14 ms·

Heat pumps _are_ amazing! The power of physics at play: spend 1 unit of energy to gain 4. Some naysayers will say that it doesn't work the 3 days of the year w

• gjm11 2y ago
  In fairness, the days when it's -15°C outside are exactly the days when you really want your heating to work well...
  • derkoe 2y ago
    Most heat pumps fall back to electric heating when it's too cold. So, on these few days you will need the same amount of electricity a typical electric heating will need.
    • tomohawk 2y ago
      which spikes the electricity demand from the grid and puts it under the most strain when its most critical for the grid to stay up, which means the grid has to be overdesigned, which means that the air based heat pumps are a poor choice for a reliable grid.
      • yurishimo 2y ago
        It depends on where you are. In many places worldwide, extreme cold is also generally quite clear from clouds unless you're literally in a storm, in which case, the high winds are just as likely to cause problems. Rooftop solar should be more than enough to offset your own usage.
        • bluGill 2y ago
          In nearly all places extreme code means dark! Sure there are less clouds, but the latitude is high and so there are not only few hours of daylight, the earth's angle is also working against solar.
      • rssoconnor 2y ago
        The demand comes at the coldest part of the day, which is typically overnight, which is far off peek demand times.
      • sanderjd 2y ago
        I don't think this conclusion follows. It is true that variability is a challenge for grids, but it is not clear that it is better to trade more total energy usage (per useful unit of work) for less variability. Variability is certainly a challenge, but not an insurmountable one, and also one that must be faced regardless nearly everywhere, as solar power has become too cost-effective to be ignored.
      • jtbayly 2y ago
        Isn’t electricity demand always going to be highest on the coldest days?
      • beejiu 2y ago
        The UK is rolling out smart meters to every property. In the past 2 winters (following on the Russian gas crisis), they have run programs that pay £3 per kWh reduced demand. This is a nice way to balance the grid during extreme demand.
        • michaelt 2y ago
          > programs that pay £3 per kWh reduced demand. That much? How do I get in on that? My energy supplier's demand reduction scheme only pays £10/month total.
          • astiela 2y ago
            octopus energy seems to be the best for energy i have seen so far in the uk alongside their smart tariffs https://share.octopus.energy/umber-squid-619 https://share.octopus.energy/umber-squid-619
          • beejiu 2y ago
            It's called the National Grid ESO scheme and you sign up through your supplier when it's open. However, some suppliers take a cut of the ESO payment. Alternatively, you can sign up to Uswitch Utrack (https://www.uswitch.com/mobile-app/ https://www.uswitch.com/mobile-app/), which passes 100% onto the customer. (Disclaimer: I used to work at Uswitch.)
    • thehappypm 2y ago
      This is untrue. Mitsubishi hyper heat units do not have this feature, and they’re the gold standard. I wish they did, though
      • sokoloff 2y ago
        Hyper Heat is a tech that is on multiple different models of Mitsubishi. All of the SVZ (ducted air handlers attachable to Hyper Heat or H2i mini-splits) do support (optional) electric resistance heater kits.
        • thehappypm 2y ago
          That’s correct, air handlers for ducted systems can absolutely have heat strips. That’s actually pretty standard. I have never seen one for a mini split though — can you share a link?
          • sokoloff 2y ago
            https://ces.mitsubishielectric.com/wp-content/themes/melco/assets/assets/pdf/SVZ_Product_Guide.pdf https://ces.mitsubishielectric.com/wp-content/themes/melco/a... documents the SVZ indoor unit's ability to have electric resistance heat and be connected to Hyper Heat SUZ outdoor units. Whether you call that mini-split or not is up to you, but it's definitely a heat pump system that is Hyper Heat and supplemental electric heat capable, and getting down to one-ton units seems "mini" to me. Mini-split means "smaller than conventional system ["mini"], condensor and evaporator are connected by long refrigerant lines ["split"]". It doesn't necessarily mean "wall/floor/ceiling indoor unit that has no ducts", though a "ductless mini-split" is the most common configuration of mini-split (because of the cheapness and ease of installation). https://zeroenergyproject.com/2022/03/09/what-is-a-mini-split-heat-pump/ https://zeroenergyproject.com/2022/03/09/what-is-a-mini-spli...
