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Heat pumps are air conditioning systems. They work on the refrigeration cycle. Rural homes in the US tend not to have connections to natural gas utilities. If

by jwie 4y ago

Heat pumps are air conditioning systems. They work on the refrigeration cycle. Rural homes in the US tend not to have connections to natural gas utilities. If winter isn’t severe enough to justify a storage tank, the home typically has an HVAC heat pump/AC unit, and really high electric bills for a month or two. Heat pumps have gotten better, but they’re never a first choice for heating for good reasons. Like most “emissions saving” initiatives the crux of it is where the electricity comes from. Burning something for heat is always more effective, cheaper, and produces fewer emissions compared to an electric heater. Heat pumps need to power a compressor, while there’s some phase change and pressure hacks to move the heat around, systematically it’s trading electricity for heat. If you’re getting electric heat from coal fired steam that’s always worse than burning the coal locally to heat something, and this is true for all emission-producing power sources.

ctur 4y ago
What? No, this is incredibly short-sighted. It overlooks the fact that much grid energy is renewable already and will become more so in the future. Go with electric sources for cooking and heating (home and water), then let the grid handle being renewable. Heat pumps are amazing technology and moving heat, vs generating it, is incredibly efficient and clean. Do not burn fissile fuels in your home.
- sokoloff 4y ago
  > Do not burn fissile fuels in your home. Completely agree; that would be incredibly dangerous and polluting (and probably illegal)!
- tialaramex 4y ago
  Buffy had it right, "Fire bad, tree pretty".
tialaramex 4y ago
You seem to have only half understood? The heat pump is only moving the heat. Burning coal doesn't move heat, it makes heat by destroying coal. Because the heat pump isn't making the heat it is able to move the same amount of heat from somewhere else (say, the outside air) into your home, using less energy than you'd need to make that heat inside your home. Because you can't destroy heat (thermodynamics) for refrigerators we have no choice, we must use heat pumps. But once you get good at this technology, it's just better regardless of whether you want to move the heat away (Air conditioning, refrigerator) or towards you (heating a home). This is how heat pumps claim seriously > 100% efficiency in many cases, they're comparing the efficiency of moving heat against making it.
- phyzome 4y ago
  It's important for people to know that at least when it comes to heating, "100% efficiency" is actually the worst possible efficiency. That's just thermodynamics. You can only get better than that.
  - saltcured 4y ago
    No, you can get much worse as well when considering heating in general. Heating efficiency is a measure of useful heat, so while of course energy is conserved in the universe, it is not 100% efficiency as measured, where we consider the consumed energy versus the successful heating of the home. Heat lost to the outside is inefficient. With natural gas heating, efficiency used to be around 50% as the exhaust gases were quite hot. They just had passive chimney flues driven by natural convection. Improvements to recover more of that heat brought efficiency up to 80% and now approaching 95% in the most modern configurations that I've read about. They now require mechanical ventilation to remove the exhaust and also have condensate drains because the heat exchangers cool the gases so much. Of course, something like a traditional wood fireplace is much worse than even those old gas furnaces, with a vast amount of energy going out the chimney.
    - phyzome 4y ago
      Sorry, I meant to say electrical heating!
      - saltcured 4y ago
        With electrical heating, if you consider transmission losses you can see that the effective home heating is less than 100% of the generated power. The power lines and equipment warm the outside too. Another benefit of the high COP heat pumps: in reducing the total power consumption at the home, it also brings a proportional reduction in those losses outside the home...
  - tialaramex 4y ago
    While this is true in some sort of physical sense, it's not really useful for home heating. The problem is that while burning stuff makes heat, that heat probably isn't where you wanted it, and you need to capture the heat and move it to where it's useful. Unfortunately burning stuff produces exhaust gases, and those too are hot, that is they contain some of the valuable heat, but the gases themselves are dangerous and unwanted. Modern boilers achieve about 94% efficiency. That is, if we make 1MJ of heat energy by setting stuff on fire, the boiler transfers 940 kJ of heat energy into hot water. The remaining 60 kJ is warm exhaust. You've probably seen the exhaust from people's homes if you live somewhere with such boilers.
legulere 4y ago
Heat pumps produce several times the heat as electricity put in. Even with a typical 40%-50% efficiency for a gas power plant you end up with more than 100% efficiency with a heat pump. If the power plant rest heat is used for instance for district heating you reach efficiency of around 90%. Add the efficiency of heat pumps on top and you end up with something very good.
throwaway894345 4y ago
Heat pumps transfer heat from the outside, they aren’t generating it so it’s entirely likely that they would result in fewer net emissions than burning coal directly. And the calculus just keeps getting better for grids that incorporate more natural gas and renewables.
KVFinn 4y ago
