[Beowulf] newbie's dilemma

Josip Loncaric josip at lanl.gov
Wed Mar 1 16:10:00 PST 2006

Robert G. Brown wrote:
> On Tue, 28 Feb 2006, Don R. Baker wrote:
>> for 8 years, but consider myself to still be a beginner.  I have a room
>> with 4, 15 amp circuits and a 20 000 btu air conditioning unit installed
>> that I can use for the next 2 years, but after that I may need to find
>> another home for the system.
> Let's see.  20KBTU is a bit more than 1.5 tons of AC, call it the
> ability to remove 5800 Watts total.  4 x 15 x 120 is is 7200 Watts peak,
> or about 5000 Watts RMS.  In my opinion this is going to leave you a bit
> light on AC if you run the circuits fully loaded, and don't forget warm
> bodies (60 W) and built in light bulbs etc. on other circuits (maybe
> several hundred W more).  You have to not only remove the heat as fast
> as it comes in but get ahead some, correct for heat that infiltrates
> through the walls, and get the room temperature down below 20C (68 F) if
> at all possible.  15-16C is more like it -- cold enough to just be
> uncomfortable.

Sensible conclusion, but: A 15 amp circuit should deliver up to 15 amps 
RMS (otherwise, a 15A heater would immediately trip a 15A breaker). 
Peak currents during the cycle can be higher.  This fine point is 
academic, though, since in this example the air conditioning capacity 
limits maximum power dissipation.

BTW, when it comes to heat dissipation, humans count about as much as a 
bright light bulb (100W+ depending on activity level -- 100W corresponds 
to 2064 kcal/day).

> I personally would reject #3 out of hand, unless you buy three year
> onsite service contracts on the Dells (spending nodes as required).
> Dell doesn't do Opterons, I don't think, as well.  HPs ditto.

Dell is Intel only, but HP sells AMD CPUs, including dual core Opterons 
(e.g. HP xw9300 workstation -- but compare costs carefully).


More information about the Beowulf mailing list