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Old 03-13-2016, 03:30 PM   #11
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Originally Posted by RamblerGuy View Post
Where did you get the information that the gas burner has more BTU'S than the electric heater? I haven't seen it.
I Googled a tech spec sheet showing a Dometic RM1282 inputs 2080 BTUH of propane. Assuming it's about 70% efficient at converting the energy input into cooling capacity, that would give about 1400 Btuh of cooling on gas.
Same sheet shows electric heater is a 210W heater. This converts to (210W x 3.4 Btuh/W) 714 Btuh. The electric heating element is probably close to 90% efficient, so about 643 Btuh of energy goes towards refrigeration.

So the gas provides about 2.5x as much cooling effort.

However, both the gas burner and the electric cycle on/off as controlled by the thermostat.

If the heat entering the food section (for this refrigerator) was less than about 643 Btuh, both can keep up, but the electric heating would be on for 2.5x as long as the gas burner would.

If the heat entering the food section was more that 643 Btuh, the electric element could not maintain temperature. The gas could maintain temperature as long as the heat entering the food section was less than about 1400 Btuh. Above the 1400 floor neither source can maintain box temperature.

All the other reefer specs I saw had about the same ratio between the gas input and heater watts.

Here's my take-away. If I start with a warm frig (or load it up with warm product), and I want it rapidly brought to set temperature - I should run the frig on gas. Once I have the box and food cooled, the electric should be able to hold it.

I'm going to take a look at my (RM135) manual and see if the "AUTO" control will monitor box temp and if it sees the electric is not holding temp, will it cut on the gas.
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Old 03-13-2016, 03:36 PM   #12
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Propane does a better job than electric.
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Old 03-13-2016, 03:46 PM   #13
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Gas gets it colder. Have had -7˚ on gas.
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Old 03-13-2016, 03:47 PM   #14
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Fans??? Diy?

This on the inside

And a couple of 120mm computer fans on the exterior.


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Old 03-13-2016, 03:58 PM   #15
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This on the inside

And a couple of 120mm computer fans on the exterior.


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I can see adding fans to the outside coils and even a circulating fan on the inside , what i see in your pic looks to be over kill in a big way . since those fins just pull the cold from the cooling plate i would think to much air on them would hurt the efficiency of the fins . IMO .
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Old 03-13-2016, 04:04 PM   #16
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"since those fins just pull the cold from the cooling plate i would think to much air on them would hurt the efficiency of the fin"

Would like to know the reasoning ??? Just asking.
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Old 03-13-2016, 04:07 PM   #17
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I can see adding fans to the outside coils and even a circulating fan on the inside , what i see in your pic looks to be over kill in a big way . since those fins just pull the cold from the cooling plate i would think to much air on them would hurt the efficiency of the fins . IMO .

It works and very well I might add!
Don't over think it.
5-10 degree difference.


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Old 03-13-2016, 04:42 PM   #18
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Those interior fans look great against the blue Dometic light. Many don't like them; I love the blue light.
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Old 03-13-2016, 06:10 PM   #19
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I have not tested my new Flagstaff with domestic fridge, however my winnie with a amish cooling unit and two fans in the chimney got colder on propane.
Hello,
I saw your post about fans in the chimney. How does one do that AND power them?
Thanks,
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Old 03-13-2016, 06:49 PM   #20
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Originally Posted by Stank Bait View Post
"since those fins just pull the cold from the cooling plate i would think to much air on them would hurt the efficiency of the fin"

Would like to know the reasoning ??? Just asking.
It circulates the air and keeps the fridge box at a constant temp, versus cold air on the bottom and warm air on the top. We did it on a TT a while back and ran an hour meter on the fridge circuit and it reduced the amount of time the element was on by a good 15%. This was at ambient temps in the 70's. I would suspect similar results on LP too.

Aaron
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