this post was submitted on 30 Aug 2026
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Ammonia is great but it's also kind of religated to being it's own thing in the refrigeration industry because of its incompatible with copper/brass which makes it incompatible with almost all standard refrigeration tools and equipment. Basically anyplace that runs an ammonia system will have their own techs because nobody else will work on it. It's pretty common for heavy industrial refrigeration but not much outside of that. It is also deadly in case of large leaks which makes people shy away from it.
CO2 though is already in use for grocery store rack refrigeration systems. Aldi is a big user of them. You also can't actually go below -40C with on a CO2 system without risking forming dry ice in the pipes. As far as efficiency goes, the big impact is from transcritical operation but even then it really doesn't make a big enough impact to negate the benefits. Rack refrigeration systems can already be hilariously efficient with high end equipment and CO2 equipment is always high end. CO2 also has a remarkably high coefficient of expansion compared to most refrigerants which gives you some pretty big efficiency gains in that regard which ballances out most of the losses. As far as leaks go I haven't noticed that they leak any more or less than conventional systems, however when they do leak, CO2 is dirt cheap. The only real downside I've seen about these systems are, transcritical complexity, sheer cost, and for some reason they seem to plug oil filters more often.
i've noticed biologists keeping CO2 cylinders connected to something near their -80C freezers, that's why i assumed it works for this kind of temperatures
Might be for keeping an inert atmosphere. Normally nitrogen would be the gas of choice for that but CO2 is cheaper and easier to store in bulk so if they don't absolutely need nitrogen then I could see CO2 being used instead. Basically you just keep the chamber slightly positively pressurized with CO2 to keep the oxygen out.
As far as temp keeping goes though basically all of the ultra low temp freezers (those not using liquid nitrogen anyways) I've seen use R-508b along with a medium temp refrigerant like R-404a or R-448a in a cascade setup to achieve those temps. I've never seen CO2 used for ultra low temp refrigeration due to it's nasty habit of turning solid below about 100PSIG.
there's no problem with getting nitrogen or argon, maybe they need it for their biological things specifically
-80 freezers will be necessary in the future but some new refrigerant will be needed for them, there's no way R23 or R116 will be approved forever (gwp 10k+). i guess that will have to be ethane/ethylene + propane cascade? if so that would be blast from the past because ethylene was used as an intermediate refrigerant in first oxygen liquefaction
I have just read and learned more about refrigeration, gasses/compounds and R values in the last 10 minutes than I ever thought I would in a lifetime.
shit sure is interesting though, as someone who grew up with the whole ozone hole thing.
thank you scientists and fellow lemmings.
TiL.. a lot!