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Science

As Heat Pumps Go Mainstream, a Big Question: Can They Handle Real Cold? (nytimes.com) 215

An anonymous reader shares a report: Heat pumps, in contrast, (to gas or oil furnaces) don't generate heat. They transfer it. That allows them to achieve more than 300 percent efficiency in some cases. Because they are more efficient, using heat pumps to cool and heat homes can help homeowners save money on their utility bills, said Sam Calisch, head of special projects at Rewiring America, a nonprofit advocacy group. In Maine, where heat pump adoption is growing, but where a majority of homes still burn oil, homeowners can save thousands of dollars in annual energy costs by making the switch, according to an analysis from Efficiency Maine, an independent administrator that runs the state's energy-saving programs.

Many heat pumps that are built for cold climates do have hefty upfront price tags. To soften the blow, a federal tax credit from last year's climate and tax law can cover 30 percent of the costs of purchase and installation, up to $2,000. As they've grown in popularity, heat pumps have increasingly been the subject of misconception and, at times, misinformation. Fossil-fuel industry groups have been the origin of many exaggerated and misleading claims, including the assertion that they don't work in regions with cold climates and are likely to fail in freezing weather.

While heat pumps do become less efficient in subzero temperatures, many models still operate close to normally in temperatures down to minus 13 degrees Fahrenheit, or minus 24 Celsius. Some of the latest models are even more efficient, and many "cold" countries, like Norway, Sweden and Finland, are increasingly embracing heat pumps. "We're starting to see evidence that the myth has been kept alive by people with an entrenched interest in avoiding the adoption of heat pumps," Dr. Calisch said. There are additional steps homeowners can take to make the most of their heat pumps, like sealing air leaks and drafts and improving insulation, said Troy Moon, the sustainability director for the city of Portland, Maine. Homeowners can also keep their existing furnaces as backup for the coldest days of the year, he said.

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As Heat Pumps Go Mainstream, a Big Question: Can They Handle Real Cold?

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  • Yes (Score:4, Insightful)

    by mspohr ( 589790 ) on Monday February 27, 2023 @12:25PM (#63327238)

    Yes

    • Re:Yes (Score:5, Informative)

      by Z00L00K ( 682162 ) on Monday February 27, 2023 @01:40PM (#63327538) Homepage Journal

      A heat pump doesn't have to take the heat from air, there are deep well heat pumps that takes the heat from underground and produces heat for the house.
      That works well in Scandinavia where the heat pumps warms water that's circulated to radiators in the house.

      • I'm not so much interested in these to heat a place...but the article alluded to them also being about to cool homes.

        It's late Feb, and in New Orleans, it's been in the mid 80's since last week.

        We'll likely get one more cool snap then Spring/Summer heat kicks in.

        Do these "heat pumps" also work cool or air condition your home?

        How does that work? How WELL does it work?

        Does it do anything for humidity like a regular Air Conditioner system does?

        I need something that keeps it in the 73-74F temp on normal d

        • by Z00L00K ( 682162 )

          They work both ways, so if you run a water/water pump as an AC then you can heat your water with it so you can take a shower. But there's going to be excess heat to be vented anyway.

        • Re: Yes (Score:5, Informative)

          by Junta ( 36770 ) on Monday February 27, 2023 @02:22PM (#63327754)

          Air conditioners are just a special subclass of heat pumps.

          Heat pumps in this context are just heat pumps that can move heat in either direction

          • Right, and they're great for climates like the southern US because then you don’t need a second system just for the small amount of heating days you have.

            • by Junta ( 36770 )

              Yep, and they have been pretty common for years in the southern US, precisely because the traditionally weaker heating performance is largely 'good enough' for the climate down here. The newness is heat pumps aspiring to get more market penetration in the northern climates where heat pumps have historically been wholly inadequate.

              • The newness is heat pumps aspiring to get more market penetration in the northern climates where heat pumps have historically been wholly inadequate.

                RTFA and you can avoid saying these things.

      • by jbengt ( 874751 )
        Yes, ground source heat pumps are a good idea, but typically 3 or 4 times the cost in new construction, even more expensive in existing buildings when replacing existing equipment, and often impractical for a particular site.
        • by Z00L00K ( 682162 )

          Even if the total system is expensive initially the cost over time could still be lower. After all if you do it right you don't have to re-do the underground work if you replace the heat pump.

        • The installation is more expensive because you have to drill or excavate to bury the coils that carry hot/cold water away from the coolant below the frost line. In the southern parts of the country that don't have a frost line, you can extend the coils horizontally at a 6-8 foot depth and achieve the same performance for half the price. The benefit over air cool is that you won't hit that inefficient slump when you get below a certain air temperature, and most air systems with spinning fans don't do well in
        • by AmiMoJo ( 196126 )

          Not these days. Just need to dig a deep hole about 25cm in diameter. There's a machine that does it.

