I have a customer installing a new computer / server room. They will have (280) pieces of equipment @ 1.5 Amps /120 volt and (10) pieces 2A / 208 volt - All single phase loads.... Plus they would like to have a 60A /3 Phase Rooftop unit to run of the generator also.
280 x 1.5A x 120V = 50,400 Watts 10 x 2A x 208V = 4,160 Watts 1 x 60A x 208V x 80PF x 1.732 / 1000 = 17,300 Watts
Not exactly, you are assumming a PF 0f 1 on your single phase loads. Which is an error on the good side. You used VA on your single-phase loads. If you assume a .9 or .8 PF you will get something less. Long story short, you need a 100-KW generator based on the numbers you gave with not much room for growth.
Is there a UPS between the generator and data room. If not your client is really waisting a lot of money for nothing gained. If there is a UPS you size the generator at 150% of the UPS input power requirement with walk in capability, plus 125% of the HVAC load.
Edited to ask UPS?
[This message has been edited by dereckbc (edited 07-01-2004).]
Higher end UPS designed to work with generators like Powerware and MGE will have control circuitry to "Walk In" the rectifiers, rather than all at once to prevent the generator from tripping. Also look for UPS systems with power factor correcting circuitry. Get with one of the UPS manufacture reps and let them get invloved in equipment specification.
Consider getting quotes from at least a couple of genset vendors based on your list of loads. Motor starting, switchmode power supplies, [UPSs] and generator automatic voltage regulators can be a problematic combination.
Producers like Kohler and Cat have sizing software with a ‘built-in’ checklist on stuff to consider for genset loads—often free for asking.
Otherwise, it can be a no-win dogfight—first between connected equipment, and soon to follow—between you and your client.
[This message has been edited by Bjarney (edited 07-01-2004).]
All comments above are good. But experience has tought me to make sure the UPS controls and the generator's regulator are compatable. Make sure you get this in writing from both the generator and UPS suppliers. If they are not compatable in the load enviroment you will have the dog fightmentioned above. Load sizing alone is not going far enough.
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