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Thu 17 Mar, 2005 03:39 pm
I have been trying to figure out if I am doing the math right.
I found a formula that said if I take the amps and multiply them by 120 then divide by 1000 will give me Kilowatts. Am I right?
this is why I need to know. we have installed a new geothermal heat pump to heat our home. We want to try and figure out if the system was running continually for 24 hours what the kilowatt hours would be.
We know that the system running at maximum is using 23 amps and we have used the formula above to figure out the kwhs
so we have 23x120=2760watts
2760 watts divided by 1000 = 2.76 kw or to round it out 2.8kw
Is this right???
That's right! (if your voltage is 120V)
P=V.A
Power(watts) = Volts x Amps
and 1 kW= 1000 W
120 vs 240
Note that a lot of heavy household equipment runs on 240v, not 120v. It that is the case, you need to multiply by 240, not 120. You can see if your heat pump is 240 or 120 by looking in the breaker box. The 240v breakers are twice the size of the 120v ones.
As a further step in your calculations - your formula will give you kilowatts but not kilowathours.
Since you are trying to find the total over a full day you'll need to calculate the hours in there too.
That would be (volts x amps)hours/1000 or in your case:
(23 x 120)24/1000 = 66.24 Kw/h
These numbers are all going to be aproximate (the 23 amosps is your system's rated max and most people don't actually get 120v AC power) but it gives you the formulas you need.
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