    • by jbengt ( 874751 )
      No, at least not air-to-air heat pumps in most places with decently cold winters. Here the median of the annual extreme is -13F (-25C). That means half the winters it will get colder than the rating of the heat pump in TFS. And even when it's above the rating, it gets inefficient as it approaches the rating. Also, whenever below freezing, the outdoor coil might frost up, necessitating a defrost cycle, which kills efficiency. But you can compromise and get a heat pump with a second source of heat for th
  • by poptix ( 78287 ) on Monday February 27, 2023 @12:27PM (#63327244) Homepage

    None of the heat pumps I looked at were rated for operation here, where it can get down to around -40 on a regular basis. This was looking at actual manufacturer specifications, not some boogeyman website.

    • In places that go below 10C ground source heat pumps work just fine. Above 10C air source are available with decent performance
      • by ahodgson ( 74077 ) on Monday February 27, 2023 @04:24PM (#63328197)

        Modern air source heat pumps can work fine down to about -15C (some claim -20). Assuming your home is decently well insulated to start with, of course.

        If you often get colder than that, you need ground source. ie. Minnesota.

        If you sometimes but only very rarely get below that, put a big resistance coil in your air handler, (or keep your gas furnace), as a backup.

        I'm heating 3000 sq ft at temps down to -12C with an air source heat pump just fine. At temperatures below about -2C it would still be cheaper to heat with gas, though.

        • Looks like the newest heat pumps can burn natural gas to assist in improving efficiency. If the waste heat is discarded in the house then this could have a big impact on cold weather operations. Details at energy.gov [energy.gov].

          It is an interesting idea. In place of using just electricity to operate the cycle, natural gas (or any other heat source) plays a role to minimize the amount of electricity required. And by making the heat pump more efficient it becomes reasonable to operate at lower temperatures.

        • by v1 ( 525388 )

          Mine sure can't. I live in Iowa and we can get some brutally cold days in the winter. This unit is a hybrid, it can reverse for AC, do heat pump for heat, or if it gets too far behind it switches over to "emergency heat", which just means the heat pump turns off and the natural gas comes online,

          IIRC mine is configured to switch to emergency heat when the difference between the thermostat and the set point is 2 degrees or more. This may not seem like a lot, but the idea is the heat pump maintains temperat

    • by Retired Chemist ( 5039029 ) on Monday February 27, 2023 @12:34PM (#63327270)

      None of the heat pumps I looked at were rated for operation here, where it can get down to around -40 on a regular basis. This was looking at actual manufacturer specifications, not some boogeyman website.

      True enough. Most of the US does not get that cold of course. For your area, I could see a heat pump along with a secondary furnace for cold weather, although the cost of both units might be impractical. I worry about ventilation issues. The article suggests improving sealing of the house. There are already issues with indoor air quality, because of houses being so tightly sealed ( radon, off gassing from plastics, etc.).

      • by Muros ( 1167213 )

        I worry about ventilation issues. The article suggests improving sealing of the house. There are already issues with indoor air quality, because of houses being so tightly sealed ( radon, off gassing from plastics, etc.).

        You can get heat exchange air vents.

      • by jonadab ( 583620 )
        > Most of the US does not get that cold of course.

        Eh. 40 below, no. 20 below, however, is a fairly normal cold winter day in pretty much the entire northern half of the continental US, and that's still below the recommended operating temperature range for a lot of existing popular models of heat pump, albeit not by as wide a margin.

        *Can* heat pumps handle winter? Sure, of course they can in principle. The underlying physics can work in principle as long as there is some ambient heat to extract. But,
      • by teg ( 97890 ) on Monday February 27, 2023 @02:05PM (#63327652)

        None of the heat pumps I looked at were rated for operation here, where it can get down to around -40 on a regular basis. This was looking at actual manufacturer specifications, not some boogeyman website.

        True enough. Most of the US does not get that cold of course. For your area, I could see a heat pump along with a secondary furnace for cold weather, although the cost of both units might be impractical. I worry about ventilation issues. The article suggests improving sealing of the house. There are already issues with indoor air quality, because of houses being so tightly sealed ( radon, off gassing from plastics, etc.).

        In Norway, new houses for the last 15 years or so have been required to have ventilation that recovers heat, be sealed, and be well insulated. Not explicitly, but there are requirements on both ventilation (1.2 m^3 per sqm per hour, 26 m^3 per planned bed in a sleeping area) and energy use.

