20 ms·

Heat pumps, more than you wanted to know (2023)

• rdsubhas 3y ago
  Heat pumps are simple, easy to understand, efficient (uses very little energy) devices. But it still blows my mind every time — that we can use the heat of the sun to cool our homes. What a wonderful time to live in!
• jakedata 3y ago
  What I know is that due to Sunday's wet snowy weather my air-source heat pump became encased in ice on the heat exchange coils. You can't physically remove the ice without risking damage to the delicate fins, so I ran it in cooling mode for a while to warm the outdoor heat exchanger and loosen the ice. I am a happy air-source heat pump user, especially when coupled with solar panels. However there are other issues people need to take into account, especially if it is difficult to access the device for cleaning or the owner is mobility impaired.
  • willvarfar 3y ago
    I'm a big fan of heat-pumps, and happily heat a big old farmhouse with a ground source pump through heavy long deep cold winters in scandinavia. However, at the small cottage I have for the first time just had the external units of two air-source pumps freeze solid due to snow blowing in in the current -16c spell. The defrost ran down inside the casing and formed a big block of ice in the bottom that has now reached up to the fan blades so the pump can't turn at all. So I'm all out of heat pumps in the cottage just when I most need them :( This is not enough to make me give up on heat pumps, but it makes me wary to rely solely on them. Am planning a big new build, and will of course go air source to underfloor heating, but am seriously considering a backup combo wood burner for the panic week that comes each year.
    • tomashubelbauer 3y ago
      When I got an air-water heat pump for my house, the installer also put in a small electric heater that is connected to the same loop going through my radiators. It is a backup in case my heat pump broke and needed to be serviced. I wouldn't rely solely on a heat pump either. The heater takes 3x the amount of energy to produce the same amount of heat as the heat pump, but since I'll almost never use it (didn't need to turn it on yet), that is negligible and the peace of mind knowing the backup is there is well worth it.
      • myspy 3y ago
        Similar setup, air-water system with a 700 litre heat storage tank, which has a heater rod as a back-up.
      • 2rsf 3y ago
        Most of the bigger setups I saw here in Sweden has this backup built in, not only as a backup of emergencies but mostly for cold days where the source heat (air, ground) is not enough
      • willvarfar 3y ago
        (parent poster) the cottage has two air-air pumps, which replaced most of the previous electric radiators. Luckily there were some electric radiators left, so they are now keeping the place just above freezing...
    • noroot 3y ago
      For this cold spell it's a little too late, but the solution for this to add some heat-coil/heat-wire on the bottom of the heat-pump housing that you can activate in those conditions. The issue is that the defrost mode will defrost all the ice from the fins, but it freezes again before it can all drain through the small drain hole on the bottom of the housing. It's somewhat a known issue with air source heat pumps, sadly. I've not run into this issue myself, but on a Dutch speaking forum (tweakers) there is a long thread about this modification to "survive" the cold spells with this small modification. You can manually attack the ice with a heating gun or hair dryer to remove it, but that's a faffy. I think manufacturers should, and probably will, add something like this themselves in the future.
      • willvarfar 3y ago
        Yeap this condense re-freezing is what's got me. And I think it's also blown in snow, we've had bad drifts too. Anyone on forums advocating for drilling bigger or more drainage holes?
        • svacko 3y ago
          Yes, I've experienced a few poeple drilling the additional drainage holes on the bottom of the outdoor unit, when they experienced similar problems not having a "nordic" unit. With the nordic unit I mean the features mentioned above - heated compressor and the heating condenser vane. Though, if it's snow blowing directly inside then I think creating some barrier or add additional shielding of the outdoor unit is required,so that you minimize the chance of the snow DDoS-ing the unit (note: check your unit's service manual for the minimum free distances from all sides of the unit, especially the front one that is the most important to be kept enough free space).
    • throwaw33333434 3y ago
      I'm building a new house and I'm based in Poland. I'm going with air heat-pump* + a simplest fireplace as a backup - not connected to central heating, no electronics. On top of that 10-20kW of solar and a place for batteries. I'll install them once they get cheaper. The house is 200m^2, so I'm hoping to pull only 200 kW/month from the grid and generate rest on my own. Also, I've been wondering how much efficiency would I get if I could put some mirror and direct the light to the unit in the winter. It could help with defrosting as well. *I was considering horizontal heat pump, but it's not worth it. It affects vegetation and future construction.
      • jve 3y ago
        Battery won't help you in winter. Just a waste of money ( At least in Baltics). It will help at nights by using electricity you made at day, but is useless in winter. My solar panels at november generated 0.00kW/h, because it was under 40cm of snow. Got some double digits at December... anyways, where it snows, don't count on your panels. Even if it didn't, the energy it produces in the period when the daytime is scarce is minuscule compared to summer. Nov-Feb inclusive (~120 days) gets me about as much as I could get in 5 ideal summer days. Or a third of what I require to cover a single month electricity usage. Of course it all depends on options government offers and in what place you live - however Poland I suspect also gets snowy. Just sell excess solar electricity and re-buy in winter. Just trying to save you some money on batteries.
        • tcbawo 3y ago
          Would electric heaters to clear the snow give you net positive energy?
    • nottorp 3y ago
      ... and your heat pump is on the ground, easily accessible. What if you live on the Xth floor? Your gas burner is small enough to be all inside and easily serviceable when it breaks in the middle of winter (why would it even consider breaking in summer?). Where do you put the much larger heat pump and how do you reach it?
    • usefulcat 3y ago
      We have an air source heat pump with a gas fired backup ("emergency" heating, it's sometimes called in the US). Don't need to use it often but it's nice to have and only added around 10-15% to the total cost.
  • tiborsaas 3y ago
    You can have an extra heater device installed into your external unit. I'm just about to have 3 units installed and they will fit this extra module.
    • tiborsaas 3y ago
      Update: just had a call and it's a hack that voids warranty. There are units with built in heaters. Picking an AC is a nightmare with OCD :/
  • raugustinus 3y ago
    Here in the Netherlands there's a huge incentive to move to heatpumps (subsidies and whatnot). I believe most of those (if not all) that are being installed have a defrosting mode which is automatically activated. I have seen mine defrosting in the last few days since it's finally below zero (celsius).
