high rise office building -- service overload?

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charlie tuna

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Florida
i have a customer who thinks his building's service is too small. somewhere he is figuring he needs 6 watts per square foot for average tenant reqirements. when he multiplies his available tenant square footage by six watts and considers what he has left after his chiller and building support equipment is running ---- he say's it's undersized. what am i missing here. also he is banking this on only loading his service to 80 per cent..... i know from expieriance his building is designed properly and has the capabilities but mathmatically i'm missing something --is it the three phase factor??? or the demand factor or the fact that he has considered only loading his service to 80 per cent?? thanks for any input............... tuna
 
I think he quite possibly figuring several things incorrectly. First, 6 watts per square foot is not shown anywhere in the general lighting load table (Table 220.12). This is probably the main concern with this calculation error. Until that one is ironed out, I would not be too concerned about the 80% thing. Ultimately, Section 220 must be used like a recipe to determine what the code requires. Now, if his tenants are actually consuming power to the tune of 6 watts per square foot, then he needs to do an investigation real soon. Thats a lot of power!!!
 
this is my oppinion:
the building has a 12000 amp 480 volt three phase service. four 3000 amp mains.
it takes two chillers and associated equipment to air condition the building. this is about 1600 amps.
i subtract this from the total service --- and that leaves him 10,400 amps.
i multiply this times 830(1.73 x 480 volts) and i come up with 8632000 watts.
i divide this (8632000) by his available tenant square footage of 750,000 and i come up with 11.50933333 watts per square foot.
he's fat!!!!! right????
 
Your numbers are correct. the only thing I see is that you are using amps to calculate MVA, KVA, VA, not watts. To get watts you have to introduce a power factor.

Granted for resistive type loads, (i.e. residential) for all intensive purposes watts will be approximately equal to VA.

Why does he think it's undersized? Is something tripping, buzzing, or burning?

Where did the 1600A for chillers and associated equipment come from?

Tell him to go have a beer and relax; or better yet have a Tuna sandwich!!
 
The customer thinks he needs 6, and you think he has 11. Did you show the customer your math and ask for his math? I'm with you; I don't see a problem.
 
Your customer forgot the 1.73 factor for 3 phase systems. If you use your numbers without the 1.73, you have 6.65 watts per square foot available.
Don
 
The POCO is probably running this building off a 500KVA transformer. OK, I'm exaggerating a little.

Steve
 
Does the building have a demand meter? I can't imagine it doesn't. Just have him call the utility and get the peak demand. That should help him sleep at night.
 
ramdiesel3500 said:
I thought you could run half of Los Angeles on a 12,000A 480V Service!!!
Click to expand...
You probably couldn't run half of LA's streetlights on that.

(I guess I could do a load calc . . . :) )
 
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