Refrigerator Cooling, Propane vs. Electric

The duty cycle on an absorption fridge with the door NEVER being opened is 2:3, or 16 hours per day. That was with an ambient temperature of 60 F.

Jim@HiTek wrote:


Two door refer, 1 person usage, 3 amp when calling for cold, 8 hours/day average On time (I avoid hot areas), $0.085/kWh rate. For me, it comes out to around $90 per year.

DrewE wrote:

Jim@HiTek wrote:
If you turn it off whenever you return from a trip, you'll likely get 7 to 10 years of useful life so I always leave mine plugged in and on all the time. The pluses for leaving it plugged in and running continuously (it's ready to go when you are!) far outweigh the minimal power usage. Your batteries are always ready too.

As far as which method cools fastest? Never saw a much of a difference those few times I had to shut it off. But my gut feeling is for my Dometic, gas was faster. Slightly. My Norcold? Seems faster with electric. I'd tend to agree that there's not enough difference to be concerned.

That "minimal power usage" of an RV fridge is somewhere in the rough vicinity of 2000 kWh per year, or perhaps $400 for the year depending on your electric rate. Maybe that's minimal to some people, but it's more than enough for me to shut it off when not in use and start it up (or do without) before taking a trip.

For a quick trip, I usually just toss perishable food into a cooler and dump in the ice from my (house) freezer.

From my calculations for my refer in my RV surviving my lifestyle, it isn't so high.

Two door refer, 1 person usage, 3 amp when calling for cold, 8 hours/day average On time (I avoid hot areas), $0.085/kWh rate. For me, it comes out to around $90 per year.

dougrainer wrote:
The BTU output of 120 and LP are almost identical. There are factors that affect how well and fast either source cools better. BUT, BOTH will be equal as long as all operational parameters are to spec.
1. 120 line voltage will affect 120 operation. Anything below 114 volts will not allow best 120 cooling.
2. LP gas pressure and the condition of the burner and burner Chimney will affect best LP cooling. Low(below 11 inches W/C) it will not cool as well. Dirty burner or Chimney will not allow the Heat BTU's to be efficient.
Last, for some reason some think because it is a HOT flame, it MUST cool better. NOT SO. The Flame itself cannot heat the boiler system to operational temps. So, ALL RV refers have a metal spiral baffle in the Chimney just above the flame. THAT spiral baffle causes the LP flame to disperse into a round heat source to heat the Boiler system efficiently. The 120 element is attached to that boiler system and is 6 to 8 inches long and transfers its heat directly to the boiler system. Remove that baffle and the LP would not cool at all. So, BOTH LP and 120 are even in cooling. A reason to run on LP would be if you have verified that the CG or source of 120 is below 114 volts. This may happen in areas where high RV usage and AC running has dropped the line voltage. Doug

Ding, ding, ding..........

Having done a "back yard" experiment I can say that my fridge takes about 6 hours of run time until the first cycle when running on 120 volts AC.

I agree with the 2000 KWH per year which is why I unplug when not in use.

k9dad wrote:
Question about refrigerator cooling during preparation for a trip. Does it cool faster when plugged into electric (in my driveway) or just leaving the propane on and cooling that way?
Thanks for any input.

The answer is ... Sometimes.

Ideally the fridge should cool at exactly the same speed on either Gas or Electric but in practice it is very hard to balance the two systems that close.. So one (and the only way to tell which is with a thermometer and a stop watch) will be faster.

Though the difference may be a good race. (that is 23 hours on one and 22:50 on the other kind of race).

Jim@HiTek wrote:
If you turn it off whenever you return from a trip, you'll likely get 7 to 10 years of useful life so I always leave mine plugged in and on all the time. The pluses for leaving it plugged in and running continuously (it's ready to go when you are!) far outweigh the minimal power usage. Your batteries are always ready too.

As far as which method cools fastest? Never saw a much of a difference those few times I had to shut it off. But my gut feeling is for my Dometic, gas was faster. Slightly. My Norcold? Seems faster with electric. I'd tend to agree that there's not enough difference to be concerned.

That "minimal power usage" of an RV fridge is somewhere in the rough vicinity of 2000 kWh per year, or perhaps $400 for the year depending on your electric rate. Maybe that's minimal to some people, but it's more than enough for me to shut it off when not in use and start it up (or do without) before taking a trip.

For a quick trip, I usually just toss perishable food into a cooler and dump in the ice from my (house) freezer.

If you turn it off whenever you return from a trip, you'll likely get 7 to 10 years of useful life so I always leave mine plugged in and on all the time. The pluses for leaving it plugged in and running continuously (it's ready to go when you are!) far outweigh the minimal power usage. Your batteries are always ready too.

As far as which method cools fastest? Never saw a much of a difference those few times I had to shut it off. But my gut feeling is for my Dometic, gas was faster. Slightly. My Norcold? Seems faster with electric. I'd tend to agree that there's not enough difference to be concerned.

Good question.
I don't know. I have never cooled the refrigerator on propane. I use electricity to cool it down before a trip.
I'm guessing there is not enough difference in cooling time to be concerned.

The BTU output of 120 and LP are almost identical. There are factors that affect how well and fast either source cools better. BUT, BOTH will be equal as long as all operational parameters are to spec.
1. 120 line voltage will affect 120 operation. Anything below 114 volts will not allow best 120 cooling.
2. LP gas pressure and the condition of the burner and burner Chimney will affect best LP cooling. Low(below 11 inches W/C) it will not cool as well. Dirty burner or Chimney will not allow the Heat BTU's to be efficient.
Last, for some reason some think because it is a HOT flame, it MUST cool better. NOT SO. The Flame itself cannot heat the boiler system to operational temps. So, ALL RV refers have a metal spiral baffle in the Chimney just above the flame. THAT spiral baffle causes the LP flame to disperse into a round heat source to heat the Boiler system efficiently. The 120 element is attached to that boiler system and is 6 to 8 inches long and transfers its heat directly to the boiler system. Remove that baffle and the LP would not cool at all. So, BOTH LP and 120 are even in cooling. A reason to run on LP would be if you have verified that the CG or source of 120 is below 114 volts. This may happen in areas where high RV usage and AC running has dropped the line voltage. Doug

My Dometic doesn't seem to care which power source is used for the initial cool down or at any time as far as I can tell. Earlier this year I used my IR gun to see which started heating the fastest but checking the temp of the burner tube over the course of an hour No significant difference as I recall. Since the electric is easier for me in the barn, that's what I go with. 24 hours and the fridge is at 32 or lower.

Mine does't have the ice maker so that might makes a small difference.