alt Hacker NewsSome 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
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)
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.
Replies
A modern heat pump (r290) uses propane has a negligible GWP of 3
CFC 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.
And 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.