    • Faaak 3y ago
      Yeah, it's really strange to have an heat pump without automatic defrost, as it's something that's really needed on cold and humid days
    • johnchristopher 3y ago
      How much does it cost in the Netherlands (with incentives such as government subsidies) to install (hardware and installation) ?
      • apexalpha 3y ago
        Other Dutch person here... with a heat pump. And the only answer is that it completely depends. We spent €30k renovating our house but that included removing the entire old heating system, installing underfloor heating, extra insulation, ventilation, remove of gas pipes, new electrical switchboard, upgrade to 400V electricity and, well, the heat pump. Just the device itself (air-water) is probably €6 or €7k excluding a €3.3k subsidy.
  • ChatGTP 3y ago
    Do you have it undercover / out of the elements some how? Mine is under a concrete stair case and I've not had this problem, even when it's down to ~ 8c and very snowy.
  • hasmanean 3y ago
    Could that have been solved by placing a tarp over the unit beforehand?
• londons_explore 3y ago
  How much energy is 'lost' in the expansion valve in a typical heat pump? Isn't it worth putting a turbine in there to recoup the energy released as a high pressure liquid passes through a small hole? Even if it's only 10%, that's still 10% of the energy use of your home for a decade - surely that pays for a micro turbine (which need not be particularly complex - the same design used in those $3 light up novelty faucets would probably work.).
  • doublesocket 3y ago
    There are various research projects looking at storing waste heat, often for the purpose of more efficient defrosting. https://www.nature.com/articles/s44172-022-00018-3 https://www.nature.com/articles/s44172-022-00018-3
  • Kichererbsen 3y ago
    I worked for a chair that studied this kind of stuff - your best bet is to figure out how to reduce the temperature lift. Due to the way the Carnot equation works (at least, that's what I _think_ it's called, this is all a while ago), that really get's the heatpump efficiency singing. reduce the heating temperature by increasing the area you're radiating from - floor heating / ceiling heating is way more efficient than radiators since you can deliver the same amount of heat at much lower temperatures to the space.
    • Firadeoclus 3y ago
      Putting fans on radiators should also increase the amount of heat that can be transferred, right?
      • joking 3y ago
        right, you can use low temp radiators or fancoils than are built for this use cases.
• volemo 3y ago
  For a novice to delve into heat pumps I recommend Technology Connections’ series on the topic: https://youtube.com/playlist?list=PLv0jwu7G_DFVIot1ubOZdR-KC-LFdOVqi https://youtube.com/playlist?list=PLv0jwu7G_DFVIot1ubOZdR-KC...
  • goryramsy 3y ago
    Technology Connections had some really good videos. I usually listen to them audio only, like a podcast, which makes for an enjoyable commute.
  • drbytes 3y ago
    That video finally convinced me to install mini splits. It has turned out to be a great choice as it has cut my propane use in half.
    • happytiger 3y ago
      My buddy just installed a dc hybrid system and it’s been pretty much amazing. He’s in a warm climate with lots of sun though, but the idea of plugging panels directly into solar panels on hot days makes so much sense. Are you in a cold climate? My biggest concern is installing splits in very cold mountain climates (my use case).
      • out_of_protocol 3y ago
        The lowest I've seen for mini splits is -30 C in heating mode. No idea about big installations P.S. previous comment with example specs: https://news.ycombinator.com/item?id=38266032 https://news.ycombinator.com/item?id=38266032
        • happytiger 3y ago
          What a kind and helpful comment. Thank you!
      • runarberg 3y ago
• robinwassen 3y ago
  I do not understand why heat pumps are so expensive in the article. In Sweden the hardware cost around $1k - $2.5k and installation $500 - $1000. It's not a complicated task. Geothermal heating on the other hand cost around $15k - $20k. Most people I know have one of these, direct electricity to heat is not really an option.
  • rcxdude 3y ago
    Heating has strong 'follow the crowd' effects: the cost of different options are heavily influenced by what's already commonly used in the local area, because the supply chain will be optimised, and local workers will be most familiar with what's most popular. Bucking the trend in any way sets you up for higher hardware costs and much higher installations and maintenance costs, even if in a different country the same option would be the most economical. (I have experienced the same pain, in a country where most heating is plumbing and radiator based, having a house set up for central air heating and wanting a replacement for the central unit, it was almost the same cost to replace that central unit as it was to rip out the whole thing and replace it with radiators, which is ridiculous on the face of it but a consequence of the supply of parts and labor for each option).
  • namdnay 3y ago
    I think the costs given in the article are for a whole house (including "ducting" which is more rare in europe)
    • gavin_gee 3y ago
      i dont think so. Seattle quotes for a gas to heat pump conversion using existing ducting and refrigerant pipes was 18K. labor costs are absurd
  • wil421 3y ago
    Are you talking about mini splits being 1-1.5k? In the US, it’s more common to have 1 or 2 large units pumping into ducts in every room of the house.
  • a_humean 3y ago
• rompic 3y ago
  Please note that they can also be very loud, especially the ones not built to be silent.
  • ChatGTP 3y ago
    They can also be crazy silent, I have one at my place I just installed, it's "air based" it's ridiculously quiet. Like most machinery, if it's mounted to your wooden or steel framed house, it's going to vibrate the shit out of it most likely. I have mine on a concrete slab.
    • rompic 3y ago
      My neighbour (illegally) put it right next to our house (between the walls of his houses and ours in a very dense area which is a very bad idea) and I basically had to move out for a few month in winter because sleeping was impossible, before I was able to convince him and get it moved (which I basically paid to be able to sleep again)
      • ChatGTP 3y ago
        Sorry to hear that? What make / model was it, do you know? Ours seems to be about 45 decibels.
        • rompic 3y ago
          Fujitsu woha080lfca
  • 2rsf 3y ago
    I suspect that there is something very wrong, or VERY cheap, with your heat pump. I have never heard a heat pump being VERY loud, and I have listened to a few that were more than a decade or two old.
