Heat Generation

Can't say I have ever seen any "rules of thumb," but can pass along some acquired observations:

Electrical: the more outlets you have the better of you will be in the long run. If possible, put each pair of outlets on its own dedicated circuit. Would also suggest using heavier-duty circuits (20 amp minimum vs. standard 10 or 15 amp in the US) (many larger UPS products require 20 amps to work at full capacity). To get a ballpark figure for total power draw for your equipment, check the power sticker (should be near the power cord) on the back of each piece of equipment for the maximum power draw for that equipment. I say ballpark, because the figure listed is usually peak draw, not average draw.

Air conditioning: Obviously, electronics can generate a lot of heat. Your best bet would be to put your network room in its own zone, with its own thermostat. That way, you can set the air conditioner to meet your specific needs in the network room without freezing co-workers in surrounding offices. As an alternative, if you are stuck sharing a zone, you might want to consider one of the portable air conditioning units, designed for just this type of situation, offered by APC (www.apc.com) and other vendors. Depending on your locale, you might also want to take into consideration that in many commercial buildings, the HVAC is centrally managed and is switched from air conditioning to heat during the winter months.

Since the majority of the power used by a PC is turned into heat, just use the conversion factor
BTU/Hr = Watts * 3.4144

to calculate your cooling needs.

Don't forget to take the lights into account.

As to power, 300 watts = 2.5 amps at 120V AC

Depending on powered periphials and add-ons, you could easily have enough draw to limit you to 3 PCs per 20 Amp circuit.

Chas

Some empiric rules of thumb:

For every KVA of power supplied to computer room equipment (measured adding the current rating in the equipment plates and multiplying it by 120 volts) you should need to provide air conditioning equivalent to 2500 BTU.
This has its reasons:
*When calculating power requirements usually the user counts maximum rating, and, if in the computer room coexist many devices, the mean value will be close to the 75% of the maximum rating, or less.
*The BTUs needs to be calculated based on watts not volt-amps, so, again, is necessary use a reducing factor, usually 75% (this depends of the input power factor of the different devices, which oscillate between 0.4 to 0.8 for normal computer load).

If you have UPSs inside the computer room, make the calculations with the UPS ratings only, forgetting about the loads powered by the UPSs. For example, if the UPS is a 2KVA unit, the maximum input current should be around 20 or 25 amps, and this is the value you should use for calculating the heat production. Be aware that some UPS units work with 208 volts in the input side; if this is the case you will need to use this value instead of 120 to calculate the power requirement.

The values of BTU obtained are not exactly, so you should select air conditioning at least for this values. As answer 1 states, you should have a dedicated thermostat; but this is easy if you install spited units locally.

About electrical power, it is not easy resume this issue, but one important consideration is to have as many circuits as possible because you don?t want to have many devices down if a breaker trips.

Regards,

Jose P Mir
jpm@jpmir.net