Advice Needed on Domestic Heat Pump

Discussion in 'General Science & Technology' started by exchemist, Dec 2, 2019.

  1. exchemist Valued Senior Member

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    8,689
    My son and I have been discussing how to reduce the household carbon footprint. We don't use the car much (we use bikes a lot) and I plan to get a hybrid or electric one next, depending on now the charging network develops in Brittany (we take the car over a couple of times a year) and the London area where we live, over the next 1-2years.

    However the gas central heating and not water system is the biggest carbon emitter. The house is big and old (Victorian, so leaky, heatwise). The least intrusive and expensive option seems to be an air-to-water heat pump. Ideally I want a system that can slot in, in place of the gas boiler we have now, and can still provide hot water at 70-80C , sufficient to heat the house and the water cylinder, using the existing pipework and radiators.

    It seems Daikin are offering a 2-stage heat pump that does this, which seems like an excellent idea if the UK is going to wean itself comparatively inexpensively and quickly off its current North Sea Gas habit. It could be just what I'm looking for. But I have not seen any other supplier that offers this.

    Does anyone have experience of this type of system, or any tips regarding possible pitfalls? Also, is the technology mature enough yet, or is it better to give it a couple more years before investing?
     
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  3. sculptor Valued Senior Member

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    are your radiators designed for steam or hot water?
     
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  5. exchemist Valued Senior Member

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    Hot water.
     
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  7. sculptor Valued Senior Member

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    ok
    now comes the hard part.
    first determine the output temperature of your current system
    180 degrees F-82 C- is quite common
    the heatpump set point is lower---the lower the set point the more efficient the system
    the heatpumt should have a setpoint at max of 120 degrees f -48.9 c
    ok
    so
    lower your output temp of your current system to 120 degrees f-48.9 c
    and run it that way for a heating season
    If you find that comfortable, then replacing your heatsource with a heatpump is doable without needing to replace the radiators.

    bear in mind that natural gas is usually a very clean burning fuel
    If you replace that with electricity produced by a dirtier fuel, then you may be doing the environment no good deed.
     
  8. exchemist Valued Senior Member

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    Thanks. Regarding the carbon footprint of UK electricity, it is already 25% from renewables and my understanding is that the last coal station in the country will soon be closed or converted to (renewable) wood pellets. There is still a lot of gas-fired generation, mostly combined cycle so 60% thermal efficiency. Maybe 50% by the time it gets to me in view of transmission losses. Given that the electricity consumption of the heat pump is less than half the gas consumption for the same amount of heat, I consider it safe to assume it will reduce my footprint, progressively more as the years go by.

    On the temperature issue, you seem to be talking of a standard single stage heat pump rather that the 2-stage one I have seen, which can allegedly produce heat at up to 80C. Obviously a 2-stage heat pump consumes more electricity than single stage, but I am not sure exactly by how much. I clearly need to find that out. I do not believe my system will heat well enough at 50C. It runs at close to 80C in winter and does the job but not with a huge amount to spare if it gets both cold and windy.

    On the plus side, London air temperatures seldom go much below 0C, so the heat pump should not have to struggle to import enough heat.
     
  9. RainbowSingularity Valued Senior Member

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    not to mention when the electrical system that is under funded and poorly maintained, falls over, your frozen to death.
    being "frozen to death" reduces your over all carbon foot print but negatively impacts on your ability to enjoy your holiday season.

    as people get pushed to switch to electricity, the electricity system will buckle under the pressure.
    the alt-right will be relying on the electrical system to collapse and cause massive impact on the average tax payer so they can justify a centrist voter base to vote for socialist funding for a capitalist profit system.

    you probably want to ask yourself if the current electrical system can sustain 20% more users in the middle of a heavy winter or summer season.
    in a heat wave will their be massive power cuts ?
    when everyone is snowed in ... and you only have electricity ...
    is freezing to death an acceptable alternative ?
    or would you rather have a gas system that is independent ?
    etc etc ...

    do not sacrifice your survival ability of independence to fit some vote buying model that is set up to fail.
     
