View Full Version : Fridge/freezer - converting watts/hr from winter to summer
December 10th, 2010, 5:45 PST
I decided to pull out the old Kill-A-Watt and do a checkup on some of my appliances. First up was my freezer. It is in my garage so it gets help during the winter but then fights the heat over the summer. This past week it has been fairly cold - 30's daytime, 20's or teens overnight. This time of year the garage only stays at most 10 degrees above ambient so it probably has been in the 20's, 30's and 40's.
I checked on it two years ago during the summer, but I didn't write the figures down of course. My average for this week was 22 watts/hour. My question is for those of you that have been more dilligent than me in keeping track of these numbers over the seasons, with a fridge or freezer in an unconditioned garage. With your freezer or fridge, what was the deviation from season to season? Am I looking at 25-30 watts/hour in the summer? I realize there are several variables - age of appliance, your min/max temps, etc. Just looking for a ballpark average.
December 10th, 2010, 10:45 PST
Freezers and refrigerators use a lot more power in hot weather...
Your 22 watts per hour? It would be 22 watts (no per hour). And your daily use at this time is:
22 watts * 24 hours = 528 Watt*Hours per day = 0.528 kWH per day
A very efficient standard size fridge/freezer will use around 1 kWH per day in a warm home (really rough estimate).
If you start making ice, the freezer will use more kWH per day.
December 10th, 2010, 12:13 PST
i think i should mention that when they publish the ratings on refrigerators that it is most likely based on not opening the doors at all so it goes downhill from there with how many times and for how long the doors are opened.
December 10th, 2010, 12:30 PST
This is one of those highly site-specific issues. My freezer at the old house is in the garage, but that garage barely gets warm in Summer due to its construction and location (shaded from sun). There is an increase in run time, but since the Winter there is also relatively mild the deviation is only about 15%. That freezer is also an old energy hog, so its consumption is high. A more energy efficient unit would consume less under "ideal" conditions, but might vary more (as a percentage) with change in temp.
Unfortunately the only figures that would work for you are going to be the ones you collect yourself.
Sorry that was of no help at all. :blush:
December 13th, 2010, 11:09 PST
bb - I did my outside fridge/freezer combo this weekend and it came out to 15 W-h. I haven't moved on to my inside fridge/freezer combo, so I'll post back when I get that figure. About watts vs. watts/hour, I believe I was wrong only in my label. I wasn't monitoring either the combo or the freezer when they were running so I can't tell you their instantaneous watt rating, I looked at the total watts and total time readings on the Kill-a-Watt for my W-h figures. I should have expressed it as W-h and not watt/hour. But not watts as you indicated.
niel - my freezer and outside combo are rarely opened, and the freezer is a chest model which replaced an upright we used to have, a change done to improve efficiency. The inside combo is another matter with constant use and ironically over the winter it has to work harder since it is about 15 feet from my wood stove.
'coot - no problem. Glad you could help. (grin)
I seem to remember that last time I checked all 3 (2 combos and the freezer I posted about above) the total figure was right around 1.5 kW per day, so once I measure the useage of my indoor combo I can at least compare to that number.
December 13th, 2010, 12:08 PST
Sorry to be such a stickler for lables... :blush:
The Kill-a-Watt has a Watts, Hours, Watt*Hour (and some others like VA, PF, Voltage, Frequency).
Watts is the rate---Like Miles per Hour. A refrigerator may run around 120 Watts (when the motor is running).
Watt*Hours is actually Watts*Time. This is like Miles driven and tells you how much energy you have used.
A 120 watt refrigerator that used 88 Watt*Hours (or 0.088 kWH) over a 4 hour period, averages out to 88WH/4H=22WH of energy consumption per hour (i.e., 22 watts average * 1 Hour). Or an average load of 22 watts.
This assumes that the 22/120 = 0.18 or 18% of the time (or about 11 minutes per hour).
