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Comment by photochemsyn | Hacker News Reader

The problematic refrigerants are pretty diverse, being made up of short carbon chains (1-4 atoms typically) decorated mainly with chlorine or flourine atoms. For example:

https://en.wikipedia.org/wiki/2,3,3,3-Tetrafluoropropene

Interestingly the best option for a refrigerant may be CO2 itself, which if collected from the atmosphere has no global warming or ozone depletion issues. The only drawback is CO2 refrigeration equipment has to operate at relatively high pressure, but this isn't a major problem:

https://www.rsi.edu/blog/hvacr/carbon-dioxide-refrigerant/

Getting rid of the chloro-flouro stuff makes lots of sense, but not producing any of it in the first place would be even better.

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More pressure means stricter requirements for all of those non-obvious steps like bending and soldering, and specialized hardware for things like joints and bearing.

Both of those mean specialized factories, supply chains, and labor. AKA higher prices unless it becomes the dominant option.

Also, in larger systems higher pressures is a safety concern.

None of that is a showstopper. But those are severe hindrances for a technology. A government can just fix every one of them, but then it would require government involvement.

Ages ago there was a company that planned to convert Tyson Chicken carcasses into gasoline via depolymerization. Problem was that’s a high pressure process, and they didn’t take that seriously enough at the start. Leaks everywhere. Neighborhood smelled like burnt chicken feathers.

They had to shut it down and redo all of the welding (I don’t recall if they fixed existing welds or pulled the whole thing apart). Afterward they still got complains about the smell, swore they’d fixed the leaks and the neighbors were imagining it. I suspect some esters were coming out the end of the pipe, and/or the dust everywhere around the place was saturated from the pilot project and every time the wind shifted they got another nose full.

I remember that company! I was wondering what had happened to them. There was a bunch of press, and then nothing.

There is one other refrigerant which very nearly checks all the boxes, but with a surprising structure: trifluoromethyl iodide. While non-combustible, it has an extremely short atmospheric lifetime of less than one month, giving it a GWP about half that of CO2 (and used in much smaller quantities).

https://en.wikipedia.org/wiki/Trifluoroiodomethane

https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=93007...

CF3I is one of the components of R-466a (Honeywell Solstice) which will be the lower-GWP R-410a replacement. I am working with CF3I in a fire extinguishing application.

CO2 was used in the very early days of refrigeration, late 19th/early 20th century, in huge industrial installations. It was known as "carbonic acid" and you can find a lot of interesting books on archive.org about it. Pressures are about 10x higher than most other refrigerants so everything needs to be built that much stronger.

AFAIU CO2 refrigeration system are making a comeback. In Europe it's apparently fairly popular for things like supermarket refrigeration, partially maybe due to ever tightening EU F-gas regulations making a big investment into flourocarbon refrigeration systems a risky proposition.

I've often wondered what other ways we could do "refrigeration" without requiring such horrible gasses, CO2 would be a nice one (and we already distribute CO2 world-wide for soda), but perhaps something could be done with piezo also.

Depending on your definition of ‘horrible’, ammonia also works well!

In Europe, and I think in much of the rest of the world except the US, isopropane or butane is used in common household refrigerators. Recently EU regulations were changed to allow these to be used in small split AC's as well, provided some flammability precautions are taken in the design and installation of the units.

In principle you could also go without phase change refrigerants with the reverse Brayton cycle, essentially running gas turbine cycle in reverse. But AFAIU these are not competitive with phase change refrigerants in the usual temperature ranges used for AC's and refrigerators.

Yes a propane/isobutane blend works well, it's basically a drop-in replacement for R-12 in air conditioners. Straight propane replaces R-22 in freezers.

The only drawbacks are that it's flammable, and that for the blend, if there is a a slow leak, the blend ratios change due to different partial pressures of the two gasses. So to recharge, you basically have to vacuum the system and refill with the proper blend.

Ammonia also works for industrial applications (the local ice rink uses it) but due to its toxicity it's not ideal for household applications.

It would be useful to be able to (easily) smell a refrigerant leak, too.

That smell you're thinking of is an additive - propane and butane are relatively odorless without it.