>Burning something for heat is always more effective, cheaper, and produces fewer emissions compared to an electric heater... >If you’re getting electric heat from coal fired steam that’s always worse than burning the coal locally to heat something, and this is true for all emission-producing power sources. Apparently you can actually save natural gas with electric heat and a heat pump. https://youtu.be/MFEHFsO-XSI https://youtu.be/MFEHFsO-XSI
altcognito 4y ago
The argument is that for regions that do not spend much time below 15 degrees Fahrenheit, they tend to be cheaper to run because they can pump more heat than electricity they use, effectively becoming 300% efficient instead of 95% efficient for say an gas heater. As the temperature differential between the desired temperature and the outside temperature increases however, the efficiency does drop and what you say is true, but for most of the populated world, this is not the situation. https://www.youtube.com/watch?v=7J52mDjZzto https://www.youtube.com/watch?v=7J52mDjZzto (edit: I think you're going to get a lot of links to the overly in depth series tech connections, but I'm leaving it here all the same)
boloust 4y ago
Heat pumps can be efficient enough to overcome the losses from coal -> electricity. So it's possible to use a heat pump to heat a space more efficiently than burning that same coal directly in the space.
deleted 4y ago
[deleted]
brnt 4y ago
Typical heatpump COP in Northwestern Europe sits at about 4, that means for 1 kWh of electricity your moving 4 kWh heat into your home. Electrical resistive heating sits at 1:1 by definition, and methods like wood, gas or oil, combustive methods, usually with modern installations at 80-95% efficiency. Further south heatpump COP improves; the rule of thumb is a smaller delta T the better. Moving heat is always more efficient than creating heat. It's elementary physics. Airconditioners, or air-to-air heatpumps, are cheap heaters for the same reason (any units sold in the last 10 years can move heat bidirectionally). Here in NW Europe by cooling bill is barely noticeable (it's no desert clime after all, although the last decade seems like it's getting there!). You don't need to set it to 18C; I really only cool when the attic gets over 28C while I work there (home office), down to 24-26, which is a few weeks a year. In winter, it heats the room at ~400% efficiency compared to the typical ~80 for gas heating. Move heat. Don't create it.
- redeeman 4y ago
  > Typical heatpump COP in Northwestern Europe sits at about 4 :) yeah, when its really quite warm outside, but not quite warm enough that you dont need heating. as soon as you even get down to 5C outside, you are not getting a COP of 4. Many vendors may tell you that, but well... :) some people were also sold bridges :)
  - brnt 4y ago
    A lot of people in my environment are in fact getting sCOP of 4. Bit better in fact: close to 5 in the group that also installed floor heating everywhere. Note that COP around freezing is almost always the worst due to frequent defrosting, so yes, COP is worse at -5 most likely. You can replace COP with sCOP in earlier replies of mine. What is true is that most people, including installers, don't know how to tune them very well, or forget to combine them with low temp radiators/ floor heating. Too high a T_out also occurs frequently. In the Netherlands, heatpumps have been standard issue in new construction for a decade now, and 4 is about the average. It's very much not imaginary, but hard to believe for people from areas used to wood and oil burning ;)
crote 4y ago
The trick is that heat pumps are using energy to move heat. Let's make an example calculation: When heating your house to burn coal, you release 1 Joule when burning the coal. It's a small plant, so it is not very efficient. You probably get 0.85 J of heating out of it. If we instead burn coal in a large-scale modern power plant, we release the same 1 Joule, but capture 0.95 J of it in electricity. Let's say we lose 10% transporting it to your home, leaving 0.855 J remaining. Now, we use that energy to move heat from outside into our home, at an efficiency of about 300% - so for every joule we consume, we move 3 joules of energy. This means our house is heated with 2.565 J. But the energy the heat pump consumes doesn't disappear - it becomes heat too. So your house gets a total of 3.42 J hotter! So 1 J of coal gets you either 0.85 J of heat by burning it directly, or 3.42 J of heat by burning it in a power plant and using a heat pump. And of course don't forget that for climate reasons it is trivial to replace that power plant with a solar farm or wind turbine. The worst-case scenario for a heat pump is that it is exactly as efficient as burning stuff directly. But in virtually all cases, it is way better.
- aftbit 4y ago
  Pretty good assessment, except I think your figure for heat efficiency of power generation is way off. I would expect to convert around 30-40% of the heat energy to electricity.
  - hedora 4y ago
    95%+ efficient coal boilers have existed since the '90s.
    - aftbit 4y ago
      This is fuel to electricity efficiency? That seems unlikely to me, both based on sources[1][2], and the thermodynamics of the Carnot equation. A Carnot cycle heat engine (which is most efficient possible AIUI) has a maximum efficiency of 1 - Tc/Th. Given a Tc of 300K (STP-ish), achieving an efficiency of 0.95 would require a Th of 6000K, well above the melting point of steel (only around 1800K). 1: https://www.eia.gov/todayinenergy/detail.php?id=44436 https://www.eia.gov/todayinenergy/detail.php?id=44436 2: https://www.energy.gov/fecm/science-innovation/office-clean-coal-and-carbon-management/advanced-energy-systems/transformative https://www.energy.gov/fecm/science-innovation/office-clean-...