      • For your area, I could see a heat pump along with a secondary furnace for cold weather, although the cost of both units might be impractical

        A more common solution is a heat pump that has an integrated resistive heating element, for use when temperatures drop below what the heat pump can handle. This means that when it gets really cold your heat suddenly gets hugely more expensive. What that does to your overall costs depends on how often that happens and how long it lasts. If you only have to use resistive heat a handful of days per year it'll be cheaper than a secondary furnace.

      • by night ( 28448 )

        Ideally houses would be designed to be efficient. With modern techniques you can get very low exchange rates with outside. To fix that you have to engineer in the airflows. The good news is you can design it in, get as healthy air as you want, and do energy recovery so most of your AC or Heat stays inside.

      • by kbahey ( 102895 ) on Monday February 27, 2023 @03:57PM (#63328119) Homepage

        I worry about ventilation issues.
        The article suggests improving sealing of the house.
        There are already issues with indoor air quality, because of houses being so tightly sealed ( radon, off gassing from plastics, etc.).

        That is a solved problem.

        There are HRVs (Heat Recovery Ventilators) that most new homes in Ontario have now.
        They take air from the outside, pump it over the heat exchange element, which is heated (or cooled) by the indoor air that is exhausted to the outside.

        It gets coupled to your furnace ducting, and runs 24/7.

    • by Turkinolith ( 7180598 ) on Monday February 27, 2023 @12:36PM (#63327284)
      Similar situation here in Montana. The heat pumps the HVAC rep I spoke with said they wouldn't really be able to hold up here and the ones they could install would only help cut costs they said if my bill was routinely over $400 a month with my current gas equipment.
    • by goomba000 ( 10192551 ) on Monday February 27, 2023 @12:39PM (#63327298)
      I live in Quebec, and it is much colder than where you live. First, it never gets down to around -40 (C or F), much less "on a regular basis". Second, almost everybody in my neighborhood has a heat pump, and they work very well down to -25C (-13F). Beyond that (extremely rare cases), we supplement with electric heating. How you can be modded +4 informative is beyond me.
      • by Frederic54 ( 3788 ) on Monday February 27, 2023 @01:06PM (#63327390) Journal

        Québec here too, my heat pump is rated -20C (-4F) so I still have regular electric heating for the few days it goes very low (we got a chilling of -40 a few week ago), else, it's pretty efficient.

      • The same argument comes up with electric vehicles. There’s always a story ready about hauling an ocean liner up a mountain every week.

        • by poptix ( 78287 )

          Except for the fact that this article specifically mentions that they're suited for use in "cold countries", the specific "cold countries" that are very similar to Minnesota -- so much so that many people from those "cold countries" settled the state.

          I like the technology, it's just not yet suitable for my area, despite the articles implying it is.

          • by teg ( 97890 )

            Except for the fact that this article specifically mentions that they're suited for use in "cold countries", the specific "cold countries" that are very similar to Minnesota -- so much so that many people from those "cold countries" settled the state.

            I like the technology, it's just not yet suitable for my area, despite the articles implying it is.

            You could also realize that it's a really good fit most of the time, and supplement with other heating (e.g. a fireplace) the days that are colder. Here - in this part of Norway - it gets down to -20 C a couple of times a year, and heat pumps works absolutely perfectly.

            • It gets about that cold in northeast Ohio (though it's considered extreme), sometimes stays that cold for days at a time, and this is one of the warmer places on the northern U.S. border. Big parts of the country get much colder.

              I would love to have a heat pump, but unless it comes with resistive heating for very cold days (which is very expensive here), I doubt it would work in most of the northern U.S.

      • by caseih ( 160668 )

        Sorry but you're not making sense. If you never get down to -40 then how can you say where you live is colder than where he lives in Minnesota? It's clearly not true. Believe or not Minnesota could well be colder than Quebec. Just because you're farther north says nothing about the regularity of brutally cold temperatures in some regions.

    • by adonoman ( 624929 ) on Monday February 27, 2023 @12:42PM (#63327310)
      I live up in Manitoba in 100-year-old drafty house, and heat pumps are starting to be used more here - so I don't think using Minnesota is a great excuse. You're better off using a buried in-ground loop if it's doable, but that's hard to put in place in small lots and old construction. But even an air heat-pump is usable, provided you have a sufficient backup heat source for the couple of days when it gets really cold. You have to take into account that when it comes to heat transfer, it's the actual temperature that counts, not the "feels like" temperature.
      • You would have to have a real efficient air heat pump for Manitoba. Much of the winter is below or around -20C. You can get heat pumps that work down to -30C but they are very expensive.
    • Sure but I don't think -40 falls into the definition of "real" cold category of the article. May be the article is more precise but I only see the headline.
      • Most of the continental U.S. is warmer than that most of the winter, but several northern states can get colder during a substantial part of winter. Parts of upper Canada and Alaska are that cold most of the winter.

