220.87 Determining Existing Loads

brycenesbitt said:
Just be sure you're not off by a factor of four.
Kilowatts are a rate. A kWh is a kilowatt that ran for an hour.
One kW for 15 minutes is .25 of a kWh.

Saying "1 year worth of 15 minute increments. I sorted it with the highest first, which was 1.7 kWh" makes no sense.

What would make sense the highest 15 minute bucket averaged 1.7kW ( 7 amps ).

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That’s the only information they offer, the kWh usage in 15 minute increments.
 
JohnHess said:
That’s the only information they offer, the kWh usage in 15 minute increments.
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Are you sure it is not kW. Average demand usage is usually kW.
Although I have never seen it, maybe you really are getting 15 minute usage and not the highest demand.

Look at any billing period and add up your recorded 15 minute values for that full month, they should be equal if the intervals are usages.
 
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It shows thousands of lines of this. On the options page there’s no option for kW. I guess because they don’t offer demand readings for residential customers. It just says download usage data.

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JohnHess said:
Yes, so I just downloaded the data from a house, 1 year worth of 15 minute increments. I sorted it with the highest first, which was 1.7 kWh. That is 6.8 kW which comes to 28 Amps.
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That procedure is correct for data of the form "kWh used during a given 15 minute interval". Which is what I would expect a watt hour meter to record. Not sure why people seem to be giving you a hard time. 28A average current over the worst case 15 minute interval for the given year of data.

Cheers, Wayne
 
wwhitney said:
That procedure is correct for data of the form "kWh used during a given 15 minute interval". Which is what I would expect a watt hour meter to record. Not sure why people seem to be giving you a hard time. 28A average current over the worst case 15 minute interval for the given year of data.

Cheers, Wayne
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Yeah, I understand what people mean when they say that kWh can’t be used to determine the demand. Usually the reading is over a longer period of time and you don’t know whether a small amount of current is being drawn the entire time or a very high amount of current is being drawn for a very short period of time.

But if we could look at an entire year and see that the highest kWh used during any 15 minute period was 1.7 kWh, then it seems like we could extrapolate that to 28 Amp being the actual maximum demand.
 
jim dungar said:
Not giving a hard time, just getting on the same page.
My experience with 15 minute interval data has always been for KW Demand not KWH.
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kWh data is very typical for residential smart meters nowadays. Usually I get hourly intervals but sometimes I get 15min (seems kinda random, may depend on rate schedule or the particular meter model) but it's always kWh. We are not talking about commercial meters with a separate demand function. Just kWh data in intervals.
 
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JohnHess said:
Yeah, I understand what people mean when they say that kWh can’t be used to determine the demand. Usually the reading is over a longer period of time and you don’t know whether a small amount of current is being drawn the entire time or a very high amount of current is being drawn for a very short period of time.

But if we could look at an entire year and see that the highest kWh used during any 15 minute period was 1.7 kWh, then it seems like we could extrapolate that to 28 Amp being the actual maximum demand.
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I've taken a conservative approach with hourly data and multiplied the average power by anywhere from 2 to 4 depending the loads connected. Multiplying by 4 effectively gives you the worst case equivalent for a 15min interval, and is almost surely way too conservative. If I'm given 15min data this operation is unnecessary. (Not to be confused with the operation of converting kWh to kW as discussed above.)
 
JohnHess said:
I believe that the residential load calculations we perform are very bloated. Sometimes they can limit what we can install for the homeowner or cause them to spend unnecessary money on service upgrades or load management products. Instead of submitting load calculations with my electrical permit applications I would like to submit 1 year of the actual maximum demand data because I know that will be much lower and more accurate than the load calc.

