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Old 11-20-2014, 09:38 PM   #121
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Quote:
Originally Posted by Floating Cloud View Post
Does someone know if using a 6.7 cu. ft. refrigerator would use over 50% more propane than a 4.3 cu. ft. Under the same conditions? Or does it not work that way?
In the manual specs for RM8551 (4.3 cu ft) the propane usage is rated at 270g or 9.5 oz per day, and for the RML8551/5 (6.7 cu ft) 380g or 13.4 oz per day. This is based on 77*F or 25*C ambient temp. The increase is less than 50%.

This is from my hardcopy manual, dated 01/2012. The numbers match the specs from this manual I found online:

http://www.dometicmanuals.com/PROD/M...257408005D233C
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Old 11-20-2014, 09:49 PM   #122
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Originally Posted by Brian B-P View Post
More interior volume means more surface area, which means more heat coming in, which means more work for the cooling unit, which means more propane burned... so it basically does work this way. It isn't quite proportional to volume, though.

In the the best versions of Dometic spec sheets, the propane consumption is given (in grams per hour or grams per day), so this could be looked up... if you can find the right two models to compare.
That's what I wanted to know, if it is proportional to volume or would some other factor figure in heavily enough that that would not be the case. So the answer is yes, mostly proportional, from what you have said. Thanks.
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Old 11-20-2014, 10:16 PM   #123
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Quote:
Originally Posted by KirkB View Post
In the manual specs for RM8551 (4.3 cu ft) the propane usage is rated at 270g or 9.5 oz per day, and for the RML8551/5 (6.7 cu ft) 380g or 13.4 oz per day. This is based on 77*F or 25*C ambient temp. The increase is less than 50%.

This is from my hardcopy manual, dated 01/2012. The numbers match the specs from this manual I found online:

http://www.dometicmanuals.com/PROD/M...257408005D233C
KirKB, that is interesting. The 4.3 has 64% of the volume of the 6.7. The propane used by the 4.3 is 71% of that used by the 6.7. A little worse than I thought it would be for the 4.3. Thank you for those numbers.
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Old 11-21-2014, 12:15 AM   #124
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Originally Posted by jamie beers View Post
The new fridge performance was obviously superior enough for Reace to opt for the 2 door fridge. Any sort of anecdotes about how much better the 2 door fridge performed in hot weather?
Is the new fridge installed the same way as the ones recently with a baffle? Like the ones without a baffle? Or another iteration?

Logically the baffle will force whatever airflow is present into the coils etc. Without the baffle the airflow can just slide up through the unobstructed area and the air in the coils will be stagnant. The refrigerator does work fine at lower temperatures so everything that can be done to cool the air and force it through the coils is critical to performance.

In my case I'm also trying to increase the airflow volume and speed, and be able to 'force' it through the coils by tipping the fan which is installed below the coils.

For comparison we need actual measurements of the temperature behind the refrigerator vs the temperature in the refrigerator??
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Old 11-21-2014, 09:07 AM   #125
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When looking at efficiency, keep in mind that the rate of heat absorption is going to be proportional to the surface area, not the volume. The smaller fridge has a higher surface area to volume ratio so if the insulation is identical it will have a lower efficiency.
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Old 11-21-2014, 10:44 AM   #126
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IMO Dometic went too far in the effort to save money and build a less expensive product. I believe the cooling system (when running at max cool) is not adequate for temperatures in the 90s and up, even when properly installed. (It can be done, witness some older Dometics, it just takes a "better" cooling system and more energy input via propane or electricity.)

You can tweak the baffling to get a bit more performance out of it, cooler coils will work better.

You can tweak the fridge insulation (door, door seals) and installation (extra insulation around the top/side/back) to reduce the load a bit and get more "coolth".

And probably most importantly you can remove the freezer and use all the cooling to do much better in the fridge.

You can put on 2 doors
+ probably better insulated doors
+ don't need to open the fridge to get in the freezer
- can't convert to all fridge
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Old 11-21-2014, 10:46 AM   #127
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Quote:
Originally Posted by jamman View Post
IMO Dometic went too far in the effort to save money and build a less expensive product. I believe the cooling system (when running at max cool) is not adequate for temperatures in the 90s and up, even when properly installed. (It can be done, witness some older Dometics, it just takes a "better" cooling system and more energy input via propane or electricity.)

You can tweak the baffling to get a bit more performance out of it, cooler coils will work better.

You can tweak the fridge insulation (door, door seals) and installation (extra insulation around the top/side/back) to reduce the load a bit and get more "coolth".

And probably most importantly you can remove the freezer and use all the cooling to do much better in the fridge.

You can put on 2 doors
+ probably better insulated doors
+ don't need to open the fridge to get in the freezer
- can't convert to all fridge
All excellent observations....
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Old 11-21-2014, 08:46 PM   #128
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Originally Posted by jamman View Post

And probably most importantly you can remove the freezer and use all the cooling to do much better in the fridge.
Yelp, exactly my feelings. With the single door at least I have been able to make a good fridge by removing the freezer in warm weather and using all the cooling for the fridge. I hope the 2 door works better because loosing this option would leave you with no options.
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Old 11-23-2014, 09:31 PM   #129
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Posted elsewhere I want it to be available here too, good tinkerer advice!

Check everything before making a plan of what you are going to do. Every install can be different for various reasons and you need to look it all over and come to your own conclusions.


Understand what you are doing or wait until you, or the person doing the work, does.

----------
Each refrigerator manufacturer has published specific clearance specs for each of their models (Usually in the Owner's Manual). Make sure that these specs have been adhered to by your RV's manufacturer.


Attached Files
File Type: pdf Refrig Install Good Explanation by refrig guy.pdf (39.5 KB, 52 views)
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Old 12-12-2014, 11:14 PM   #130
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What may explain the wimpy 6.7 is simply it is a helium, ammonia and water frig instead of the hydrogen, ammonia and water like we have used for years. (It may not be but people much smarter then me have come to this conclusion)

The hydrogen has been blamed for fires and manufacturers have turned to helium for some models a few years ago. Helium was a second choice because it simply does not perform as well as hydrogen.

Manufacturers realize it and came up with innovative ideas like removal freezer cabinets to provide more cooling for the refrig area in warmer climates.

The helium absorption refrigs also have a narrower temperature band. So cooling the condenser is most critical.

With this belief I am installing more sophisticated fan control and burner protection. Too high, or low, temperature in the burner area can cause permanent degradation to the cooling performance in all absorption frigs.

Is the RMD8555 a hydrogen .... or a new mix? Some believe the manufacturers know the helium frigs are falling short of user requirements ....

Looking forward to finding some heat in February to test my assumptions
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