        (N.B.: -40F = -40C.)

    • by geekmux ( 1040042 ) on Monday February 27, 2023 @12:51PM (#63327334)

      None of the heat pumps I looked at were rated for operation here, where it can get down to around -40 on a regular basis. This was looking at actual manufacturer specifications, not some boogeyman website.

      Uh, just to be fair here, unless your living quarters are literally underground, there aren't many solutions that are "rated" (meaning actually functional) at 40 below zero.

      Source: Lived in Alaska for three years. 40 below is what we would warm up to in the afternoon from 60 below. Only damn thing that really heated the house was technology thousands of years old; fire.

      • by AmiMoJo ( 196126 )

        You appreciate though that those are extreme conditions that don't affect most people. The population of Alaska is 0.2% of the population of the United States according to a quick Google search. About 730k people.

        For the vast majority of people living in cold areas, air source heat pumps are fine. For the rest, ground source or some other form of heating. People need to get the message that heat pumps work in all but the most extreme conditions.

    • by chill ( 34294 ) on Monday February 27, 2023 @01:02PM (#63327368) Journal

      Where exactly do you live? Because none of the weather almanacs I've looked at show anywhere in Minnesota "regularly" getting down to -40.

      Even in the ice hells that are Tower and Pine City, where the state record lows are frequently set, the average winter lows are still single digits.

    • I know some of them are rated for -35C. The question is what percentage of the year is temperature below -35C? Even a heatpump good until -18C like mine could still be better than nothing.

      • Where I live, about sixty days per year have night time temperatures between -30 and -35C. Another sixty have night temperatures below -20.

        I haven't heard of any going to -35, only -30, so that is news to me. I'm glad to hear the technology is progressing!

    • None of the heat pumps I looked at were rated for operation here, where it can get down to around -40 on a regular basis. This was looking at actual manufacturer specifications, not some boogeyman website.

      Maybe with wind chill, but for St Paul the record low is -41 [wikipedia.org].

      Either way, I live in central Alberta where it can regularly reach -40 Celsius!!! (which is -40F)

      Actually, not so regularly, we get -40 at night a few times a winter, and once every couple years the daytime high will be under -40, but for the most part temperatures are somewhere between -5 and -25, which is within the range of the cold climate heat pumps.

      And for anywhere with proper winter you're going to need a backup heat source. You can do an e

      • As you mention, heat pumps will come with "auxiliary heat" settings. Assuming a central heat pump system, it seems simple enough to me that rather than operating a relay to turn on a direct resistant heater, it simply turns on the gas/oil furnace instead.

        You might even want to mess with the set temperature a bit, because you don't want to turn on the auxillery heater until the last possible moment, really, not until the heat pump's efficiency is not only seriously degraded, but it simply can't produce enou

        • These conversations always require context. Most houses in North America have forced air systems. Many/most in Europe use water circulation. With forced air systems, you need to turn on the auxiliary heat well before the heat pump can't keep up. With a heat pump, the "take off" temperature is much lower than resistive electric or gas and the forced air will feel cold even if the heat pump is operating efficiently. It feels cold because your body can't warm the air around you. So the thermometer will sh
    • by njvack ( 646524 ) <njvack@freshforever.net> on Monday February 27, 2023 @01:13PM (#63327418)

      I grew up in Minnesota; there's nowhere in the state where it gets to -40 on a regular basis. Even if you live in Moorhead, -40 is exceptionally cold.

      Not to say Moorhead is a good candidate for a heat pump install! Even if the heat pump won't cut it for one day a year, you absolutely need to have an alternative solution in place. "It is exceptionally cold" and "my heat doesn't work" is a recipe for a bad day. Some systems come with resistive heating backup -- it's very expensive to run, but dead simple and if you only need it a couple days a year, maybe okay. But some parts of MN are in a climate where a regular gas or oil furnace and AC may make the most sense.

      Even in the Twin Cities, though, an air source heat pump is probably a good option. Talk to an installer.

    • You are hitting the theoretical limits here. At -40, there is little heat to pump. Efficiency goes down drastically when the temperature difference is large. From memory, 20 to 30 degrees max. Have a look at COP and SCOP if you're interested.
    • by night ( 28448 )

      There's hybrids, mine can do heat pump to -10F, and falls over to natural gas if needed.

