Dometic 1292 Fridge Power Consumption

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Heli_av8tor

Heli_av8tor

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Last month I installed the ?Amish? cooling unit. It?s cooling great but seems to be running all the time.

I put a Kill A Watt meter on the line to test. I ran the test for 4 days (95.33 hours). Total KWH = 36.92.
The fridge draws 442 watts when cooling.

This computes to running 88% of the time. Seems excessive and doesn?t leave much reserve capacity for hotter weather. High Temps during the test period were 75 to 85 degrees and the lows were 50 to 60 degree range.

Any thoughts?
 
Pretty typical for a larger absorption unit, in my experience.  The big box takes a lot of cooling and there is only so much that can be achieved with the amount of evaporator space available behind it.  That's one of the reasons why a residential performs so much better in the larger sizes.
 
Would it be beneficial to pack the box with maybe jugs of water or some such items?
Thoughts are that it's harder to cool and maintain temps and empty box rather than one that's full.
Of course it would be better if the items were already prechilled.

Corky

PS, I am assuming the OP isn't full time.
 
Though not full-timers we?ve been living in it since January 2nd. And the fridge is far from empty  ;)

The test was started several days after restocking so everything was at final temperatures.

Running about 34 degrees in the fridge side and 10 degrees in the freezer. We use a remote thermometer so the door is never opened to check temps.

We have full hook-ups available but prefer to run fridge on LP. That way solar meets all electric power requirements except when running the convention oven or W/D. I did the test on electric because our LP use seemed much higher than before replacing the cooling unit.
 
Heli_av8tor said:
our LP use seemed much higher than before replacing the cooling unit.
Click to expand...

That seems odd...

1 Have you used AC for the WH in the past?
2 Are you having to run the gas heat?
3 Are using more gas for the stove top?

I really don't know much about the ?Amish? cooling unit. So it may be normal.
 
Yes, it?s odd. I don?t have hard data on the change in LP usage. The 87% run time over 4 days is hard data.

Pre new cooling unit the furnace was run many mornings to take off the chill. Almost never since replacing the CU. The WH is on propane and its use hasn?t changed, nor has the stove. If anything other LP appliances were used less. Yet the LP tank is dropping faster than before.

Oh well, guess I?ll have to live with it.


 
I'm glad that I saw this thread, thanks for posting up your findings.
I have been pondering the purchase of the same unit as yours, but now I think more research on my part is needed.

Thanks again

Corky
 
IIRC, RV fridges when plugged in to 120v are power hogs.  This occurred when we were at a park for 4 months and had the old Dometic plugged in.  We were charged about $100+ a month for electric and I couldn't understand why.  Since it wasn't AC time and only minimal use of other electric appliances, it had to be the fridge.  Adding to the cost was the blended rate of electric charged by the park. 
 
I have read comments that absorption fridges just "sip" LP, and while that may be true with smaller units and in cooler weather, that certainly wasn't my experience with my Norcold 1210 in my previous rig last summer in AZ. The burner was like a small blowtorch running probably a 90% cycle similar to yours, and it burned a lot of propane
 
I think about how much cooling a 12,000 BTU ac unit would put out versus cooling a small fridge a bit colder and I am skeptical it is working at peak efficiency.  I don?t know much about absorptive cycles but I was under the impression previously that they weren?t bad, just a high cost high pressure system so avoided unless necessary.
I did see another Amish unit that replaced the absorptive system with a compressor unit but then you lose the propane option.
 
Heli_av8tor said:
I put a Kill A Watt meter on the line to test. I ran the test for 4 days (95.33 hours). Total KWH = 36.92.
The fridge draws 442 watts when cooling.
Click to expand...

36.92 kWh of heat energy directly converts to 12,597 BTU/hr.

Back2PA said:
I have read comments that absorption fridges just "sip" LP, and while that may be true with smaller units and in cooler weather, that certainly wasn't my experience with my Norcold 1210 in my previous rig last summer in AZ. The burner was like a small blowtorch running probably a 90% cycle similar to yours, and it burned a lot of propane
Click to expand...

A gallon of propane contains 92,000 BTU/hr.  Divide this into the 12,597 BTU/hr used over the 4 day test and and the above fridge will use about 0.14 gallons of propane over the same period of time.  That's about 1 gallon a month.

As to which energy source is the least expensive, a gallon of propane contains 28 times as much energy as a kilowatt-hour of electricity so just do the math. 

At 14 cents per kWh for electricity, propane's break-even point is $3.96 per gallon.
 
Lou, Thanks for taking the math to the next level. I didn?t have the energy equivalent figures and hadn?t yet taken the time to look them up.

Assuming your numbers are accurate my perception of propane usage is out of whack or I have a leak.
 
Lou, your number appears to be off by a decimal point.  This site https://www.rapidtables.com/convert/energy/kWh_to_BTU.html gets the same number but 10 times greater.  If correct, Tom's fridge should use 10 gallons of propane a month rather than  one.  So at 3.95 a gallon, Tom's cost would be 39.60 a month. 

Tom's actual usage of 36.92 kWh over 4 days is equivalent to 277 kWh's a month.  At .14 a kWh, the cost of electric would be $38.77.  That's comparable to propane at 3.95 a gallon. 

Tom, when checking my actual electric charge for the 4 months we were at a park, it was considerably less than $100.  Don't have the exact numbers but likely closer to $50.00 a month.  Our Domestic was the power hog.  So, that would be more in line with your usage. 
 
I haven't had time to check Lou's numbers myself. But slipping a decimal was common back when we used slide rules.

Lou, you're not still using yours are you?  ;)  ;D

Tom
 
Thanks, Gary.  It wouldn't be the first time I slipped a cog.

I'm on the road and used the calculator on my tablet, which is just one step up from  a slide rule.  Your numbers look more realistic, though much higher than I've seen using my single door Norcold and water heater.

Many thanks for the catch!
 
The entire calculation is suspect because it assumes the LP and electric heaters have the same efficiency.  Not likely, in my opinion.  I would be greatly surprised if the LP burner consumed more than 3-4 gallons/month.
 
I can't address the propane consumption, but when I replaced my RV fridge (large)  with a big residential my electric bill went down by at least $40 per month (up to four months history now).

Ernie
 
My fridge power usage was cut in half with the residential fridge.  Compressor wattage was somewhat less than the electric heat elements and the duty cycle much less. Despite the claims of Norcold and Dometic, their fridges are poorly insulated and the lack of air circulation inside creates hot spots that have to be compensated for with lower temperatures at the chill plates.
 
Gary RV_Wizard said:
My fridge power usage was cut in half with the residential fridge.  Compressor wattage was somewhat less than the electric heat elements and the duty cycle much less. Despite the claims of Norcold and Dometic, their fridges are poorly insulated and the lack of air circulation inside creates hot spots that have to be compensated for with lower temperatures at the chill plates.
Click to expand...

Compressor based refrigeration is inherently more efficient than absorption, just look at the amount of waste heat above and beyond the BTUs transferred  out of the box each type generates.

Norcold and Dometic refrigerators are meant to be installed in cabinetry while household refrigerators are designed for, and sometimes require, free airflow around their exterior skin. When mounted in a cabinet the refrigerator box itself only provides part of the total insulation, the rest comes from the surrounding cabinetry.  Every cabinet mounted refrigerator I've seen has had additional fiberglass insulation surrounding the fridge, installed by the RV manufacturer when they built the cabinetry.
 
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