Generator sizing

[hhsting]

I have switchboard replacement in outpatient hospital like setting that has essential branch. In the time existing switchboard disconnected and new switchboard install they are powering the hospital thru temporary generator.

However they need to determine existing loads so they can size the temporary generator accurately. Can they use NEC 2017 Article 220.87 for sizing the temporary generator in my setting

 

[ron]

Seems like a reasonable approach

 

[hhsting]

Seems like a reasonable approach

Would it be ok to use 30 days metering approach?

 

[don_resqcapt19]

Many commercial occupancies will have a demand meter. Check to see if that supplying utility has that information.

 

[hhsting]

Many commercial occupancies will have a demand meter. Check to see if that supplying utility has that information.

If they dont then 30 day metering would be acceptable ?


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[electrofelon]

If they dont then 30 day metering would be acceptable ?


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Have you read the exception to 220.87?

 

[hhsting]

Have you read the exception to 220.87?

Yes I meant that they say they have utility bills data that shows only kW not kVA for one year. So still in that condition one year period of utility data of kw be used?

 

[don_resqcapt19]

Yes I meant that they say they have utility bills data that shows only kW not kVA for one year. So still in that condition one year period of utility data of kw be used?

You need the 15 minute demand data....if may not be on the bill, and you may have to ask for it.
You can also use the 15 minute kWH values...take the largest for the past year, and multiply by 4 to get a 15 minute demand number. Again that will not be on the bill, however you may be able to log in and download that data.

 

[hhsting]

You need the 15 minute demand data....if may not be on the bill, and you may have to ask for it.
You can also use the 15 minute kWH values...take the largest for the past year, and multiply by 4 to get a 15 minute demand number. Again that will not be on the bill, however you may be able to log in and download that data.

I dont follow utility bill has monthly kwh for 12 months. Can I select the largest one and use that?


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[herding_cats]

I'm certain you can get kWh and kW data from the POCO. Smart meter billing can be looking at 256 samples per second in some cases. They catch everything. The bill will show maximum kW demand. They get hit with that. kWh really does not matter. Energy kWh and Demand kW are totally different.

 

[zbang]

I'll be the third person to say "You have to ask for it." (I suppose you could put a data logger on the line for 30+ days, but calling the PoCo is probably a lot easier.)

 

[don_resqcapt19]

I dont follow utility bill has monthly kwh for 12 months. Can I select the largest one and use that?


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No...there is no way to get a peak demand from that and you need the peak demand to size a generator.

 

[don_resqcapt19]

The bill will show maximum kW demand.

While that is the case for some utilities, that is not information that my utility provides on the bill. They likely would have it on request, but it is not on a commercial occupancy bill in my area.

 

[herding_cats]

In my area the max kW is on every bill. Under "actual demand", as well as kVAR, kVA etc. If it's not on the bill, I can assure they have the data. How could they bill demand charges if they didn't ?

 

[Birken Vogt]

For PG&E it is printed on most larger bills, and it seems they will provide it when asked for any commercial occupancy, in 15 minute increments, going back a year or 3.

 

[don_resqcapt19]

In my area the max kW is on every bill. Under "actual demand", as well as kVAR, kVA etc. If it's not on the bill, I can assure they have the data. How could they bill demand charges if they didn't ?

I thought so too, but I recently did a FOIA request for one of our local schools because I thought they wasted money on replacing an existing single phase 600 amp 120/240 volt service with a new 1200 amp 3 phase 208Y/120 volt service.
The transformer that fed the original service was a100kVA and the new service is supplied by three 25 kVA transformers connected in a wye secondary. There is no reason that they needed the new service, but I wanted utility documents to talk with the school board.