  • by fatalexe ( 845503 ) on Monday February 27, 2023 @12:33PM (#63327266)
    This has been solved since the 1940s. It isn't cheap but geothermal earth coupled ground-source exchange loops boost efficiency quite a bit. Since at depth the temperature stays constant this is a. non-issue.
    • by HiThere ( 15173 )

      That's still going to depend on where you live. One of the above comments came from Alaska. If you've got permafrost, I don't think a ground loop heat pump is going to do much for you. Minnesota? I don't know. That can get hot in the summer, so possibly the ground temperature would suffice....but you might need a BIG ground loop. You're pulling heat from a limited area. True, you're recharging it in the summer when you cool the place, but ... think of it as a battery. It's not generating the heat th

      • by jbengt ( 874751 )

        True, you're recharging it in the summer when you cool the place, but ... think of it as a battery. It's not generating the heat that you extract with the ground loop, it's repaying what it's previously been charged with.

        The storage effect of a ground loop is minor compared to the efficiency gained by having milder source/sink temperatures. (Wells work even better, if you can drill them, since they're deeper and get into ground that has a steadier year-round temperature, and they take less footprint if sp

      • The Alaska Center for Energy and Power did a study on the use of ground loop heat pumps in AK, and found that although there aren't many of them (yet), the users of the existing ones are quite satisfied with their performance. Surprisingly to me, most of the installations are horizontal loop systems. I would think that you'd be much better off going deep. Apparently it's because drilling equipment is limited in availability and expensive, but backhoes for digging shallower horizontal loop systems are cheape

    • by kalieaire ( 586092 ) on Monday February 27, 2023 @01:09PM (#63327400)
      Geothermal is expensive because Specialized Labor, Specialized Equipment, Scheduling (the driller guy and the electric utility to identify the utility lines). If this was a requirement in all new construction, the costs would be much more affordable. Also, with heat pumps as efficient as they are, there are a couple of design options available. Hybrid Natural Gas + Heat Pump. This solution is flexible for homes with Natural Gas where there's a small burner that adds heat into the heat pump intake. This gives the Heat Pump the boost it needs in frigid weather. And of course, Geothermal Heat Pump where it can pull heat out of the ground. Beyond the standard considerations, there are other options as well. In Nebraska, there's a local movement where people are building greenhouses that can handle hot weather of the summer and cold frigid winters. They bury a series of 12" diameter pipes 8' deep before they build the greenhouse over it. Year round, the air coming out of the pipes is 50F. This is something a home owner can easily do by getting a permit, hiring someone to do the work (trenching is serious business and should only be done if you have experience because people die in them when they're not properly dug given existing conditions). Filling it with proper gravel and sand bed at the bottom, placing the pipe inside, filling with more sand/gravel, and then regular soil backfill. Then you just run a blower line right up to your heat pump and all is good.
    • Isn't cheap is an understatement. A well-off neighbor has a geothermal heating system and it was around 50K to have it setup. I love the idea and I hear it works great, but the price is a definite turn-off.
  • by bobthesungeek76036 ( 2697689 ) on Monday February 27, 2023 @12:35PM (#63327272)
    I live in the DFW area in Texas and I have heat pumps in my house. It does struggle when it gets below 20F. When we had that cold spell in Feb 2021 my house was around 55F inside (I did not lose power) so it struggled big time. I have two 3-ton units and my house is a 2900ft2 two story. But that doesn't happen very often so all in all the heat pump works.
    • Yep, I live in New Zealand where daytime winter temps can be around 8 degrees C and overnight it can drop to as low as -6 or so.

      We have a large Panasonic heat pump but we still have to use supplementary heating (a wood-burner) during the winter months because when it's really cold, all the pump does is "take the chill off things" rather than actually heat the place to a comfortable temperature.

      Regardless of how efficient these things are, you reach a point where it spends most of the time trying to de-ice t

      • In much of the U.S. temperatures get much colder, and the indoor temp MUST be at least +10C to keep pipes near outside walls from freezing. We also have high humidity during much of the year, although, thankfully, not during the very coldest months.
    • I'm surprised. I'm in FL and every heat pump has a resistive auxiliary unit. It only runs once or twice a year. You can smell it.
      • I'm surprised. I'm in FL and every heat pump has a resistive auxiliary unit. It only runs once or twice a year. You can smell it.

        I had that purposely turned off at the thermostat. Not sure how much electricity that would use but since it has two (2) 60A breakers per unit probably a bunch. And I was trying not to kill the grid during the winter storm.

  • I was looking at some articles describing how modern heat pumps could work in colder climates.

    What I could not find was, what does "work" really mean? What is a realistic indoor temperature you can achieve with a heat pump, when let's say the outside air is 0 degrees F for a week or so.

    • by msauve ( 701917 )
      I would define "work" as being over 100% efficient. i.e. Generate more heat than simply using an auxiliary electric heater.
      • I would define "work" as being over 100% efficient.

        You need to be about 200% to beat a gas furnace.

        When gas is burned for heat, nearly all the heat is available.

        When gas is burned to generate electricity, the efficiency of a modern gas turbine is about 50%. So your heat pump needs to be at 200% just to break even with burning the gas directly.

        simply using an auxiliary electric heater.

