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Old 09-27-2017, 12:21 PM   #1
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Refrigerator Test

Too many refrigerator threads out there to decide where to post this so decided to start new. Many of us continue to struggle with the absorption refrigerator performance in high ambient temperatures. After marginal to poor refrigerator temps the past two trips I'm now conducting a test of increased airflow across the condenser while stationary. Freezer has been ok. I think the freezer is fine because the liquid ammonia passes through that evaporator first and then through the refrigerator evaporator (in series). My theory is if there is not enough liquid ammonia being generated at the condenser due to poor airflow (stagnation of the air column behind the fridge) then the freezer is using it all to make set point and the refrigerator section is suffering further down the line. This is an older 19 with single door Dometic RM2510 fridge (5 CF) with the sidewall venting at both bottom and top. It does not have an auxiliary "Texas" fan from the factory. I have read that these fans (sometimes factory supplied or aftermarket add-ons) can help, but I'm not convinced the tiny computer fans typically supplied are enough volume. I currently am trying a larger 12" fan with 3 speeds (12V Fantastic Endless Breeze model) sealed externally to the top louver and monitoring fridge and freezer temperatures with Accurite system. Outside temperature about 85 and should near 90 in the next couple of hours. I'll report back with results.

It is interesting to note that when you read the Dometic installation manual closely and utilize sidewall venting both top and bottom it should have included their Innovator fan system. It should also have a curved baffle at the top to guide the warm air out of the top louver and not allow it to get trapped above. I have to look closer to see if a baffle is needed based on the actual configuration at the top (it is hard to see without removing the top louver).
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Old 09-27-2017, 12:51 PM   #2
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not enough liquid ammonia being generated at the condenser due to poor airflow (stagnation of the air column behind the fridge)
I agree that poor air flow is most likely the culprit. I'm don't blame stagnation as much as very poor circulation due to the turbulence created by the minefield of obstructions on the back of the fridge.

At any rate, with my ducted baffles "straightening out" the air flow and a dedicated hot exhaust flue my fridge works well. I'll be interested to see your results with the change in fan etc.


Ron
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Old 09-27-2017, 01:52 PM   #3
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Originally Posted by Ron in BC View Post
I agree that poor air flow is most likely the culprit. I'm don't blame stagnation as much as very poor circulation due to the turbulence created by the minefield of obstructions on the back of the fridge.

At any rate, with my ducted baffles "straightening out" the air flow and a dedicated hot exhaust flue my fridge works well. I'll be interested to see your results with the change in fan etc.


Ron
Ron: I've caught bits and pieces of your work from other posts. Can you remind me what your fridge model is, venting configuration (top outlet vs. side?) and the hottest ambient that you have encountered where the fridge still worked well?

Please provide more info on the dedicated hot exhaust flue. Is this something that would need to be taken through the roof?

Thanks.
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Old 09-27-2017, 02:44 PM   #4
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Since you have a Dometic RM2510 fridge (5 CF) with the sidewall venting you might want to view this (very long) thread on the Casita Forum. https://www.casitaforum.com/invboard...ge-run-better/ They have done extensive testing with the smaller side vented units and come up with some solutions for better operation. Most recent refrigerator threads here are dealing with the top vented 6 cu ft. RM?-855? and its issues.
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Old 09-27-2017, 05:25 PM   #5
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Originally Posted by rubicon327 View Post
Ron: I've caught bits and pieces of your work from other posts. Can you remind me what your fridge model is, venting configuration (top outlet vs. side?) and the hottest ambient that you have encountered where the fridge still worked well?

Please provide more info on the dedicated hot exhaust flue. Is this something that would need to be taken through the roof?

Thanks.
My fridge is the RM8551. The top vent is on the roof. Hottest ambient temperature? Well some days in Baja can be pretty warm but I never measured the outside temperature, just went for a swim instead. This summer crossing Montana I know it was about a 100 F. We had frozen food across Canada and back through the U.S. Except for a few nights when we were plugged in we ran the fridge on propane.

Several folks were trying to improve their cooling and since I had my fridge out I did a couple of mods of my own design.

