About our FridgeBernice picked out the Frigidaire 11.5 cu. ft. top freezer refrigerator. We've been using it in the little 400square foot carriage house that we're renting during the build and think it's a great choice for a tiny house. It's narrow, just 24" wide, and runs very quietly — very important when you're sleeping in the same room with it! One question we had when we bought it was exactly how much energy it would use, since we're going to be running off solar panels part of the time. But how do you know? Energy by the Label
Measuring RealWorld Energy UseThe numbers on the label are based on measurements under laboratory conditions, But how well does this predict actual energy usage? Once we had the refrigerator set up here and filled with food, we were ready to measure how much electricity it used in real life. This is easy to do with a special electrical meter called a "KillAWatt Meter" that measures many different electrical parameters at once  Volts, Amps, Watts, VoltAmps, Frequency, Power Factor, kiloWattHours, and Hours. It's the last two that are of interest to us, the meter watches the power use over a period of time, and continuously records the total kWh used and the run time.
The KillAWatt is easy to use, you just plug it into an outlet (at the end of an orange extension cord in this case) and then plug the refrigerator (grey cord) into the meter. It will accumulate data as long as it's plugged in, just unplug it from the wall to reset the kWh and time counters to zero. These photos show it after it ran for a bit over a day. Power consumption was 0.98 kWh over a period of 31:17 = 31.28 hours. We can multiply by 24 hours per day/31.28 hours to get daily power usage, 0.98 x 24/31.28 = 0.752 kWh per day. This tells us our actual usage was about 90% of the 0.852 kWh per day predicted by the label. Again, dividing by 24 hours per day and multiplying by 1000 W per kW gives us 0.752/24 x 1000 = 31.3 W used if it ran continuously. We ran a much longer test over a period ending 11/17/2016, using 39.43 kWh over a period of 985 hours (41.04 days) for a daily usage of 39.43/41.04 = 0.961 kWh per day. Power used is 0.961/24 x 1000 = 40.0 W used if it ran continuously. Here in Phoenix, Arizona the temperatures were quite high through October, so the longer time sample included hotter weather when the refrigerator would have been running more during each day. The Bottom LineSo when all was said and done, for our fridge the energy usage label gave a very good estimate of what you can really expect! The label said we could expect to use 0.85 kWh per day, and our measurements showed we used between 0.75 and 0.96 kWh per day.
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February 2017
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