    • rompic 3y ago
      See my comment below. The heat pump of my neighbour was perfectly within spec (Fujitsu woha080lfca). It emitted around 69 dB (measured on our side of the property, also checked by an expert). Allowed (on the border of the property) were 35 dB (rule of thumb: you should not hear it in the surrounding soundscape; note that this is a logarithmic scale so I think it's a factor of 6 or something) It was especially bad when it had less than 8 degree Celsius because it would defrost every 30 minutes or so. As I wrote before: location is also an important part: his house is hard walled, ours is a prefab house built out of wood. There are only 4 Meters between our houses, it was approx. 2 meters from our wall blowing in our direction. They only thing they could have made worse is putting it in a corner. I didn't only hear it, I felt it. In the end I managed to convince him that I pay an acoustic expert to explain to him that 65 dB is way louder than 35 dB and that putting an acoustic hood around it does not solve the problem (approx -10 db).
• cousin_it 3y ago
  It's fun to think about theoretically more efficient methods of heating. 1) Heat pump - you use electricity to move heat from the outside in. It has efficiency over 100%, because you get all of the electricity's energy, plus some of the outside heat. 2) But generating electricity at the power plant uses heat in the first place, and wastes a lot of it. Let's bring the fuel to the house and make a heat-driven heat pump. This way you get 100% of the fuel's heat, plus heat from outside. 3) But this is still wasteful, because fuel burns hotter than the temperature you want in your house. So you could generate some electricity along the way, and use it to power domestic appliances. This way it will do useful work, and then 100% of it will also end up heating the house, because there's nowhere else for the energy to go. 4) And even that is still wasteful. The house is too hot in summer, and during the day, and too cold in winter, and during the night. A large enough heat reservoir, like thick walls, can smooth out this variation and give you average temperature all the time. 5) And believe it or not, even that is still wasteful. The human body produces enough heat to be warm in most temperatures, given good insulation. So we go from needing thick walls to needing thick clothes, which are much cheaper. 6) And even that is still wasteful! Because you don't need thick clothes either. So we arrive at the perfect solution for staying warm: a pill that makes your body heat up without fuss when it's cold, and lose weight along the way. Combine with clothes to taste.
  • everdrive 3y ago
    >So we arrive at the perfect solution for staying warm: a pill that makes your body heat up without fuss when it's cold, and lose weight along the way. Only part of this your body doesn't automatically do on its own is the "without fuss" bit. And that part can be trained.
  • jamessb 3y ago
    > a pill that makes your body heat up without fuss when it's cold, and lose weight along the way. A mitochondrial uncoupler like 2,4-Dinitrophenol will do this [1], but I don't think the risk of death is worth it. [1]: https://en.wikipedia.org/wiki/2,4-Dinitrophenol https://en.wikipedia.org/wiki/2,4-Dinitrophenol
  • JohnVideogames 3y ago
• jacknews 3y ago
  It's not more than I want to know. It seems ground-sourced is a much better idea than air-sourced, and it seems to me you could install the ground loop with/under/around the foundations for new builds. As far as indoor distribution goes, it seems like a low-temperature hydronic system would be most efficient, and most comfortable. Or at least a hydronic (instead of refrigerant) loop to multiple chiller/heater units, which would be easier to install and change.
  • andruby 3y ago
    Typically the installation cost for ground-sourced is a lot higher, especially when it's not a new build. Air-sourced is the same as regular A/C and thus about as cheap to install. You're right that ground-sourced should have better efficiency and thus running costs, especially in winter.
    • bill38 3y ago
      A few years ago, Google had an advanced research project for ground source heat pumps. They spinned it off in Dandelion energy.
  • frankus 3y ago
    Ground-source real-world cost effectiveness for residential use isn't that great (see here, although unfortunately paywalled: https://www.greenbuildingadvisor.com/article/geothermal-heat-pumps-reputation-vs-reality https://www.greenbuildingadvisor.com/article/geothermal-heat...). The gotchas are the energy used to run the circulator for the ground loop, and the fact that over the course of a heating or cooling season the ground temperature lowers or raises, respectively, by enough that the COP isn't even much greater than an air-source system (but this would definitely vary by climate). Coupled with the much higher installation cost, it's a bit hard to make a system pencil out for a building the size of a single-family house.
• bluemax 3y ago
  Several companies are developing thermo acoustic heatpumps that will have some advantages over regular heatpumps. They should produce less noise, don't use greenhouse gasses and work in a wider range of temperatures. https://www.blueheartenergy.com/ https://www.blueheartenergy.com/ https://www.equium.fr/en/home https://www.equium.fr/en/home
  • DrScientist 3y ago
    Anybody got any actual experience of these yet?
    • hasmanean 3y ago
      LBNL had a solid state thermoacoustic resonator the size of a coin, which I read about but never saw it in the market. It was supposed to be able to extract heat from anywhere.
  • rihegher 3y ago
    Equium is using helium, a non renewable gas. Not a greenhouse gas but not really sustainable either.
    • bill38 3y ago
      They fill the core of their heat pump with helium at 30+ bars and seal it. That's all. It's not used continuously. So not a big quantity used.
• rjmunro 3y ago
  I hate the sentence: > Heat pumps are unique in that they are a tool for fighting climate change, where we have the technology today. No. They are not unique at all. We have electric cars, wind turbines, solar panels, hydroelectric, nuclear, recovery of methane from waste, "smart grid" technology and many many other things today. And not just "the technology", in some theoretical sense, we have all of the above actually working now. There's also things like more efficient light bulbs and electronics that use less power when not in use that are now nearly 100% of the market. You can't buy incandescent light bulbs or TVs that use several watts of power in standby mode any more.
  • hasmanean 3y ago
    That sentence is not aimed at the consumer, but is a very efficient mechanism for capturing government subsidies.
  • stinos 3y ago
    No. They are not unique at all. In my opinion they still are pretty unique because their efficiency is higher than 100%. Which was what I thought the sentence would continue with when I started reading it. Cannot be stressed enough. It's like magic :] Sure your LED is more efficient than your incandescent light bulb, but it still produces heat which is not intended nor really wanted. In my book there's no comparing that to a heat pump. That being said, not really a fan of such sentences either.
    • rjmunro 3y ago
      % electrical efficiency is not a useful measure. What matters is how much do I save (measured in money and/or carbon emissions etc.) compared to taking other measures, such as a more conventional heating solution, better insulation or installing solar panels. If you measure the efficiency of solar water heating in the same way, it uses no electricity, so it's efficiency is infinite.
