On 15/12/15 23:16, Andrew Gabriel wrote:

You use the Watts figure for aircon, and the VA figure for sizing
the power circuits.

Power factor of about 0.9 is a pretty good worst case estimate. I had to
take a power and mass inventory of a small but extremely dense computer
room a few years back (for floor loading and aircon). The main power
distribution panel had a power/VA/PF meter built in. This was mostly HP
and Viglen gear IIRC, total power in the few 10's of kW.

Buy a watt meter or two for dual supply systems (around £10).
Check the power consumption of each system.
Allow for growth (both extra disks and cards in systems, and extra
systems and storage arrays - consider how much spare rack space
you have and space for more racks).
Add power consumption of lighting and any other electrical equipment,
unless it will normally be off and controlled by occupancy sensors.
If the room contains electrical switchgear and distribution boards,
allow for heat given off by those.
If you expect people to work in there for extended periods, add 100W
per person for non-physical activity, or 200W for people doing things
like assembling/racking servers.
If the room has windows, calculate the solar gain (this can be very
considerable).
Calculate heat leakage into the room from non-airconed adjacent areas
(including any room below and the outdoors) at a 10C temperature
differential.
Computer rooms are usually made airtight for effectiveness of automatic
fire extinguising systems, but if yours isn't and it's large, you might
want to allow for 2 air changes/hour (again at 10C temperature
differential), or more if people will be frequently opening the door.