back to the issue of cooling

Robert G. Brown rgb at phy.duke.edu
Wed Apr 23 09:51:41 EDT 2003


On Wed, 23 Apr 2003, Steven Timm wrote:

> The problem with the above calculation is that oftentimes the cost
> to get the electrical infrastructure into your facility in the
> first place is much, much greater than the cost of the electricity
> it delivers.  We are spending $560K here at Fermilab to add 250 kVA
> of electrical capacity to our floor.  We calculate that the
> cost of the electricity to run the machines over 3 years will only
> be $50K.

Indeed true.  However, the infrastructure cost is amortized over a
longer time, as well, and it varies strongly and nonlinearly from site
to site, depending on how much capacity you already have "handy" (or how
far they have to go to find a transformer with the capacity to deliver
it).  If you have 250 kVA worth of machines running in your machine
room, and spend 8 cents or so a kVA-hour, then power and cooling
combined for your room would cost about $250K a year (so that's a fairer
measure of the running capacity you are purchasing, even if you don't
use it right away).  Amortized over ten years the cost of the renovation
would be roughly $60-65K per year, including interest.  That's still
high -- you obviously had to install some BIG transformers to get the
capacity you need or something -- but not insanely high.

> We considered whether to actually put a weighting factor into our
> bids so that more electrically-efficient machines would be preferred,
> but then when we thought about it, we figured that (1) these
> machines are usually slower so you need more of them (2) they
> also use up more floor space which isn't free, and (3) within
> the same CPU speed class, those machines which use up the most
> electricity are also likely to be the ones with the biggest fans
> which are the best cooled internally.

Indeed and agreed.  If you like, what matters is getting the most work
done per dollar spent, regardless of how you get the work done.

   rgb

> 
> Steve Timm
> 
> 
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-- 
Robert G. Brown	                       http://www.phy.duke.edu/~rgb/
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567  Fax: 919-660-2525     email:rgb at phy.duke.edu



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