  • frankus 3y ago
    Space heating/cooling, along with water heating, are the overwhelming majority of household energy use. In fact, in a heating-dominated climate there isn't much of win from having efficient lights and appliances, because the space-heating system has to make up for the energy not wasted by the lights/appliances. So it's unusual ("unique" is a high bar) in that it's one of the largest privately-owned energy-consuming devices where existing technology can result in substantial energy savings and emission reductions.
• MCUmaster 3y ago
  [flagged]
  • andruby 3y ago
    It's just a centuries old technology, Air Conditioning and Refridgerator, used in reverse. It's been in use in other parts of the world since a very long time. I have no idea why it's only now becoming a "hot" topic in the US. We've been using heat pumps for multiple decades in Europe. https://en.wikipedia.org/wiki/Heat_pump#History https://en.wikipedia.org/wiki/Heat_pump#History
    • MCUmaster 3y ago
      There’s an obvious PR component here, it’s not a mere coincidence when anything becomes an all-platforms hot topic.
      • pjc50 3y ago
        Well, there is certainly PR and a push for heat pumps .. as a means of addressing climate change. You can even read that in these articles you keep dismissing.
    • feintruled 3y ago
      Heat pumps are culture wars now, believe it or not. https://www.telegraph.co.uk/money/net-zero/why-heat-pumps-will-never-work-britain-gas-boiler-net-zero/ https://www.telegraph.co.uk/money/net-zero/why-heat-pumps-wi... DT article to illustrate, not necessarily to inform. The idea I believe being that heat pumps are part of a supposedly unnecessary and costly push to Net Zero driven by industry and shadowy interest groups but which are just another means of a) enforcing control and b) screwing money out of 'the little guy' and siphoning tax dollars off compliant governments. And thus one is able to wave away an article absolutely bursting with scientific detail and research as 'well, it's all a bit convenient, isn't it?' I honestly despair.
      • andruby 3y ago
• hasmanean 3y ago
  In theory burning high grade fuel to produce heat is stupid. CHP (combined heat and power) systems have more than 90% efficiency even with yesterday’s technology because all the inefficiency is used to heat your house. The temperature of a natural gas flame is 2770C. Using it to heat a house to 30C is ridiculous. Instead you should run a gas turbine off of it to produce electricity. The exhaust should run a steam turbine which makes more electricity. Then a heat pump can capture more energy from the exhaust (and from your bath water etc) to pump more heat into your house. The electricity can be used to charge an electric car or run a gpu inside your house (and produce even more heat). Heat pumps should be utilitarian and 10x cheaper, and used in multiple places. They should not be something you “invest” in with a 10 year payback time.
  • Angostura 3y ago
    > The temperature of a natural gas flame is 2770C. Using it to heat a house to 30C is ridiculous. Why?
    • cjfd 3y ago
      Entropy. Delta S = Delta Q / T. An efficient use of energy produces as little entropy as possible. Here the loss is Delta Q / 303 - Delta Q / 3043. T in Kelvin.
    • kragen 3y ago
      the carnot limit for 2770°/0° is 1 - 273/3043 = 91% the carnot limit for 30°/0° is 1 - 273/303 = 9.9% so if your gas flame is really 2770° (which i doubt, the adiabatic flame temperature for methane in air is only 1963° and actual flames are even colder than that) you're wasting 90% of your exergy by diluting it down to 30° also tho i do not want to go to your house if you heat it to 30°
      • pi-e-sigma 3y ago
        Carnot limit has nothing to do with heating efficiency, only with converting heat into mechanical work
• switch007 3y ago
  Fun fact: when a £X subsidy is made available, the cost goes up by exactly £X, which is a total coincidence. ;)
  • JoeAltmaier 3y ago
    Maybe temporarily. Competition exists, the free market is real.
• throw0101d 3y ago
  Also note that one doesn't have to go 'all-in' on heat pumps, and there are dual fuel / hybrid systems available: > A dual-fuel heat pump works in conjunction with a furnace. During the summer months, the heat pump works like a high-efficiency central air conditioner. In mild spring and fall weather, it provides cost- effective and efficient heat. As the temperatures drop in the winter months, the pump shuts off and lets your furnace take over. * https://www.lennox.com/buyers-guide/guide-to-hvac/glossary/dual-fuel https://www.lennox.com/buyers-guide/guide-to-hvac/glossary/d... * https://www.trane.com/residential/en/resources/glossary/dual-fuel-heat-pump/ https://www.trane.com/residential/en/resources/glossary/dual... More of a thing when heat pumps were more expensive and/or not as capable as they are now: going down to only 5C or -10C, whereas now units can go down to -25C. They could also still be useful in places with less reliable power (rural? coasts?), as a heat pump need more electricity, whereas a furnace just needs to power a fan and an ignition system, so a small portable generator can handle the load (or it won't tax your battery system as much).
  • bradfa 3y ago
    Dual fuel is also useful if electricity is expensive but gas is cheap and if you know what the efficiency curves look like for your appliances. I recently did this calculation and effectively when ever a heat pump would be less than a COP of 4, my gas furnace would likely cost me less money for the same amount of heat output. Our electric rates have effectively doubled in the past 5 years while gas has dropped in price. Obviously this situation is going to be region-specific and gets even more complicated with time-of-use billing. Ideally a smart thermostat would be able to consider all these variables and pick the most cost effective heat source for a dual-fuel setup but I don't think any of them are quite that useful yet. Only a handful of centrally ducted heat pumps on the NEEP list (https://ashp.neep.org/#!/product_list/ https://ashp.neep.org/#!/product_list/) have COP >4 at 5F outdoor temperatures.
• dave333 3y ago
  I have a gas furnace and a separate AC unit - I wonder can I replace the AC unit with a heat pump and keep the gas furnace? I could keep the existing thermostat and have the heat pump work with a new second thermostat so I can set the heat pump to kick in the heat at a lower temperature than the gas furnace. Maybe turn the gas furnace thermostat down once a month to operate it to prevent problems.
  • mschuster91 3y ago
    Yes, of course, that's the "dual fuel" setup mentioned in the article. In Europe, it's very common as we mostly use water to distribute heat. Either connect the heat pump and the gas furnace in parallel and run whatever you want depending on circumstances (i.e. normal operation is handled by heat pump, but the heat pump kicks in at low temperatures or high load), or run them in series with an optional bypass (i.e. the heat pump heats the water prior to entering the gas furnace).
