14 votes

Heat pumps used to struggle in the cold. Not anymore.

12 comments

  1. clayh
    Link
    We have 3 heat pumps now and I’ve had heat pumps my entire life. They may be more efficient now, but they are significantly less reliable. Rarely do 6 months go by without us having a problem with...

    We have 3 heat pumps now and I’ve had heat pumps my entire life. They may be more efficient now, but they are significantly less reliable. Rarely do 6 months go by without us having a problem with one of them. Two of the units are Mitsubishi mini-splits (one ducted and the other with wall-mounted heads). The other is a more traditional unit. The more traditional one is a Bosch unit.

    At the moment, the Bosch (less than 3 years old) is broken. The wall-heads mini split exploded 2 days ago, when a circuit in it blew, causing all the coolant to leak out.

    We never had problems like this in the 80s and 90s. Quality has plummeted.

    10 votes
  2. [9]
    scroll_lock
    Link
    Comment box Scope: summary, information Tone: optimistic Opinion: not really Sarcasm/humor: none Residential reliance on natural gas is no longer necessary for the overwhelming majority of the...
    Comment box
    • Scope: summary, information
    • Tone: optimistic
    • Opinion: not really
    • Sarcasm/humor: none

    Residential reliance on natural gas is no longer necessary for the overwhelming majority of the population. Modern cold-climate heat pumps are increasingly available and extremely efficient, even at negative temperatures.

    Context - what's the problem?

    Keeping homes comfortable in frigid winters and blistering summers can account for more than half of an average American household’s energy usage and generate about 441 million tons of carbon dioxide each year. But because heat pumps move heat instead of creating it, they can be three to four times more efficient than traditional heaters and slash a home’s carbon dioxide emissions by as much as eight tons per year.

    3-4x efficiency improvement not only means much fewer emissions, but a lower energy bill!

    In October, the Energy Department announced that eight manufacturers participating in its challenge to produce efficient residential cold climate heat pumps had created appliances that would enter commercial production as early as this fall. These heat pumps were shown in tests to be capable of operating at 5°F (-15°C) or lower “with energy performance well beyond current best-in-class products,” according to the Energy Department.

    Carrier, one of the companies that participated in the Energy Department’s heat pump challenge, said its technology could operate at full capacity at 0°F (-18°C). Trial units of these heat pumps were field tested in homes in Syracuse, New York, and the company said they operated reliably, though not at full capacity, down to -13°F (-25°C).

    In lab testing, the units were able to operate down to -23°F (-31°C).

    Emphasis/tweaks mine. These are real-world tests of heat pumps in very cold climates. They are extremely economical in sub-freezing temperatures and still perfectly suitable for freak cold periods. The lab data indicates that further progress on this front is all but inevitable.

    In addition to climate benefits, there are personal ones:

    “Cold climate heat pumps can lower bills while maintaining comfort in very low temperatures, especially for people who use inefficient systems that rely on propane, oil or electric resistance,” she said.

    She added that some people in places with higher electricity rates could see savings because cold climate heat pumps will switch to backup electric resistance heating less often.

    “They’re very reliable,” she said. “They can control the comfort significantly better than a furnace.”

    5 votes
    1. [8]
      bmhatfield
      Link Parent
      The challenge here that I see folks missing is two fold: When it's very cold, the COP of low-temperature heat-pumps drops significantly, as does the experienced performance (more defrost cycles...

      The challenge here that I see folks missing is two fold:

      1. When it's very cold, the COP of low-temperature heat-pumps drops significantly, as does the experienced performance (more defrost cycles leading to cold air intervals inside)
      2. Electricity is much more expensive than Natural Gas / Propane / Oil in many areas, especially the Northeast US.

      Combined, the experienced reality of heatpumps is massive electrical bills in the deep winter, and lack of indoor comfort caused by defrost cycles. For us, our equivalent propane was $200/mo, the electrical cost was $1000+.

