Peak Demand help me understand please =)

[Johnny B.]

Hello everyone,

I am doing a remodel for one tenant space, then the city requires that I do a load calculation for the whole service including all the other tenant meters. I use NEC 220.87 Determining Existing loads. I have about 5 meters on the the main service. I call the power company and ask them for the peak demand of each meter. They tell me, "None of the meters are demand meters so I can only give you the highest KWH" I am reading a few sources probably not reliable ones that are saying that the peak demand is the average of the highest kilowatt hour demand in a fifteen minute period. So can I take per say the highest kilowatt hours in the day, and convert to KW and call that peak demand? I am not sure since other sources are telling me peak demand is more instantaneous. Do I just need to go with the exception of NEC 220.87 and have someone go out there with a ammeter and have it recorded for 30 days?

 

[don_resqcapt19]

Hello everyone,

I am doing a remodel for one tenant space, then the city requires that I do a load calculation for the whole service including all the other tenant meters. I use NEC 220.87 Determining Existing loads. I have about 5 meters on the the main service. I call the power company and ask them for the peak demand of each meter. They tell me, "None of the meters are demand meters so I can only give you the highest KWH" I am reading a few sources probably not reliable ones that are saying that the peak demand is the average of the highest kilowatt hour demand in a fifteen minute period. So can I take per say the highest kilowatt hours in the day, and convert to KW and call that peak demand? I am not sure since other sources are telling me peak demand is more instantaneous. Do I just need to go with the exception of NEC 220.87 and have someone go out there with a ammeter and have it recorded for 30 days?

You cannot mathematically create a demand reading where the meter does not have a demand register.

 

[mayanees]

Hello everyone,

I am doing a remodel for one tenant space, then the city requires that I do a load calculation for the whole service including all the other tenant meters. I use NEC 220.87 Determining Existing loads. I have about 5 meters on the the main service. I call the power company and ask them for the peak demand of each meter. They tell me, "None of the meters are demand meters so I can only give you the highest KWH" I am reading a few sources probably not reliable ones that are saying that the peak demand is the average of the highest kilowatt hour demand in a fifteen minute period. So can I take per say the highest kilowatt hours in the day, and convert to KW and call that peak demand? I am not sure since other sources are telling me peak demand is more instantaneous. Do I just need to go with the exception of NEC 220.87 and have someone go out there with a ammeter and have it recorded for 30 days?

It looks like your best course of action is to record the demand over a 30-day period to find the 15 minute peak interval as described in 220.87. You may have to wait for the peak of A/C season, or the peak of heating season, whichever is higher.

 

[Jraef]

"Peak Demand" is a specific term related to having a Demand Meter. You don't need that value, you just need to determine the load on the entire service, either by doing a load calc for each individual unit and combining them, or as suggested, rent a recording meter and put it on the whole service entrance.

 

[Carultch]

So can I take per say the highest kilowatt hours in the day, and convert to KW and call that peak demand? I am not sure since other sources are telling me peak demand is more instantaneous. Do I just need to go with the exception of NEC 220.87 and have someone go out there with a ammeter and have it recorded for 30 days?

If you did that, you would be naively assuming that demand is constant throughout the day, and it would defeat the purpose of measuring demand.

 

[Jraef]

So can I take per say the highest kilowatt hours in the day, and convert to KW and call that peak demand?

No, and here is why.
Let's say your highest day (24hr period) showed 50kWh. That could be 2kW for 23 hours steady and 4kW for 1 hour, or it could be 50kW for one hour, and nothing the other 23 hours; both would add up to 50kWh. In the first case however, your peak demand is 4kW and in the second one, it is 50kW. Vastly different values of peak demand.

 

[Srv52761]

Call the poco again.
When we needed demand data for programming our heating schedule in our schools the poco installed interval meters for a couple of months.