    • throw0101d 3y ago
      Note that your furnace needs to be designed to support this. Generally it is extra logic so that you have a "Heat_1" source (HP) and a "Heat_2" source (switch to burning).
      • dave333 3y ago
        I was hoping that the heat pump could just hook into the existing ductwork (replace the AC unit) and use its own separate thermostat. The existing thermostat might try to turn on the non-existent AC just nothing would happen.
        • throw0101d 3y ago
          > I was hoping that the heat pump could just hook into the existing ductwork (replace the AC unit) and use its own separate thermostat. The inside unit (furnace, air handler) and outside (AC, HP) unit need to have some level of compatibility. Check the sticker on your furnace to find the model number and see its capabilities.
• refurb 3y ago
  I've never tried one, but they seem uniquely suited to clothes dryers. Use the cold side to dehumidify the air, then pass it over the warm side to heat it up. Net-net, no extra heat in the room it's operating in (beyond the motor and such), and a nice self-contained unit that doesn't need external venting.
  • shellfishgene 3y ago
    Most modern clothes dryers work exactly like that.
    • frankus 3y ago
      A number of newer ones are ventless (although still very much the minority in North America), but only some use an actual heat pump to recycle the heat. IME most of the cheaper ventless dryers just reject the heat (but not the moisture) into the room they're operating in. This is still a win because it doesn't depressurize the house (any air you vent out of the house is eventually replaced by outside air, sometimes via dirty areas like crawlspaces and attics). But the heat pump ones can run off of a low-power (~1500W) circuit whereas the condensing ones typically need a higher power (~5kW) circuit.
  • timbit42 3y ago
    You can also get heat pump water heaters, although they take heat from the room.
    • foobiekr 3y ago
      I've wondered about these - why don't they do the same split that HVAC pumps use? It seems really bizarre as a design. Components would also mean replacing the tank would be more cost effective and circuit routing would be easier.
• losvedir 3y ago
  Hey, that's fun. That's the first "(2023)" I've seen on HN. This is a pretty useful guide for me since I've wanted to look into getting a heat pump for my home. But it doesn't get into the first stumbling block that much: _finding_ a contractor! It mentions contractors some, but doesn't talk about those that do heat pumps vs those that don't. Around where I live in Northern Indiana, I haven't really found anyone that's got a ton of experience installing, working with, and (importantly!) repairing, heat pumps.
• JCM9 3y ago
  Generally a fan of heat pumps but the big issue remains where does the electricity come from to power them. Burning coal or gas to make electricity to power a heat pump isn’t great. Cost wise too I know a bunch of folks that switched from gas to electric heat pumps only to be shocked by their electric bills. Highly efficient natural gas setups remain much better for many settings.
  • mechagodzilla 3y ago
    Given the lifetime of the equipment and the relatively rapid transformation our power grid is undergoing, there are probably few places in the US where a heat pump doesn’t come out significantly on top emissions-wise. With an entirely natural gas grid, you only need a COP of 2 or so to beat the most efficient direct natural gas setups. Ten or fifteen years from now coal generation will probably barely exist in the US and we will have another few hundred GW of wind and solar.
  • Lutger 3y ago
    It isn't great, but perhaps surprisingly so using gas to create electricity and the electricity for a heat pump, is still a lot better than using a regular gas boiler. In other words, you'll get more heat out of a m3 of gas when you use it to create electricity and power a heat pump with the generated electricity, generally speaking. So it is an improvement even if the net is 100% dirty. But it isn't, even in winter we can get a lot of electricity from renewable sources. I think there are two big issues with heat pumps: they are expensive and require well insulated homes. Both problems can be solved.
  • bluGill 3y ago
    My local utility generated more wind electric than all customers used last year. The rest of the US needs to catch up.
  • ThatPlayer 3y ago
    Having multiple possible sources for electricity is an advantage for price stability. For example California's gas prices tripled this time last year. In general I think natural gas prices will continue to go up as people switch to electricity or more efficient gas setups. Less gas usage means additional fees for infrastructure. As prices go up, more people will switch. It's a feedback loop. At some point it won't be worth it to run the infrastructure for natural gas anymore.
• prepend 3y ago
  I had a furnace die and had to replace it last year. The hvac company was really down on heatpumps and said that due to the climate (doesn’t get too cold in the winters gets really hot and muggy in the summers) the heat pump would be less efficient than a traditional furnace and AC. I like my hvac company so didn’t push too hard but wondered if this was true or just their inexperience.
  • Lendal 3y ago
    Not inexperience. Motivated reasoning.
  • projektfu 3y ago
    They don't like heat pumps mainly because their customers "don't feel the heat" from them. The heat comes out at lower than body temperature (85F/30C) so the customers don't feel like they're really working, whereas a gas furnace or electric heater usually heats to 120F/50C. So, customer satisfaction is often lower even though they are saving money and polluting less. But, you know, that 85F is plenty to heat a room to 72F and keep you warm.
    • avidphantasm 3y ago
      Our Mitsubishi Hyper Heat heat pumps put out noticeably warm air, definitely warmer than 30C.
      • projektfu 3y ago
        That sounds nice. They are mini split or ducted?
  • caleb-allen 3y ago
    I can't imagine that a traditional furnace and AC could be less efficient than a heat pump, unless you almost never turn your heat on—a heat pump is many times more efficient, in terms of energy consumption, than a traditional furnace. That said, if it's rare to run your heating then a standard AC unit is probably marginally more efficient than a heat pump for just the cooling operation
• stevekrouse 3y ago
  From the author of that article: https://heatpumpshooray.com/ https://heatpumpshooray.com/
• DanielHB 3y ago
  I am always amazed at how many people know this stuff deeply, I feel most people actually live in apartments with either central building heating or district heating and never ever need to think about this stuff. Especially considering buildings have less wall/roof area to lose heat from on a dwelling by dwelling basis, even a small-ish building with gas heating with average insulation would still be much cheaper to heat than a house by square meter.
  • Tagbert 3y ago
    In the US, housing is heavily biased to single-family houses. About 81 million detached single-family vs about 30 million multi-unit housing. https://www.statista.com/statistics/1042111/single-family-vs-multifamily-homes-usa/ https://www.statista.com/statistics/1042111/single-family-vs...