My question is what the "maximum demand" is, exactly. Our area is served by a very large PoCo and is mostly smart meters now, so I assume that data will be available thru their website. But I am not sure exactly what form it needs to be in to tell me the average load in place of the VA number I get when doing a load calculation.
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Hopefully it is a kW meter and not kWH only. You should be able to pull 12 months of load data online though. There also are tons of hidden demands factors and alternative calcs in the code that aren’t always used. You could have an engineer evaluate


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kcunningham59 said:
Hopefully it is a kW meter and not kWH only. You should be able to pull 12 months of load data online though. There also are tons of hidden demands factors and alternative calcs in the code that aren’t always used. You could have an engineer evaluate


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Unfortunately it is only kWh. I’ve found what others here mentioned to be true, residential meters like this do not record demand, only usage.
 
JohnHess said:
Unfortunately it is only kWh. I’ve found what others here mentioned to be true, residential meters like this do not record demand, only usage.
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And without an AHJ approved method of analyzing the data it is meaningless for your needs.
 
jim dungar said:
And without an AHJ approved method of analyzing the data it is meaningless for your needs.
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The good thing about my state is that every municipality is bound by the UCC and regulated by the state. So the state could put out guidance and make determinations that the local AHJ has to follow.

Since my state is also pushing hard for electric vehicles and other electric appliances, this seems like it would be a good thing for them to work out. I’ll give it a shot.
 
JohnHess said:
Unfortunately it is only kWh. I’ve found what others here mentioned to be true, residential meters like this do not record demand, only usage.
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15 minute kWh values fall within what 220.87 asks for.

To convert the 15 minute kWh, multiply it by 4 to get the equivalent "average kilowatts reached and maintained for a 15-minute interval". Then take the maximum value of all of those 15 period numbers for a year and that would be "The maximum demand data is available for a 1-year period.". To convert it to kVA, you will need to make some estimates on what the power factor is unless the utility measures that and reports it.

This is the way the utility determines maximum demand for commercial bills.
 
JohnHess said:
The good thing about my state is that every municipality is bound by the UCC and regulated by the state. So the state could put out guidance and make determinations that the local AHJ has to follow.

Since my state is also pushing hard for electric vehicles and other electric appliances, this seems like it would be a good thing for them to work out. I’ll give it a shot.
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The DCA is your only option if you want to try and avoid the bloated load calc. I'll give it a 50-50 chance so it's worth a shot. :giggle:
 
electrofelon said:
I agree with ron, 15 minute kwh values X 4 are exactly equivalent to 15 minute demand no?
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Not any more than a 1 hour KWH value should be, but we know peak usage is not the same as peak demand

Multiplying by 4 is a waste of time. Just find the highest interval and divide it by 15. This is your maximum average demand per minute, but it is still up to the AHJ.

I would have no problem with just using the highest 15 min KWH interval vale and saying it is equal to KW demand. But what do I know, I am retired and only have the authority my wife gives me.
 
wwhitney said:
I'm confused--if you have 15 minute kWh data for a year, that is obviously sufficient for 220.87, so what's the problem?

Cheers, Wayne
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A lot of inspectors outright say that there’s no way a 100 amp service on a single-family dwelling can support a 48 amp EV charger because they’ve always seen load calculations of the dwelling being in the 80 amp range.

So when coming to them with data saying that the house is actually under 20 amp, many are just going to call BS. Having guidance from their governing body would prevent this from becoming an issue.
 
jim dungar said:
Not any more than a 1 hour KWH value should be, but we know peak usage is not the same as peak demand
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We seem to have a difference in understanding. Let's assume PF = 1 for simplicity.

What does it mean when the utility tells you on a commercial account that the demand during a given 15 minute interval was 1 kW? My understanding is that it means that the average power used during that 15 minute interval was 1 kW. It could have been 3 kW for 5 minutes and 0 kW for 10 minutes, or whatever, but it's an average over the 15 minute interval.

Is that correct? Because that definition of 15 minute interval demand means exactly that 15 minute interval demand = kWh used in this 15 minute interval * 4 intervals/hour. So the data is equivalent to 15 minute kWh data.

Cheers, Wayne
 
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