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Heat Pumps Take on Cold Climates

spectrum.ieee.org

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Re: Heat Pumps Take on Cold Climates

#21

Post by swechsler »

fullstop wrote: post #4
sokoloff wrote: post #2

> 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. This claim defies thermodynamics (and I expect better from IEEE). Heat pumps are bound to be less efficient as the spread between inside and outside temperature grows. (They might be just as effective or they might be just as efficient as current heat pump tech , bu…

Are they perhaps referring to geothermal heat pumps?

No, they specifically say "air source" heat pumps. And geothermal isn't new.

Re: Heat Pumps Take on Cold Climates

#22

Post by solardev »

fullstop wrote: post #4
sokoloff wrote: post #2

> 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. This claim defies thermodynamics (and I expect better from IEEE). Heat pumps are bound to be less efficient as the spread between inside and outside temperature grows. (They might be just as effective or they might be just as efficient as current heat pump tech , bu…

Are they perhaps referring to geothermal heat pumps?

No, they're talking about air source ones (which is what's popular these days):

> At about 4 °C, most air-source heat pumps currently on the market start operating at less than their full capacity, and at some point (usually around -15 °C), they can no longer do the job at all. At that point, an auxiliary heat source kicks on, which is less efficient.

> But advancements in compressor technology over the last five years have addressed that issue. By controlling the compressor motor’s speed, and improving the timing of when vapor is injected into the compressor, engineers have made heat pumps efficient in colder temperatures.

Re: Heat Pumps Take on Cold Climates

#23

Post by DannyBee »

sokoloff wrote: post #2

> 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. This claim defies thermodynamics (and I expect better from IEEE). Heat pumps are bound to be less efficient as the spread between inside and outside temperature grows. (They might be just as effective or they might be just as efficient as current heat pump tech , bu…

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.

Re: Heat Pumps Take on Cold Climates

#24

Post by ajross »

lcvw wrote: post #3

Is there a way to get your house (currently with hydronic gas heat) retrofitted for heat pumps that doesn’t result in either a ton of demo or ugly lines all over the exterior? I tried to switch over last year only to find the savings were not that great in my climate, and that it would have an unacceptable aesthetic cost.

> Is there a way to get your house (currently with hydronic gas heat) retrofitted for heat pumps that doesn’t result in either a ton of demo or ugly lines all over the exterior?

It's literally the same physical design as an air conditioner. So... yes, unless you hate seeing AC units too, I guess.

Re: Heat Pumps Take on Cold Climates

#25

Post by sokoloff »

ajross wrote: post #18
sokoloff wrote: post #2

> 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. This claim defies thermodynamics (and I expect better from IEEE). Heat pumps are bound to be less efficient as the spread between inside and outside temperature grows. (They might be just as effective or they might be just as efficient as current heat pump tech , bu…

If you want to get nitpicky: Cycle losses aren't the only source of inefficiency and in fact the end-to-end efficiency curves of most domestic heat pumps tend to be pretty flat through their useful range. Basic thermodynamics, provided a refrigerant that is well matched to the cycle (which is what the article is actually about), isn't really the core design point.

I've never seen a CoP curve that was not downward sloping with decreasing outside temperature.

Do a google image search for "heat pump cop curve" and glance at the results. All of them are significantly downward sloping because the underlying thermodynamic cycle effect is very strong (agree not the only) limit.

Re: Heat Pumps Take on Cold Climates

#26

Post by devsatish »

I just got one installed last month in middle of winter at my home in New England.

The air from heat pump feels more comfortable than the dry air from the furnace. I got installed with a the furnace back-up option, that way if the heat-pump can't generate the heat, it switches to propane (it becomes very cold here in New England in Winters). From my experience, the heat pump is working well in 30F and above weather (-1.C)

Heat pumps burn a lot of electricity, luckily I have solar to off-set that cost, although Solar generation is low in Winter, it adds up well over the year.

Heat Pumps + Solar is the way to go.

Re: Heat Pumps Take on Cold Climates

#28

Post by sgerenser »

cwoolfe wrote: post #11

As someone who switched to a heat pump recently, you should know "your mileage may vary." Don't confuse physical efficiency for cost efficiency. In many places, natural gas is still more cost efficient, even if it isn't as efficient in terms of physics.

Natural gas is dirt cheap in most of the U.S., so it does make it hard for heat pumps to compete, especially if electricity is expensive. Just checked my most recent gas bill and I only paid $1.09/therm (plus 7% sales tax and $10 fixed fee).

OTOH if you’re heating with propane or fuel oil, heat pumps are probably a good alternative.

Re: Heat Pumps Take on Cold Climates

#29

Post by bryanlarsen »

sokoloff wrote: post #17
bryanlarsen wrote: post #13

Earlier quoted context omitted.

" just as efficiently " as what? The way I read it was "just as efficiently as a conventional furnace". IOW, a COP of 1 at bitter cold temperatures.

the next words are "[as] they do", so I naturally read it as 'those same heat pumps'.

Yes on rereading it definitely appears phrased the way you interpreted. But as you said that's nonsensical so my brain must have dumped the nonsensical interpretation. :)

Re: Heat Pumps Take on Cold Climates

#30

Post by epistasis »

free_bip wrote: post #5

I have my doubts about heat pumps ever being viable for Canadian and other high-latitude countries -40 degree winters. Everywhere else though, they probably should be the standard.

What fraction of the population lives with -40 degree winters? That's the only reason they might not be viable, in that they require customization that is only useful to a tiny tiny tiny fraction of the population.
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