        That isn't a fair comparison because resistive heating is not the alternative.

        • Many heat pumps are paired with resistive heat. Certainly in new construction they are as one isn't going to put in a heat pump and a furnace at the cost of a fortune. To make sense, the heat pump/resistive heat combination needs to have a lower operating cost than a gas furnace and separate air conditioner.
    • I'm in Québec, we often are in the 0F to 15F range for weeks or months, I set mine to 73F and it's 70-73 depending of the room.

    • by HiThere ( 15173 )

      What the realistic temperature you can achieve will depend on how well-insulated your house is. ... Well, there are other factors too. What the radiating surface it counts, how exposed you are to thermal conduction, etc. And, of course, how much heat pump you're using.

      So the question as asked cannot reasonably be answered. You need to look at your particular case, and see what your options are.

      Here's a place to start: I you don't have any powered heat source, how rapidly does your house cool down to wha

    • by poptix ( 78287 )

      You're looking for the "Delta T" (Î"T) on the spec sheet. That's the temperature difference it's able to maintain between input and output.

    • by jonadab ( 583620 )
      > What is a realistic indoor temperature you can achieve with a heat
      > pump, when let's say the outside air is 0 degrees F for a week or so.

      Depends. Different models of heat pump can move different amounts of heat. The amount and quality of insulation your house has also matters, and of course the amount of surface area your house has, how badly the windows leak heat (are they modern triple-pane windows?), how often you open the doors, etc.

      In principle, you can use heat pumps to make your house a nic
    • by anegg ( 1390659 )

      I was looking at some articles describing how modern heat pumps could work in colder climates.

      What I could not find was, what does "work" really mean? What is a realistic indoor temperature you can achieve with a heat pump, when let's say the outside air is 0 degrees F for a week or so.

      How well it "works" depends on the temperature differential you are trying to achieve (interior temps versus exterior temps), how well insulated your house is, what the exterior temperature is, and the rated heating capacity of your heat pump ("bigger" means more BTUs output). A system properly sized for your climate and house should be able to heat up to the upper 70s (F) at least for all outdoor temperatures, but will probably require a secondary heat source (backup heat). Sizing for the extreme tempera

    • Bare minimum in my mind would be keeping water pipes running along or near walls from freezing. This requires about +20C/+68F most of the winter, but during the very coldest days, even that isn't enough, and we have to keep the water running at a trickle until the cold finally lets up.
  • From direct, recent personal experience: a traditional single stage forced air, ducted heat pump is good until around 36 degrees F or so, at which point it starts blowing lukewarm air. Moreover, at that point it usually will switch to dreaded and exhorbitantly expensive "auxiliary heat," which means heating up a wire and literally burning up any electricity savings. It's fine for keeping an unoccupied house at 50 degrees F or so so the pipes won't freeze, but not comfortable, Below that point, I have fou

    • From direct, recent personal experience: a traditional single stage forced air, ducted heat pump is good until around 36 degrees F or so, at which point it starts blowing lukewarm air.

      Depends on the unit and your home's insulation. We've had multiple days in a row with lows below 32, and I have mine set to 72, it had no problem keeping up. It's a few years old, variable speed, so not you know, builder grade, but didn't have to run at 100% or full-on anyway.

      I don't doubt your experience though, every home is different with respect to drafts or insulation, and the unit this one replaced couldn't really keep up in the winter and ran "aux" heating on the coldest days, but also I replaced it

  • Oh really? (Score:5, Informative)

    by jbeaupre ( 752124 ) on Monday February 27, 2023 @12:54PM (#63327340)

    "Heat pumps, in contrast, (to gas or oil furnaces) don't generate heat. They transfer it. That allows them to achieve more than 300 percent efficiency in some cases."

    Heat pumps DO generate heat. The compression step is work and adds more energy (heat) to the working fluid. That's where most of the electrical energy is going. Not losses in the motor or compressor, but in compressing the fluid.

    The ability to drag more heat along is why they can get >100% efficiency ... assuming the temperature gradient isn't too large. At 100% efficiency, the amount of heat being transferred + heat from compression is in balance with the electrical power required.

    • Re:Oh really? (Score:4, Informative)

      by 140Mandak262Jamuna ( 970587 ) on Monday February 27, 2023 @01:30PM (#63327502) Journal
      In second year, in Thermodynamics class, Prof Bhaskar ( of Bhaskar and Venkatesh fame) taught us never to use the term "efficiency" for heat pumps (and air conditioners). The term he insisted on using is Figure of Merit.

      FoM was defined as the heat output divided by mechanical energy input.

      You see heat is a low quality form of energy, mechanical energy easily goes to heat, but very difficult to convert heat to mechanical energy. Heat pumps need high quality mechanical energy/electrical energy to run.

