Measuring power

[Nick Cleaton]

On Wed, 2009-04-29 at 12:23 +0100, Jasper wrote:
> 2009/4/29 Nick Cleaton <nick at cleaton.net>:
> 
> >
> > One possibility might be to measure the heat output of the servers,
> > rather than the electricity input.  If you assume that the servers lose
> > heat mainly by pumping hot air out with fans, you'd need to measure both
> > the air flow rate and the difference between output air temperature and
> > input air temperature.
> 
> Fascinating, but there would be no way of calibrating this, unless you
> built an identical server room that you could play with.

Not really.  If you know how much air is being heated up by how many
degrees each second, you can look up the specific heat capacity of air
and convert that number to the power in Watts required to perform that
heating.

A computer is just a complicated heater, after all.

Some energy will escape as RF radiation instead of heat, but server
cases are designed to block that stuff, so probably not much.  I think
the main error would be due to heat radiated from the server case or
conducted to the rack or the adjacent servers.  I'd guess (based on
nothing in particular) that most of the heat would come out via the fans
though.