Tuesday, August 16, 2016

insulated refrigerator freezer 2

INDEX to the series

Another chart from last night on the superinsulated refrigerator freezer.

I want to know, using my smart meter data, if the refrigerator's standby energy use is any different (hopefully less) with the "blanket" of insulation I added to the freezer compartment. My previous test was inconclusive because the ambient temperature was different from the one measurement I made before I added the blanket. I wish now I had taken more measurements.

The standby electrical usage of a thermal box type applicance, like a refrigerator, a freezer or even a hot water heater varies mainly with the temperature of the air around it (the ambient temperature) and the insulation.

In order for me to make a meaningful comparison, all things (controllable variables) should be kept the same. The ambient temperature is not really a controllable variable but it is from an experimental point of view.

So I am taking snapshots of my smart meter data and reading each manually. I see a graph of my usage at any time and I can pick out the appliance. I can measure it very accurately. But with the software I have now, I cannot tabulate or totalize usage by appliance over say a month or a year. So I am estimating to get an idea for ranking, highest to lowest. I am also learning a lot about how my appliances behave as electrical loads and explaining as I go (the INDEX). I can "see" my electricity use with my smart meter data, but just how useful is it?

(click any pic to enlarge) I should compare measurements at the same ambient temperature. I could make a graph of standby usage with temperature for each of these type of electrical loads. If I took a number of readings at different temperatures, I would be able to plot how the appliance usage varies with ambient temperature. Better efficiency would tilt the slope of the line. Better thermal boxes would not vary as much with ambient temperature. It is really ALL ABOUT INSULATION for thermal boxes. The more the better.

The nights here are still pretty warm. About the same as for the previous test 20C so this will qualify as a repeat for comparison. And to shake down the method. There were a few mistakes this time also.

Not as careful as I should have been, I see this morning that I left the Exterior Moisture Control ON last night. This switch activates a heater in the door gasket. I want that OFF! I had thought I left it OFF. I am going to put a piece of tape over the switch so that it stays OFF.

One thing I notice about the chart is that the fridge seems to be coming ON for shorter periods each time across the chart. I remember that my bedtime snack was a small dish of ice cream, so I had opened the freezer door about an hour before the chart. Its possible that the fridge was still recovering. I should make sure next time that the fridge has not been opened for at least several hours before the measurement.

The chart covers from about 22:30 to 01:30. The width of the peaks are 0.92cm, 0.80, 0.76 then 0.72. I am using cm as an analog for time. Time on the chart I measure to be 1.92cm = 1 hour.

The peaks also seem to drop down slightly, the first two are higher than the last two. I see that the base load drops about 25 watts at about midnight. I am not sure what turned OFF in the house. I was asleep. This is my whole house electrical usage so the fridge is riding on top of the base load.

Let's do some calculations anyway.

Here is the same chart in CorelDraw with the measurements added.

For the first two peaks, the fridge is using (275-125=) 150 watts and for the last two (250-100= 150 watts so the instantaneous power is the same as the last tests.

For the first peak, run time is 0.92 and cycle time is 1.84 so the duty cycle is (0.92/1.84=) 0.5. The second is (0.80/1.69=) 0.47. The third (0.76/1.65=) 0.46. I cannot calculate the fourth since I don't see the complete cycle. Doing the same calculation as before (power x time x duty cycle) I calculate for the three peaks 1.8, 1.69 and 1.66 kWh per day or 1088, 617 and 604 kWh per year. Quite a wide spread and more usage than before.

I know the insulation does not make the refrigerator use MORE power. Something about my measurement or the method is not right. And there was that dish of ice cream.

There must be an easier way to do this. I should let a computer monitor my energy use!

I am not discouraged.

Thanks for your interest

George Plhak
Lion's Head, Ontario, Canada

Update - The metal frame of the fridge where it touches the door gaskets is now covered with dew (condensation) so I see that the switch for Exterior Moisture Control really is activating heaters in the door frame. The dew isn't usually there. I wonder how much energy that takes and when the heaters come on? I think I remember reading that the heaters are activated by a time delay relay in the fridge that starts when the door is opened using the same switch that turns on the fridge light.

INDEX to the series


George Plhak said...

A friend commented:
I retired my mid 90's Wood's allfridge and was rated under 300kw/yr. It was replaced a year ago with an Amana with a similar rating but included a freezer section. The new one is saving energy due to the fact that the old one had failing gaskets. I got the new one since it had the old style fins on the back side.( I had been looking for one of these for years.) My old one did not have this feature, and when I added insulation to the sides of the box, the power usage went up considerably due to the fact that the cooling fins were built into the sides and the insulation slashed the efficiency by cutting off the ability to cool. In your case it might be better to get a new one, but if you want to improve the energy consumption, get one with the fins on the back and add insulating board on the sides. The energy consumption of any fridge is closely dependent on ambient temperatures which must be taken into account for any serious comparisons. Jim

George Plhak said...

Thanks Jim
My cooling fins are at the very bottom on the fridge. I learned from you.
Fins at the back are also easier to clean. Dusty fins reduce the heat transfer to the air. I get at mine, way down at the bottom once a year and also clean the fan. The fan cools the fins and the heat evaporates the water in the condensate tray. A more compact design with everything down at the bottom. The heat from my fridge comes out the front. Considering the fridge is using 150 watts when it is ON and it is only ON 50% of the time, the net heat is about 75 watts, which is not a lot. I am confident that I added insulation to the insulation which was already there.