      For airconditioners, there is no other way to cool, so they have no real competition. But heat energy is often much cheaper than electricity. Thus even with a figure of merit of three or four, if heating oil or firewood or natural gas is three or four times cheaper, heat pumps wont win economically.

      So it was not all mere FUD that kept the heat pumps from getting wider acceptance. Before low-ambient heat pumps, they did not work two or three months a year, and when they did work it was not the critical cold months. And the cost benefit was complex and variable.

      BTW I recall the Figure of merit used in test problems back then was 6 to 8. May it drops to 3 for low ambient heat pumps. I would have expected it to reach well over 10 by this time for A/C in moderate climes.

      • by AmiMoJo ( 196126 )

        Oil/wood/gas aren't really cheaper, it's just that the cost is externalised. You don't pay directly for the emissions, the endometrial damage, the effect of pollution on health, and the climate change.

    • In reading the specifications on my heat pump there is a point where the outside temperature is so low that running it would mean pumping heat outside. Not all heat pumps will pull waste heat from the compressor motor. In fact I suspect that it is rare for a heat pump to pull heat from the motor as that would complicate the running of the pipes. I have seen systems that use the waste heat from the motors to preheat water headed to the water heater, none I've seen will use that heat for warming the house.

    • by jbengt ( 874751 )

      Heat pumps DO generate heat. The compression step is work and adds more energy (heat) to the working fluid.

      Work is not Heat. They're both energy, but heat is the kinetic energy of molecules transferring from one body to another due to a temperature difference. Of course, that's not considering the inefficiencies of motors, friction in the compressor, etc.

  • I'm in Québec (Canada) and it is cold as Maine, my heat pump (Fujitsu, high seer, inverter, energy star) is only rated at -4F (-20C) and we often have less than this, so you still need a regular heating system (gaz/electric). A heat pump working at this range, sometimes, needs to stop to heat the exterior module to avoid freezing. There's heat pump rated at lower than this (like, -15F) but it starts to be expensive...

    All in all it works pretty well, it's efficient, we like it in winter and of course in

  • ...where heat pumps might not work totally optimally, that means the whole concept is just horrible and we shouldn't use heat pumps anywhere? C'mon people, don't be such special unique crybaby snowflakes. There are plenty of places all over the world where the temperature ranges are just fine for heat pumps (like here on Lawn Guyland NY for instance) so why do we feel the need to piss all over the concept?
  • by endus ( 698588 ) on Monday February 27, 2023 @01:19PM (#63327448)

    2 grand is a little low. 20 grand would be closer to 30% for what I was quoted in a cold climate. We were redoing all of the HVAC anyway and I wanted to go with a heat pump over oil. I was willing to pay more for the heat pump, but it was a LOT more.

    • by teg ( 97890 )

      2 grand is a little low. 20 grand would be closer to 30% for what I was quoted in a cold climate. We were redoing all of the HVAC anyway and I wanted to go with a heat pump over oil. I was willing to pay more for the heat pump, but it was a LOT more.

      For what? Here in Norway - which is a pretty expensive country - I can get a good heat pump usable down to -30 C for about $2k (add $500 for installation) . However, I also added ventilation with heat recovery every room in the house, and that cost another $15k.

    • by jbengt ( 874751 )

      2 grand is a little low. 20 grand would be closer to 30% for what I was quoted in a cold climate.

      Do you have a huge house? Or are you talking about a ground-source heat pump system? Because my son just got an air-to-air heat pump with gas heat backup installed to replace his old system for around $10,000, which was only about $1,000 more than a regular gas furnace with central A/C.

  • by bb_matt ( 5705262 ) on Monday February 27, 2023 @01:27PM (#63327492)

    I guess it could be termed a "hidden cost" if you don't _know_ what your home really needs to be totally efficient.

    Over here in the UK, whilst sort of renowned for our damp but mostly benign climate (when compared to extremes in other countries), heat pumps are also going sort of mainstream - depends how much money you have, I guess.
    But we're way behind colder European countries, where home insulation efficiency is, on average, much better than ours.
    We have an aging and inadequate housing stock and many properties have really poor insulation.
    I guess we always relied on cheap fossil fuels, right?

    I've looked into getting one fitted into my property, but it's an old stone building from 1880 - sure, we've got double glazing, panelled insulation inside etc - but the energy rating is still not good enough for heat pumps to be as effective as the gas heating we currently have.
    There's also very few places to fit the heat pump, so it's going to be a specialist install.

    We've done the math, to insulate to an acceptable level and install a heat pump, we'd break even in about 15 years.
    The same applies to solar energy for uses other than heating (obviously) - the break even is 15 years.

