3 Way Refrigerator Testing and Performance

MuttonChops

@grassgd ; Interesting and very detailed.  Thank you.

I've not decided how to correct the 'Tube Exhaust Extension' position issues caused by road travel vibration.  I do find your simple "extension" to the Tube Extension as a possible way to provide a base to firmly position the tube.

My rig has two 3-inch 12VDC fans at the upper vent grid but I still lack real-world experience on how helpful they are and when ambient temps are above 90F I really try to be at a full hook-ups site - - - more for A/C than to help the Fridge - - -

Your research method and data reporting is AAA grade.  Thanks again.

P.S.  After reading several of the TaB-400 Norcold 3-Way Fridge has been discontinued
posts. And a few posts on the energy demand of a compressor 2-way [DC, AC] I'm wondering if just getting a 2-way with Li-ion Batteries and a reasonable portable solar panel Wattage is not a better solution.

grassgd

George101 said:

Very much appreciate the data. I have the 180.3 and I have one 5 inch exhaust fan installed last year.   I’m experiencing worse temperatures with propane while running the fan.

yesterday running the fan my fridge got up to 59, with an outdoor temperature of around 96.  After running the fan all night it was still at 57.

this morning I turned the fan off around 7 and by 830 the fridge was 35.

today without the fan running at all the fridge went up to 49 with an outside temp of around 94.

all of this was with the fridge empty.

I found when testing on propane if I used the 4 1/2 inch fan on the lower vent with it blocked off (see below pic),  it did not cool just like you saw.  I think too much air cools the entire exposed/uninsulated system too much for the propane to heat the boiler up enough to boil the ammonia.  Thant's why I said in cooler or cold weather a fan may not be beneficial when on propane and may actually hurt.  To use a fan may actually involve having it controlled by a temperature sensor on ambient air or on the pipe coming out of the boiler to ensure you do not overwhelm the heat generated by the propane (I haven't proved this but suspect it).

 

One of my original thoughts was to provide fan cooling to the condenser only but without pulling the unit out to build an air duck to have a fan flow blow ambient air from the lower vent opening and pass only over the condenser.  I tried a couple simple attempts to replicate this but not been able to isolate air to the condenser like I think it needs to be without cooling other parts of the system.

The arrangement shown above cooled great on 120 v, in 95 degree temps I saw max refrigerator temp of 25 degrees and low temp of 17 degrees at night with mid 70 degree ambient.

At the end of the day I may give up too like others have and change the unit too.  

grassgd

webers3 said:

Temp from 25 to 45 is what I had in my 3 way without doing any mods. I either had a frozen food or spoiled food. Your mods and tests are a commendable effort but I am afraid exercise in futility. I finally decided that I  had better things to do when camping than babysit the fridge. 

I agree the last thing we want to do is babysit the fridge. 

Having some past experience with process engineering, I am sure if one knew the proper operating parameters - required temperature ranges for each part of the refrigeration system, one would know how to provide proper cooling to make the unit work like it should.  That's why I believed cooling of the condenser would be the best place to start, but that is not easy to do without pulling the unit out to install some duck work to do that. 

Switching to a compressor frig sounds good but presents additional requirements for batteries and solar charging for extended boondocking. I  have a 120 watt solar panel and that has been enough when boondocking and running the Adle, lights and water pump but not sure if it could handle additions recharging of refrigerator requirements.

Denny16

Our 193- watt solar panels keeps the battery charge whilst running a compressor type AC/DC fridge.  You might need to get at least a 100,Al Holston AGM or Lithium battery, and add an additional 100-watt portable solar panel.
 Cheers 

johnfconway

webers3 said:

Temp from 25 to 45 is what I had in my 3 way without doing any mods. I either had a frozen food or spoiled food. Your mods and tests are a commendable effort but I am afraid exercise in futility. I finally decided that I  had better things to do when camping than babysit the fridge. 

It's possible that NuCamp does indeed peruse these posts. Based on what's been posted by owners who measured refrigerator performance in moderately hot to very hot trailer cabin temperatures while boondocking, they may have come to the conclusion that selling trailers with refrigerators that cannot keep food at a safe temperature is a lawsuit waiting to happen.

