Can someone here explain why heatpumps are the new hotness? (Sorry.) Despite the hype, all I can discern is that they are just air conditioners that can pump in the other direction ("reverse cycle"), and the thermodynamics is poorly explained in the popular literature. Why are they suddenly the thing that can save the world? What am I missing?

My degree is in physics. I can handle the truth.

Thank you.

@robpike they're the best way we have to heat a house with electricity. Electrification is a key path to decarbonization. You might enjoy Saul Griffith's book Electrify on the topic

@nelson @robpike to expand on this just a bit: you can get zero-emission electricity, so a heat pump house can be zero-emission. A gas-heated house, by definition, can’t be zero-carbon.

Side-effect: lots of places that never needed cooling are increasingly going to need cooling, so might as well switch to heat pumps. (That’s my situation in SF.)

@robpike Along with the ability to support electrification, as others have mentioned, heat pumps can reach 3-500% efficiency — better than fossil fuels and vastly better than electric resistance heating.

@robpike

I'm not sure why but the general ability for them to run and not quickly develop ice in near and sub freezing seems.to E somewhat new.

But you can pump 3-5 times as much heat than your system consumes (and recoup a lot of that heatas well).

Had one in the 80s and 90s growing up in Florida.

@robpike 350 to 400% efficiency generating heat compared to gas boilers (max 98% efficiency) _plus_ ability to cool is an efficient way to reduce primary energy use and equip houses for climate change effects. That's it. That's the story.

Plus maybe for affluent people that can afford photovoltaics and a buffer battery, reduced grid dependency.

@robpike My degree is not in physics, but my understanding is that heat pumps use less energy because they transfer heat instead of creating it. https://natural-resources.canada.ca/energy-efficiency/energy-star-canada/about/energy-star-announcements/publications/heating-and-cooling-heat-pump/6817#b5

Thanks to all for this instructive and fascinating thread. I have a much better understanding now.

@robpike I’m probably the only naysayer in the replies; I installed a heat pump around 7 years ago. I have yearly service because they don’t work. When they do work they don’t get cold enough or hot enough. I also have to get them cleaned out frequently due to mold growth. I have spent more on service visit fees than I would care to add up.)

(Population size = 1. lol )

(I live in the US; Central MA. Not the most extreme temperature range but definitely not a temperate zone.)

@robpike Not quite sure I understand the question, given the physics background, but they're more efficient than raw heating because you don't have to expend all the energy you're adding into the target area, you're transferring it from elsewhere, and the energy used to drive the transfer is considerably less that the energy transferred. Generally expressed as "efficiency > 1" but I imagine that makes any engineer wince, as it does me.

@parsingphase @robpike basically a heatpump is working like a refigerator or a airconditioner in reverse. The thing about these is that for one amount of electrical energy you put in a heatpump you get out four to five times the amount of heat that you may produce with the electricity alone. This makes these systems so attractive for a step towards carbon free heating - especially when the household uses solar cells to produce electricity

@Muellers_Kabinett @parsingphase @robpike The really clever bit of using an air conditioner in reverse to cool the outside and heat the inside is that the "waste heat" from the electricity consumed by the mechanism gets added to the total going out the heat-emitting end.

So they're actually better at being a heater than being an air conditioner, because physics.

@trouble @robpike How does the "zone" thing work? Does each room have its own heat pump? Or are you replacing air ducts with long distance coolant lines?

@robpike it’s a real marketing error to not call them “anti-fridges” as that is exactly what they’re.

@landley @Muellers_Kabinett @parsingphase @robpike although, perhaps ‘warmness’ would be more accurate, since they don’t get to as high a temperature as a gas fired heater, yet.

@steely_glint @Muellers_Kabinett @parsingphase @robpike You're aware you can set the target temperature with a thermostat, right? (Device on the wall with numbers and buttons on it?)