          • deleted 2y ago
            [deleted]
    • deleted 2y ago
      [deleted]
  • magicalhippo 2y ago
    We have a air-to-air heat pump (minisplit). We also have heat foil in the floors. We've had weeks around -20C and below most winters. I do hear the minisplit working hard those weeks, but we just needed a bit of extra help from the floor heating to have a comfortable 20C indoor.
  • Mountain_Skies 2y ago
    Depends on how many of those days there are. If it's only half a dozen or so, I can deal with putting on an extra layer of clothing in the house for a handful of days per year. As long as it's warm enough inside to prevent damage like pipes freezing, a small amount of personal discomfort for a few days is acceptable.
  • turtlebits 2y ago
    Get a few space heaters, they're cheap. Many new homes that are heat pump only will also require some sort of resistive heating as a backup.
• wernerb 2y ago
  This needs far more attention. Combi boiler installers tend to massively oversize the CV. But with heat-pumps you need to be far more accurate. And it does not make sense to design for a temperature that occurs only a couple of days in the year. You can just have the backup heater kick in which is far more efficient for a couple of days than having a heavier heatpump for the rest of the year that can not modulate back as much as a smaller heatpump.
  • stilley2 2y ago
    I recommend this technology connections video which dives into this in wonderful detail https://youtu.be/DTsQjiPlksA?si=gx18FGOcjsv5PpNg https://youtu.be/DTsQjiPlksA?si=gx18FGOcjsv5PpNg
  • rssoconnor 2y ago
    > than having a heavier heatpump for the rest of the year that can not modulate back as much as a smaller heatpump. Aren't basically all modern heatpump variable speed, and thus can modulate back? That said, I totally agree with your overall point about right-sizing your heat pump, but it is more about saving money on the unit rather than worrying about cycle times.
    • bluGill 2y ago
      Modern heatpumps can modulate, though it isn't 100%. I recommend people consider two smaller heat pumps in many cases - it costs more upfront but can modulate down more and if one system breaks the other can handle everything most days of the year (some rooms will be a bit uncomfortable)
• verelo 2y ago
  So, i have a house in Haliburton Ontario. Historically we drop a cool $3k a year on propane. Last year we installed a Mitsubishi hyper heat ductless system. We used zero gas this year. Read it again, zero. It’s lakefront, very remote, and the largest electricity bill i got was around $450 for a month and then they dropped back to something more like $250. The savings are huge, I’m no longer stressed about running out of gas…and the heat pump performed well beyond its advertised specifications. We had a few -25C days and it was humming hard, but the house stayed a comfortable 20C inside. The house is around 3000sqft and we didn’t even get the largest unit, i can’t stress enough that they actually operate better than advertised. We would run a fire from time to time but we did that with propane too, it’s mostly ornamental. https://photos.app.goo.gl/FCwLJQAtoG67g9y86 https://photos.app.goo.gl/FCwLJQAtoG67g9y86 https://photos.app.goo.gl/TwiMaSAj9hGxYqby6 https://photos.app.goo.gl/TwiMaSAj9hGxYqby6 https://photos.app.goo.gl/gYVYvVEB3whLCv1dA https://photos.app.goo.gl/gYVYvVEB3whLCv1dA https://photos.app.goo.gl/49RcBdBuUZ2jVN3J7 https://photos.app.goo.gl/49RcBdBuUZ2jVN3J7
  • Siecje 2y ago
    That's a lot of lines going to the outdoor unit. Is there two per indoor head?
    • matthiaswh 2y ago
      It looks like that unit may have 3 indoor heads. Two lines per head. Power to each head. Power to the outdoor unit.