That said, if you're at 11,000 ft. elevation like @bergger, the 3-way may be just fine. If you take that trailer one state south and park it at 6000 ft., it's a whole different story.

grassgd

Denny16 said:

Out 193- watt solar panels keeps the battery charge whilst running a compressor type AC/DC fridge.  You might need to get at least a 100,Al Holston AGM or Lithium battery, and add an additional 100-watt portable solar panel.
 Cheers 

I am running a 81 amp hour led acid battery now with the 120 watt solar panel setup and currently use a full size Chevy Express van to pull my T@B 320s but was looking at getting a smaller vehicle.  If I need to haul multiple solar panels along, a smaller vehicle may not work or may need to pull a supply trailer in tandem to haul solar panels!

Just kidding........but this is really frustrating.  There must be a way to get these propane refrigerators to work properly and dependably.  I can't help thinking it has to be getting the proper cooling where need (I suspect to the condenser only) but varied cooling as the ambient air temperature changes.  As I've seen, too much cooling air while on propane and the unit stops cooling almost completely even with 90 degree plus ambient temps.

grassgd

Ended my testing yesterday - HOA says move off driveway so it's back in storage unit. 

Been looking at the data trying to make sense of anything with a focus on process temperatures readings with an IR multimeter and started looking at that data. I admit the data collection could be better with fixed temperature probes attached to fixed points vs handheld IR device plus recording the temperatures continuously Like I did with the refrigerator and ambient temperatures. 

I wanted to see if the refrigerator's ability to drop the temperature from ambient temperature as a function of the boiler temperature measured at the top pipe entering the slope pipe going to the condenser. I thought this would show if too much cooling was overwhelming the refrigerators heat input to be able to boil the water/ammonia liquid and stop cooling. Here is a graph:



I had hoped for a clearer trend with less data scatter.

Next looked at the condenser temperature's vs delta temperatures:



There seems to be a slight trend but a couple of extreme data points.

I did not see a perfect answer in the first two graphs although there seems to be a slight trend in each so I tried to look at the data to come up with something that would give a clearer picture. I decided to look at the refrigerator delta temperature vs the differential temperature of the boiler temperature minus the condenser temperature: 

This seems to confirm the best refrigerator performance is with the highest difference between the boiler temp and the condenser temp.  

Next step is to consider how to maximize this differential temperature.  Perhaps with auxiliary cooling to the condenser without cooling the rest of the system.  I tried doing this but could not isolate the condenser like it may need to be.

Any thought or comments would be helpful, but I am encouraged with these results but will need to continue working on this perhaps with better data collection and try to make a condenser cooler duct/vent system to test.

Denny16

@grassgd, whilst the test results of you 3-way fridge is interesting, I think the best option is to upgrade to a 100AH lithium battery, which your existing 120-watt solar should keep up with.  Then (this ismrhe hardest part), part ways with the 3-way fridge, and install the new AC/DC Isotherm Cruise compressor fridge, nüCamp is currently using in the TaB320.  The 100AH lithium will power this fridge  quite easily, and your existing solar setup should be able to makeup the draw from the fridge’s overnight draw.  Then you can get some sleep, knowing your food is safe.
 Cheers 

webers3

@grassgd I agree with @Denny16, I’ve done it, my ICECO works great with lithium, set the temp and forget it. If you do give up your 3 way you’ll have to find something else to do to keep busy 😊

grassgd

One other thing I noticed during testing is the side vent cover deflects air exhausted down.   Bottom vent has air flowing in and upper vent air hot air exits out and downward.  When on natural venting (no fan assist) this doesn't seem to be a problem but with a fan pushing hot air out of the upper vent, the hot air has enough velocity to reach the lower vent air intake. 

Looking at the vent profile, the air is first deflected down on an angle then hits a vertical portion of the vent that forces the air directly down. 

Does anyone know the manufacturer of these side vents? 

If I install a fan in the upper vent opening, I would consider replacing the upper vent with a vent that doesn't have this profile which deflects the air down so much or modifying the existing vent to eliminate the vertical portion of the vent.

grassgd

Denny16 said:

@grassgd, I think the best option is to upgrade to a 100AH lithium battery, which your existing 120-watt solar should keep up with.  Then (this ismrhe hardest part), part ways with the 3-way fridge, and install the new AC/DC Isotherm Cruise compressor fridge, nüCamp is currently using in the TaB320.  The 100AH lithium will power this fridge  quite easily, and your existing solar setup should be able to makeup the draw from the fridge’s overnight draw.  Then you can get some sleep, knowing your food is safe.
 Cheers 

I may end up there, but I'm going to play with the 3 way a little more first. I am retired and like a challenge to keep me thinking anyway. 

