Keeping a refrigerator in an off grid environment is a challenge and expense. In this series, we cover our experience with several units. In the previous Tips 2 & 3, we spoke of the new Frigidaire unit, here I’m seriously pleased to follow up on that last bonus tip with good power news
One of the more difficult parts of creating and living within your power budget is getting good power data to use. Yes you can “worst case it” by using UL power listed on appliances. The result, however, will be a moderate to largely exaggerated system budget. Yes, you will have more than enough power, yet the price tag may scare you away from your off grid move! So realistic power numbers are crucial.
What is the duty cycle of a refrigerator? Its the percentage of time that the compressor is on versus off. The worst case assumption is to assume 100%, or that it is on all the time. You could assume 50%, but again, its just a guess. The duty cycle will be affected by:
- Room temperature for the refrigerator
- How often, and how long either door is left open ( That is, how many kids and adults feeding from it)
- Quality and thickness of the refrigerator’s insulation
- How well the magnetic strips seal the doors closed
There are probably others, but those are the big ones that come to mind first. The good news here is that I recently purchased a P4400 “Kill a Watt Monitor for measuring power. Below we start with a real refrigerator model, and a real family of 4 and a 24 hour measurement period. Without further delay, here are the initial facts:
- Frigidaire 18 cubic foot freezer/refrigerator (ice maker not used)
[ Label inside reads Electrolux model FRT18IL6JW1 ]
- Measurement time of 24.67 hours. Timer has unit off 7hrs at night.
- Power measured was 640 Watt Hours total. 115-130W when compressor running, 44W light when door open.
- Test conditions: “Normal” family of 4, 2 adults, 2 teens. Kitchen temperature mostly 65F since winter.
Ok, what does all the data mean? Well if we did the worst case calculation, and ignore the light inside, we get 24hr x 130W or a total of 3120 WH. So if you left the door open, or took it off, that’s the power required in your budget.
What about our 50% duty cycle? Still you would have 1560 WH on your budget! The actual measured value of 640 WH is less than half of that. How much power do we save simply by using the timer to turn it off at night? If you 640 WH adn divide it by the actual 17.67 hours of plugged in time, you get 869 WH. You save and 229 WH every day, by simply using the timer at night!
Now this is not a perfect number, but much better. I would guess that in the summer the value might be somewhat higher because the kitchen temperature can be 80F sometimes in August. We’ll have to revisit this measurement this summer to provide you with the best possible information!
- UPDATE note: The freezer part of the unit was about 85% full with frozen blueberries. This helps the freezer hold its temperature during the nightly power off time. In a similar way the refrigerator was moderately full too. I’m certain if we tried this with everything empty the results would be worse.
[Note: The series continues with the updated refrigerator data]
Was this information helpful? What do or would you use for your off grid fridge? What’s your experience? Please share your thoughts in the comment section below: