A few weeks ago we were at Mingus Park on the Oregon Coast. Mingus Park is in a really, really hilly part of the coast; there’s not much of a flat spot anywhere near the park.
This is where we ended up parking for the first day. All day, about 8 hours. The back of the van was a good two feet higher than the front, way out of the most optimistic leveling requirements for a propane fridge.
Fortunately for us, we have a marine compressor fridge, rated to operate on a 30 degree heel indefinitely.
This got me thinking about the differences between compressor and propane fridges.
Compressor fridges use basically the same technology that your household fridge does – a refrigerant, R134A in most cases, a compressor, and a condenser and evaporator coils. If you have a fridge at home, you know how these work. Turn them on, and forget them.
- You can operate them on slopes that would kill a propane fridge.
- They cool down very quickly; my fridge just went from an internal temp of 33*C to -6*C in the freezer in a couple of hours.
- They maintain the temperature even when outside temps are broiling. I pulled my fridge the other day and had it running outside in direct sunshine; the exterior got too hot to touch (about 52*C according to my temp sensor) and the inside was still at 4*C.
- They’re smaller, lighter, and require less venting.
- They use up a lot of battery power. On a typical day, mine might use anywhere from 20Ah to 70Ah, between 20% and 80% of my battery reserves. Boondocking for more than two or three days is out of the question without solar panels or driving to recharge the batteries.
- The compressor makes noise. Very little noise, barely audible, to be truthful. (When was the last time you heard your household fridge?) Roadtrek uses Norcold fridges. The larger Norcolds use the Danfoss compressor, which runs at variable speeds, so the noise level goes up and down. The smaller Norcolds use the Sawafuji compressor. The Sawafuji compressors run at a single speed; their piston design is more of a thunk-thunk-thunk rather than the whirrrrrrrrrrrr of the Danfoss.
Propane fridges use ammonia as the coolant. The refrigerator works by separating and combining ammonia with water and hydrogen gas, using heat as the energy source for the process. The critical part is where the ammonia gas is recombined with the water; this takes place in the lower zigzag part of the plumbing (the black coil in the photo) and depends on gravity for the coolant flow. This is why you can’t use a propane fridge on steep slopes; the ammonia cycle is broken if it can’t flow down the tube in a continuous downhill path, and the fridge can sustain permanent damage if left running without coolant flow for a long enough period.
- Silent. They make no noise at all.
- They run on heat, not electricity, so they can run on propane as well as battery or alternator/generator/shore power.
- They run for (almost) ever on very little propane. A fridge can run for a couple of weeks on a single tank of propane.
- No moving parts. No fans, no pumps.
- They take a long time to cool down. Typically you have to start them the day before you leave.
- They can only maintain about a 20*C (40*F) to 30*C (60*F) differential between outside temp and fridge temp.
- You have to be reasonably level for them to work; extended operation outside their leveling requirements can result in permanent damage to the fridge.
- They’re heavier and require a fairly large amount of venting to the outside because of the propane.
- You need to switch them from propane to battery while traveling and fueling.
As with most things in a Class B, there is no right or wrong choice. If you’re a light sleeper and the noise would bother you, you should probably look at a model with a propane fridge. Or maybe you can get used to it. If you boondock a lot, then propane might be for you. Or you can get solar panels. If, on the other hand, you park in hilly places where flat ground is at a premium, then a compressor fridge might suit you better.
Due to the greater flexibility and more space saving design of compressor fridges and freezers, expect manufacturers to use them in more models as time goes on.