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Discussion ... ASHP(Air/Air) with Solar pv ....

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  • michaels
    michaels Posts: 28,226 Forumite
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    There doesn't seem to be any move to suggest people on mains gas use an ashp instead for heating/hot water with a side advantage of AC and possible positve pressure air filtering for humidty control/alergens. Does the maths not stack up? Obviously having spare export PV might make the sums even better.
    I think....
  • Martyn1981
    Martyn1981 Posts: 14,877 Forumite
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    zeupater wrote: »
    Hi All

    There's a strong rumour that a shiny new arrival is expected at the Z household before the weekend .... I wonder what it will be ? ... :think:

    HTH :shhh:
    Z

    If possible, could you please detail all issues, costs, considerations etc when this is installed. I'm still really interested, but have let it slide.

    Mart.
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW). Two A2A units for cleaner heating. Two BEV's.

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
  • zeupater
    zeupater Posts: 5,358 Forumite
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    michaels wrote: »
    There doesn't seem to be any move to suggest people on mains gas use an ashp instead for heating/hot water with a side advantage of AC and possible positve pressure air filtering for humidty control/alergens. Does the maths not stack up? Obviously having spare export PV might make the sums even better.
    Hi

    The idea is really a combination of comfort and carbon reduction as much as pure money-saving on this one. The actual savings calculation would be dubious for us at the least as I've never measured logs as they've been used so wouldn't be able to tell what the benefit is likely to be by month until we've lived with it for at least one season. The primary idea is to utilise spare shoulder month pv capacity to provide a little heat in the same way that we have done for years with an oil-radiator and fan-heater, but increasing the available heat provision through the combination of utilising the COP multiplication effect and the ability to increase the run-hours to incorporate much duller cloud conditions ..... there may be some 'top-up' use on chilly evenings too, but again, that's what we sometimes do at this time of year with resistance heating already.

    At the moment we tend to ramp shoulder month heat provision up or down by varying the frequency and run-time of the log burner, this might mean a six hour burn each day, every couple of days or maybe twice a week - it's really this that we're looking to address ... logs may be a carbon-neutral fuel, but there's nothing wrong with burning less ... :cool:

    HTH
    Z
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
    B)
  • zeupater
    zeupater Posts: 5,358 Forumite
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    Martyn1981 wrote: »
    If possible, could you please detail all issues, costs, considerations etc when this is installed. I'm still really interested, but have let it slide.

    Mart.
    Hi

    You didn't think that I'd be holding back on this opportunity by any chance ?? .... :D .... the idea is to get it in and settled now so that it's fully ready and I fully understand how to optimise performance before the Autumn season arrives .... I'm also interested in future automation and integration with around 10kWh of usable energy storage (Panasonic/Tesla/Aquion) but that's another story for another time, but be assured, the kit I've gone for will suit the vision - that's why it was chosen ...

    HTH
    Z
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
    B)
  • Martyn1981
    Martyn1981 Posts: 14,877 Forumite
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    zeupater wrote: »
    Hi

    You didn't think that I'd be holding back on this opportunity by any chance ?? .... :D ....

    HTH
    Z

    :rotfl: No I didn't, but I thought it only polite to ask nicely. :)

    Further to what you've said to Michaels, I've noticed that my 400W oil rad does make a noticeable difference, so 3 or 4 times as much heat (for the money) would probably allow some deliberate leakage out of the living room. Also, since I believe the rad is cheaper than whole house heating (when that's enough) multiplying it by 4 should be acceptable when more heat is needed (than the rad) but avoidance of the GCH is still possible.

    But all this aside, I'm still keen on the AC side of things. The last two years have been fine, and that's why I've been overly lazy on this issue, but when we get a long hot period and the house's thermal mass is overflowing and won't go back down, I'd happily pay good money for some AC, even if only 2 or 3 weeks a year. When the all day and night temp is over 23/24C for a few days I really start to feel quite ill, and act like a bear with a sore head!

    Lately I've found sitting in the garden with my feet in the dogs paddling pool quite pleasant, but that's another story. :D

    Mart.
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW). Two A2A units for cleaner heating. Two BEV's.

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
  • zeupater
    zeupater Posts: 5,358 Forumite
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    edited 2 June 2016 at 6:15PM
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    Martyn1981 wrote: »
    :rotfl: No I didn't, but I thought it only polite to ask nicely. :)

    Further to what you've said to Michaels, I've noticed that my 400W oil rad does make a noticeable difference, so 3 or 4 times as much heat (for the money) would probably allow some deliberate leakage out of the living room. Also, since I believe the rad is cheaper than whole house heating (when that's enough) multiplying it by 4 should be acceptable when more heat is needed (than the rad) but avoidance of the GCH is still possible.

    But all this aside, I'm still keen on the AC side of things. The last two years have been fine, and that's why I've been overly lazy on this issue, but when we get a long hot period and the house's thermal mass is overflowing and won't go back down, I'd happily pay good money for some AC, even if only 2 or 3 weeks a year. When the all day and night temp is over 23/24C for a few days I really start to feel quite ill, and act like a bear with a sore head!

