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lmchenry

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If I know the kwh per month usage on a particular business, can I determine the service size needed for the business?
 
lmchenry said:
If I know the kwh per month usage on a particular business, can I determine the service size needed for the business?
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If you know KWH per month, this business already has a service. Are you trying to size a gen-set?
 
Dividing by 720 will give you the average load in watts.
You probably also need the peak load, available with a recording wattmeter. How long you need to leave the meter on to capture the peak load, a day or a year, depends on what they do for a living.
 
They are adding on to the business and I dont think the service is big enough. At peak month they used 3397 kwh.
 
Take the 3397 kWH for the month and divide it by the number of hours it was operational during that same period. So if it is a 24x7 business and the period for the bill was for 30 days, its power usage averaged over a month is 3397/(24*30)=4.7kW
 
lmchenry said:
They are adding on to the business and I dont think the service is big enough. At peak month they used 3397 kwh.
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You need to go through the facility and identify the existing loads; then add the new loads to the list; and then go to the code and do a load calculation.

The minimum for a single family residence is 100 kW, and many use less than 1 kW average during a month. There is not enouigh information in the electric bill to estimate the service size; unless they have a demand-based rate and there is a record of peak demand recorded on the bill.
 
Don't forget to account for power factor

My choices:
#1: calculate the load
#2: try to find a similar load to ratio out an estimate

Can you specify the load/business type? As many as frequent this site, I bet someone has seen something similar.

For a poor load factor (say 15%) 3397/730/15% = 31 kW.

Assume 80% power factor: 31 kW / 80% = 38.75 kVA

An average business load factor might be 40-50%. A high load factor would be 60-80%

Another way might be:

5 days/week, 2 shifts per day (use 17? hours), 4.3 weeks in a month.
5x17x4.3 = 368 hours of working time
3397/368 = 9.2 kW
Assume 85% power factor:
9.2/85% = 10.8 kVA

[edit: typo]
 
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lmchenry said:
If I know the kwh per month usage on a particular business, can I determine the service size needed for the business?
Click to expand...
The KWH is of no value in determining the size of the service. You can have a demand of 100 kw for 1 hr and 5 kw for the rest of the month. The service must be sized for the max demand. You need to calculate the load as if it were a new service. As recommended, get the existing load and use 220 of the NEC for the rules and calculations.
 
bob said:
The KWH is of no value in determining the size of the service. You can have a demand of 100 kw for 1 hr and 5 kw for the rest of the month. The service must be sized for the max demand. You need to calculate the load as if it were a new service. As recommended, get the existing load and use 220 of the NEC for the rules and calculations.
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So true. Ultimately you will need the load calculation.

While the kWh alone is of no value, combining it with other information like the type load, operating characteristics, etc. can give you a "sanity check" on what you might need to prepare for or even if you are in the ball park.
 
bob said:
The KWH is of no value in determining the size of the service. You can have a demand of 100 kw for 1 hr and 5 kw for the rest of the month. The service must be sized for the max demand. You need to calculate the load as if it were a new service. As recommended, get the existing load and use 220 of the NEC for the rules and calculations.
Click to expand...

I gotta agree. Look at all of your motor loads in horse power. Look at your HVAC load. Any other heaters or equipment?
Do a load calculation of the existing building and add the addition.
You are going to have to have it done for a plan review if you want a permit.
 
lmchenry said:
If I know the kwh per month usage on a particular business, can I determine the service size needed for the business?
Click to expand...


No - not without getting more info.

Steve
 
jrannis said:
I gotta agree. Look at all of your motor loads in horse power. Look at your HVAC load. Any other heaters or equipment?
Do a load calculation of the existing building and add the addition.
You are going to have to have it done for a plan review if you want a permit.
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Jrannis,

Agree.All loads should be calculated including HVAC Load as you mentioned. But can we have any rule to estimate electrical load(KW) of HVAC load in BTU/Hr, because suppose they might not have nameplate data or catalog to estimate electrical load.

Pls advise.

gk
 
Get the demand load from the utility.

KWH is just there units of measure for charging the customer, the KW value however will tell you what you need to know. Typically you also get peak demand values.
 
James@CHA said:
Get the demand load from the utility.

KWH is just there units of measure for charging the customer, the KW value however will tell you what you need to know. Typically you also get peak demand values.
Click to expand...

I almost always get the demand load frm the utility. However, you have to take that info with a grain of salt. The POCO will almost always demand a job lower than an Engineer will. Remeber, the POCO only cares about their wires. It doesn't cost them a nickel if your switchboard burns down.
 
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