Ammonia versus Compressor Fridge...

[SidecarFlip]

After all the talk about Danfoss compressor fridges and how much better they were than the old school Ammonia Units, I decided to 'fiddle with mine and do a long term test using a remote digital recording thermometer.

First thng I did was open up the rear cavity. My fridge is a side vent, that is, not through the roof, intake low (with plumbing and control board) and the upper vent vertical on the side of the camper at the height of the top of the fridge.

I opened it up and removed the one small 12 volt muffin fan Suburban had installed. It was a cheapo sleeve bearing fan, very noisy. I replaced it with 2 Fluid Dynamic Bearing 120 MMM high flow computer fans (23 bucks, E-bay. Had to make up a set of brackets as I wanted the fans as close to the upper condenser as possible. Suburban has already installed a snap action thermostat (on at 90 off at 70) so I wired both into the existing thermostat.

I also added a lot of R13 unfaced insulation between the fridge and the cabinet. I actually stuffed almost 1/2 roll in. Plenty now.

I also fabricated an upper baffle that fits tight against the back of the upper condenser and screws into the camper side,inside, effectively channeling the air flow with no turbulence as it passes through the condenser.

I took a full 20 pound bottle of propane (valved off my second bottle) and set the fridge on gas only (it is shore powered sitting in the yard.)

So far, it's been running for 3 weeks straight on that bottle, I'm expecting over a month. Amp draw with the fans running is 1.8 amps, with the fans off. .2 amps..Temperature swings (day and night) (and the camper gets the afternoon sun on the fridge side) is 4 degrees.

Last year I had to run the fridge on setting 5 to maintain 40 in the compartment. It't drifting between 33 and 36 inside now..... on setting 2...

I measured the cool down time from ambient as well. It took exactly 3 hours from ambient to 33 degrees.

Still chugging along out there as I post this. When it runs out of propane, I'll post it.

If it ever dies, I'll install a Danfoss unit but for now the old school fridge appears to be doing well.

[Kayteg1]

SidecarFlip wrote:
Looks to me like your 14 year old fridge is doing fine....

Yeah, even I knew the fridge is good, I am impressed having negative F in freezer with 100F all around.
Refrigerator side could use some boost, so I will check for that.
One note I forgot to add, the camper sits on north side of the house, so between 1 pm and 5 PM it is getting some shade.
You can see some results on fridge performance.
Also propane seem to give me couple degrees less, than 120V, but that is minimal.
Bottom line >>> ammonia freezer can give you 0F with 100F outside.

[SidecarFlip]

Looks to me like your 14 year old fridge is doing fine....

[Kayteg1]

TEST RESULTS
This is for my Dometic 6cu-ft 3-way refrigerator with separate freezer door. About 14 years old.
Rated 1500 BTU/hr
2.7 amp @120v=324W
18 amp @12v = 216W
Actual consumption @120v was 400W at start, 350W later
Loaded with 2 gallons of juice in refrigerator and 2l of water in freezer. All started at 80F
I open the door for few seconds for readouts, what I think makes it real life test.
1st row is time, amb=ambient temp come from my roof-mounted weather station, inside measured on countertop.
fd/rf is temp next to juice in refrigerator, measured with stick thermometer.
flr/fr is freezer floor measured with stick thermometer.
fd/fr is temp of water in the clear bottle measured with infra-red, what is not very accurate, so take it with 😉
tm-amb-ins-fd/rf-flr/fr-fd/fr
12--80--80--80----80----80
1---87--84--78----64----80
2---90--86--78----35----71
3---91--88--74----23----55
4---94--90--69----17----46
5---94--90--68----13----36
6---92--90--64-----8----32
7---93--90--63-----9----32
8---89--89--57----12----36
10--79--85--55-----8----32 (water froze)
6---64--74--47----10----32 ......day 2
9---76--75--45-----9----26 (thermostat cycled off)
10--87--78--40-----0----15
12--94--87--42-----5----18
1---99--90--40-----2----13
4--103--96--39-----0-----6
5--104--94--40-----0-----3
6--100--96--40-----0-----1
8---93--95--40---(-5)----1
10--88--92--34---(-3)----4
turned off for the night/switched to propane
6---77--82--50----40----40..... day 3
7---77--82--50----30----36
9---86--85--48-----5----24
11--88--89--50-----2----11
12--92--92--55-----0----11
1---95--94--55-----0-----7
3--102--97--50---(-2)----2
4--103--98--50---(-2)----2
5--103--99--52---(-6)----1
7---99--99--50---(-5)----0

[Kayteg1]

Don't know about the same.
I was taking older RV refrigerator apart and 120V element was 180W, the 12V element was 140W.
I just measure the 120V element in my camper and it draws almost 400W.
Can't measure propane, but 400W is serious heater for small fridge.
Running the first series of tests right now. Stay tuned.

