NEC code section for Demand Factor for IT room loads and HVAC equipment
- Thread starter Aks401
- Start date
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- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Load calcs are all in Article 220, have you looked there?
I have looked at article 220. I could not find anything specific to IT room loads.
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Then that is your answer. I haven’t done a load calc for some time, I don’t believe there are demand factors for any type of HVAC. There is an allowance for non coincident loads, ie heat and cooling.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
I think in part VI there is some kind of allowance for a demand factor for electric heating if there are more than four electric heaters.
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Please reply back if you find demand factors.
IT loads suck. There are no demand factors. Computer nameplates have inflated numbers so the computer can handle the worst case install (maximum RAM, maximum disk drives, all bus slots occupied, etc). Power supplies are often spec'd oversize so they last longer (e.g. 1300W power supplies installed when 800W would have been enough). Redundant power supplies make it double suck, as now you have two oversized circuits to feed it in case one power supply dies. I've never seen a computer draw its nameplate amps. If they have no nameplate then you're stuck using the power supply wattage. You could possibly instrument them to get a better feel for true load, but usually that is difficult unless they are all configured the same and you have the means to test them under load.
I would also not treat them as continuous loads if using their nameplate amps or power supply rating. They do run continuously, but their current draw varies with computing load and processing, so it does not meet the definition of continuous load.
There is probably no relief for cooling either. If the HVAC designer is sizing the HVAC off of computer nameplates for sizing, the cooling system will be oversized. Often times, the HVAC is sized per the room feeder size to allow for IT growth up to the limit of power available. But all this makes for oversized HVAC and the larger circuits they will require.
I would also not treat them as continuous loads if using their nameplate amps or power supply rating. They do run continuously, but their current draw varies with computing load and processing, so it does not meet the definition of continuous load.
There is probably no relief for cooling either. If the HVAC designer is sizing the HVAC off of computer nameplates for sizing, the cooling system will be oversized. Often times, the HVAC is sized per the room feeder size to allow for IT growth up to the limit of power available. But all this makes for oversized HVAC and the larger circuits they will require.
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
The only thing that "saves" you on multiple supplies is that the chassis is going to draw the same amount regardless of the number of supplies. And while it doesn't affect the draw, some chassis may need two supplies to run but have one or two more installed (for n+1 or n+2 redundancy).
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