this post was submitted on 28 May 2024
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Air conditioners are already heat-pumps. This change would moreso replace furnaces.
Every heat pump is an air conditioner, not every air conditioner is a heat pump. They require a reversing valve to function both ways.
The furnace doesn't need to change. I have a nat gas furnace with an electric heat pump. You can also do electric heat pump with an electric air handler. There are plenty of combos.
That said, every year I run the numbers and despite my heat pump being ~300% efficient my 95% efficient nat gas furnace is still cheaper to operate (based on the cost of each energy source). I'd LOVE to go solar and operate as close to 100% electric as possible but with my old growth trees and shitty house orientation I wouldn't even break-even in the lifetime of the panels. :(
Just curious, so numbers are the deciding factor for heating, not environmental impact? For example if your were wealthy would you choose lowest impact option, or would numbers still dictate your choice?
It is a good question.
Where I live, electricity costs around $0.28/kWh, but generation is typically >85% renewable (predominantly hydroelectric).
My heat pump (4.7 COP when heating) would cost $0.06 to run for every 1kWh of heat it produces, with only 0.03kWh of that electricity coming from fossil fuel sources.
Gas - which I don't have at my house - would have pricing in the neighbourhood of $0.15/kWh. Even at 95% efficiency getting 1kWh of heat from gas would cost $0.16, using 1.05kWh of gas.
35x the fossil fuel usage and 2.5x the price, for the same quantity of heat. Some luck of living in a moderate climate where an air-source heat pump almost never loses efficiency, to be fair.
This is correct. And given the way the grids interconnect it would be hard if not impossible for me to be able to quantify environmental impact. I would assume even though there is still a lot of coal generation in-use it would still be more environmentally friendly for me to run the heat pump but I just don't know.
If money was no object I would absolutely choose the lowest impact option. I would even do a solar install even though it would likely end up being a net-loss for my specific case.
Thanks for your honest answer.
I think many people believe gas is at least preferable to coal environmentally wise, but turns out in quite a few instances it's worse. (fossil fuel companies did a good job marketing gas as cleaner for a long time)
https://theclimatecenter.org/energy-efficiency/study-shows-natural-gas-fracking-more-harmful-than-coal/
They're heat pumps in a technical sense, but coloquial terms, a "heat pump" is a heat pump which can actually heat a space.
The outside is a space too.
It's weird that there are any AC that can't function in heating mode at this point. In Australia at least, you'd be hard pressed to even find one that doesn't support heating.
I, for one, would support a law that requires any new unit over a certain size must be reversible and maybe even a tier where they must have variable speed compressors. But I can already hear the Republicans lying that the feds are coming to steal your window units.
Of course, even modern window units (and portable AC) support reverse cycle. But conservatives will find a way to complain about it, agreed.
This way it's $5 cheaper! Profit.
Here in Cali there are a ton of homes that have wood burning fireplaces in them so often that’s viewed as the “heater” if need be and the AC is for cooling.
AFAIK most American AC units can be retrofitted to be heat pumps pretty easily. You're just making it flow in reverse, after all.
In automotive at least, it's pretty common to size the evaporator and condenser coils based on their expected operating temperatures and (therefore) pressures. Usually this means condenser is a lot bigger than evaporator.
If you reverse the flow with the right valves and compressor setup, then the heat exchangers will still be sized wrong for efficiency. I suppose you could design a bidirectional system from the start that trades off for middling efficiency in both modes.
I'm not at all convinced that there are a substantial number of such bidirectional-sized residential systems installed in North America. But it's also possible that the residential folks don't care much about HX efficiency.
That makes sense, but also most heat pumps I know of are also AC units - like those mini splits installed in new apartments these days.
Would that not also be a balanced system?
And even if we're talking about lower efficiency it's still more efficient than burning gas in a furnace right?