[Old-Biscuit]

Propane and electric are 'equivalent' in heat transfer
Propane flame is roughly 18*F hotter then electric element BUT propane flame is radiate heat transfer via spiral baffle---electric is conduction (direct contact)

Same/same

Propane can 'start' cooling process a bit quicker due to flame 'heating' up perk tube quicker but once process is started (ammonia liquid to vapor) electric and propane same.

[pianotuna]

Hi Jeff,

I see little difference between cool down between propane and electric. Have you done actual measurements?

[SCVJeff]

jimh425 wrote:

SCVJeff wrote:
where exactly can I find AC?

Your diesel pusher probably has a generator, so you have it near you all of the time. 🙂

whats the point? Heat is heat, in fact the fridge is more efficient on LP. That's why speed cooling on startup is always done on LP

[jimh406]

SCVJeff wrote:
where exactly can I find AC?

Your diesel pusher probably has a generator, so you have it near you all of the time. 🙂

[SCVJeff]

jimh425 wrote:
I don't usually camp when it is that hot unless I've got AC running. I'm a bit surprised that those of you using propane at 100. Why not use AC mode?

where exactly can I find AC?

[SidecarFlip]

Kayteg1 wrote:
With HVAC the biggest issue is insulation.
I do have one of those 7 foot tall fridge/freezer at home and it does use the same size compressor the 5 footer does, yet the huge freezer goes below 0F easy.
I assume the insulation and door gaskets is playing huge role here.
Just for the sake of it, we are expecting 100F this weekend.
I will start my ammonia refrigerator and see how low it will go.
My plan is to start it before noon in full heat and time it.
Any other suggestion for the test?

If the board is Thermister controlled, you can only get the refrigerator section to around 32-34 no matter what you do unless you get one of those adjustable 'snip the top' Thermister replacements. Stock Thermisters will start to cycle the propane to the burner at that 32-34 temp.

Do a 'dollar bill test' on the door gaskets. If you can easily pull the bill out (no effort) with the door closed and latched, it's either door gasket time or adjustment time. You want good resistance to the bill coming out.

Door gaskets tend to take a 'set' after a while and not seal tightly but there is a fix straight from the Dometic Shop manual and I haven't tried it because my fridge is pretty new but...

You can take s some insulation and roll it up and place it between the gasket and the fridge door and the heat the gasket with a blow dryer and let it cool. That will cause the gasket to assume the shape of the insulation wad behind it and seal properly.. I would assume that would apply to any RV Fridge, ammonia or compressor.

Right out of the Dometic manual. I'd do the bill test first to see it it seals properly however.

Probably work for a home fridge as well.

[BadgerMcAdams]

jimh425 wrote:

BadgerMcAdams wrote:
Where we camp, they don't have the new Tree to AC adapters yet...

Do they have the generator to camper adapters? 😉 I'm assuming it cools off at night.

Just picked up a generator over the winter, so it will have to do until they get the new Tree upgrades done 😉 LOL, I have wanted to get some cheap electrical boxes and nail them to trees as a joke.

"Oh Look dear, they have electricity here!"...Yeah, I know, I'm not right.

Yeah, the fridge cools down at night, but I think that adding the additional insulation around the box should help keep the internal temp from rising as much as quickly as it does.

I will eventually sell the TC...The wife is wanting a TT. But until then I want to try and get it working as well as possible. Considering I only paid $400 for it off of Craigslist, I think I have got my money's worth out of it, and minor upgrades can't hurt when I eventually sell it.

[pianotuna]

Put a gallon of water in the freezer, and 2 gallons in the fridge.

Monitor the temperature remotely so the doors don't need to be opened and note the figures on an hourly basis. ambient, inside RV, fridge, and freezer.

If you run just the fridge on electric and route the power through a kill-a-watt meter, some information will become available about duty cycle. My back yard experiments indicated 2:3 with no connection to the ambient temperature once the fridge had finished cooling down.

Thanks for offering to do this.

Kayteg1 wrote:
With HVAC the biggest issue is insulation.
I do have one of those 7 foot tall fridge/freezer at home and it does use the same size compressor the 5 footer does, yet the huge freezer goes below 0F easy.
I assume the insulation and door gaskets is playing huge role here.
Just for the sake of it, we are expecting 100F this weekend.
I will start my ammonia refrigerator and see how low it will go.
My plan is to start it before noon in full heat and time it.
Any other suggestion for the test?

[jimh406]

Try it empty and full.

[Kayteg1]

With HVAC the biggest issue is insulation.
I do have one of those 7 foot tall fridge/freezer at home and it does use the same size compressor the 5 footer does, yet the huge freezer goes below 0F easy.
I assume the insulation and door gaskets is playing huge role here.
Just for the sake of it, we are expecting 100F this weekend.
I will start my ammonia refrigerator and see how low it will go.
My plan is to start it before noon in full heat and time it.
Any other suggestion for the test?

[jimh406]

BadgerMcAdams wrote:
Where we camp, they don't have the new Tree to AC adapters yet...

Do they have the generator to camper adapters? 😉 I'm assuming it cools off at night.