The big issue is what happens to the refrigeration gases at end-of-life because they have such high global warming potential. The units are nominally hermetic, so they should last their entire life without leaking much refrigerant. If you have an old AC unit, try to dispose of it responsibly by not sending it to a landfill. A responsible recycler/disposal facility will reclaim the refrigeration gases for recycling or disposal.
There really aren't good alternatives available for purchase right now. Almost all units sold today will contain gases which have low Ozone Depletion Potential but still have high Global Warming Potential (~2000-9000x as potent as CO2).
There is a heat pump hot water heater available from Sanden using CO2 (ironically) as a refrigerant, which has a GWP of 1. It is pretty darn expensive.
This whole area is really a place we need some startup innovation. Both products that use something other than HFCs for refrigeration and some kind of business model or non-profit which will have the goal of getting old units out of the hands of consumers responsibly.
> If you have an old AC unit, try to dispose of it responsibly by not sending it to a landfill.
Considering someone stole the AC unit off the roof of the house next door to me in the middle of the night (it was a rental property and nobody was currently living there).
You know - meth.
Anyhow - something tells me there might be some valuable material inside an AC unit, so why anyone would just take it to the landfill (unless it has an A/C recycling program - some do)...
For things like window units and fridges, this will at least allow one of the better drop-in replacements for HFCs to be on the market. The charge size limit of 150g will still prohibit things like central AC units and mini splits, unfortunately.
People are so worried about a little isobutane or propane in their refrigeration devices but we have constant pressure tubes forcing methane into many of our homes at 60psi. HCs would be great refrigerants and I think we can deal with the flammability...
The natural gas pressure at a stove inlet is supposed to be something like 0.25 PSI, not 60 like in the underground service lines. A pool boiler might need slightly higher, but in general the pressure in the building lines is very low.
You can also operate the CO2 in a 'trans-critical' mode which gets around some of the issues of the low critical temp. This is done by using a gas cooler to cool supercritical fluid in place of the typical condenser.
There aren't really many good alternatives that are cheap, have very low GWP (less than 100), are non-toxic and non-flammable. HFOs are probably the closest to this, but even these are often mildly flammable and typically quite expensive (often > $50/kg).
Over here it seems CO2 refrigerators are increasingly common for supermarkets, warehouses etc. AFAIU it can be made about as efficient as HFC's, but the up front cost is higher due to higher pressures. OTOH CO2 is cheap, as you say, and there's no risk the next iteration of the F-gas legislation will make your new investment EOL.
Seems like it would be easy to fix within any particular jurisdiction by requiring some deposit on any new fridge which could be redeemed when it was disposed of.
There really aren't good alternatives available for purchase right now. Almost all units sold today will contain gases which have low Ozone Depletion Potential but still have high Global Warming Potential (~2000-9000x as potent as CO2).
There is a heat pump hot water heater available from Sanden using CO2 (ironically) as a refrigerant, which has a GWP of 1. It is pretty darn expensive.
This whole area is really a place we need some startup innovation. Both products that use something other than HFCs for refrigeration and some kind of business model or non-profit which will have the goal of getting old units out of the hands of consumers responsibly.