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Comment by jakedata | Hacker News Reader

My non-electric refrigerator operates along similar lines but uses a propane burner to dissociate ammonia from water in a continuous cycle. Devices such as this can operate on many different heat sources including kerosine. Absorption refrigerators have been available for over a century but they are neither cheap nor inherently safe. https://en.wikipedia.org/wiki/Absorption_refrigerator#Single...

My next off-grid refrigerator will be solar-electric with a high efficiency compressor. Even factoring in the cost of additional solar panels and a storage battery it will be cheaper to purchase and certainly cheaper to run.

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At my offgrid cabin I converted a $300 chest freezer to a fridge by using an external thermostat that toggles power off/on based on temp. I have it turn on at 37 degrees and turn off at 35. It uses such little power that it's not even a factor for my small solar setup.

Chest freezers are great because they dont have a front-facing door which lets all the cold fall right out.

Indeed. Not as easy to organize as one with a front facing door, but we keep stuff organized in milk crates and it's worked great for our family for many years now.

What’s not safe about them? I thought that absorption refrigerators were developed to be safer than existing refrigerators, before non-toxic working fluids were discovered.

Einstein-Szilárd fridge. Yes, that Einstein and that Szilárd. https://en.m.wikipedia.org/wiki/Einstein_refrigerator

Ammonia is a very dangerous chemical. From a thermodynamic and environmental perspective it's one of the best refrigerants for many applications but we can't use it in residential buildings because you'll die if you breath it in.

The E-S refrigerator was used because it's high reliability made it safe for certain critical applications, not because it used a safe working gas.

> Ammonia is a very dangerous chemical. From a thermodynamic and environmental perspective it's one of the best refrigerants for many applications but we can't use it in residential buildings because you'll die if you breath it in.

FWIW I’ve only seen propane/ammonia cycle fridges inside residences so I don’t understand what you mean by “can’t use it in residential buildings”

Scale. A small personal fridge in an RV or small apartment isn't a big deal. But a system big enough to power comercial refrigeration or air conditioning to a residential building will involve enough coolant that any leak would be serious problem.

Yeah, but indirect (with e.g. water/glycol between the condenser and the indoor air handler) systems can be combined with scrubber tanks (basically just water+baffles, I think) that the blow-off from a leak or a pressure relief valve is forced through, in order to contain most of the ammonia.

Many supermarkets use ammonia refrigeration. Many food warehouses and packing plants use it as well- resulting in incidents fairly often. It's still used.

Few people sleep in supermarkets.

Anhydrous ammonia is the favored refrigerant for big commercial and industrial systems. These need professional management anyway, and the plumbing containing ammonia tends to be outdoors. Gaseous ammonia is buoyant, so goes up.

The amount of anhydrous ammonia that would be needed to operate an RV fridge could kill you easily. Operation in an enclosed space is another source of risk.

Excellent point, and the difference here is really interesting! Residential refrigerators use a mixture of 90% ammonia and 10% water. This is not very dangerous at all, but it also isn't nearly as energy efficient as pure ammonia because it has different thermodynamic properties.

Pure ammonia is dangerous because it has an extreme affinity for water and it will dissolve into any water it comes into with. If you breath in ammonia gas, it will dissolve in the mucus of your lungs and draw in more water from the surrounding tissue, flooding your lungs and killing you. If the ammonia is already mixed with a little bit of water, this isn't an issue (hence why you can have ammonia cleaning products in your home).

All that said, I was wrong about E-S chillers. I did some more reading and both E-S and absorption chillers use hydrous ammonia.

The burner is potentially problematic. Inefficient combustion can lead to carbon monoxide, a poorly maintained burner can start a fire. Gas leaks, kerosene spills, etc. Electric refrigeration is much safer.

https://www.cpsc.gov/Recalls/1998/cpsc-warns-that-old-servel...

That's a recall from 1998. Surely the appliances produced now are both safer and more efficient?

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