With the testing I did, the unit can perform well on hot days, I saw that.  I just need to understand what causes it to not perform well on other days or times. 

There are many larger 3 way units in larger RV's that have more controls on them and I assume they perform well - or maybe the have the same problem, I don't know.  Apparently these larger unit have a better natural draft with the hot air exiting the roof and not on the side at the very top of the unit like on  the T@b 320s. My testing showed increasing the flue height with the temporary exhaust flue helped alot without adding fans or baffles, etc.

Grumpy_G

This seems to confirm the best refrigerator performance is with the highest difference between the boiler temp and the condenser temp.  

My old buddy Carnot agrees. My older 320 has the 3163 fridge which has the deck stacked against it: The whole burner, evaporator, condenser assembly is on the left side of the fridge which is the opposite side of where it optimally should be. There is basically no way for cool air to reach the condenser unless the AC is keeping the inside of the trailer cool. But then the fridge would run on AC as well which generates less overall heat. 

As I mostly camp without hookups I might try to route a little cooler air from under the trailer to the left side of the fridge. There is already a vent hole under the fridge but it's not doing much as there are so many other ways warm air can get to the condenser. Maybe another fan is in order. 

grassgd

George101 said:

Very much appreciate the data. I have the 180.3 and I have one 5 inch exhaust fan installed last year.   I’m experiencing worse temperatures with propane while running the fan.

yesterday running the fan my fridge got up to 59, with an outdoor temperature of around 96.  After running the fan all night it was still at 57.

this morning I turned the fan off around 7 and by 830 the fridge was 35.

today without the fan running at all the fridge went up to 49 with an outside temp of around 94.

all of this was with the fridge empty.

I saw this during my testing too.   

I may have said this earlier, I think the fan, especially one with a lot of air flow overwhelms the propane's ability to provide enough heat to boil the ammonia.  The fan is not only cooling the condenser but all the other exposed portions of the system so the liquid ammonia/water going back to the boiler gets too low.

When running on 120 volt power I saw the system perform fantastic with the large fan because I assume the 120 volt heater could provide sufficient heat to overcome the extra cooling of the system, not only cooling of the condenser.  Do you see the refrigerator cool very good with the 5 inch fan when on 120 volt power?

grassgd

It may be some time before I can perform addition test but the next time, I will try to use a 6 probe meat thermometer to record temperatures on the refrigerator to monitor the temperature out of the boiler, a couple temperatures on the condense, and the other 3 at various points on the absorption section and inlet to the boiler. This will be in addition to the ambient air and refrigerator internal temperature. Hopefully this will provide data to determine the temperature profile of the system when the unit is cooling good and not cooling good.   

I hope to make something to allow cooling of the condenser only with a cooling fan which hopefully will allow the propane to perform with the aid of additional cooling without putting too much load on the propane's heating ability and verify if my assumption on this is correct.

grassgd

Used the trailer in October without any additional testing or modifications and I am ready to cry "Uncle"!!!!!. The unit simply would not perform as it had in the past which was not great but we could get by.  This time we used it to store non refrigerated items and used an ice chest in the vehicle.   

Now I'm on the task of choosing a 12 volt compressor refrigerator to replace it.

dragonsdofly

@grassgd thanks for the update. A follow-up or determination is always appreciated. 

gulfarea

@grassgd I also have a 2019 320 and first thing I did was get rid of that gas refrigerator and am so happy I did! Art

rcarlson1957

Did a few things that helped with my 3 way frig in my 2018 T@B. 1 - installed dual fans on inside of exhaust vent with an external controller with pushbutton controls mounted by frig controls. Tapped into 12v power for the fans. 2 - put a battery powered fan inside the frig and use rechargeable batteries for it). 3 - installed a wireless Engbird Temp monitor I use with an app on my phone to keep tabs on the temp. 4 - I always precool frig day before initial departure and store a few frozen water bottles in frig. 5 - I run frig on 12v going down the road (after I replaced stock battery with lithium battery - it would kill a stock one before I got to camp). 6 - never back the frig too full so it has room internally for adequate air flow. 7 - cut strips of screen to go across each vent opening on both the intake and exhaust vents to keep the mud daubers out.