4 ms·

> Heat pumps are about 250-300% efficient. Sure. When we’re talking about the temperature band they work in. Once it hits 0C the efficiency is very low, and by

> Heat pumps are about 250-300% efficient. Sure. When we’re talking about the temperature band they work in. Once it hits 0C the efficiency is very low, and by -10C is almost doing nothing at all. At that point you have two things happening… 1. You are using electricity to warm your coils outside to keep frost and snow off them. 2. You are using drastically inefficient heat for your home. 200-300% in their band under ideal conditions, maybe. Seems like cherry picking.

wtallis 4y ago
200-300% efficient is what a very bad heat pump would do under ideal conditions. Good heat pumps have a coefficient of performance above 3 for temperatures above freezing (and above 4 for only mildly chilly outdoor temperatures), and still well above 2 at temperatures around 15°F/-10°C. My 10 year old apartment has a heat pump rated for a CoP of 2.3 at a temperature of 17°F/-8°C, which is actually below the record low outdoor temperature for this area. This isn't some exotic new equipment or a model designed for cold climates; it's what was cheap and mainstream a decade ago.
- SV_BubbleTime 4y ago
  Cool. But, how much of the US gets below 17F? I think it’s a lot.
  - wtallis 4y ago
    17°F isn't the point at which my heat pump stops working. It's just the lower temperature conventionally used as a point of comparison on the spec sheets for such devices. There's another column on the spec sheet for 47°F (where my heat pump model is listed as having a CoP of 3.6). And as for the question about colder climates: it's not a matter of whether an area can occasionally experience temperatures below eg. 17°F. What matters is whether you'll ever experience daily highs that are cold enough to prevent heating the house.
    - 8note 4y ago
      The question is what the cop is at -20C though, which is a fairly common winter temperature, and you really need heat at -40
      - wtallis 4y ago
        I was responding specifically to this bit: "Once it hits 0C the efficiency is very low, and by -10C is almost doing nothing at all." I've refuted that. If you want to discuss some more distant goalposts, I won't be able to offer firsthand evidence.
        SV_BubbleTime 4y ago
        You are free to refute that. Doesn’t make it wrong. At -10C you are hardly pulling anything from the air, but you are spending electricity to keep your coils free of frost, as inefficiently as possible. Do you not know how a heat pump works in cold weather?
abigail95 4y ago
What heat pump model are you using for your numbers so I can confirm its specs?
- 8note 4y ago
  For pretty standard specs, you should be able to look at any old heat pump
jillesvangurp 4y ago
I'm not cherry picking, I'm merely describing the status quo in a place of the world that can be pretty extreme compared to NY. You are talking about air source heat pumps. There are actually variants of that technology that work fine at -20 and below. -20 is actually quite far above absolute zero. The challenge is not that there isn't enough energy but finding and pumping liquids around that can absorb that "heat" and actually stay liquid. Efficiency indeed drops below zero. But it still works. However, ground source heat pumps are not dependent on the air temperature at all and work anywhere you can get a decent temperature gradient from the ground. Which is pretty much anywhere except maybe on top of the arctic ice sheet in e.g. Antarctica.. Stick a few pipes in the ground and get them deep enough and you can have an nice cozy house pretty much anywhere that is not located on a few miles of ice. NY is perfect for that. No permafrost there and stable temperatures below ground throughout the year. And again, they have been doing this for decades in places like Finland, Sweden, Norway, Greenland, etc. That's because this stuff works and is reliable and efficient enough. This is not some new kind of science fiction technology. Millions of households depend on this when it gets to minus 40C and below (about the same in C and F). And having lived in Sweden and Finland, I can tell you that they like their houses heated properly there and it really gets that cold up north. They don't use gas in houses there at all and never have. There are no gas distribution networks there. Oil based heating has been phased out in most places there a long time ago. But people forget that that stuff has to be trucked in and trucking anything in gets tricky when there's a few meters of snow on the roads. Heatpumps, resistive heating, district heating, and wood based stoves is pretty much all they use there. District heating is not common outside the more populated areas (i.e. most of the Arctic region) with the exception of the larger towns and villages.
magicalhippo 4y ago
This guy[1] ran a test on his home during last winter, and found that his mini split had a COP of around 1.5-2.5 down to -10C. The data wasn't terribly correlated to temperature, though he didn't have a mini-shed for the outside unit to protect it from snow, so it probably had to defrost more often during the less-cold, snowy days. FWIW here in Oslo, we've been using a mini split as the main heat in our home, where it's often -15C for long stretches during winter, and can get down to -25C. It's in the main livingroom, and we do supplement the upstairs bedroom with resistive foil floor heating during the coldest periods. Other than that it's doing great, and comparing the electricity bills with friends and colleagues who don't have a heat pump it's definitely helping a lot. [1]: https://youtu.be/fxEqVuiHhM0?t=523 https://youtu.be/fxEqVuiHhM0?t=523