by jwie 4y ago

ctur 4y ago

What? No, this is incredibly short-sighted. It overlooks the fact that much grid energy is renewable already and will become more so in the future. Go with electric sources for cooking and heating (home and water), then let the grid handle being renewable. Heat pumps are amazing technology and moving heat, vs generating it, is incredibly efficient and clean. Do not burn fissile fuels in your home.

sokoloff 4y ago
> Do not burn fissile fuels in your home. Completely agree; that would be incredibly dangerous and polluting (and probably illegal)!
tialaramex 4y ago
Buffy had it right, "Fire bad, tree pretty".

tialaramex 4y ago

You seem to have only half understood? The heat pump is only moving the heat. Burning coal doesn't move heat, it makes heat by destroying coal. Because the heat pump isn't making the heat it is able to move the same amount of heat from somewhere else (say, the outside air) into your home, using less energy than you'd need to make that heat inside your home. Because you can't destroy heat (thermodynamics) for refrigerators we have no choice, we must use heat pumps. But once you get good at this technology, it's just better regardless of whether you want to move the heat away (Air conditioning, refrigerator) or towards you (heating a home). This is how heat pumps claim seriously > 100% efficiency in many cases, they're comparing the efficiency of moving heat against making it.

phyzome 4y ago
It's important for people to know that at least when it comes to heating, "100% efficiency" is actually the worst possible efficiency. That's just thermodynamics. You can only get better than that.
- saltcured 4y ago
  No, you can get much worse as well when considering heating in general. Heating efficiency is a measure of useful heat, so while of course energy is conserved in the universe, it is not 100% efficiency as measured, where we consider the consumed energy versus the successful heating of the home. Heat lost to the outside is inefficient. With natural gas heating, efficiency used to be around 50% as the exhaust gases were quite hot. They just had passive chimney flues driven by natural convection. Improvements to recover more of that heat brought efficiency up to 80% and now approaching 95% in the most modern configurations that I've read about. They now require mechanical ventilation to remove the exhaust and also have condensate drains because the heat exchangers cool the gases so much. Of course, something like a traditional wood fireplace is much worse than even those old gas furnaces, with a vast amount of energy going out the chimney.
  - phyzome 4y ago
    Sorry, I meant to say electrical heating!
    - saltcured 4y ago
      With electrical heating, if you consider transmission losses you can see that the effective home heating is less than 100% of the generated power. The power lines and equipment warm the outside too. Another benefit of the high COP heat pumps: in reducing the total power consumption at the home, it also brings a proportional reduction in those losses outside the home...
- tialaramex 4y ago
  While this is true in some sort of physical sense, it's not really useful for home heating. The problem is that while burning stuff makes heat, that heat probably isn't where you wanted it, and you need to capture the heat and move it to where it's useful. Unfortunately burning stuff produces exhaust gases, and those too are hot, that is they contain some of the valuable heat, but the gases themselves are dangerous and unwanted. Modern boilers achieve about 94% efficiency. That is, if we make 1MJ of heat energy by setting stuff on fire, the boiler transfers 940 kJ of heat energy into hot water. The remaining 60 kJ is warm exhaust. You've probably seen the exhaust from people's homes if you live somewhere with such boilers.

legulere 4y ago

Heat pumps produce several times the heat as electricity put in. Even with a typical 40%-50% efficiency for a gas power plant you end up with more than 100% efficiency with a heat pump. If the power plant rest heat is used for instance for district heating you reach efficiency of around 90%. Add the efficiency of heat pumps on top and you end up with something very good.

throwaway894345 4y ago

Heat pumps transfer heat from the outside, they aren’t generating it so it’s entirely likely that they would result in fewer net emissions than burning coal directly. And the calculus just keeps getting better for grids that incorporate more natural gas and renewables.

