Propane vs. Electric Refrigerator Cooling Time

[Gary RV_Wizard]

What is a dual compressor refrigerator? Our 13 cu ft 12v fridge takes about 4 or 5 hours to cool enough to load.

An absorption-type"RV fridge" has a two-stage cooling unit, with separate chill plates in freezer and fridge. Those two chill plates directly cool their respective areas. To convert it to a compressor-type, two separate compressor loops is a good way to provide individual cooling to those chill plates.
However, a fridge designed for compressor cooling (aka a "residential fridge") typically has only one chill plate in the freezer and uses a thermostatically controlled fan to circulate chilled air from the freezer to the rest of the fridge. It only needs one compressor.

 

[meierjn]

Replace the cooling unit with a dual compressor one from JC Refrigeration. I did. It gets cold enough to make ice in 30 minutes. Seems perfect for your needs.

If you’re handy you can install it yourself. I paid ‘an expert’ to install mine and regretted it instantly.

My fridge was installed new last year. It works far better than the old/failing one that it replaced. They ain't cheap!

 

[meierjn]

I tried the frozen water jug and propane on Friday. The fridge seemed to cool down quicker. Thanks for all of your replies.

 

[Mark_K5LXP]

Looking at the specs for my Norcold fridge:

Electric element 300W, 1024Btu
Gas mode - 1500Btu

So, inferred that gas has the edge in terms of cooling energy and hence less time. Well, wonder and guess or measure and know. I have a temperature logger thing so over a couple of evenings I ran the fridge on electric and then on gas. I chose evenings because it's a tad cooler here and there wouldn't be any influence of sun on the RV. I started it at nominally 9PM and let it go overnight. The fridge is completely empty, set to 4, with the logging recorder on the center shelf.

The top graph is electric, bottom graph gas. On electric, it took about 7 hours to reach temperature, with gas it was around 11 hours (long red lines) and I'm not sure on gas if it ever reached the cold limit. The short red lines indicate where the power or gas was shut off. Nominal overnight temperature was around 80F.

So a few observations. At least with mine, the cooling time is absolutely less on electric, and actually goes into thermostatic control. So that could imply a burner problem, but just looking it seems OK (even blue flame). It's readily apparent that once the sun hits the side of the RV the fridge can't keep up. Nominal air temp when I shut the gas off (short red line) was low 100's, inside the RV was probably 10F more than that. So definitely worst case in terms of heat load but evidence that it might need some help in terms of a burner check and active coil cooling.

Another takeaway I learned is that this thing is no Yeti in terms of cold preservation. In just a matter of a couple hours the fridge was warming up and literally hot within 12 hours. Having contents in there would slow that down a lot, but a useful data point to know that especially during the heat of the day you don't want to leave this thing unpowered for very long.

I have a couple other experiments in mind, namely seeing if electric can keep up with heat load at 100F ambient and if a fan on the inside reduces cooling time.

Mark B.
Albuquerque, NM

 

[Gary RV_Wizard]

Interesting data, Mark, and thanks for running that experiment. Your fridge has a higher wattage electric heater than many, which probably helps electric performance.

I've always wondered just how ambient temperature affects cooling in an absorption fridge. The hotter it is, the easier to bring the coolant to a boil (less heat input needed), but the harder to condense it back to a liquid. And there must be a similar effect at the chill plates where there is another cycle of evaporation and condensation. We know from observation that cooling slows and even stops at some high ambient (100+?), and also at low ambients (near or below freezing)

 

[Mark_K5LXP]

I wouldn't have thought the electric side was different wattage than most. I can measure that with a meter but I have no way to measure gas pressure or volume. Just gotta base it on faith the regulator's good and the orifice/burner isn't gunked up. I've cleaned mud wasp nests out of there but the flame seemed OK. May take a closer look at that as gas mode is what we use the most when camped. I have a fridge thermometer in there and it's usually OK, but we don't ever camp in 100+ temps outside and even higher inside. Maybe the electric element couples to the boiler better than hot air from a flame. In any event I know I was close with a 6 hour head start plugged in, and works well enough to keep up in mid 80's ambient. From there I'd bet the next step would be fans in the condenser vent.

Mark B.
Albuquerque, NM

 

[Gary RV_Wizard]

Interesting that the lower btu electric heater is apparently delivering more heating btus to the boiler than the gas burner. It's in direct contact whereas the burner applies its flame under the plate at the bottom, so maybe more efficient heat transfer?

I wouldn't have thought the electric side was different wattage than most.

Perhaps it's the smaller cu ft fridges that have smaller heaters? For example, A Norcold 662/6052/8652 has a 200W electric and 1200 btu gas burner., but the 6062/8662 models has the 300W/1500 btu like yours. I never compared the heaters on various models before.

