Commercial Electricity Usage Calculation

de2

Member
Location
Newark, NJ
Hello,
I was asked to do a estimated electricity cost for one of my commercial client. This is a simple calculation but I wanted to run by forum members because I have few questions;

kwh electricity is 1Cent/kwh (to make calculation easy)

Item#1) Refrigerator, Name Plate Data; 120V, 5A, 600Watt, on 24hrs/30days

Item#2) Desktop computer, Name Plate Data; 120V, 2.5A, 300Watt, on 24hrs/30days

Item#3) Lights, 120V, 0.83A, 100Watt, on 24hrs/30days

(600*24*30) + (300*24*30) + (100*24*30) = 720kwh

720kwh * 1c/kwh = 7.20$

Item#1) Refrigerator does not use full name plate watt for the entire 24 hours of a day. Once it reaches the set temp, it will go to idle mode. How do you calculate this?

Item#2) Desktop computer is same as refrigerator, it will not be using full watt when it not being used.

Item#3) Lights will be using full name plate watt, no question here.

How would you approach this calculation?
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
Hello,
... estimated electricity cost

Item#1) Refrigerator does not use full name plate watt for the entire 24 hours of a day. Once it reaches the set temp, it will go to idle mode. How do you calculate this?

Sit down in the kitchen for an hour and have coffee. Pay attention to how long the refrigerator runs.

Item#2) Desktop computer is same as refrigerator, it will not be using full watt when it not being used.

Figure for 8 hours per day - 5 days a week

How would you approach this calculation?
Or, as ef suggested, you could buy/rent a power monitor (or monitors) and monitor each for an hour/day/week. Depends on the budget, required accuracy, time available.
 

de2

Member
Location
Newark, NJ
This facility is 40000sq ft. There are 6 tenants, sharing the facility.
There is only one electric meter.
There is no designated electrical panel for each tenant, its all spider net style wiring.

My client has over 200 pieces of devices that are all plug connected to the wall receptacles.
My goal to make educated assumptions and calculate the electricity usage based on what is there.

I know that I can not use name plate data for refrigerator, heat oven, desktop computer, printer, scanner, monitor... Because these devices do not consume name plate data all the time.
 

JFletcher

Senior Member
Location
Williamsburg, VA
Does your client want approximated energy use for each of the six tenants to calculate their usage and subsequent billing / rent? If so, there may be legal issues with that route.

That aside for the moment, measuring the power draw on 200 devices individually is going to take a lot of time. Measuring the current on the branch circuits would be faster and probably produce better results. You could also go by square footage or the nature of loads. New refrigerators and computers, they probably had one of those approximate energy Youth and cost per year stickers on them when they were sold, you might find those helpful.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
This facility is 40000sq ft. There are 6 tenants, sharing the facility.
There is only one electric meter.
There is no designated electrical panel for each tenant, its all spider net style wiring.

My client has over 200 pieces of devices that are all plug connected to the wall receptacles.
My goal to make educated assumptions and calculate the electricity usage based on what is there.

I know that I can not use name plate data for refrigerator, heat oven, desktop computer, printer, scanner, monitor... Because these devices do not consume name plate data all the time.
That would make me nervous. Sounds like an illegal occupancy, ie it was a single tenant space that he has broken up without permits, because doing it legally would have likely triggered a tenant improvement plan, which would have required separate meters. Maybe it’s different in NJ, but that’s the way it is here in every western state I have worked in.
 

broadgage

Senior Member
Location
London, England
Sounds fraught with potential arguments and disputes to me.

I would divide the electricity bill in proportion to the square footage occupied, or if possible install a metered sub panel for each tenant.
 
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