commercial building demand load

[jisennock]

I am looking at a commercial building generator install project. A question has come up concerning the demand load of the existing MDP and related distribution panels. Can anyone point me in the right direction as to how to calculate a demand load for a commercial building?

Thanks !!

 

[bennie]

Re: commercial building demand load

Should this be an existing building, the serving utility can supply the peak demand on the building, from past readings.

The connected load, on commercial buildings, in most cases, is close to the calculated load. Often the continuous load offsets any reduction due to diversity factor.

There is recording ampmeters available on the market.

 

[jisennock]

Re: commercial building demand load

Unfortunately, the building is on a military base and is not seperately metered, thus no utility information is available. The building occupant is looking at the total ampacity of the breakers in the distribution panels (1900 Amps in a 1200 Amp Panelboard and 800 Amps in a 400 Amp panelboard) and is concerned. Because many of these breakers feed other panels throughout the building I would like to show the user some calculations "proving" that the installation is O.K. but I don't know what to show him.

 

[bennie]

Re: commercial building demand load

The total of breaker ratings is irrelevant. My home will have an 800 amp service if I added the numbers on the branch breakers.

The best and most accurate method is to connect a recording wattmeter on the service conductors. This should remain for a period of time to observe a pattern.

Charlie the utility guy may have more information.

The other Charlie too.

 

[arneykaner]

Re: commercial building demand load

Take at least three readings on the service feeder load during the times of the day that represent highest demand - 8:30; 10:30; 2:30.
Make sure, all load that could work simultaneously
is on. Calculate avarage of your readings.
Multiply the calculated avarage by 1.25. This is the size of your load. Note: some municipalities require the load readings to be done by a licensed
electrician.

 

[charlie b]

Re: commercial building demand load

You could perform a service load calculation as if you were designing a new building from the ground up (sorry about the pun, Bennie). But you would have to know the all of the building?s existing loads. Begin in Section 220, and start adding up the loads. Start with VA/ft2 from Table 220.3A for the type of facility. This gives you lighting loads. You can either add 1 VA/FT2 for general purpose receptacles, or walk through the building and count them all (allowing 180 VA for each one you find). Add in any other items that are named in Section 220.3(B). When you get to the ?motors? section, and follow the path to the 430.X sections named therein, you will find that you will have to add 25% to the largest motor in the building. Section 220.10 takes you through sizing the service. In your case (i.e., not a dwelling unit), you will probably not get to use any demand factors to lower your total load.

The Other Charlie