How do I calculate Expected Peak Demand - Residential

[CCWest1]

Guys,
I've submitted a request for new a new residential service (actually 2 for the same property) to my POCO who is NYSEG upstate NY. I sent them load calculations, etc. and so far the only thing they kicked back was, wanting to know my expected Peak Demand in kW and kVA. From what I found, To calculate expected peak demand, you need to identify the highest average power consumption (measured in kW) over a specific time interval, typically 15 or 30 minutes during a billing period. From what I understand an example would be, when a family arrives home say after 5pm and into the evening, appliances, lighting, etc. are used which would be at a higher consumption rate than in other parts of the day.

I am building a small modular with an attached garage and placing a mobile home that will be permanently connected to electric sewer and water. This is what the 2 services is about. So far they haven't said no on the 2 services, just asking for the Expected Peak Demand. I don't know how to go about figuring this out. I am attaching my load calculations for both the modular and the mobile. Thanks!

 

[ron]

The NEC doesn't give you any method to calculate it other than the Article 220 options, which the bottom number will be you demand. It is conservably high, but that is the only way unless you have a similar occupancy that you could measure per 220.87

 

[xformer]

IMHO... The EVSE load should be calculated on the stationary structure and not on the mobile home.

 

[electrofelon]

Just fyi you will probably have ONE service with 2 meters and 2 sets of service entrance conductors. I don't know why they ask for the peak demand, it's dumb they are going to come up with their own calcs to size their equipment anyway (I am in NYSEG territory). I just make something up. For a typical residence I would probably put something like 60 amps or 14 KVA

 

[CCWest1]

The NEC doesn't give you any method to calculate it other than the Article 220 options, which the bottom number will be you demand. It is conservably high, but that is the only way unless you have a similar occupancy that you could measure per 220.87

Thanks! I'll check that out.

 

[CCWest1]

Just fyi you will probably have ONE service with 2 meters and 2 sets of service entrance conductors. I don't know why they ask for the peak demand, it's dumb they are going to come up with their own calcs to size their equipment anyway (I am in NYSEG territory). I just make something up. For a typical residence I would probably put something like 60 amps or 14 KVA

Yeah, that was my impression after reading their email. They said if I didn't know how to figure out peak demand, I should ask somebody since there wasn't anyone in their office that could help. Uh huh...

 

[CCWest1]

Just fyi you will probably have ONE service with 2 meters and 2 sets of service entrance conductors. I don't know why they ask for the peak demand, it's dumb they are going to come up with their own calcs to size their equipment anyway (I am in NYSEG territory). I just make something up. For a typical residence I would probably put something like 60 amps or 14 KVA

The NEC doesn't give you any method to calculate it other than the Article 220 options, which the bottom number will be you demand. It is conservably high, but that is the only way unless you have a similar occupancy that you could measure per 220.87

Thanks for pointing me in the right direction. I started looking at demand factors in article 220 for the various appliances, cooktop, motors (well & Heat pump/AC) and added them together to come up with a peak demand. Please see attached calculations and tell me what you think. I came up with 30.6kW by adding both the modular and mobile together.

 

[electrofelon]

Thanks for pointing me in the right direction. I started looking at demand factors in article 220 for the various appliances, cooktop, motors (well & Heat pump/AC) and added them together to come up with a peak demand. Please see attached calculations and tell me what you think. I came up with 30.6kW by adding both the modular and mobile together.

Although they both have the word "demand", "demand factors" and "demand" in the context of power metering really have nothing to do with each other. What NYSEG is asking for is the highest 15 minute average power consumption. Demand factors in article 220 are unrelated.

 

[CCWest1]

Although they both have the word "demand", "demand factors" and "demand" in the context of power metering really have nothing to do with each other. What NYSEG is asking for is the highest 15 minute average power consumption. Demand factors in article 220 are unrelated.

Ok. Anyways, I came across this post from 2016 to someone asking the same question as mine.

Can someone explain how to calculate expected peek demand on a residential home

From jaggedben, senior member,
"There's an entire nine page article in the code on this, Article 220. I'd say read it through and ask us specific questions if you don't understand. Basically you take the square footage of the living space and multiply it by a required factor, then add all the other specific loads and appliances, and then you get to reduce those by specific factors listed in that Article. That's about as concise an explanation as can be given.

This, by the way, is what the code requires. It may or may not be a realistic calculation of what peak demand will really be. That really depends on who lives in the house."

This sounds like what I posted as my calculations regarding demand factors.

 

[CCWest1]

Yeah, that was my impression after reading their email. They said if I didn't know how to figure out peak demand, I should ask somebody since there wasn't anyone in their office that could help. Uh huh...

Thought I would share this with you all. I came across a demand calculator from United Power. See attached.

 

[electrofelon]

Can someone explain how to calculate expected peek demand on a residential home

I don't think you can really do anything more than an educated guess. Remember it's a 15 minute average, so something like a water heater Could easily be on the whole time. Something like a dryer or oven will be cycling in and off. Same with electric heat. All I know is every time I see a demand figure it's surprisingly low.

 

[Fred B]

I don't think you can really do anything more than an educated guess. Remember it's a 15 minute average, so something like a water heater Could easily be on the whole time. Something like a dryer or oven will be cycling in and off. Same with electric heat. All I know is every time I see a demand figure it's surprisingly low.

I think I have used some number derived from the total 200A of the main disconnect and the 83% rule that lets undersize the service conductor due to diversification. Their form has nothing to do really with the NEC load calculations, Give them total of all load potentially on the system for the total connected load and then use the 83% for anticipated peak demand.

Thought I would share this with you all. I came across a demand calculator from United Power. See attached.