      So while everything in the article is true - and it's a huge leap that we've moved from "don't work when it's very cold" to "you can depend on only a heat pump year-round" - the experienced reality isn't QUITE what's being sold. Especially not lower energy BILLS, despite there being lower energy USE (theoretically).

      EDIT: I'll also clarify that this isn't just my lived experience. There are a number of folks in a group I am in who all switched to heat pumps as their primary heat source around the same time. Nearly all (but not all) experienced the same themes and sticker shock at their electrical bills.

      6 votes
      1. [6]
        scroll_lock
        (edited )
        Link Parent
        Comment box Scope: comment response, information Tone: neutral Opinion: lightly Sarcasm/humor: none The heat pumps described in this article have higher COPs than models that have been on the...
        Comment box
        • Scope: comment response, information
        • Tone: neutral
        • Opinion: lightly
        • Sarcasm/humor: none

        The heat pumps described in this article have higher COPs than models that have been on the market in the past. It is specifically talking about new heat pumps that are only just barely entering commercial production. So that anecdote is not applicable.

        If you read the CCHP Technology Challenge Specifications discussed here, the detailed specifications (p.6) require that heat pumps in the challenge have COP values of 2.1–2.4 at 5°F (-15°C). That means the heat pump can operate at 210–240% efficiency in these particularly cold conditions—minimum. Many can do even better.

        In contrast, a resistance heater operates at 100% efficiency. A gas furnace operates at 80–95% efficiency. So unless the electricity to heat a given space is more than 2.4x more expensive than the gas to do so, the heat pump is still a cost saving. In New England, it only sometimes gets below 5°F (-15°C) anyway, and rarely below 0°F (-18°C). From a cost perspective, New Englanders are not going to see major cost increases because their heat pumps will mostly be working super efficiently. The occasional cold spell may reduce the efficiency of the units somewhat, but only briefly.

        I hear your propane example, but that seems anomalous even for the northeast. The cost of generating electricity will continue to drop in the near future as the cost of solar and wind continue to decline. If you're purchasing a heating system for the future, it's best to think about future energy costs and not just anecdotal past costs or even exclusively current ones.

        I don't see any problem with having a woodstove or gas furnace as a backup to a heat pump, if indeed the area is cold enough and electricity prices are unusually high, but I don't think it is necessary anymore for the climate most people live in.

        4 votes
        1. [5]
          vord
          Link Parent
          The raw efficiency doesn't tell the whole tale though. @ACEmat could probably explain it better. One therm of gas is roughly equivalent to 100,000 BTU. So if you have a house that needs...

          The raw efficiency doesn't tell the whole tale though. @ACEmat could probably explain it better.

          One therm of gas is roughly equivalent to 100,000 BTU. So if you have a house that needs 50,000BTU/hr, that means you're using about 1/2 therm per hour. 1 kW is roughly equivalent to 3,500BTU. So to heat the same house for an hour with resistive heat it'll take about 14kWh. A COP of 2.4 will translate to an electric use of about 5.8 kWh for a heat pump.

          So then you take your prices and can figure out your hourly costs. If we take electricity at $0.13/kwh and gas at $1.63 per therm:

          Gas heat: ~$0.81
          Electric heat: $1.82
          2.1 COP heat pump: ~$0.86
          2.4 COP heat pump: ~$0.75

          So while the heat pumps do have the potential to be better (and generally are when temps are over 30F), it still will result in sticker shock for somebody coming from gas during the coldest parts of winter. And that shock will be better/worse depending on costs of electricity and gas. If gas is heavily subsidized, the math looks even worse for heat pumps.

          3 votes
          1. [4]
            AugustusFerdinand
            Link Parent
            Am in Colorado, gas is $1.01/therm, lowest electricity rate (off peak hours) is $0.12/kWh... Gas heat at 80% for 100M BTU: $1,262.50 Heat pump at 250% for 100M BTU: $1,406.80 ...and that's with...

            Am in Colorado, gas is $1.01/therm, lowest electricity rate (off peak hours) is $0.12/kWh...