wtallis 4y ago

200-300% efficient is what a very bad heat pump would do under ideal conditions. Good heat pumps have a coefficient of performance above 3 for temperatures above freezing (and above 4 for only mildly chilly outdoor temperatures), and still well above 2 at temperatures around 15°F/-10°C. My 10 year old apartment has a heat pump rated for a CoP of 2.3 at a temperature of 17°F/-8°C, which is actually below the record low outdoor temperature for this area. This isn't some exotic new equipment or a model designed for cold climates; it's what was cheap and mainstream a decade ago.

SV_BubbleTime 4y ago
Cool. But, how much of the US gets below 17F? I think it’s a lot.
- wtallis 4y ago
  17°F isn't the point at which my heat pump stops working. It's just the lower temperature conventionally used as a point of comparison on the spec sheets for such devices. There's another column on the spec sheet for 47°F (where my heat pump model is listed as having a CoP of 3.6). And as for the question about colder climates: it's not a matter of whether an area can occasionally experience temperatures below eg. 17°F. What matters is whether you'll ever experience daily highs that are cold enough to prevent heating the house.
  - 8note 4y ago
    The question is what the cop is at -20C though, which is a fairly common winter temperature, and you really need heat at -40
    - wtallis 4y ago
      I was responding specifically to this bit: "Once it hits 0C the efficiency is very low, and by -10C is almost doing nothing at all." I've refuted that. If you want to discuss some more distant goalposts, I won't be able to offer firsthand evidence.
      - SV_BubbleTime 4y ago
        You are free to refute that. Doesn’t make it wrong. At -10C you are hardly pulling anything from the air, but you are spending electricity to keep your coils free of frost, as inefficiently as possible. Do you not know how a heat pump works in cold weather?

abigail95 4y ago

What heat pump model are you using for your numbers so I can confirm its specs?

8note 4y ago
For pretty standard specs, you should be able to look at any old heat pump

jillesvangurp 4y ago

I'm not cherry picking, I'm merely describing the status quo in a place of the world that can be pretty extreme compared to NY. You are talking about air source heat pumps. There are actually variants of that technology that work fine at -20 and below. -20 is actually quite far above absolute zero. The challenge is not that there isn't enough energy but finding and pumping liquids around that can absorb that "heat" and actually stay liquid. Efficiency indeed drops below zero. But it still works. However, ground source heat pumps are not dependent on the air temperature at all and work anywhere you can get a decent temperature gradient from the ground. Which is pretty much anywhere except maybe on top of the arctic ice sheet in e.g. Antarctica.. Stick a few pipes in the ground and get them deep enough and you can have an nice cozy house pretty much anywhere that is not located on a few miles of ice. NY is perfect for that. No permafrost there and stable temperatures below ground throughout the year. And again, they have been doing this for decades in places like Finland, Sweden, Norway, Greenland, etc. That's because this stuff works and is reliable and efficient enough. This is not some new kind of science fiction technology. Millions of households depend on this when it gets to minus 40C and below (about the same in C and F). And having lived in Sweden and Finland, I can tell you that they like their houses heated properly there and it really gets that cold up north. They don't use gas in houses there at all and never have. There are no gas distribution networks there. Oil based heating has been phased out in most places there a long time ago. But people forget that that stuff has to be trucked in and trucking anything in gets tricky when there's a few meters of snow on the roads. Heatpumps, resistive heating, district heating, and wood based stoves is pretty much all they use there. District heating is not common outside the more populated areas (i.e. most of the Arctic region) with the exception of the larger towns and villages.

magicalhippo 4y ago

This guy[1] ran a test on his home during last winter, and found that his mini split had a COP of around 1.5-2.5 down to -10C. The data wasn't terribly correlated to temperature, though he didn't have a mini-shed for the outside unit to protect it from snow, so it probably had to defrost more often during the less-cold, snowy days. FWIW here in Oslo, we've been using a mini split as the main heat in our home, where it's often -15C for long stretches during winter, and can get down to -25C. It's in the main livingroom, and we do supplement the upstairs bedroom with resistive foil floor heating during the coldest periods. Other than that it's doing great, and comparing the electricity bills with friends and colleagues who don't have a heat pump it's definitely helping a lot. [1]: https://youtu.be/fxEqVuiHhM0?t=523 https://youtu.be/fxEqVuiHhM0?t=523