Determining kWh Use  Estimating
To estimate the energy use of a piece of equipment, take the power use, in watts, from the nameplate, divide by onethousand, and multiply the result times the estimated operation time, in hours. This is especially helpful when a rough estimate of consumption is needed.
For example: How much energy does a refrigerator use per day? The refrigerator’s nameplate says it is rated at 1200 watts. We estimate that it runs about 20 percent of the time.
Dividing 1200 watts by 1000 gives us 1.2 kilowatts of power use. Take 20 percent of 24 hours a day, which equals 4.8 hours. The daily energy use is found by multiplying 1.2 kilowatts times 4.8 hours which equals 5.76 kilowatthours of energy use. The annual energy use for this refrigerator is 5.76 kilowatt hours per/day times 365 days per year, or about 2100 kilowatt hours a year.
