KW usage

[ceb58]

Please help I am brain dead after a 16hr day. I am trying to come up with a demand for a gen install. I requested and received the last 12 months power usage. For the last 12 months they averaged 2023kw/hr. I come up with them averaging 11.54 amps per hr. Am I any where close?

 

[kwired]

Sizing a generator for average consumption may not allow for peak demand.

What is voltage/phases?

 

[Volta]

Please help I am brain dead after a 16hr day. I am trying to come up with a demand for a gen install. I requested and received the last 12 months power usage. For the last 12 months they averaged 2023kw/hr. I come up with them averaging 11.54 amps per hr. Am I any where close?

As Kwired was pointing out, if you can get the peak demand load you may be able to use it, but not really just a simple average. Is this a location with a demand meter?

 

[rattus]

Please help I am brain dead after a 16hr day. I am trying to come up with a demand for a gen install. I requested and received the last 12 months power usage. For the last 12 months they averaged 2023kw/hr. I come up with them averaging 11.54 amps per hr. Am I any where close?

FWIW, "kw/hr" and "amps/hr" should be simply "kw" and "amps".

Demand should be listed on the POCO bills if it is a commercial account. If not, perhaps you could base it on the size of the customer's service, or maybe monitor the current for a few days.

I have computed--with a pencil yet--many, many electric bills in my youth, but I must admit I have never done the monitoring.

 

[ceb58]

Sizing a generator for average consumption may not allow for peak demand.

What is voltage/phases?

120/240 1ph they do not list a peak demand

 

[kwired]

120/240 1ph they do not list a peak demand

11.54 amps @ 240 volts is 2770 VA. (remember this is what you figured as average)

If you have an individual or multiple loads requiring more than that to use at one time you need to have capacity to handle them.

Also you may need extra capacity to allow for motor starting - utility power is more stable for this than a generator is.

 

[charlie b]

For the last 12 months they averaged 2023kw/hr.

FWIW, "kw/hr" . . . should be simply "kw" . . . .

Not necessarily. If this really is an average value provided by the utility, it could have been in terms of kilowatt-hours. But if so, then we would need to know whether that is an average day's worth of energy, or an average week's worth, or an average month's worth, or whatever. On the other hand, if the utility is saying that the average power level was 2023 kilowatts, on a 240 volt system, then you are talking about a current level of 8,400 amps. So the information given here is not making sense.

CEB, how about resting up from your 16 hour day, and giving this another shot? What exactly did the utility give you?

 

[mivey]

Not necessarily. If this really is an average value provided by the utility, it could have been in terms of kilowatt-hours. But if so, then we would need to know whether that is an average day's worth of energy, or an average week's worth, or an average month's worth, or whatever. On the other hand, if the utility is saying that the average power level was 2023 kilowatts, on a 240 volt system, then you are talking about a current level of 8,400 amps. So the information given here is not making sense.

CEB, how about resting up from your 16 hour day, and giving this another shot? What exactly did the utility give you?

Based on the info ceb gave (2023kW??, 11.54 amps, 120/240 1 phase), they gave him data that showed an average of 2,023 kWh/month. But that does very little to help with the gen size.

 

[Besoeker]

FWIW, "kw/hr" and "amps/hr" should be simply "kw" and "amps".

Demand should be listed on the POCO bills if it is a commercial account.

If it's a bill for energy it would be kWh.

 

[Jraef]

If you took 12 months worth of bills that only show kWH, added them together and divided by 12 to get an average, that is only an average of your monthly kWH use . That has LITTLE to do with peak demands or peak use or peak anything. You could have 2023kW for 1 hour and it is 2023kWH, or you could have 20.23 kW for 100 hours or you could have 2.023kW for 1000 hours, it all comes out the same. There is no way to determine demand from a kWH bill. You either have to have a peak reading from the utility, or add a recorder for a month.

 

[charlie b]

I am confused about another aspect of this question.

I am trying to come up with a demand for a gen install.

What is the intent for this generator? Will this replace the utility feed in its entirety? Will this provide a back up for 100% of the present demand load? Will this only provide a back up for certain loads? You can't size a generator without knowing what it will serve, and there is no rule that says it has to serve the same demand that the utility is serving.

