Transformer sizing AC question.

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cubdh

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This question may sound stupid but i have looked and looked in the NEC book and I cannot find the Air conditioning rules in 220.

There is the lighting demand factor for office/banks in 220.40
There is the receptacles demand rules for office/banks in 220.44
There is the kitchen equipment for "Other than dwelling" banks/offfice in 220.56

BUT I cannot find anything about Air Conditioning for Office or banks.
Am i blind?? Looking in the wrong place????
Maybe you can help me.

Question:
This question is with respect to transformer sizing
Is there a VA/sq ft. factor for AC in office/ banks?
If we know the total connected AC nameplate loads for office spaces in a building do we just add all of them up and use it at 100%
I have a building with 8 small office spaces. Each has a 9 kva AC nameplate.
do i just multiply 9 kVA x 8 and use 72 kVA for transformer sizing purposes

Help on this matter is greatly appreciated.
 
I am using NEC 2008

Table 220.3 refers me to Article 440 part 4
I have looked at 440 part 4 in the past but it seem to only talk the conductor rating and loading. It does not talk about how much loading capacity we should put aside for office or banks.

I found the AC rules for dwellings and it is basically 100% AC or heating, which ever is larger. I am not sure about multi dwellings.

But in any case i am wondering about the office space. Do we just add up all the AC nameplate loadings?? This does not seem right because what if the AC capacity is way overkill. Let us say it can cool 3 x the area adequately. I am just guessing in this case we would not use 100% of all the AC nameplate kVA.

I cannot find AC provisions for Office space which would help in transformer sizing for a particular building
 
cubdh said:
But in any case i am wondering about the office space. Do we just add up all the AC nameplate loadings?? This does not seem right because what if the AC capacity is way overkill. Let us say it can cool 3 x the area adequately. I am just guessing in this case we would not use 100% of all the AC nameplate kVA.
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IMO, if it is possible for all of the units to run at the same time, then you would use 100%.

You might have "overkill", but all the units can run at the same time, and that needs to be taken into account. They just won't run as long.
 
Yes you are right John. And that point cannot be disputed.
The only thing that bothers me is that right now I am about to size a transformer to 225 kVA for an office that can easily easily be fed by a 112.5 kVA. And the sole reason for this 225 kVA is because of their massive AC loads.

And this is not the first time i have seen something like this. I guess the utility just has to absorb the losses. But i think there should be a remedy for this problem.
We should meter from the primary side i would think, but we dont.

Anyway thanks everyone.
100 % it will be
 
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