kwh to kw calculations

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misterbill1972

misterbill1972

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I am working on a existing building. The customer has asked me to create a peak demand summary on the existing loads based on connected load amps.
I have aquired the total kWh used monthly how do I convert this into kW?
 
Divide the KWH by the number of hours associated with the measured KWH. For example, if this is a one-month reading, from a 30 day month, then divide by 720 (i.e., 30 days times 24 hours).

PLEASE NOTE:
This will not give you a peak demand value. It is an average value only. It is not possible to determine the peak value from the total value. It is like knowing that someone traveled 100 miles in a total of 2 hours, and calculating that their average speed was 50 MPH. This will not tell you whether or not they spent any of that time speeding at 80 MPH, and the rest at a slower pace, or whether they maintained a steady 50 MPH for the whole trip.
 
misterbill1972 said:
I am working on a existing building. The customer has asked me to create a peak demand summary on the existing loads based on connected load amps.
I have aquired the total kWh used monthly how do I convert this into kW?
Click to expand...

You cannont determine the peak kW or he kW used at any point during the month with just the total kWh. You simply do not know what the loading was at various points in time to accumulate to this total value. It could have been the same each day throughout the month, or the loading could have happened all in one day.

This is similar to saying that I drove my car 100 miles last month (30 days). You do not know if I drove 3.3 miles each day throughout the month or if I drove all 100 miles in one day and none the rest of the month.

Charile you must have posted your response as I was typing mine, but I'm making basically the same point as you are.
 
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If you got the kWH number from the unility, they should also have peak demand figures available.
As the two older gentlemen have already mentioned, the peak value can't be derived from the kWH.
db
 
mull982 said:
You cannont determine the peak kW or he kW used at any point during the month with just the total kWh. You simply do not know what the loading was at various points in time to accumulate to this total value. It could have been the same each day throughout the month, or the loading could have happened all in one day.

This is similar to saying that I drove my car 100 miles last month (30 days). You do not know if I drove 3.3 miles each day throughout the month or if I drove all 100 miles in one day and none the rest of the month.

Charile you must have posted your response as I was typing mine, but I'm making basically the same point as you are.
Click to expand...

This is just a rough estimate based on kWh given to me from utility co.What they are saying is max demand kW does not sum up to the kWh?
 
misterbill1972 said:
What they are saying is max demand kW does not sum up to the kWh?
Click to expand...
No. The maximum Kw demand is merely an instantaneous value. KwH is an accumulation of power over time.

For example, say the maximum power peak was 36.8 Kw. That has nothing to do with the KwH used in a month.
 
Powermeter

Powermeter

misterbill1972 said:
I am working on a existing building. The customer has asked me to create a peak demand summary on the existing loads based on connected load amps.
I have aquired the total kWh used monthly how do I convert this into kW?
Click to expand...

You may have hok a powermeter to record the energy consumption and peak demand.

Some energy meters have peak demand recorders but i suspect your meter may not have it.

Powermeter is the way to go..



Cheers.
 
peak accuracy, peak estimates, peak type/time

peak accuracy, peak estimates, peak type/time

Are you sure the POCO does not have demand data for this load or a similar load?

Having a demand meter is the only accurate means. The problem with some demand meters is that the interval may not be short enough for what you are doing. The average demand over an hour will not show you the short-time stress your equipment sees. Be sure you have a short enough demand interval to get the data you need. The POCO meter may only use 15, 30, or 60 minute intervals.

Don't forget that kW is only part of the story. The equipment sees the kVA. The smaller the power factor, the smaller kW is relative to kVA (pf = kW/kVA).

You could also do a load survey and calculate the demand or run some test loads. The survey data would have to include which processes were run during which part of the year. This would yield an estimate.

Another means is to use a load shape from a similar building & operation that has demand data and scale according to the kWh data you have. You might have to make a few tweaks for minor differences. If there are a lot of differences, you are basically going to be making a load survey. This will yield an estimate.

One more thing. You asked for a peak demand profile. There are two demand interval peaks we usually look at: the coincident peak (CP) and the non-coincident peak (NCP).

The NCP is the highest demand at any point during the time period. The CP is the demand at a time that has a particular significance. The CP could be coincident with other plant loads, other local utility loads, or state-wide utility loads, etc.

An analogy: kWh is like distance and kW is like speed. Supposed you drove 140 miles in 2 hours. Your average speed (like an average demand) is 70 mph. During the trip, you went 90 mph at times, 80 mph at times, 70 mph at times, and 65 mph at times.

Your NCP number is 90 mph. An important point in time is when you passed the highway patrol. That would be your CP.

Most of the time, we are only concerned with the NCP. This is used for sizing equipment, most rates, etc. But suppose a plant sets the NCP at night and has a lower peak during the day? They may want to consider a rate that gives them a discount because electricity is cheaper at night.

If a plant is having trouble with a particular piece of equipment, we may only be concerned with the peak that occurs when the equipment is running.
 
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mull982 said:
Charile you must have posted your response as I was typing mine, but I'm making basically the same point as you are.
Click to expand...
Both valid of course, but your format for the units was accurate. As was the OP.
:wink:
A little off-topic.....
I am actually something of a stickler (or even a pedant) on that kind of detail.
Our business is primarily the design and manufacture of electrical (mostly power electronic) systems. When we send any communication to a customer or a supplier, I'd like it to reflect professional status.
Using incorrect terminology could compromise that.

Just my take.
 
Besoeker said:
Both valid of course, but your format for the units was accurate. As was the OP.
:wink:
A little off-topic.....
I am actually something of a stickler (or even a pedant) on that kind of detail.
Our business is primarily the design and manufacture of electrical (mostly power electronic) systems. When we send any communication to a customer or a supplier, I'd like it to reflect professional status.
Using incorrect terminology could compromise that.

Just my take.
Click to expand...
I think I've tried to bust Charlie's chops on that before, but he is too stubborn.:D
 
Besoeker said:
But for the smilies, that response seems more arrogant than stubborn.....
;)
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He might be, but his other postings that I have read don't indicate that. I just figure it is something he doesn't see as a big deal, even though it is terminology used in a field in which he excels.

I cringe when I hear someone talking about how many "kilowatts" they used. But I consider the source and let it go. Sometimes I grow weary of trying to correct that error over and over. The problem is, those people hardly ever use those terms and the corrections just don't have any sticking power. They have other things that are more important to them. They could probably quote sports stats for the past 30 years with no errors.

IMO, people who work in our field should know better and try to do better. I catch myself being impatient sometimes, and have to step back and realize my expectations of people may not fall in line with reality.
 
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