Sunday, July 10, 2016


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I got a nice clean recording of my refrigerator energy use last night. This pic is the "Last Three Hours Real Time History" view of my Blueline EnergyCloud software. Recorded in the middle of the night, from about 2am to 5am. I got up shortly after 5am and plugged in the freezer. That's the spike at the right. (click any pic to enlarge)

Normally the freezer and the refrigerator run overnight but that makes a confused recording. With the freezer off, the recording is beautifully clean and shows the regular cycling of my old Fridigaire model IDT186001 against the house background of about 100 watts. The house background consists of my network (necessary for the Blueline hardware to work sending my data to the cloud), a few chargers and wall warts, the light in the basement I forgot to switch off last night plus a few LEDs for path illumination that are on all night but turn off in the day. I think I might have turned on a bedside lamp at 3:30 for a few minutes to check the time. You can see a little upclick at about that time.

Here is a longer view at six hours. That is a water heater peak at about 1:20. Notice that the vertical scale kW changes (steps back) when the water heater is present because of the size of the peak. That's the same refrigerator running in the background but its 150watts looks small compared to the water heater. the refrigerator runs much more often so usage adds up. All the graphs in the Blueline software do this vertical scaling thing automatically. It is important to watch the axes, both time and kW.

Some test conditions: It is the middle of the night in the summer. The refrigerator door has not been opened for at least eight hours.

The energy used by the refrigerator is about 250watts less the background 100watts (which the house is using elsewhere) or 150watts. The refrigerator comes on about every hour for about 20 minutes. Which means as a rough guess, the refrigerator is on ABOUT A THIRD OF THE TIME using 150 watts. I calculate more carefully below.

The temperature shown at the top right of the pic is the outside temperature (12C) at the meter. The inside house temperature is about 21-22C. In the winter, the house temperature will be cooler so the refrigerator is working moderately hard right now. It will work harder still when the house temperature is higher and the refrigerator door is being opened occasionally, new food is being inserted etc. So this should be considered a sort of minimum for the refrigerator.

I should be measuring the inside temperatures of the refigerator and freezer compartments. I should be at least measuirnt the internal temparature at the conclusion of my peak period inhibit.

So now I'd like to turn the graph into an amount, the amount of energy consumed by the refrigerator. I had commented that none of the provided software does that for me so I am going to use a graphics program to help me do the calculation. I am using CorelDraw. I will do it in a bit more detailhere to explain the concept but only present the results on other appliances. I intend to do this for at least my major consuming appliances. Hopefully I will be able to use this information to help me decide on improvements.

Here I am in CorelDraw with the same pic I showed above. I have added guidelines with Corel which I have carefully placed at the edges of the power waveform, where it rises and where it falls. I find it difficult to judge time on the horizontal axis so will use some tools to help me. I will use guidelines to snap dimension tools to I can make fairly precise measurements of the time by comparison. More below.

I have also placed guidelines along the top of the peaks at 250 watts. These are quite uniform so one guideline will do. I have placed another along the baseline at 100 watts. I will use these kW amounts for the calculation.

I have added horizontal dimension lines in cm. Any units will do as long as they are all the same. I want to compare the lengths (times) of the refrigerator power waveforms to compute the time. One hour I have measured as 2.08cm.

I see that the ON time measurements are in the range of 0.64 to 0.67 so I will take the average (0.66+0.67+0.64+0.64/4) = 0.6525cm or (0.65/2.08) = 0.31 of an hour or about 18.8 minutes. This is about how long the refrigerator is ON using 150watts.

I can see from the cycle times that the refrigerator is coming ON every (1.74+1.77+1.73/3) = 1.75cm or (1.75/2.08) = 0.84 of an hour or about (0.84x60) every 50 minutes. This means that the refrigerator is running (0.31/0.84x100) = 36% of the time.

In kWh this would be (0.150x0.36x24) = 1.296kWh every day or (1.296x365)= 473 kWh per year. This is if I don't open the door and don't ask it to cool any new food.

My refrigerator still has the EnergGuide lable showing 691kWh per year expected usage so at least I am on the right page. As near as I can make out, my old refrigerator is from the 1990's.

I notice looking at newer refrigerators the other day that modern units use half the amount of electricity. I also notice that the wall thickness of newer fridges seems twice as thick as mine. The new ones have much thicker insulation in the walls and the door.

Time for a new fridge? Or should I better insulate mine?

Thanks for your interest
George Plhak
Lion's Head, Ontario, Canada

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