3 ms·

this feels pedantic. They are clearly not talking about the theoretical bounds, but instead in practice. The claim can be literally true. It may be they are

this feels pedantic. They are clearly not talking about the theoretical bounds, but instead in practice. The claim can be literally true. It may be they are at x% efficiency in both cases, where x is optimal for bitter cold but not for mild winter.

sokoloff 3y ago
> The claim can be literally true. It can be. Would you take an even-money wager that the CoP curve will be flat [or increasing] with decreasing outside temp vs my wager that it will be downward sloping with decreasing outside temp?
- DannyBee 3y ago
  The claim is true. You've transformed their claim into something else. What they wrote is " But heat pump manufacturers say they now have the technology to heat homes just as efficiently in bitter cold as they do in milder winter temperatures." That is about whether they gained the technology to make the finished units as efficient in bitter cold as they are currently efficient in mild winter. Given they were inoperative in bitter cold, and fairly inefficient in mild winter, this is almost certainly trivially true. Here is a real curve: https://hvac-talk.com/vbb/attachment.php?s=f7eb5f83efc8804403081f85ab72d79d&attachmentid=822851&stc=1&d=1615838362 https://hvac-talk.com/vbb/attachment.php?s=f7eb5f83efc880440... If we all mild winter 32F, and bitter cold -10F, they would only have to improve efficiency by 2x at bitter cold to make it as efficient as current heat pumps as mild winter. That is easily possible. As for whether they are strictly flat/decreasing, they are not. Here is more data: https://connect.fujitsugeneral.com/3cfb13a7-a386-4697-aa3e-58187dfd578f https://connect.fujitsugeneral.com/3cfb13a7-a386-4697-aa3e-5... You can see capacity, input power, and efficiency do not have a strictly linear (flat or decreasing) relationship with outdoor temperature. This is an artifact of it being impossible to good at all things at once. It is also obvious to every reader you can not make a "maximally efficient in all" cases heat pump as efficient in bitter cold as in mild winter. So rather than assume that is what they are claiming by adding a lot of implicit things to it, i would just read it in a straightforward manner and when I do, it seems pretty easily true.

sokoloff 3y ago

> The claim can be literally true. It can be. Would you take an even-money wager that the CoP curve will be flat [or increasing] with decreasing outside temp vs my wager that it will be downward sloping with decreasing outside temp?

DannyBee 3y ago
The claim is true. You've transformed their claim into something else. What they wrote is " But heat pump manufacturers say they now have the technology to heat homes just as efficiently in bitter cold as they do in milder winter temperatures." That is about whether they gained the technology to make the finished units as efficient in bitter cold as they are currently efficient in mild winter. Given they were inoperative in bitter cold, and fairly inefficient in mild winter, this is almost certainly trivially true. Here is a real curve: https://hvac-talk.com/vbb/attachment.php?s=f7eb5f83efc8804403081f85ab72d79d&attachmentid=822851&stc=1&d=1615838362 https://hvac-talk.com/vbb/attachment.php?s=f7eb5f83efc880440... If we all mild winter 32F, and bitter cold -10F, they would only have to improve efficiency by 2x at bitter cold to make it as efficient as current heat pumps as mild winter. That is easily possible. As for whether they are strictly flat/decreasing, they are not. Here is more data: https://connect.fujitsugeneral.com/3cfb13a7-a386-4697-aa3e-58187dfd578f https://connect.fujitsugeneral.com/3cfb13a7-a386-4697-aa3e-5... You can see capacity, input power, and efficiency do not have a strictly linear (flat or decreasing) relationship with outdoor temperature. This is an artifact of it being impossible to good at all things at once. It is also obvious to every reader you can not make a "maximally efficient in all" cases heat pump as efficient in bitter cold as in mild winter. So rather than assume that is what they are claiming by adding a lot of implicit things to it, i would just read it in a straightforward manner and when I do, it seems pretty easily true.