December 14th, 2010, 5:22 PST
Fully understood, I've been an electronics hobbyist my whole life. My Dad couldn't wire up a circuit in our house to save his life, I was finding his mistakes when I was 12 (hey Dad, you know you can't cross the black wire and the white wire?). :D
December 14th, 2010, 8:24 PST
If you check the specs on any kind of standard refrigeration equipment you will see that they are rated for 55 to 95 degrees ambient temperature operation.
It all has to do with the refrigerant properties, at cold temperatures the refrigerant doesn't evaporate as well than at higher temps. and at the high end of the spectrum the refrigerant doesn't condense as well. Any time the equipment operates out of the specified temperature range power consumption will go up.
At the low end of the temperature range, refrigerant could condense in the compressor during the off cycle, upon startup the oil can be washed out of the compressor, or break internal parts( piston, rod, crank shaft etc) because liquid refrigerant does not compress.
The newer scroll compressors are more tolerent of this situation,manufactures are not using them in the small units yet.
If you are using refrigeration equipment in a cold environment you should add a crankcase heater. They are available in self regulating ceramic stick on from
Unfortunately they use additional power.
December 14th, 2010, 19:27 PST
My mother always told me a full fridge is more efficient than an empty one.
December 14th, 2010, 19:42 PST
that's no wives tale as that is true. an empty frig when opened will lose all of its cold air nearly instantly as it rolls straight out the bottom and warmer air entering from higher up. now items in a frig will block that air from exiting the frig and it takes longer for items to heat up that have already cooled.
December 14th, 2010, 19:43 PST
My mother always told me a full fridge is more efficient than an empty one.
Nope: it's true.
The empty (or less-full) 'frige/freezer has less internal mass than a full one. The greater mass will maintain temperature against change because it requires more energy to alter its temperature.
December 15th, 2010, 4:51 PST
LucMan - Well, so far the outside fridge has been out there for about 5 years and the freezer for about 2, no problems yet. I do have to adjust the fridge's internal temperature setting every winter and summer, colder in the winter or else things thaw in the freezer compartment (ironically), and warmer in the summer or else things in the fridge compartment freeze up.
My final reading on my my outside combo was 12 W-h, down from the initial 15. I believe the average outdoor temps dropped during the testing period which would account for the change. As of this morning after only 12 hours of testing my indoor combo was around 50 W-h. Ouch. But as I mentioned before it is only about 15-20 feet from my wood stove (a very large model which was opened all the way last night since temps were around 16 F), plus it has an ice maker. I'll report back with the long-term average in a day or two.
I am now considering making a radiant barrier shield for the fridge. I have plenty of radiant barrier in my garage so I could set up a proof-of-concept in a few minutes. In a final form I'm thinking of a simple wood frame of about 4' X 2', sitting about half-way between the fridge and stove. First I want to get some final numbers w/o any shielding, then I'll try the POC.
December 23rd, 2010, 10:42 PST
Final reading on my inside fridge combo = 51 W-h. Ouch again. Outside freezer was 22 and outside combo was 15, so a total of 88 W-h or 2112 watts each day. Obviously my indoor fridge is killing me, again I'm sure that's because of my wood stove. I'm off for 5 days so I'll rig up a heat shield in my spare time and see if that helps much.
What worries me is I think the last time I took all of these measurements (as I said earlier) I think my total was about 1500 watts. Now that I have all of the numbers above here where I can find them in 6 months, I'll have to do it all again and compare.
I'm now seriously considering creating an off-grid system to handle this load permanently, plus maybe a whole-house ventillator that runs 24/7 (about another 50 W-h, but I haven't checked it with the Kill-a-Watt in a while). So that would be about 3312 watts, times 2 for system losses, 6624, divided by my average winter insolation, 3.5, equals a solar array of at least 1890 watts. Which leaves me with a large margin over the summer. Sound about right?
I already have a 22 kW battery bank and could get by with a 250 watt inverter. I believe there is one about that size on NAWS which also has a secondary AC input, I need to check. I have a 6 kw inverter but that is way too big for this job. My biggest issue is dealing with a 250-foot run and installing the array. I've talked in the past here about going for a 10 kW array but my other half has other home improvements on her priority list right now. I might be able to convince her on a 2 kw array for now. :-)
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