Yeah - mercaptan I believe? I knew that, I guess I just assumed they wouldn't use a non-odorized propane..

https://en.wikipedia.org/wiki/Tert-Butylthiol - Because propane is delivered as a liquid and vaporizes to gas when it is delivered to the appliance, the vapor liquid equilibrium would substantially reduce the amount of odorant blend in the vapor.

https://en.wikipedia.org/wiki/Ethanethiol is used for propane (usually) but for the small amounts in a recirculating setup they may skip it.

Interesting, thanks for the info.

I did a quick search on how much refrigerant is in a household refrigerator. Internet says 30 to 180 grams.

I wouldn't be very concerned with 100 grams of propane. Your kitchen has probably 20kg of air. You ain't going to get even close to the flammability limit releasing a 100gm of propane into it.

Which is about 5000 BTUs or about the same amount as 3/4 a cup of gasoline, if I did the math right.

So not nothing, but not very worrisome either.

R22 is also flammable. But probably not as much as propane. But you aren't going to get anything dangerous with the small amounts used in HVAC. It would need to be a propane/pure oxygen mixture to even approach danger.

There's the Peltier Effect, which only has the itty bitty downside of requiring about 4 times as much power as a traditional compression-based cooling system.

You're looking for magnetocaloric refrigeration and the giant magnetocaloric effect:

https://www.sciencedirect.com/science/article/pii/S007964251...

> The only drawback is CO2 refrigeration equipment has to operate at relatively high pressure, but this isn't a major problem

So far it has been a problem for scale. There are very few consumer appliances that use CO2 as a refrigerant. I can think of 1 right now - and it's 3x the price of it's alternative that uses traditional refrigerant.

I thought that the variable and linear compressors could use a smaller system because they’re designed to run almost constantly instead of in bursts.

They’re also more efficient, but more expensive. So I wonder how much of the price differential is the refrigeration loop, and how much is using more expensive processes to offset the lower tonnage for the system.

Most new technology heating and cooling systems are expensive because they serve the rich eco-nerd and commercial markets, both of which are willing to pay a premium for the real benefits of the technology.

Hopefully the recent pro heat-pump moves across Europe and the US Administration's invocation of the DPA to support domestic heat pump manufacture will push this stuff out to the mass market instead of just in the houses of the wealthy.

EVs are just now breaking out of that pattern, only after competitive pressure from companies like Hyundai, Kia, VW, and GM who have made nearly affordable EVs.

CO2 heat pump water heater for houses is widely used in Japan. Some EVs have CO2 heat pump.

https://www.green-cooling-initiative.org/network/best-practi...

Also good and cheap!

The trouble is that high pressure means more embodied energy, and when we start talking about embodied energy, "CO2 equivalent of 250 gallons of gas" isn't that much. Just releasing the gasses into the atmosphere once or twice might pencil out.

Regardless they are very widely deployed in existing equipment which can't be upgraded, so a program to collect and burn these gasses is a very good thing.

order of magnitude nit: the article mentions 250 gallons of gas, not gas for 250 miles - so roughly 25x worse

Thank you, updated.

This seems like a better place to point out (rather than editing the original to say something different) that this actually undermines the argument: stainless steel is only about 6kg CO2 per kg, and a gallon of gas burned is around 8.

That number for steel is a lot lower than I expected, but here it is:

https://en.wikipedia.org/wiki/Embodied_energy#In_common_mate...

I had a refrigerator using propane, sadly, it didn't last very long (just a few years) before it died. It was a low end unit and repair was more than a new one, which happened to use conventional halocarbons.

>Getting rid of the chloro-flouro stuff makes lots of sense, but not producing any of it in the first place would be even better.

Science doesn't work like that though. You can't study something until it does exist. However, we just don't study something long enough (we just can't think of everything to test against) to see what the true long tail effects will be.

Yes, there's lots of things that would be amazing if we could un-invent them. But wishing won't make it so. We just need to be much more ammenable to the fact that somethings don't work and just STOP using them rather than shrugging shoulders and kicking the proverbial cans down the road

They do work though (for the people who use them), that's the whole problem.

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