    • bob1029 3y ago
      In the US, you have to be fairly diligent as a homeowner to not get taken for a ride by the various HVAC technicians. The more you know about your own system, the more you can save. Even if you don't intend to do any work yourself.
      • kube-system 3y ago
        I know better and I still get taken for a ride. When it's 90F+ outside and the start capacitor fails on my AC compressor, I don't have much room for negotiation.
        • sokoloff 3y ago
          Given that you know what it is and know which end of a screwdriver to hold, you could reasonably have a start (or combined start/run cap) that matches your unit on hand and DIY replace it before calling anyone.
• 2-718-281-828 3y ago
  are heat pumps interesting to you folks because you have one or think about getting one or because the technology is in some aspect particularly impressing/counterintuitive/ingenuous? i ask because this topic is popping up regularly and so far i fail to see why.
  • pjc50 3y ago
    Rather like electric cars, they're a technology lots of people are thinking about getting for environmental reasons, but also a big fixed investment so people are keen to understand.
  • stinos 3y ago
    the technology is in some aspect particularly impressing Yes, because for every unit of energy you directly put into it (in the form of electricity) it outputs more energy (in the form of heat). Which is unlike any other typical heating system, which usually puts out less or at max the same amount.
    • 2-718-281-828 3y ago
      like a perpetuum mobile?
      • stinos 3y ago
        No because that doesn't exist in practice. The losses of converting the generated energy back into electricity make that impossible.
        • 2-718-281-828 3y ago
          that's not true. i saw a working implementation of a perpetuum mobile in a youtube video.
          • stinos 3y ago
            Sorry but no. Then it wasn't a perpetuum mobile. There's no way to violate the laws of thermodynamics. Likely the video was not showing everything, and/or giving a false impression/explanation. Typcial example are those toy birds picking water: it looks like a perpetuum mobile, but it in fact uses the energy present in the water. Once the water evaporates all it stops. Adding new water constantly makes it run forever, but that's by the grace of adding energy into the system hence defeating the idea.
• JoeAltmaier 3y ago
  The labor issue might be due to the seasonality of the business. (The labor issue: 300,000 HVAC professionals in the USA but just 145,000 companies). In fact, the business is initiated just two days of the year! The first hot day of summer and the first cold day of winter. When somebody's old system breaks and they find out exactly when they need it most! So it's always an emergency, and always when it's very unpleasant to work outdoor. Seems clear why nobody is going into the business. One of those 'dirty jobs'. Maybe a business model that spread things out? Like, a contract to support heating and cooling year-round, schedules upgrades, does periodic testing to anticipate breakdown. I imagine now it's more like folks that have snow-plow trucks, promise to plow out your parking lot after each big snow. They work just a couple days a year in Iowa, and have regular jobs the rest of the year. The companies are less than half a dozen trucks typically, with a huge demographic spike at 'one guy, one truck'
• ortusdux 3y ago
  I replaced my electric water heater with a heat pump unit, and it paid for itself in 2 years.
• ppsreejith 3y ago
  This doesn't explain how they work though? I've found the following simplified model of how heat pumps work useful, and why they have > 100% efficiencies (Typically 300% - 400% or more compared to burning/ resistance heating which can only reach 100% efficiency). Heat always flows from a high temperature to a low temperature. However, we want heat to go the opposite way (i.e. from the cold outside to our warm houses). There's a technique to do this. We use a gas (the refrigerant) to transfer heat. We first expand the gas (which cools it) until it cools below the cold outside. We then bring it near the cold outside where it now starts absorbing heat until it matches the cold outside temperature. We then move the gas and compress it until it's temperature matches/exceeds our desired warm inside temperature. Then, we bring it to the warm indoors where heat will now flow out of it. During the entire cycle, the gas is inside a closed loop. It exchanges heat through radiators. The compression & expansion cycles uses energy (technically they can be offset against each other a bit) which is added to the gas (conservation of energy) raising its temperature. Thus by supplying a little electricity, we're able to move heat from the cold outdoors to the warm indoors. The high efficiencies are because for using X units of energy, we're able to heat the house by X+Y units where Y is the heat transferred from the outside. Typically Y >> X.
  • cubefox 3y ago
    By that measure of energy, burning oil or gas also has >>100% efficiency, as you only need energy to get it out of the ground, transport, and to light it. The energy stored in the oil is analogous to the "outside heat" for heat pumps.
    • duckmysick 3y ago
      That's the thing though: the energy is stored in natural gas or oil but I still need to extract it. I can't heat my room by pumping it full of natural gas or filling it with oil. To raise the temperature of my 300 square feet room by one degree I need the same amount of energy, no matter the source. But the ways of delivering that energy aren't the same. If I have a simple gas burner, I need to know how much gas do I have to burn to heat my room. It will keep me warm, but it's not a good idea. Burning gas with a flame makes other gases that I don't want inside. I need to vent them, but I will lose some heat through that. I can also get a gas furnace that condenses those byproduct gasses in a second heat exchanger for extra efficiency. Maybe seal it up better too. It needs a little electric power for ignition, so I need to take that into account. But overall, it would be more efficient. I would need less gas to heat my room. Even though I'm using gas in both examples, the efficiency is different. It depends on how I convert that gas into heat. I can also burn that gas in a generator to produce electric power. Then I can use that electric power for a resistive heater. Not a great idea, but it's an option. I don't have to burn the gas myself. I can delegate generating power to a gas-fired power plant and buy power from them. And I can use a heat pump instead of a resistive heater. My heat pump will use less power than a resistive heater, so that's good, I suppose. The question remains: how much gas do I (or a power plant) have to burn to heat my room. The answer depends on what do I use the gas for and how. That's the efficiency.