            Gas heat at 80% for 100M BTU: $1,262.50
            Heat pump at 250% for 100M BTU: $1,406.80

            ...and that's with only using the lowest possible electricity rate.

            I'm also waiting for this "solar/wind will make electricity cheaper" to happen. Electric providers aren't stupid, they know not to build more than they can sell for a profit and none of them are eager to make electricity prices go down. Looking at the 10 year price history for electricity in Colorado the base rate in January of 2014 was $0.04604/kWh in January of 2024 it was $0.07136/kWh; adjusting for inflation the 2014 rate was $0.06. In the same amount of time Colorado went from producing 7,975GWh to 21,318.5GWh of renewables annually.

            3 votes
            1. [2]
              DynamoSunshirt
              Link Parent
              Great data points. I wonder what's pushing electricity costs up so high, if renewables are getting so much cheaper and so many grids are incorporating renewables? Something in my mental model must...

              Great data points. I wonder what's pushing electricity costs up so high, if renewables are getting so much cheaper and so many grids are incorporating renewables? Something in my mental model must be wrong, because it just doesn't add up. Unless it's just corporate greed.

              I do worry that solar is somewhat pointless in much of the USA during the cold half of the year. In the Northeast, we get so little daylight and so much cloud coverage I doubt we coud meaningfully rely on solar October-April. Unless we massively overbuild it, I suppose?

              1 vote
              1. vord
                Link Parent
                The northeast should be exploring wind like their lives depend on it.

                The northeast should be exploring wind like their lives depend on it.

            2. vord
              Link Parent
              Am in South Jersey. Gas is $1.61/therm, cheapest electricity (winter rate) is about $0.23/kWh. The good news is milder climate means that the heat pump is usually operating closer to 4-6 COP. More...

              Am in South Jersey. Gas is $1.61/therm, cheapest electricity (winter rate) is about $0.23/kWh.

              The good news is milder climate means that the heat pump is usually operating closer to 4-6 COP. More good news is that I have a 15kw solar array on the roof that came with the home that drastically tips the scales.

              You're right that at utility scale, green energy will never mean cheaper rates. The good news is that solar (and wind) are fairly cheap to install at home, which helps counteract that. Check Project Sunroof, I've found it fairly accurate for a quick guesstimate. Unless you have assets, the subsidized loans are the way to go...NEVER USE A SOLAR LEASE.

      2. vord
        Link Parent
        When did you guys switch? Even three years ago this tech was in its infancy. I have a not-cold-climate system that was installed in 2021, and I can say with a degree of certainty that it's still...

        When did you guys switch? Even three years ago this tech was in its infancy. I have a not-cold-climate system that was installed in 2021, and I can say with a degree of certainty that it's still infinitely better than electric baseboard.

        I will agree that during cold spikes, you'll definitely pay more than gas. I retain a backup heating system for a prolonged cold snap for just such occasions. But for those of us where average temps rarely drop below 30, it's still a pretty solid win if you're looking to keep gas out of your home (like its seriously bad for you).

        I think the correct answer in the future is going to be some sort of combo unit where you could have a small auxilary combustion heat source attached to the outdoor coils to aid in those sub-zero conditions.

        2 votes
  3. kacey
    Link
    Somewhat relatedly, it’d be nice if there were a way to simultaneously push for improved house air sealing + insulation (or the envelope overall), and retrofits for existing buildings. For folks...

    Somewhat relatedly, it’d be nice if there were a way to simultaneously push for improved house air sealing + insulation (or the envelope overall), and retrofits for existing buildings. For folks that don’t feel that they can switch to electric heating, it would at least let them cut costs on fuel, which helps everyone long term.

    I don’t think it’s possible to make “inspect homes using a variety of equipment, model energy over the day/year, and meticulously retrofit walls & windows” as interesting as a cool new technology straight outta science fiction, though, so I’m probably chasing a pipe dream.

    1 vote