  10. parmalee peripatetic artisan Valued Senior Member

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    2,678
    Ha! That's our indoor temperature when I wake up in the morning, during the coldest parts of winter (in the "mountains"--hills, really--of New England). We use a woodstove exclusively, but our house is a small A-frame with 18' x 22' footprint.

    Has radiant floor heating been adopted much in the UK yet? It's huge on the Continent, of course, and somewhat popular in the US. Both water and electric-based systems exist now, and there are more options than previously available, as you mentioned least intrusive. They're quite efficient, and are especially useful where high ceilings account for significant heat loss.
     
  11. exchemist Valued Senior Member

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    8,689
    I am not au fait with new builds in the UK, I'm afraid. A great deal of our housing stock is old brick or stone houses from the Victorian era, like mine.

    But underfloor heating seems to be drifting off-topic, as I am not interested in ripping up all my floors, at vast expense.
     
  12. parmalee peripatetic artisan Valued Senior Member

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    OK, though I was actually referring to style that goes between floor joists, without having to tear the floor up.
     
  13. exchemist Valued Senior Member

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    Oh thanks, that is more interesting, though quite a major intrusion throughout the house.
     
  14. Baldeee Valued Senior Member

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    Most new stock of housing (actually for the past 50 years or so) has concrete flooring, making underfloor heating of the ground floor quite a pain to retrofit.
    Your Victorian pad would probably be okay, especially if there is a basement/cellar underneath.

    From what I have heard (very little) heat pumps work great if you have a well-insulated house, not so great if the house leaks like a sieve.
    If your current system has little headroom then I’d be surprised if a heat pump would be able to cope.
    Maybe you should see if there is a combination that might work better, where you can survive with the heat pump most of the year but supplement it with something else for those really cold periods?
     
  15. exchemist Valued Senior Member

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    Yes there is a cellar under part of it. And interesting that you say retrofitting it might be easier in my house than in some.

    But clearly the reason why underfloor heating is proposed must be to get enough surface area of heater to allow adequate heating at a lower water temperature than used with a conventional gas boiler. What I am not clear about is how it manages to provide hot water effectively, if it only heats to say 50C or so. That's why I was intrigued by this "cascade" two-stage system, but it does not sound as if anyone on the forum knows much about this. It may be a new thing. Obviously the snag is that it needs electricity to power both stages, reducing the overall efficiency gain, but I don't know by how much.

    I'll need to contact a supplier to find out more. I've been holding off on that to try to get more info myself first, as I dislike having to deal with somebody's sales pitch unless I am well enough briefed beforehand to show him I can't be bamboozled and he needs to treat me as an equal.

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  16. parmalee peripatetic artisan Valued Senior Member

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    You would be limited to the ground floor, of course, and relying upon radiators for the upper floors. While I don't recall actually having been in anyone's basement in London, I suspect they're similar to houses from the same era in Philly, New York, Providence (RI), etc. With readily accessible floor joists, installation is fairly straightforward and not terribly labor intensive. The tubing covers a lot of surface area, consequently lower water temps are sufficient.

    One thing to look out for though is overly complicated control systems. Obviously, some degree of regulation and monitoring is essential, but some systems tend to go overboard.

    Having lived in a number of old, drafty buildings--including old mill buildings with no insulation and more single-paned windows than actual walls--I find radiators rather frustrating. Once they've been running--for several hours--they're fine; but then you feel disinclined to ever turn them off. And forced air sucks for innumerable reasons. Floor heating is efficient and warms a place surprisingly swiftly.
     
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  17. exchemist Valued Senior Member

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    OK I'll bear that in mind. If it can be done from below it may not be too dreadful.
     
  18. iceaura Valued Senior Member

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    The engineering types in my region think heat pumps are inherently inefficient here - mind, this is northern winter with a frequent need to maintain large temp differences between outside and inside air, a situation in which heat pumps do not shine unless geothermal somehow.

    They recommend direct electrical resistance heating of some suitable liquid fed into underfloor tubes, with serious insulation - especially if solar electricity is the source.
     
  19. exchemist Valued Senior Member

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    OK. I'm in London.
     

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