KVFinn 4y ago

>Burning something for heat is always more effective, cheaper, and produces fewer emissions compared to an electric heater... >If you’re getting electric heat from coal fired steam that’s always worse than burning the coal locally to heat something, and this is true for all emission-producing power sources. Apparently you can actually save natural gas with electric heat and a heat pump. https://youtu.be/MFEHFsO-XSI https://youtu.be/MFEHFsO-XSI

altcognito 4y ago

The argument is that for regions that do not spend much time below 15 degrees Fahrenheit, they tend to be cheaper to run because they can pump more heat than electricity they use, effectively becoming 300% efficient instead of 95% efficient for say an gas heater. As the temperature differential between the desired temperature and the outside temperature increases however, the efficiency does drop and what you say is true, but for most of the populated world, this is not the situation. https://www.youtube.com/watch?v=7J52mDjZzto https://www.youtube.com/watch?v=7J52mDjZzto (edit: I think you're going to get a lot of links to the overly in depth series tech connections, but I'm leaving it here all the same)

boloust 4y ago

Heat pumps can be efficient enough to overcome the losses from coal -> electricity. So it's possible to use a heat pump to heat a space more efficiently than burning that same coal directly in the space.

deleted 4y ago

[deleted]

brnt 4y ago

Typical heatpump COP in Northwestern Europe sits at about 4, that means for 1 kWh of electricity your moving 4 kWh heat into your home. Electrical resistive heating sits at 1:1 by definition, and methods like wood, gas or oil, combustive methods, usually with modern installations at 80-95% efficiency. Further south heatpump COP improves; the rule of thumb is a smaller delta T the better. Moving heat is always more efficient than creating heat. It's elementary physics. Airconditioners, or air-to-air heatpumps, are cheap heaters for the same reason (any units sold in the last 10 years can move heat bidirectionally). Here in NW Europe by cooling bill is barely noticeable (it's no desert clime after all, although the last decade seems like it's getting there!). You don't need to set it to 18C; I really only cool when the attic gets over 28C while I work there (home office), down to 24-26, which is a few weeks a year. In winter, it heats the room at ~400% efficiency compared to the typical ~80 for gas heating. Move heat. Don't create it.

redeeman 4y ago
> Typical heatpump COP in Northwestern Europe sits at about 4 :) yeah, when its really quite warm outside, but not quite warm enough that you dont need heating. as soon as you even get down to 5C outside, you are not getting a COP of 4. Many vendors may tell you that, but well... :) some people were also sold bridges :)
- brnt 4y ago
  A lot of people in my environment are in fact getting sCOP of 4. Bit better in fact: close to 5 in the group that also installed floor heating everywhere. Note that COP around freezing is almost always the worst due to frequent defrosting, so yes, COP is worse at -5 most likely. You can replace COP with sCOP in earlier replies of mine. What is true is that most people, including installers, don't know how to tune them very well, or forget to combine them with low temp radiators/ floor heating. Too high a T_out also occurs frequently. In the Netherlands, heatpumps have been standard issue in new construction for a decade now, and 4 is about the average. It's very much not imaginary, but hard to believe for people from areas used to wood and oil burning ;)

crote 4y ago

The trick is that heat pumps are using energy to move heat. Let's make an example calculation: When heating your house to burn coal, you release 1 Joule when burning the coal. It's a small plant, so it is not very efficient. You probably get 0.85 J of heating out of it. If we instead burn coal in a large-scale modern power plant, we release the same 1 Joule, but capture 0.95 J of it in electricity. Let's say we lose 10% transporting it to your home, leaving 0.855 J remaining. Now, we use that energy to move heat from outside into our home, at an efficiency of about 300% - so for every joule we consume, we move 3 joules of energy. This means our house is heated with 2.565 J. But the energy the heat pump consumes doesn't disappear - it becomes heat too. So your house gets a total of 3.42 J hotter! So 1 J of coal gets you either 0.85 J of heat by burning it directly, or 3.42 J of heat by burning it in a power plant and using a heat pump. And of course don't forget that for climate reasons it is trivial to replace that power plant with a solar farm or wind turbine. The worst-case scenario for a heat pump is that it is exactly as efficient as burning stuff directly. But in virtually all cases, it is way better.

aftbit 4y ago
Pretty good assessment, except I think your figure for heat efficiency of power generation is way off. I would expect to convert around 30-40% of the heat energy to electricity.
- hedora 4y ago
  95%+ efficient coal boilers have existed since the '90s.
  - aftbit 4y ago
    This is fuel to electricity efficiency? That seems unlikely to me, both based on sources[1][2], and the thermodynamics of the Carnot equation. A Carnot cycle heat engine (which is most efficient possible AIUI) has a maximum efficiency of 1 - Tc/Th. Given a Tc of 300K (STP-ish), achieving an efficiency of 0.95 would require a Th of 6000K, well above the melting point of steel (only around 1800K). 1: https://www.eia.gov/todayinenergy/detail.php?id=44436 https://www.eia.gov/todayinenergy/detail.php?id=44436 2: https://www.energy.gov/fecm/science-innovation/office-clean-coal-and-carbon-management/advanced-energy-systems/transformative https://www.energy.gov/fecm/science-innovation/office-clean-...