6.7 Frig Tinkering ideas?

[KirkB]

Originally Posted by Floating Cloud

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

[float5]

Originally Posted by Brian B-P

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.

[float5]

Originally Posted by KirkB

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.

[Klem]

Originally Posted by jamie beers

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??

[dbailey]

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.

[jamman]

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

[cpaharley2008]

Originally Posted by jamman

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....

[Kountrykamper]

Originally Posted by jamman

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.

[Klem]

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.

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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.

[Klem]

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

[Patandlinda]

Originally Posted by Klem

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

Great ! Is Dometic waiting for our warranties to run out ?

[NJ Joe]

Originally Posted by Klem

Hi Joe,
Great idea, I can hang the yarn on plastic suction cups just like I did on our sail boats, that will bring back fond memories!

Amazing you can get the data logger that inexpensively, I hadn't thought of the RC aircraft suppliers. Maybe I can find turbo charger(s) to install in my new air box and duct

Thanks for sending off the picture, I've got til late January when the weather is good enough for our I-5 boogey to south Cali and then head east : )

Thanks! Mel

I did hear back from my aerospace resource. It turns out that it is not easy to model this since there has not been much study done of this particular problem. It looks like data collection of actual measurements is going to be the best approach.

[Parker]

Originally Posted by Patandlinda

Great ! Is Dometic waiting for our warranties to run out ?

They're doing a ton of work on our fridge right now, which I'll share when it's completed. Essentially, Dometic authorized the local RV shop where I first took the Escape for warranty service, to install a new cooling loop. I still believe that it's worth taking the Escapes in for warranty service (or complaints) while they're still covered. I don't really know if this is going to fix anything, but they are at least finally doing something.

[LeonW]

Originally Posted by Parker

They're doing a ton of work on our fridge right now, which I'll share when it's completed. Essentially, Dometic authorized the local RV shop where I first took the Escape for warranty service, to install a new cooling loop. I still believe that it's worth taking the Escapes in for warranty service (or complaints) while they're still covered. I don't really know if this is going to fix anything, but they are at least finally doing something.

Great news -- and I, for one, am very anxious to hear the result.

Leon

[Klem]

Originally Posted by Patandlinda

Great ! Is Dometic waiting for our warranties to run out ?

Before there was internet forums like this it was easier for manufacturers to put you off until you gave up ....

Reading this from 2007 will give you a glimpse at what Dometic is up against .. they are struggling to produce a fire safe refrigerator that still keeps your food as cold as required.

http://rx4rv.com/archives/21

I have spent a couple hours in the past two days talking to folks that really understand the problem(s) and have a few solutions. I will be mailing my cooling unit out next week to be tested and hopefully 'repaired'.

It looks promising to me.

[Klem]

Originally Posted by NJ Joe

I did hear back from my aerospace resource. It turns out that it is not easy to model this since there has not been much study done of this particular problem. It looks like data collection of actual measurements is going to be the best approach.

Thanks for checking Joe.

I'm feeling comfortable with my airflow at this time and am trying to do everything I can to make sure the cooling unit is as good as it can be.

Turning over rocks and finding interesting info ....

[Klem]

Originally Posted by Parker

They're doing a ton of work on our fridge right now, which I'll share when it's completed. Essentially, Dometic authorized the local RV shop where I first took the Escape for warranty service, to install a new cooling loop. I still believe that it's worth taking the Escapes in for warranty service (or complaints) while they're still covered. I don't really know if this is going to fix anything, but they are at least finally doing something.

Congratulations Parker! Great advice for others to pound Dometic, the problem can no longer be ignored by them!

[Jubal]

" I will be mailing my cooling unit out next week to be tested and hopefully 'repaired'."
Please provide details.

[Patandlinda]

Has anyone drilled holes in freezer compartment ? And had any improvement ?

[Vicki A.]

Mine is off to the shop on Wednesday, it will be interesting to see what Dometic tells to do.

Not only does it not cool when air temp is above 75*, the last night off Matagorda Madness I woke to find the alarm had gone off. Went to bed at 10:30, fridge temp was 38*, woke up at 2:30 a temp was 52*...no power on the 120 side. I figured it was too late to save the food, and I wasn't going out to turn on the gas, so I waited til morning. Turned on the gas and in 45 min the freezer temp started to fall but not the fridge. The shop guy just giggled when I said a fridge problem!