• peter_l_downs 3y ago
  I had heat pumps added to my home this past summer, primarily to provide air conditioning. This article is a good overview of what I learned in the process. I'll add a few lessons: - Get a few quotes and iterate on the plan. Save the contractor you'd most prefer to work with for last, because you'll have a much better idea of what you want by then, and your knowledge will save you money. - There's a fun puzzle to retrofitting older homes (no existing ducts): where you place the lines, where you place the units, and where you place the heads are all variables to play around with. This is part of the reason for getting different quotes. Only the last two contractors I spoke with were able to come up with ways to keep all the external lines on the side of my house and away from the street. Only the very last contractor offered a ducted system for bedrooms, so I have head units downstairs but the upstairs is vented. - No one will run a real Man J calculation, they all use proxy calculations. This should be fine but you almost certainly want to slightly undersize your system. If your system is always turning on and then turning off (because it is oversized and heating / cooling the room very quickly) you'll end up with humidity and mildew problems, you want it to be running "low and slow" while it's on. - They work amazing for air conditioning. For heat, your existing boiler + radiators is often nicer and more cozy. It's also often cheaper — heat pumps are electrically efficient, but natural gas costs vary significantly by location and for me (~Philadelphia) heating with my boiler is a lot cheaper than doing it with the heat pumps. - I live in an older home, so before I installed heat pumps I had to replace my ancient windows for modern ones that didn't constantly leak energy. I'm happy with the results but it adds a lot to the startup cost.
  • amluto 3y ago
    Even Manual J (in my quite limited experience) can give wildly inflated results. For example, if a big window has a tree in front of it or a reasonably reflective or insulating window treatment (and you close it on a hot day!), then your Manual J software may estimate the heat load as if the sun were shining full blast through the glass all the time and give a huge number. I intentionally had a contractor install a unit that was undersized per Manual J in a room, and, as tested during a nearly-record-breaking heat wave, it kept up without coming close to its limits. Fortunately, a lot of modern systems have respectable turndown ratios (better than 5:1 is not that hard to find), so as long as you use controls that can operate the system all the way down to minimum power, oversizing is not that bad.
• vhodges 3y ago
  Sigh, I need this a few week ago ;)...I just replaced my failed gas fired furnace with a Fujitsu XLTH 3 ton ducted mini split in the Fraser Valley (Mission BC). I only got 2 quotes (and spoke with a third, but not quoted beyond ballpark). I ended up going with the local installer (which was the lowest, but I also worked with them on the furnace and liked them anyways). It ended up being 20k CAD installed. If we're approved for all of our rebates (likely) we'll get 11k CAD back for a net of 9k which isn't too bad. Our unit is supposed to be rated for 110% of heating capacity at -15c. We'll see , it's supposed to drop to -8c or so later this week :) We're looking forward to having cooling this summer (which we've never had)
  • barbazoo 3y ago
    As a valley neighbour I'd be interested in an update when the time comes.
    • vhodges 3y ago
      Now that it's warming back up a bit, here's that update: It was mostly okay. It kept working even with the -20c windchill and was always putting out heat. It's kind of subjective but I feel it struggled a bit eg the 'room' temperature shows a degree or two below the set temp. It never felt cold in the house (but a bit cooler?) The sensor is probably in the control unit which IS in the hallway over the garage (and that side of the house always seems a bit cooler) so take that info with a grain of salt.
• 1970-01-01 3y ago
  The more you think about it, the more it makes sense to harness geothermal. A big breakthrough there could benefit our environment more than any other tech, except fusion.
  • simonebrunozzi 3y ago
    Cheaper digging would be the breakthrough.
    • 1970-01-01 3y ago
      Or vaporization of bedrock with a super laser
    • barbazoo 3y ago
      For residential purposes it seems to only require a depth of <2m [1]. Is moving dirt here a main cost? [1] https://www.energy.gov/energysaver/geothermal-heat-pumps https://www.energy.gov/energysaver/geothermal-heat-pumps
  • barbazoo 3y ago
    Do you know what current limitations of residential geothermal are? From looking at https://www.energy.gov/energysaver/geothermal-heat-pumps https://www.energy.gov/energysaver/geothermal-heat-pumps it looks like you'd need quite a bit of space, so basically single family homes with somewhat of a yard. For bigger setups it would make more sense to capture the heat locally and distribute them to a whole neighborhood given how much deeper it would need to go.
    • 1970-01-01 3y ago
      The vertical system looks to be about the size of an average driveway or garage. Done at scale, mainly for new construction, system sizing isn't a problem.
      • barbazoo 3y ago
        Could it be under a garage or a driveway tough or does it need to be accessible like a septic tank?
• m3kw9 3y ago
  From the comments and article, heat pumps are not ready for prime time and also still version 1.0. And you know what first time adopters have to go through
• turtledragonfly 3y ago
  Apropos of nothing, I had a not-great experience switching from an oil furnace to heat pump. Maybe somebody else going through research will benefit from my woes. Some day I'll make a blog post for it: 1. Noise levels (inside) * Fundamentally, a heat pump runs more often than a furnace. So, air is semi-constantly blowing out of your vents, rather than a few bursts throughout the day. Also, the air is tepid, rather than warm. Previously, there was a "yay, the furnace is on" moment of enjoying the warm air. Now, it's more of a "jeez when will this thing shut up again?" throughout the day. It reduces my quality of life. * One of our vents points at my back where I sit to work. With the furnace, that was enjoyable. With the heat pump, it's a nuisance. I taped over the part that blows on me. Similarly, we have a vent in the bedroom that we mostly keep covered with a pillow these days, due to the noise. * In documentation, noise is often measured in decibels — indicating max loudness. And by that measurement, the heat pump is no worse than the furnace (maybe even a bit quieter). But the fact that it's on near-continuously at that noise level is what causes my annoyance. So, it's not just loudness, but also how continuous it is. * We had existing ductwork, so the heat pump's air handler uses that (just like the old furnace). This is a common situation, but what nobody mentioned, across multiple estimators, is that it's likely the old ductwork will be "under-sized" relative to the new system. This means higher static pressure, and importantly, more noise at the output vents. Talking to the technicians, this is a bit of a crapshoot — you might get lucky with noise levels, or might not (like me). * Loudness will also vary depending on how far from the central unit you are (my house is fairly small), how many vents there are, and various other factors. * In theory, you can determine if the above will be a problem by doing measurements beforehand. None of the estimators mentioned this; they just want to sell you the system, of course. I didn't realize until too late that you can probably find someone, pay them a few hundred dollars, and get this information upfront. There's a whole science to it, with specialized tools. Look up "Manual J, S, D, T measurements," for a starter. * However, even if you get that info, it still depends on your sensitivity to these things. For instance, my wife is much less bothered by the noise than I am. 2. Thermostats We got a fairly modern "communicating" system. This means the outdoor and indoor units talk to each other, allowing better efficiency. This sounds nice, but what it means is that you will be locked in to your vendor's choice of thermostats, since the communication protocol is proprietary. These are generally more expensive than the alternatives, and you won't have many options — perhaps only one. If you get a "non-communicating" system, you will be able to try various different thermostats — eg: a simple one from your hardware store, or a Nest one, etc. 3. Other * The old oil furnace was a simple machine, with a lifetime warranty on the heat exchanger (basically a hunk of cast iron) and can basically last forever with decent maintenance. The new heat pump has a 12 year warranty, and the system might last 25 years with good maintenance. The HVAC estimator seemed proud of this, but to me it doesn't seem like an especially long time. * If you use old ductwork like mine, it may not be insulated to modern standards. This is both a noise issue and potentially a condensation issue when the AC mode is running. * It's very difficult to know when the "emergency heat" mode is being used — where resistive electrical strips are used to generate extra heat, if the heat pump isn't producing enough. This mode is much more expensive than the heat pump alone. It boggles my mind that such simple (and useful) information is so hard to obtain. * If you want to get government subsidies, do your research about what exact make/model is covered by it. Ironically, sometimes the more modern and efficient systems are not subsidized, presumably because there is some lag to update policies. * Generally, remember that the estimator who might come to your house is a salesman, first and foremost (: 4. Pros Okay it's not all bad; some positives include: * AC in the summer. Probably the biggest positive. * No dependence on oil — both for cost and environmental concerns and risk of tank leakage (ours was aboveground, so less of a worry) * No carbon monoxide worry, since there's no combustion going on. But overall, I'm not sure it was worth it for my case.
