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Some background info for context. (for those that may not be familiar). Heat pump conjures up an image of an appliance, but it is a principle of physics. Heat
by thelastgallon 1mo ago
Some background info for context. (for those that may not be familiar).
Heat pump conjures up an image of an appliance, but it is a principle of physics. Heat can be created by burning fuel or electric resistance. Cold can't be created. Cold is the lack of heat. Cold is 'created' by removing heat. Fridge keeps the inside cool by moving heat from inside and dumps it outside. This movement of heat is called heat pump (pumping heat in a specific direction).
If we can do this for cold, we can also do this for heat. After all, we always have heat in the environment until we get to 0 degree Kelvin. Which means we can have heat pump water heater in the garage. Or heat pump furnace.
Creating heat from fuel/resistance is at most 100% efficient (most likely a LOT less). Heat pumps are 400% - 500% efficient per unit of electricity, because the idea is just to move heat. In one direction, or another.
All of this is great, until we get to the refrigerant used to transfer the heat. These are very specific chemicals. Mostly synthetic chemicals. Historically, these were Chlorofluorocarbons (CFCs). CFCs caused ozone depletion and have high GWP of 14,400.
What is GWP? CO2 is a warming gas that has Global Warming Potential (GWP) of 1 (the standard). Earth radiates heat back into the atmosphere (exactly the same as get from Sun) and CO2 acts as a barrier for the radiated heat from earth, retaining heat in the atmosphere and warming the planet. Why Greenhouse Gases Make the Planet Warmer: https://www.youtube.com/watch?v=AIBk0pGV_BQ https://www.youtube.com/watch?v=AIBk0pGV_BQ
But, there are lots of other gases that have higher GWP. Fluorinated gases: Hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride are synthetic gases used for refrigeration (maybe other applications). Fluorinated gases replaced CFCs, which were causing ozone depletion. But they have high GWP. HFCs: up to 12,400, PFCs: up to 11,100, NF3: 16,100, SF6: 23,500 (https://www.epa.gov/ghgemissions/fluorinated-gas-emissions https://www.epa.gov/ghgemissions/fluorinated-gas-emissions)
So, we have to find better alternatives for refrigerants. Because, these leak. And everybody on the planet is going to buy ACs. CO2 is a terrific refrigerant because it has GWP 1 and leaking of CO2 is perfectly okay. With 40 - 60 billion tons of CO2 from fossil fuels, CO2 leaks from refrigerants are less than a rounding error.
- roughly 1mo agoAnd also we have a large overabundance of CO2 we need to figure out something to do with, and using it in the heat pumps we’re all going to need to adjust to our overabundance of CO2 seems like a quite parsimonious arrangement.
- asdfman123 1mo agoThere's no need to worry about how much CO2 these systems can either capture or accidentally leak. I estimate they use less CO2 than is released when burning a tenth of a gallon of gas. Not significant carbon sequestration, and an insignificant amount to leak to the atmosphere.
- deleted 1mo ago[deleted]
- vel0city 1mo agoCFC is a fluorinated gas. Its in the name. Chloroflurocarbon. So you're saying "Fluorinated gases replaced [fluorinated gasses]". CO2 is not a terrific refrigerant. It requires comparably very high pressures to be effective and has a low critical point reducing their effectiveness in a lot of normal temperature ranges. More modern refrigerants like HFOs usually have a GWP of <1 and don't require anywhere near as high of pressures, with R-454B being around the same as R-410A.
- londons_explore 1mo agoEurope is using lots of refrigerants like r600 (isobutane) and r290 (propane). They work really well, with the downside they are very explosive. However stories of airconditioners blowing up are really rare - it seems the risk is probably worth it for the environment.
- Teknomadix 1mo agoI've been recharging the AC system on my vintage daily driver — a late 1960s Mercedes-Benz sedan — with common off the shelf campstove propane for 30 years. Keeps me cool regardless of outside Los Angeles heat. Requires a bit of care while doing a recharge, but it's nothing too crazy. My grandfather ran a dairy farm in Connecticut, he showed me this trick in the 80s. We used propane to keep all the cooling equipment in the milk houses running smooth back then. I'm curious about isobutane now.
- londons_explore 1mo agoIsobutane doesn't work well unless a system is designed for it - things like different diameters for the pistons in the compressors etc. Nearly all refrigerators/freezers in Europe are isobutane, and have been for 20 years.
- sidewndr46 1mo agoPropane, butane, etc. are not explosives. They are not going to just energetically decompose. They are combustible, but it turns out most things worth having on earth are combustible
- wernerb 1mo agoA modern heat pump (r290) uses propane has a negligible GWP of 3
- sidewndr46 1mo agoThe only reason CFCs exist is because the US established a de-facto ban on propane as a refrigerant. You can't trademark, copyright it, or any other form of IP.
- 0cf8612b2e1e 1mo agoIs there a safety concern for propane? What is the steel man rationale that is not shareholder value?
- s0rce 1mo agoFlammable I guess
- sidewndr46 1mo agoThe shareholder value is being able to continue to develop and sell additional generations of refrigerants.
- quickthrowman 1mo agoYes, if you release propane into an enclosed space like a mechanical room and then introduce a spark, it could cause an explosion. The explosion risk (in a commercial setting) is mitigated by having gas detection sensors and an exhaust fan that runs when the gas detection alarm trips along with horn/strobes at any entrance to the mechanical room and inside the mechanical room. In a residential setting, I’d only feel safe if the condenser (outdoor unit) used propane with a liquid to liquid heat exchanger and separate glycol loop that runs inside to the air handler coil.
- s0rce 1mo agoThere are commonly sold flammable refrigerant things now in the USA, I see a bunch of small fridges using alkanes and cycloalkanes, not sure about HVAC.
- qlte 1mo agoHow is that a de facto ban, you can't trademark the common names of plenty of substances ubiquitous in daily life. The manufacturers of refrigerants don't seem like they could completely dictate what appliance manufacturers choose to use in their products. It seems for refrigerators there are actually specific carve outs in EPA venting regulations to allow R-290 (propane) along with a couple others. https://www.epa.gov/snap/substitutes-household-refrigerators-and-freezers https://www.epa.gov/snap/substitutes-household-refrigerators... If vendors don't use it, possibly due to flammability, whether a real risk or as imagined by consumers that's a completely different situation. I can't find anything claiming it's banned or even discouraged by the government.
- bronson 1mo agoAll good points. So, why don't we use CO2 in minisplits? Split systems are most popular in new construction and retrofits, so why are we settling for modern refrigerants like R32 with a large GWP of 675? It's because CO2 has to be run at more extreme temperatures and pressures, fine for factory-made connections inside a single unit but a showstopper for field joints.
- hypertexthero 1mo agoThanks for this summary. Very useful and informative. After the 2026 heat wave in Europe and elsewhere, and expectations of things getting hotter with global warming and El Niño, it’s already past the time to prepare, but better late than never. Will governments have to subsidize solar/inverter/battery/heat pump systems to keep people going? What are people doing to get ready for a “hot house Earth” future around the world?