 

[Besoeker]

If you took 12 months worth of bills that only show kWH, added them together and divided by 12 to get an average, that is only an average of your monthly kWH use . That has LITTLE to do with peak demands or peak use or peak anything. You could have 2023kW for 1 hour and it is 2023kWH, or you could have 20.23 kW for 100 hours or you could have 2.023kW for 1000 hours, it all comes out the same. There is no way to determine demand from a kWH bill. You either have to have a peak reading from the utility, or add a recorder for a month.

Don't disagree.
But you'd have to pick the month on months with the highest demands if the generator has to meet all needs.

 

[Robert Hutcherson]

Please help I am brain dead after a 16hr day. I am trying to come up with a demand for a gen install. I requested and received the last 12 months power usage. For the last 12 months they averaged 2023kw/hr. I come up with them averaging 11.54 amps per hr. Am I any where close?

Call your utility service planner and ask him to provide the peak kilowatt demand for the past 12 to 24 months. In florida, they provide this data to contractors. Take the highest peak KWD and add 25% and this will provide you generator sizing close enough to provide a budget for the project. Usually a good idea to meet with an electrical engineer familar with these type projects, to look at how service, and switchgear are effected as well as number of transfer switches needed for stepping loads. Good luck.

 

[Robert Hutcherson]

120/240 1ph they do not list a peak demand

I did not see this post. My mistake. If this job is for a residence, or light commercial you may have to perform service calc for loads that are supported by generator.

 

[rattus]

If it's a bill for energy it would be kWh.

Bes, my aging mind recalls that demand is a measure of the maximum power drawn over a 15 minute period or something like that. Usage would be stated in KWH; demand would be stated in KW.

 

[charlie b]

Bes, my aging mind recalls that demand is a measure of the maximum power drawn over a 15 minute period or something like that. Usage would be stated in KWH; demand would be stated in KW.

That is what I believe as well. And that is why the numbers given in the original post do not make sense. So after our OP has had a chance to rest up, he can perhaps clarify it all for us.

 

[mivey]

Bes, my aging mind recalls that demand is a measure of the maximum power drawn over a 15 minute period or something like that. Usage would be stated in KWH; demand would be stated in KW.

It is NOT the measure of the maximum power in a 15 minute (or whatever interval) period. It is really the energy drawn over the period divided by the time of that period so it is the average power over that period. The maximum power drawn would most likely be higher.

 

[hurk27]

I just did a store with 60% of the load was cooling units, and 5 tons of AC, not only did I have to figure for the peak demand, but to make sure all these motor loads don't all starting back up at the same time, to lower this I gave the owner the option of having his refrigeration guy put time delays with different times on each cooling unit and the AC, so they all wouldn't try to come on at the same time.

200 amp single phase 120/240 service had a peek demand of 24kva, so I used a 30kva generator with a 200 amp ATS

 

[Jraef]

Don't disagree.
But you'd have to pick the month on months with the highest demands if the generator has to meet all needs.

Yes, you're right.

I think the other points raised about how much the generator has to run are pointed as well. Usually, you determine the generator size by doing a demand calc on the specific loads you have to serve. For instance if it's a residence, I'd pick the fridge, stove, PCs (my bias), maybe one TV, lights (if separate from general receptacles) and maybe another 1500W on a kitchen receptacle (gotta have that espresso in the morning...). Sacrifice the A/C (unless it's an old person) and the 50" flat panels, surround sound, video games, hair dryers and garden lights when on a generator. You get the picture.

 

[ceb58]

I am confused about another aspect of this question.What is the intent for this generator? Will this replace the utility feed in its entirety? Will this provide a back up for 100% of the present demand load? Will this only provide a back up for certain loads? You can't size a generator without knowing what it will serve, and there is no rule that says it has to serve the same demand that the utility is serving.

OK, here goes. The gen. will be a stand by system for a fire dept. It will provide 100% of the load. They are going to add 8300sq/ft to the building that will be bays for the trucks. The existing motor loads will just move from the old section to the new. They plan on renovating the old part for sleeping quarters. The only addition to the load will be the lighting for the new part and 1 more 5 ton a/c unit. They cook,heat and water heater is gas. I have requested a peak demand load from the poco but have not heard back from them yet. After talking with gen. rep it looks like a 40kw unit will suffice but I will need to show AHJ the calculations since the building has a 400 amp service on it and I am looking at setting 2 ATS to feed the 2- 200amp sub panels. The largest load I have seen from what I have is from last Aug. when they averaged 2971 for 31 days