This demand billing form really has nothing to do with the expected peak demand and wouldn't use it to figure out the EPD.
POCO basically uses the form to allow them to put in a smaller transformer and have you hold the bag for failure from overload without them giving you information. Try asking for AFC or Z of the transformer, you'll almost never get it from them.

I'd say aim high but reasonable from perspective of a #00A service. It is interesting that NY will be asking that we calculate for adding EV, Heat pump and full electrification but POCO will not provide for the future loads.

 

[CCWest1]

I think I have used some number derived from the total 200A of the main disconnect and the 83% rule that lets undersize the service conductor due to diversification. Their form has nothing to do really with the NEC load calculations, Give them total of all load potentially on the system for the total connected load and then use the 83% for anticipated peak demand.


This demand billing form really has nothing to do with the expected peak demand and wouldn't use it to figure out the EPD.
POCO basically uses the form to allow them to put in a smaller transformer and have you hold the bag for failure from overload without them giving you information. Try asking for AFC or Z of the transformer, you'll almost never get it from them.

I'd say aim high but reasonable from perspective of a #00A service. It is interesting that NY will be asking that we calculate for adding EV, Heat pump and full electrification but POCO will not provide for the future loads.

Thanks Fred.
I came up with the total connected load for the Modular of 35.9kW and the Mobile of 30.0kW. Added together that's 65.9kW. Multiplied by .83 comes to 54.69kW. Does this sound reasonable?

 

[electrofelon]

Thanks Fred.
I came up with the total connected load for the Modular of 35.9kW and the Mobile of 30.0kW. Added together that's 65.9kW. Multiplied by .83 comes to 54.69kW. Does this sound reasonable?

Sounds very high to me. I would guess more like 15kw. I'm guessing they will provide a 25kv transformer anyway, but you can say 25 just to make sure they give you the better transformer.

 

[MyCleveland]

Thanks Fred.
I came up with the total connected load for the Modular of 35.9kW and the Mobile of 30.0kW. Added together that's 65.9kW. Multiplied by .83 comes to 54.69kW. Does this sound reasonable?

Never ran into a request like this in my area. I think "Fred B" nailed it, they are trying to make you put in writing what your max demand will be.

Do not go down this road. If forced, place the load you calculated for each service and attach your PDFs with the form.
If they choose to serve you with a smaller transformer, and they will, it will be their problem to fix if your actual demand exceeds their tranny selection.

Are you using 220.85 (NEC 2020) for sizing a single set of service conductors to serve both units? Look it over, should be able to feed both with single set of 225A conductors.

 

[kwired]

Two different families occupying same house could have totally different demand schedules and peaks. There are averages that can be somewhat expected but everyone is different.

 

[Flicker Index]

A/C + electric furnace: You just don't add those two together. Common sense says they don't come on together.

However, this is a reasonably probable overlap:
Someone starting a wash, then shower, start the dryer and cook.

So, at minimum you add up the big boys. Water heater, dryer and oven preheat and perhaps one burner boiling a pot of water. All of those are likely to have 15 minutes of sustained on-time. Then add A/C / heat pump or electric furnace.

You can count on A/C (after returning from setback) and water heater to run at full load for 30 minutes plus. Oh and pool equipment if present.
EV is perhaps the largest load, but that's very much household dependent.

If this isn't one of the kind development, I wonder why they didn't just kind of assume from nearby customer usage data from smart meters.

 

[CCWest1]

Sounds very high to me. I would guess more like 15kw. I'm guessing they will provide a 25kv transformer anyway, but you can say 25 just to make sure they give you the better transformer.

OK, I guess I should post my connected load calcs for each unit. Both the Modular and the mobile will have their own EV chargers, which adds roughly 5 to 6kW to each. I did not add the EV chargers into calculating expected peak demand. But I did multiply the well pump and AC/Heat pump by 125% into the peak demand calcs. Maybe I shouldn't have done that? Not sure. Anyway, I already sent my connected load calcs to NYSEG, but, obviously not the expected peak demand calcs yet. My 30.6kW is close to your suggested 25kW. I'm thinking maybe not sending the actual peak demand calcs and just fill in the 25kW on their form. Though one of the comments here suggested I do send the calcs so that they have it in writing in case the tranny they give me is undersized and something goes wrong, it's on them and not me. I already posted my Peak Demand calcs above, but I am posting it again here so it will be easier to compare to my connected load calcs.

Thanks guys for your advise. I appreciate you!

 

[electrofelon]

OK, I guess I should post my connected load calcs for each unit. Both the Modular and the mobile will have their own EV chargers, which adds roughly 5 to 6kW to each. I did not add the EV chargers into calculating expected peak demand. But I did multiply the well pump and AC/Heat pump by 125% into the peak demand calcs. Maybe I shouldn't have done that? Not sure. Anyway, I already sent my connected load calcs to NYSEG, but, obviously not the expected peak demand calcs yet. My 30.6kW is close to your suggested 25kW. I'm thinking maybe not sending the actual peak demand calcs and just fill in the 25kW on their form. Though one of the comments here suggested I do send the calcs so that they have it in writing in case the tranny they give me is undersized and something goes wrong, it's on them and not me. I already posted my Peak Demand calcs above, but I am posting it again here so it will be easier to compare to my connected load calcs.

Thanks guys for your advise. I appreciate you!

If I was trying to come up with a demand figure, I wouldn't use any of the 125% stuff. In fact I would do the opposite and probably use 66% of things like MCA and full load motor current.

Again, I really wouldn't worry about it too much I don't even think what you put there will affect anything. For a dinky residential project, they're just going to give you a 25 KVA in almost all cases.