    Tough one. Given we'll be selling in a few years, it isn't a hard choice - but if we weren't? - say goodbye to the savings.

  • Why do we have to go all-in with something or another? Hybrid water heaters are gaining traction in CT and seeing real-world energy savings.

    It's about cost, yes, but as a homeowner, I've learned that we sometimes have to redo things 2 or 3 times which is more expensive than getting it right or less wrong. Of course, many times that is bad/no data, people jumping at 'savings' or not doing their homework, but you can get stung even after doing your homework.

    With unreliable electric, fluctuating fuel costs a

    • by PPH ( 736903 )

      With unreliable electric

      Something to consider. During our sometimes week long power outages, I can run my gas furnace from a small generator (just need to power the fan plus controls). Gas hot water and cooking and I'm pretty much set for anything our shithole power company can dole out.

  • I lived with an air-source heat pump for 3 years in Northern Virginia, which is not exactly a frigid climate. The thing seemed to run constantly and could barely heat the house to lukewarm in Winter.

    When I replaced a forced-air gas furnace in MA over a decade ago, I almost went with the hybrid heat-pump plus natural-gas furnace option. They lost the sale because they said I couldn't modify the conditions (temperature, etc.) under which it would switch from gas to heat pump. (When I found the tech manual o

    • Indeed at that price for electricity, I can't imagine the heat pump is competitive with gas even when no auxiliary heat is in use.
  • I have three heat pumps for heating / cooling (two in the main house and one in the greenhouse) and all three do the job I ask of them. All are high efficiency models (SEER 20+). Main thing with them is that they like to stay at a set point so you don't want to do the 'turn the heat down for the night' thing since it takes too long to get the temp back up in the morning and running it hard you've lost any gain you expected. They don't blow out very hot or very hot air, rather just very warm and very cool so you pretty much let them run all the time and your house just stays at a comfortable temp all the time. I actually prefer that to the old system where in the summer the house would get hot and then the system would cycle on and blow crazy cold air for 10 minutes. As a result they work best as part of a whole system with other improvements like better insulation. We did spray foam insulation at the same time and been very happy with the overall result. But if you have bad insulation you might not be able to get the house warm if your leakage is higher than what your heat pump is putting out. I find we we've had those cold times in TX when it gets to the lower teens or even 10F then the system does seem to struggle to keep the temp up, I suspect if I replaced windows that would help a lot since my windows are old and leaky. They do work but not a panacea you have to think of them as working as part of a system that includes insulation and other things.

  • I guess that depends on what you call "real cold".

    I would suggest under 200 kelvin is really cold. Not many people live in areas like that!

  • ... a water source heat pump. Put a coil under the dock and pull heat out of the lake. It's much more efficient, since the lake doesn't freeze, so my source/sink temp is guaranteed to be above 0C.

    I'd also like to troll our state ecology department. Who scream about anything that can warm up the lake. "Won't you please think of the poor fishies?"

    "But I'm taking heat OUT of the lake. So that's good for the fish, right?" Stand back and watch the ensuing aneurysm while they try to counter that argument.

  • The question that gets missed in the discussion around heat pumps, along with electric cars, is can the local electric grid cope with the extra demand?

    Here’s in the U.K. if you want to upgrade the circuit to your home to cope with the new demands you are putting on it. Then the answer, in some parts of the country at least, is that they will be ready to upgrade you in the mid 2030s.

    The same answer is being given to companies that want to build more generation capacity.

    I am keeping my gas heating and j

  • I live in Québec, Canada. 47,8 North, and the only time I had to rely on something else than my two heatpumps in two years is once this year when we hit a record cold day of -29.9C (-21.3F). Since I've installed the heatpumps, I've saved hundreds of dollars in energy in a province where electricity is cheap and winters are cold. I would recommand cold weather heat pumps to anyone.
  • I installed a gas stove on one end of my house and a gas log fireplace at the other end. I use them rarely but when power is cut I can be warm and even warmer cooking tasty food. Of course I've backup heaters and a small Weber grill which makes a fine small heater too.

    Learn from disasters like Texas.
    Own clothing and a sleeping bag rated for FAR below anything you might UNreasonably encounter. Heat should be for comfort and to prevent plumbing freeze, not for survival. A Coleman zero-degree sleeping bag is c

  • by HotNeedleOfInquiry ( 598897 ) on Monday February 27, 2023 @03:46PM (#63328081)
    Have another great benefit. You can choose to heat or cool a single room or rooms without blowing air throughout the house. I know that with a conventional furnace, you can control the registers, but the single house thermostat will still require that most of the house is the same temperature.
  • I have a heat pump in my electric car.

    A few weeks ago it was -25c. You could hear the heat pump working, but the cars cabin was still roasty-toasty.

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