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Yes, heat pumps slash emissions even if powered by a dirty grid | Installing a heat pump now is better for the climate, even on U.S. electricity generated mostly by fossil fuels. Here’s why

www.canarymedia.com Yes, heat pumps slash emissions even if powered by a dirty grid

Installing a heat pump now is better for the climate, even if you run it on U.S. electricity generated mostly by fossil fuels. Here's why.

The article doesn't go into it, but a key advantage they have is that heat pumps move heat, rather then trying to generate it. So they can move a lot more heat into your house than would be generated by running the electricity they use through a resistor. This makes them effectively more than 100% efficient (the exact amount depends on temperature) as compared with burning a fuel or resistive heat.

60 comments

Heat Pumps are just Air Conditioners with a reversing valve. They're not some special magic.
- Increasingly, they also tend to have variable-speed compressors, which offer further efficiency benefits. I think the distinction between A/C and heat pump is useful for consumers.
  
  Just got a Bosch Inverter (variable speed) last summer, and the remainder of the summer and through the winter, my electric usage is down by about 30% over last year's even though I lowered the thermostat temp in summer and increased it in winter.
  
  Old system was 20 years old. I was hoping to see some ROI after this surprise expense, and it has exceeded expectation so far.
- Hey, pedant here.
  
  Air conditioners are heat pumps too, and it's not the reversing valve that differentiates them. Heat pumps move heat, reversing valve let's you decide which way to move it.
  
  That's exactly what I said. Air Conditioners are heat pumps which only pump one way.
  
  I like pedants. Is it correct that they're not necessarily equally efficient in both directions? "Air conditioner" to transfer heat away, vs "heat pump" to transfer heat in? Even though both are heat pumps.
- Can you convert an existing AC system to do both and save money on getting a whole new system installed?
  
  It's probably not worth it. If you have a system more than 10 years old, then you're probably going to have to replace the accumulator as well if it uses a different kind of refrigerant. It's likely cheaper to buy a whole unit and furnace than messing with it.
  
  You have a furnace that provides heat, air handler that moves the air, and compressor that forces heat in a certain direction (inside to outside in the case of AC) with coils in the air handler to make use of that (re)moved heat.
  
  Heat pumps have several features that make them a bit more than backwards AC, like defrost systems, VFDs and often dual-fuel controls. If it snows where you are, you'll also want it off the ground. So, best to get a new system.
  
  As another said, you might be able to reuse the coolant lines and coils in the air handler. It might not be a bad idea to keep the furnace for backup when it's extra cold.
  
  I believe so but you need a new compressor - the heat exchanger in the house can stay the same I think.
- so why do they have to cost 4-5x what it costs to get an Aircon installed?
  
  I posted this elsewhere in this thread, but here seems good too:
  
  Obligatory Technology Connections ( @TechConnectify@mas.to): Old HVAC industry practices are holding us back and costing us money. But we can fix it.
  
  TL;DW (but you really should, it's a great video): "Recommended" heat pumps are often oversized and overpriced compared to what is actually needed, and homeowners need to be aware of this.
  
  Lobbying, probably.
- Heat Pumps are just Air Conditioners with a reversing valve. They are some special magic.
Cool yeah, uh I'll do that as soon as I have a bunch of that money stuff.
- Obligatory Technology Connections (@TechConnectify@mas.to):
  
  Old HVAC industry practices are holding us back and costing us money. But we can fix it.
  
  TL;DW (but you really should, it's a great video): "Recommended" heat pumps are often oversized and overpriced compared to what is actually needed, and homeowners need to be aware of this.
  
  He also made a condensed version on his other channel.
  
  Condensed version
  
  NTL;W
- Same with Solar Panels, Home Battery Storage system, and honestly just completely redone insulation along the perimeter and siding.
  
  You know what, on second thought, I would rather just move tf out of this place.
Because it's 3-500% efficent duh
I have recently upgraded from a furnace to a condensing furnace, so in the winter my house now emits room temperature soda water rather than hot steamy smoke.

My air conditioner was brand new when I moved in and is in early middle age; when it is ready for retirement I'm replacing it with a heat pump system keeping my current furnace as emergency heat.
Does the paper have any results that say they're still cleaner on a dirty grid? As far as I can tell it's only cleaner in the future after at least a 50% decarbonization. Which is reasonable, even in my fairly conservative city most of our power is low on carbon.
- The thing is heat from the outside gets moved inside of the house using a heat pump, and to facilitate this movement you need somewhere between 1/2 and 1/4 of the energy you end up moving. E.g. a heat pump with (coefficient of performance) of 4 would move 4kW of heat into your house and use 1kW of electric energy to accomplish this. Gas by comparison moves 4kW of gas to your house and burns it there to get 4kW of heat.
  
  So you could burn a bit more than 1kW of gas in a modern gas electric plant, turn it into electricity and use it to run a heat pump and you would end up emitting less CO2, the real world grid might skew that worse because generally you don't end up burning coal to heat housing but you might still use it for electricity. So generally even though it might be unintuitive the more complicated and lossy way to heat your home (the heat pump powered by fossil powered electricity) , is the more effective one compared to burning the same fossil fuel directly because you use the heat pump to capture heat from the environment.
- Maybe not in the article, but I've heard in other places that a carbon heavy grid still gets enough energy to the heat pump that the heat pump's efficiency can offset that increase.
  