1. I removed the rear baffle and packed the cavity between the f.g. sidewall and the baffle with foam. Much better for those days when the sun is beating down on the exterior.

2. I replaced the plywood baffle with an aluminum one. It has three vertical fins. Two of them "straighten out" the turbulent air flow caused by the multiple protrusions on the back of the fridge. The 3rd separates the hot exhaust flues from the vicinity of the condenser. The condenser should be getting cooling air, not hot exhaust.

In other parts of the world Dometic fridges used in hot climates receive the exterior venting flue.

Others have used other means to duct the hot exhaust away from the condenser. Whether I'm just lucky or it was one specific item that I did, I don't know but I'm happy with the result.

Ron

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Old 09-27-2017, 06:22 PM   #6
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Originally Posted by Ron in BC View Post
.

2. I replaced the plywood baffle with an aluminum one. It has three vertical fins. Two of them "straighten out" the turbulent air flow caused by the multiple protrusions on the back of the fridge. The 3rd separates the hot exhaust flues from the vicinity of the condenser. The condenser should be getting cooling air, not hot exhaust.

In other parts of the world Dometic fridges used in hot climates receive the exterior venting flue.
Ron
Hi Ron, I found your post with a picture of the aluminum baffle, that looks real effective! You mention the exterior flue, have you installed one? (I see you mention it and have a picture on another post so just checking)

Thx Mel K
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Old 09-27-2017, 06:37 PM   #7
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No, I don't have one. I discovered that they exist when I was already doing my mods. I inquired to Dometic North America and they basically seemed to indicate that they didn't know of any such vent. I sent an inquiry to Dometic Australia but they were very slow to respond. By then I'd given up waiting and decided to make the baffle fins act as a dedicated flue area for the hot exhaust.

Had that flue been available I certainly would have installed one. I'm happy that my substitute method is also giving me good results. I guess anything that keeps the hot flue gases away from the condenser is an improvement on the original.

Ron
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Old 09-27-2017, 11:24 PM   #8
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Ron
I looked through your old posts and the baffle makes a lot of sense to me. What would you estimate is the distance (clearance) between your baffle edge and the refrigerator backplane and/or pipes etc?

Looks like I'll pull the frig this winter and add insulation and a baffle!

Thx, Mel K
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Old 09-28-2017, 08:04 AM   #9
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Preliminary results

Started the test yesterday with fridge already on propane coming off a recent trip. Aux fan hooked up. Dismal fridge temp of 66F and freezer at 23F around 1pm with outside temp at 88F. By 4:15pm fridge temp went UP to 73 and freezer to 30. Baffled. Something isn’t right. Confirmed that I have good airflow through the rear enclosure. Changed over to ELECTRIC mode setting “5”. By 9:30pm fridge was 57F and freezer 9F. Turned it to “max” setting. Going in the right direction. This morning fridge was 33F and freezer -8F. Liking those temperatures. Overnight temp was around 65F so that helped some of course. My aux ran the whole night. So it seems electric mode works ok which agrees with driveway performance before leaving for trips. Many times where we camp there are no hook ups and the weather can get hot so I need to get better performance on propane in warm weather. I have read some of the Casita and fiberglassRV posts and it’s usually lack of airflow across the condenser or propane regulator that is cited as probable causes.

Moving forward:
Since propane regulator is over 7 years old should I replace due to possible low pressure? Maybe I should measure first to confirm. What regulators are folks happy with? Marshall Excelsior MEGR-253 is what I hear a lot about. I think it is what I have now.

In concept propane with higher BTU is supposed to allow fridge to perform better. As stated above I need to confirm proper pressure first. I might have a bright blue flame, but it could be weaker than it should be. I also agree with Ron that there is excess heat from the flue that can’t be discounted. I will look closer at doing a better baffle around the condenser and arranging a divider of some sort so that hot flue gas is not interfering with condenser cooling.

Any further thoughts are appreciated.
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Old 09-28-2017, 09:39 AM   #10
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I think the fan maybe interfering with the cooling differential between the freezer and refer, if you turn the fan off, the differential may decrease quicker. Is the unit full or empty?
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