12 ms·

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 abov

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?

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?