 

[Mark_K5LXP]

I've had my RV over 8 years and this is the first time I've looked at the fridge critically since I've had it. It's always worked "good enough" for what we need with nominal accommodation. If other units have notably less watts/Btu then it might explain why people post about having issues with their absorption fridges. From a basic physics standpoint the shortcoming I see isn't so much cooling capacity but limited insulation. No question it's a tradeoff of utility vs volume but I would've bet it could do better than it does keeping the heat out. It is what it is, but I still wouldn't trade it for power hungry compressor fridge for camping off grid.

Mark B.
Albuquerque, NM

 

[Professor David]

Interesting data, Mark, and thanks for running that experiment. Your fridge has a higher wattage electric heater than many, which probably helps electric performance.

I've always wondered just how ambient temperature affects cooling in an absorption fridge. The hotter it is, the easier to bring the coolant to a boil (less heat input needed), but the harder to condense it back to a liquid. And there must be a similar effect at the chill plates where there is another cycle of evaporation and condensation. We know from observation that cooling slows and even stops at some high ambient (100+?), and also at low ambients (near or below freezing)

Concerning w the high temps these days. We are expecting 104 here today and recently had a record hot day of 110 recently. My Norcold 1211IM is not working well at all. For future reference… At about what ambient temp will the unit just stop working? Actually, I think my unit is failing due to mechanical failure and will take it to a local shop for diagnostics tests tomorrow.

 

[RayIN]

It really increased my Norcold 1200LRIM efficiency when I zip-tied one of these to the bottom line of the cooling unit, point up towards the roof vent, so much so, I had to reduce the temperature setting by one notch to prevent milk from freezing in the bottom of the frig.

 

[gwinger]

It really increased my Norcold 1200LRIM efficiency when I zip-tied one of these to the bottom line of the cooling unit, point up towards the roof vent, so much so, I had to reduce the temperature setting by one notch to prevent milk from freezing in the bottom of the frig.

I'm getting ready to do basically the same thing. I have everything I need to get started. I am going to use a thermo-disc to control the fan. Thermo disc will be attached to the return line of the condenser chamber. The disc is rated at 130º "on" with 115º "off". That line seems to be the hottest part.
I will add a bypass switch so I can turn the fan on manually.

 

[Mark_K5LXP]

This 'heat dome' is giving me lots of fridge testing opportunities...

Ambient 103F around 5PM. Don't know the inside temp of the RV, it just flashes '99' above that point (never considered I'd normally be in there over 100F). This graph shows it goes out of regulation around 10AM and not back into regulation until around 4AM the next morning. Not a huge departure, rising to abut 42F but still demonstrating it can't keep up. I had a small fan blowing on the fins inside the fridge and it made zero difference in the initial cooldown time. If the heatwave continues to next week I may try an external fan blowing onto the condenser coil.

Mark B.
Albuquerque, NM

 

[meierjn]

Lots of good info here and suggestions with the responses to this thread. Please keep them coming. Thanks everyone!

 

[RayIN]

I'm getting ready to do basically the same thing. I have everything I need to get started. I am going to use a thermo-disc to control the fan. Thermo disc will be attached to the return line of the condenser chamber. The disc is rated at 130º "on" with 115º "off". That line seems to be the hottest part.
I will add a bypass switch so I can turn the fan on manually.

My fan is controlled by the ARP/Fridge Defend unit. This add-on device will turn off all power to the fridge if the boiler temperature rises about the safe limit, plus control the fan.

 

[Professor David]

It really increased my Norcold 1200LRIM efficiency when I zip-tied one of these to the bottom line of the cooling unit, point up towards the roof vent, so much so, I had to reduce the temperature setting by one notch to prevent milk from freezing in the bottom of the frig.

Installed two additional fans with temp sensors. One in lower access area and one up top. What a difference! 92 today. Had to turn the unit down 3 clicks. Unit was really struggling on hot days.

 

[Trivet]

I'm loving the data. Please keep it up.

I noticed that you used the specs for your refrigerator for the watts. I have a different refrigerator--a 1200LR, the one with four doors. The specs on the data plate say 660 watts, but I know for a fact that the heating elements are 450 watts--there are two of them, at 225 watts each. I assume the "additional" watts on the data plate are due to a defrost cycle that my Norcold has.

Have you confirmed that your heating element is 300 watts? You said you could measure the electric draw, but I'm not sure you actually have yet. A lot of people don't realize that what's on the data plate is the maximum possible (like on ours, extra for the defrost cycle), which is not necessarily the wattage it draws just running. But it could be if your refrigerator doesn't have a defrost cycle.

Also, about that fan on the fins--I've been experimenting, too, due to the extreme heat and my Norcold not making me super happy. I have a thermometer on the top shelf, right near the fins, and one on the bottom shelf, and I can't detect any effect of that fan when it comes to the temperature difference at the top and the bottom of the refrigerator. It does keep the fins from freezing up (which is not an issue when it's 105 degrees outside), but that's pretty much it.

What DOES affect the temperature at the bottom is if the thermometer is placed below something that's blocking air above it. Sometimes there was a 10-degree difference.