Commercial and industrial accounts not on our C1 Rate (look on your electric bill) are subject to charges for electric demand. Demand, measured in kilowatts or KW, is billed at the level reached during the highest 15 minute period in the month. The average electric use during each 15 minute period is measured and the highest period used for billing.
Demand can also be useful in helping track the effect that turning equipment on and off has on your bill and a graph of demand against time can reveal patterns in your energy use.
Want to know what your “instantaneous demand” is? Just follow these directions.
1. First, you’ll need two numbers off the meter.
The first one might be embossed on tape on the face of the meter. It should have something on it like “Mult = 40” or similar. This multiplier is commonly 1, 40, or 80 but may be as high as 400. If you don’t see this number then it is likely “1”. This number, by the way, is the ratio between the actual current and voltage through the wires to the amount that registers on your meter.
The second number is always on the face of the meter. It is the “K” factor and should read something like “Kh 1.8”. The actual number varies significantly between various meters and manufacturers. The “K” factor is the multiplier to show how much power is used each time the wheel or “caterpillar bar” goes around.
With these two numbers, you are now ready to calculate your instantaneous demand.
2. Time how many seconds it takes the wheel or the “caterpillar bar” to go around.
3. Now, find the equivalent kilowatt-hours per hour, which is our demand in kW.
Each time the bar goes around is “K” x Multiplier in watts.
There are a thousand watts in a kilowatt so divide by 1,000.
Find how many rotations of the wheel or “caterpillar” in an hour by dividing 3,600 seconds by the number of seconds taken to rotate back to a certain point.
Multiply the energy measured by each wheel rotation by the number of rotations in an hour.
Here’s an example:
23 seconds for the meter wheel to go around.
3.6 x 40 / 1,000 = 0.1440 kW in the time it takes the meter to go around.
3,600 / 23 seconds = 156.52 rotations per hour.
0.1440 x 156.52 = 22.5 kW instantaneous electric demand
Take this measurement a few times over fifteen minutes, average it, and you’ll get a feeling for what your electric demand was during that period. Try it when your air-conditioning or your air compressor is running and when it isn’t. Try it when your parking lot lights are on. It can be fun to get a feeling for your energy use patterns.
Remember, our demand meters are looking at each 15 minute period during the month. If you are on a rate that includes electric demand your meter timing is likely to show a demand less than on your bill unless you just happen to be measuring during the highest period.