      • bluGill 2y ago
        Looks like it. I'd suggest anyone looking at a system like that install at least 2 separate outdoor units. That way if one breaks the other can still work - and most of the year it will be powerful enough to handle the whole house (some rooms will be a little uncomfortable but bearable)
        • verelo 2y ago
• thechao 2y ago
  > Disclaimer: I self installed one for my house (13kWth) and I'm very glad I did My HVAC guy keeps telling me to install a couple of heat pumps (he doesn't like driving out to me), solar panels, and an in-house battery; what sort of complexity was this job? Are there online sources you used?
  • matthiaswh 2y ago
    Installing heat pumps doesn't require a ton of domain knowledge (assuming you're already a handy person), but it's a lot of work. It took 3 guys who do it for a living 160+ man hours to install our mini-splits. They had to drill through walls, attach channels to the siding, crawl into a tight crawlspace, do some plumbing when they hit a water pipe with their drill, wire up electrical, and add breakers to the panel. The only thing that might catch you up is designing the system and ensuring you right size it for your heat load requirements. I'm sure you could research this pretty well, but your HVAC guy might also be happy to consult on that portion.
    • turtlebits 2y ago
      If you have a good spot (ie exterior wall), installing a mini split can be an easy DIY. It probably took me a max of 6 hours to do it all.
  • sumtechguy 2y ago
    With this sort of work let the HVAC guys do the research for you. Call 3 of them get quotes. Then research what they are offering. Pick the one you like. Last time I did this around 2008 it was about 5k-15k I was quoted. I asked all 3 for a small, medium and large systems. For me it was mostly an in place replacement. The ducts were already there. The refrigerant lines were all ready in place. The biggest cost was the unit themselves and some change out of the controllers. The labor was about 1 days worth of work for 4 guys. You can also gain quite a bit by just fixing drafts and putting in proper insulation. Which can be much cheaper to do. I also had the guys go thru and fix an leaks in the duct system. That way the air was coming out where it should. It is amazing how badly that is installed many times. I also had them put in an attic fan which vented the attic when it got to about 110F. Insulation would have helped more there and I screwed up and put it off. If your house is older than 2000. I say go thru and review the existing insulation and look for drafts first. It trimmed my bill from about 350 a month to 200. My new house has excellent insulation the house is slightly bigger and the power bill is in the 80-150 range (less because I got solar, but I figured out the actual cost anyway). It has one unit and an air valve to switch between the floors. So the total cost is lower but the one unit will run longer. That savings I am getting is mostly because of better insulation.
• corbet 2y ago
  -18°F here (-28°C) here this winter. The heat pump (Mitsubishi) definitely worked hard and burned through our net-metering credit, but it did what we needed it to do. -15°C is just not even remotely a problem.
• dghughes 2y ago
  >Some naysayers will say that it doesn't work the 3 days of the year where it's -15°C outside, That used to be true but modern air-source heat pumps are better. But even so the efficiency drops it's just physics. Even if a heat pump can grab heat at -15C it will need to run longer when it's very cold, reducing lifespan of the unit. At some point it will just switch over to pure electric so your power to heat 1:4 is now 1:1. Ground source heat pumps are far better and even more efficient that air source but quite expensive to install.
• switch007 2y ago
  Just to be clear, it works perfectly at -14c and above? Or is there some disappointing performance in an intermediate range? I'm in Northern England and it's not uncommon for weeks of -5c to 5c in winter, some snowy days, plus serious damp making it feel even colder. So I'm curious if a similar system would be similarly amazing here. I've read many people say they work perfectly because it won't hit -20c (a nice Strawman...)
  • Aspos 2y ago
    At low temps COP is lower, meaning you'll not get 4 units of heat for 1 unit of energy spent, but COP is still higher than 1 meaning using heat pump is still cheaper than using basic electric resistive heating. I think Northern England climate is ideal for heat pumps -- it never gets too cold, never gets too hot.