  You're also installing a system that is easier to decarbon in the future, which isn't the case for natural gas.
  
  It is really not hard. Heat pump coefficients of efficiency floor at 1, but typically range between ~2.5 and 7. That is, for every joule of energy they consume, they pump 2.5 to 7 joules of heat into the conditioned space.
  
  So you have to just look at efficiencies involved.
  
  The electric heat pump (theoretically ~250-700% efficient at warming a space)
  
  The efficiency of energy transmission on the electrical grid (maybe around 90% ish? Depends on a lot of factors)
  
  The fossil fuel furnace (theoretically something like 90-100% efficient)
  
  The efficiency of the residential fossil fuel delivery system (last I read, something around 5% of natural gas ends up just leaking)
  
  The efficiency at conversion of chemical to electrical energy by fossil production plants (and this one is rough -- I see numbers like 40-60% efficient)
  
  Still, we're just summing stuff. And while I won't pretend any napkin math here is the same as a formal research project, we can plainly see that the HUGE energy efficiency of heat pumps can easily eclipse the inefficiency of fossil electrical production, all else being equal. Of course, whether it actually WILL be better than a fossil furnace will depend on local factors, but these places are increasingly becoming edge cases. And then, on top of that, you unlock future potential to seamlessly switch fuel sources from fossils to renewables, which becomes very important in lifecycle cost analysis.
- I think the point is to compare the heat pump with an electricity heater, there may be other ways that generate less carbon footprint of course
  
  The point is to compare a heat pump with a natural gas furnace.
  
  The efficiency of getting electricity to a house may be less, but a heat pump has an energy efficiency greater than 1.
- I've done energy models for houses here in Saskatchewan (~560 tCO2e/GWh) and at the moment, they are not cleaner than heating with natural gas, which is the typical primary heat source. Obviously, it would depend on grid carbon intensity, so there is a level of grid 'cleanness' where heat pumps would become cleaner, but that tipping point depends on a number of factors.
  
  You could do a rough estimation with the seasonal heating efficiency of a heat pump based on the heating-degree-days of your location versus a certain efficiency of natural gas furnace. Burning natural gas is about 0.18 kgCO2e/kWh. So, if you have a heat pump that's 200% seasonally efficient, you'd need the grid carbon intensity to be about 0.38 kgCO2e/kWh (380 tCO2e/GWh) to be equivalent to a 95% efficient natural gas furnace.
  
  Notable, but outside of very cold climates (which I think I feel safe describing Saskatchewan as being), heat pumps are a LOT more than 200% efficient. In mild climate, they can be 2-4X that.
  
  The 200% seasonal efficiency is a bit off, Nordic models, measured with the "colder" European climate zone, get 300%+ and have guaranteed output at -25C / -13F. Example model from Mitsubishi:
  
  It's worse than 5.5x or 4.3x in warmer areas but the right model air source heat pumps work fine down to pretty damned cold. Norway and Sweden have a ton of them as they spend a ton of energy on heating and this saves homeowners a ton of money every year.
  
  Best models optimized for average climate now reach 5.5x or better in the green, moderate zone, SCOP of 4.3 is actually pretty terrible but this one is built to be ice proof.
  
  Example latest bestest heat pump with 6+ seasonal COP:
Can someone post what the five grid scenarios they cover are? I do not have access to Joule.
The biggest barrier is cost, because you still need a standard heater ~~and AC~~ for times when it is either ~~too hot~~ or too cold for the heat pump to function.

It's definitely more efficient, and most of the time you won't need the backup. But when you need it, you really need it.

Edit: I stand corrected.
- Heat pumps can run in very cold weather; and the worst that may happen is that you need some additional resistive heat to handle the demand. You don't need a completely new system to supplement heat with current technology.
  
  And a heat pump is an air conditioner that moves heat both ways. A lot of heat pumps today operate in dual mode, so they can act as air conditioners as well
  
  Straight up since my grandma got one installed at her house she hasn't had to use her in wall heaters or her fireplace
  
  And in AC mode that thing is great
- Technology Connections did a video on this recently. The need for backup, even in Chicago, is way over estimated.
  
  The caveat there is that he lives in Town Home. Someone living in a stand alone home will have four exterior walls and a higher b/u heating requirement. I'd also like to point out that Chicago isn't even close to the end all / be all of cold. He makes a big deal out of -12f but other areas in the country will go to -30 or even -40 nearly every winter.
  
  The furnace in his place is comically oversized though.
- "Heatpumps" are the same technology as your regular minisplit air-conditiors. You can get some that have a range of between -30 °C and 50 °C (-22 F and 122 F).
- Hey bud, just wanted to let you know, "standard AC" is already a heat pump
- You don’t need additional AC, a heat pump is an AC. For very cold, you’re right, but it has to be VERY cold, like 0F or lower. My last heat pump system had fall back heating coils which are only 100% efficient opposed to a heat pump’s >100.
- Needing supplemental hot/cold only really applies to the heat in regions where it gets very cold. An ac is a heat pump, just one way.