    Lately I've found sitting in the garden with my feet in the dogs paddling pool quite pleasant, but that's another story. :D

    Mart.
    If I get a COP of 3 or 4 I'll be pretty disappointed .... with anything approaching normal shoulder month daytime temperatures (this is what is being targeted) it should be closer to 6.0 than 5.0 and I've got both the equipment and ability to measure the performance to ensure that it does perform as expected ....

    We also use an oil-radiator on the 400W setting on cloudy days. One of the main advantages of the unit we've gone for is that the energy consumption can easily be restricted, so in poor conditions it will be capped to far less than 400W, but where it's going to be installed simply playing with the internal double doors and using them as baffles (as we do with the log burner) I'd expect to be able to make use of as little as 100W to 140W of spare pv generation in really poor conditions which should provide ~500W to 800W of heat .... when it's bright, open everything up and well over 3kW of heat should be provided by ~600W, when it's really bright or sunny we'll either still be exporting, running the current resistance heating elsewhere or (eventually) charging the storage for evening/overnight usage, which, of course, would include running the heat pump on a low (restricted) setting when it's dark ...

    I agree on the cooling too - we've got an old portable aircon (cooling only) unit which tends to be used to cool the thermal mass when it's been really hot for a while, although that's not very often it's bliss when you have it. That reminds me, the unit really could do with a re-gas if we decide to keep it, so I'll see what the installers say when they're here ....

    HTH
    Z
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
    B)
  • michaels
    michaels Posts: 28,226 Forumite
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    So electricity costs about 4x mains gas per kwh.

    If you were replacing a gas boiler that is used for heating and DHW and say didn't use gas for anything else so could cancel gas and avoid the standing charge would it ever make sense to switch to an ashp given the external temperature profile and heating requirement - for example probably 75% of our gas use is when the external temperature is below 10 degrees c etc
    I think....
  • michaels
    michaels Posts: 28,226 Forumite
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    This looks like a fairly definite answer:
    2013 study showing real world cop around 2x
    http://www.narecde.co.uk/air-source-heat-pumps-vs-gas-boilers/#.V1FZNyHm270
    I think....
  • Cardew
    Cardew Posts: 29,044 Forumite
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    edited 3 June 2016 at 12:48PM
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    michaels wrote: »
    This looks like a fairly definite answer:
    2013 study showing real world cop around 2x
    http://www.narecde.co.uk/air-source-heat-pumps-vs-gas-boilers/#.V1FZNyHm270


    The EST study referenced in your link is for Air to Water heat pumps(and Ground to water). This is for Heat pumps that deliver hot water to radiators/underfloor heating and Domestic Hot water to a tank. There are hundreds of posts on that 12 month trial and its further 12 month extension.


    This discussion is for Air to Air heat pumps, that can double as air conditioning in summer. These are very common abroad - particularly the USA where the warm(or cold) air is ducted to every room.


    The COP's quoted for Air to air heat pumps are much higher than air to water. I have not seen any independent trial giving 'real world' COPs but IMO they would be way higher than Air to water.


    As said earlier, my biggest concern would be the potential noise problem to Z's household and neighbours - there is a thread running on this subject.(not all air to Air)


    http://forums.moneysavingexpert.com/showthread.php?t=4357449
  • Martyn1981
    Martyn1981 Posts: 14,877 Forumite
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    edited 3 June 2016 at 3:52PM
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    michaels wrote: »
    This looks like a fairly definite answer:
    2013 study showing real world cop around 2x
    http://www.narecde.co.uk/air-source-heat-pumps-vs-gas-boilers/#.V1FZNyHm270

    Hiya Michaels. Remember that this isn't a 'fair fight' between a heat pump and GCH, it's actually 'rigged'.

    What Z and I were pondering wasn't a replacement for GCH all of the year, but a cherry picked solution for part of the year.

    So instead of an ASHP that could provide all heat, all year, it's a much smaller solution (and cheaper) that can supply the smaller amount of heat needed just during the warmer colder months, so to speak.

    This way you get to play with, or distort, the average. So, let's say the COP in Dec is 2, but the COP in Mch is 5 due to the warmer temps outside, you might at first think the average is 3.5 (2+5/2), but you have to take into account the scale of heating needed, let's say 10x more in December, so a real (weighted) COP average (in this example) might be (10x2 +5)/11 = 2.27.

    But if you leave the coldest months to the GCH (Nov to Feb) and use the HP for the 'warmer colder' months Mch/Apr & Sept/Oct, you get to raise the COP average significantly and pick days where the much smaller HP can still supply a significant percentage of the heat requirement ...... effectively 'pick your fight'.

    Also, last winter was quite warm, so I noticed many days where the heating was only on in the morning and evening, but I used my oil rad to keep the chill off one room during the day, so whilst the COP may be lower, it would still be highly beneficial to multiply that electrical input by a factor of 2 or more.

    Mart.
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW). Two A2A units for cleaner heating. Two BEV's.

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
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