• vizzah 3y ago
  Is there a conspiracy? Why everyone is talking about heatpumps these days? Including in the UK. In Europe air conditioners come with heat-pumping functions since ages ago.. all installed aircons can heat or cool. But I personally found such heating ineffective and lame. What's going on?
  • barbazoo 3y ago
    I think it gets clicks. Lots of people are passionately for/against them for ideological reasons.
  • cpncrunch 3y ago
    >Why everyone is talking about heatpumps these days? Because of their efficiency. They are typically 200-400% as efficient as electric resistance heaters, because the energy is used to move the heat from outside. >I personally found such heating ineffective and lame. If it's a proper heat pump, the heating won't be ineffective or lame. It should pump out air > 30C, and is sufficient to keep your house at 21C even when outdoor temp is 0C.
    • vizzah 3y ago
      but it should be on most of the day, for the air indoors to remain at 21C. Once stopped, the air cools off very quickly, compared to other heating methods. Underfloor heating is a best heating option in my opinion, perhaps mixed with a couple IR panels on the walls. With heatpumps it takes too long for the the warm air to descent and make legs/feet feel comfortable :(
• kyleblarson 3y ago
  I don't have an idealogical horse in this race, but I bought a ~2500sqft home a few years back in an area where summer highs can get to 100f and winter lows can reach -25f. The house only had a 20 year old electric furnace and no AC. Replaced it with a large heat pump system with a new electric furnace for backup heat when it gets super cold. Also included an air filtration system. It was a big cash outlay, but totally worth it as we now have AC in the summer so we can keep windows closed when the smoke is bad, the filtration system works really well for the smoke, and the system almost never needs to use the furnace backup. Speaking with the previous owner, the winter electric bill savings have been around 30%.
  • pkulak 3y ago
    I'm surprised it's only 30%. Even a COP of 3, which is pretty modest for a modern heat pump, would be 60% savings (abouts, not sure if my math is right).
    • pandaman 3y ago
      Most houses consume electricity for the purposes other than heating too.
    • sokoloff 3y ago
      People commonly (by default) compare electric bills on $$ rather than on kW*hr, so an increase in rate would reduce the savings-as-compared. Different baseline electricity use and thermostat preferences could play a significant role as well. (Previous owners may have gone for a lower daytime setting and a deeper setback because of the inefficiency. A new owner with a more efficient system may quite reasonably choose to bias towards greater comfort than the prior owner did.)
    • Projectiboga 3y ago
      New guy might be getting more comfort by heating more while still using less total electricity.
• gavin_gee 3y ago
  pretty good post. The big gap is a section on noise. Citys like seattle have incredibly tough noise limits at property boundaries for heatpumps. with many high density single family houses close to the property line. it makes it difficult to find a quiet heatpump. (stupidly there are noise limit differences for a heat pump vs an AC unit) As far as I can tell there are no efficient heatpumps available on the market that can sit legally less than 6 feet from the property line in Seattle and supply a 5 ton system
• r0m4n0 3y ago
  Converted my house to heat pump last year and seen a full year of what the cost savings look like. Saving 50% over gas in the winter, saving 30% in the summer over my old AC. I don’t miss the furnace firing up and the noises it would make when it pushed tons of hot air. Getting much more constant temperature instead of being hot sometimes and cold the next. Negative: Not a fan of the weird noise the unit outside my bedroom window makes at a more consistent rate through the winter and it annoys my neighbor too. Overall got the home warranty to cover about 10k of the 16k replacement, after learning about going to arbitration here on HN! Definitely happy with the conversion overall thus far. Jury is still out on long term reliability
• c_o_n_v_e_x 3y ago
  For someone who's not in the industry, the Author has done a reasonable job. I'd add a few things: - Heat pumps have been around a while. In the southern US, there are lot of older HVAC techs with a negative perception of HPs based on problems with older technology. Older HPs had less of an ambient operating temperature range, in which case the emergency heat would activate, reducing savings. - Re: fragmented markets, different states/cities/towns/municipalities have different rules, processes, procedures, etc. - Re: the desire for drop-in installations, the construction permitting and inspection process is a big fat roadblock which is linked to the problem above.
• theogravity 3y ago
  Bay area resident here that had a heat pump installed last month. The heat pump, air pusher, comm units + labor came out to $23k for the highest 4 ton Trane efficiency unit (no heat strips either). The labor cost probably was 100%+ of the system itself, so I feel the article has a degree of accuracy to it.