 10 
> megawatts of power though. (so 46 of them could well have asked for 500 
> Megawatts).  I know that *ONE* 2 million sq. ft planned facility in San 
> Jose is speced at 190Megawatts (the city council is forcing them to put in 
> a cogen plant with that capacity before building it though...)
>
> I think the 60-100KW/sq. ft. is an arithmetic error though.
>
>     -jcp-



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