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Heat Pumps Take on Cold Climates

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Re: Heat Pumps Take on Cold Climates

#51

Post by solardev »

atoav wrote: post #19
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…

My father has a heat pump that works fine in alpine climate (half of the winter snow outside) for more than a decade now. Not sure about the precise english terminology here, but his hear pump works using the deep ground water next to our house. The temperature of that water slightly dips in winter, but it is no more than a degree. It is a very old house that before had a oil heating system and I think the replacemen…

This is common in some parts of the world (which is great!), but not in the US. They're quite a bit more expensive, especially compared to modern mini-split air-source heat pumps that can cost just a couple thousand dollars and don't require any digging or duct installations, just a small hole in the wall.

Re: Heat Pumps Take on Cold Climates

#52

Post by sgerenser »

grumpyinfosec wrote: post #44
sgerenser wrote: post #28

Earlier quoted context omitted.

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.

Thats kind of high. I only pay $0.78 a therm here in Wisconsin. 1 therm is around 30kwh so im paying like 2.5c a kwh vs 17c for electricity. So unless I can get a CoP of 700% from a air source heatpump im literally lighting money on fire. That really is the main issue, as much as I care about emissions I don't care enough to spend money on a heat pump to then spend more money on utilities. And the calculus gets worse…

Looks like Wisconsin has lower than average natgas prices vs. rest of U.S.: https://www.eia.gov/dnav/ng/ng_pri_sum_a_EPG0_PRS_DMcf_m.htm

Re: Heat Pumps Take on Cold Climates

#53

Post by goalieca »

epistasis wrote: post #30
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.

A huge chunk of canadas population in Quebec, Ontario, prairies, and BC see -20 for weeks on end. -40 is more rare but happens every year. Huge chunks of the mid-western USA see those as well. At -30 my furnace is basically on continuously.

Re: Heat Pumps Take on Cold Climates

#54

Post by sgerenser »

data_ders wrote: post #43
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.

For how long is gas likely to be cheaper? It’s generally more scarce right? Does anyone have predictions on US price over the next few decades?

Fracking has made natural gas extremely cheap in the U.S over the past several years. Apparently, right now its at the lowest inflation-adjusted price since 1990 per the WSJ: https://archive.is/8wEi7

Re: Heat Pumps Take on Cold Climates

#55

Post by sokoloff »

DannyBee wrote: post #23
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.

> 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?

Re: Heat Pumps Take on Cold Climates

#56

Post by rssoconnor »

I very recently replace my forced air gas furnace with a forced air heat pump (with 10 KW of auxiliary restive heater as well) in southern Ontario.

Over the last 11 days or so (February with a combination of cold and unseasonably warm days) I've used 1047.15 kWh of electricity, of which I estimate half to two-thirds is used on the heat pump. Taking the new ultra-low overnight pricing into account I'm paying an average of 9¢ (CAD) per kWh. I've been trying to pre-heat my home at the tail end of the ultra-low overnight rates (2.8 ¢/kWh) leading up to the 7 a.m. cutoff time.

My gas furnace was my only gas appliance, so I can remove now remove it and save on the month connection charge which is about $30 a month, even in the summer when I don't use gas.

Canada also, at least for now, has a pigouvian carbon tax, so I'll be saving on that as well.

Re: Heat Pumps Take on Cold Climates

#57

Post by sgerenser »

solardev wrote: post #34

If you're considering a heat pump, be sure to check the minimum operating temperature before you buy, and/or make sure you have a backup heat source. I live in a rented apartment with a mini-split, and it worked great for 363 of the last 365 days. Those two days, we had a sudden cold spell and temperatures went down to -6 F (which isn't that cold), but we found out the hard way that our unit was only rated to -4 F. O…

I don’t think it’s normal for a heat pump to just stop working completely like that vs. just getting more and more inefficient. Wonder if perhaps it iced up and the defrost wasn’t working.

Re: Heat Pumps Take on Cold Climates

#58

Post by grumpyinfosec »

sgerenser wrote: post #52
grumpyinfosec wrote: post #44

Earlier quoted context omitted.

Thats kind of high. I only pay $0.78 a therm here in Wisconsin. 1 therm is around 30kwh so im paying like 2.5c a kwh vs 17c for electricity. So unless I can get a CoP of 700% from a air source heatpump im literally lighting money on fire. That really is the main issue, as much as I care about emissions I don't care enough to spend money on a heat pump to then spend more money on utilities. And the calculus gets worse…

Looks like Wisconsin has lower than average natgas prices vs. rest of U.S.: https://www.eia.gov/dnav/ng/ng_pri_sum_a_EPG0_PRS_DMcf_m.htm

seems pretty comparable to the other colder parts of the country. (besides the east coast) The warmer parts of the US i'd imagine are less sensitive to residential gas prices.

Re: Heat Pumps Take on Cold Climates

#59

Post by [deleted] »

sokoloff wrote: post #25
ajross wrote: post #18

Earlier quoted context omitted.

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.

[deleted]

Re: Heat Pumps Take on Cold Climates

#60

Post by NDizzle »

sgerenser wrote: post #57
solardev wrote: post #34

If you're considering a heat pump, be sure to check the minimum operating temperature before you buy, and/or make sure you have a backup heat source. I live in a rented apartment with a mini-split, and it worked great for 363 of the last 365 days. Those two days, we had a sudden cold spell and temperatures went down to -6 F (which isn't that cold), but we found out the hard way that our unit was only rated to -4 F. O…

I don’t think it’s normal for a heat pump to just stop working completely like that vs. just getting more and more inefficient. Wonder if perhaps it iced up and the defrost wasn’t working.

It's my experience that they do stop working completely at some temp. The defrost cycle creeps up to 100% and there goes the heat.
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