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

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  • ASavvyBuyer
    ASavvyBuyer Posts: 1,737 Forumite
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    “ Hi All

    Seeing that it was ~7C overnight and 13C outside now it's 21.4C where I'm sitting and that's after opening some internal doors .... currently generating ~1250W and consuming just about half (630W) and have probably been providing a steady 2.0kW.t to 3kW.t of heat (system ramps up and down as necessary) for most of the the last 5 hours ....

    No GCH or logs burned so far this year ...
    Originally posted by zeupater

    Hi Z

    How is your system coping with the present cold weather?
    Have you noticed a drop off in efficiency and is it still producing enough heat to not need the CH or Log Fire?
  • zeupater
    zeupater Posts: 5,358 Forumite
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    edited 8 November 2016 at 11:58PM
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    “ Hi All

    Seeing that it was ~7C overnight and 13C outside now it's 21.4C where I'm sitting and that's after opening some internal doors .... currently generating ~1250W and consuming just about half (630W) and have probably been providing a steady 2.0kW.t to 3kW.t of heat (system ramps up and down as necessary) for most of the the last 5 hours ....

    No GCH or logs burned so far this year ...
    Originally posted by zeupater

    Hi Z

    How is your system coping with the present cold weather?
    Have you noticed a drop off in efficiency and is it still producing enough heat to not need the CH or Log Fire?
    Hi

    Good timing on the question actually as yesterday turned out to be the start of the winter heating season here. A number of less than bright days meant that MrsZ's lower DHW temperature threshold was reached so the GCH boiler was fired up to top up the hot water reserves for the first time since early spring. Seeing that the house had cooled considerably over the last week and the forecast for overnight temperatures was pretty low prompted me to sweep the chimney, wash down the log burner and light that for the first time too.

    The log burner & heat-pump supplemented by solar gain on what turned out to be a reasonably bright day were pretty impressive and the combination will undoubtedly be used to provide heat whenever conditions suit. Considering that the garden was white-over this morning, the temperature on the hall thermostat was higher this morning than yesterday, but with the amount of internal thermal mass we have it'll take a few days of to recharge to normal levels, but that's pretty normal at this time of year.

    Until yesterday the heat-pump has been providing all of our heat, warming the main living area during the day and then releasing it through the rest of the house overnight. The additional heat source in combination with a relatively warm autumn (so far) has delayed the first use of the log-burner by at least 2/3 weeks and with using the heat-pump whenever there's sufficient generation the house has been noticeably more comfortable. As for efficiency, the idea is to run the heat-pump to match pv generation wherever possible therefore the target usage ambient temperatures aren't low enough to make much difference - the engineering data book suggests a COP of around 6 at 15C, ~5.5 at 7C and ~4.5 at freezing point (depending on load etc but typical) - even at -10C a COP of over 4 should be achievable according to the published specification, but the unit isn't there a a main heat-source when it's really cold, that's where the log-burner and GCH progressively take over ....

    HTH
    Z
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
    B)
  • ASavvyBuyer
    ASavvyBuyer Posts: 1,737 Forumite
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    zeupater wrote: »
    Hi
    ..
    Until yesterday the heat-pump has been providing all of our heat, warming the main living area during the day and then releasing it through the rest of the house overnight. The additional heat source in combination with a relatively warm autumn (so far) has delayed the first use of the log-burner by at least 2/3 weeks and with using the heat-pump whenever there's sufficient generation the house has been noticeably more comfortable. As for efficiency, the idea is to run the heat-pump to match pv generation wherever possible therefore the target usage ambient temperatures aren't low enough to make much difference - the engineering data book suggests a COP of around 6 at 15C, ~5.5 at 7C and ~4.5 at freezing point (depending on load etc but typical) - even at -10C a COP of over 4 should be achievable according to the published specification, but the unit isn't there a a main heat-source when it's really cold, that's where the log-burner and GCH progressively take over ....

    HTH
    Z

    Thanks, that's really helpful. Looking forward to getting ours installed next week.
  • Martyn1981
    Martyn1981 Posts: 14,873 Forumite
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    zeupater wrote: »
    the engineering data book suggests a COP of around 6 at 15C, ~5.5 at 7C and ~4.5 at freezing point (depending on load etc but typical) - even at -10C a COP of over 4 should be achievable according to the published specification, but the unit isn't there a a main heat-source when it's really cold, that's where the log-burner and GCH progressively take over ....

    HTH
    Z

    That's impressive.

    My plans are struggling. The price is a bit higher than I'd like, and the install location too tricky/messy. I have a back up plan for a far simpler install in the conservatory as it's to be 're-built' next spring. At that point if it's insulated enough (both for heat and cold) then it may be worth considering an install in there to cool down / heat up the adjoining living room. But I need to make sure I'm not wasting energy, fighting with nature.

    Can't help thinking the idea is great, but I'm pushing it trying to make it work in my case. Ponder, ponder, ponder!
    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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    Martyn1981 wrote: »
    That's impressive ....
    Hi

    Engineering data book for performance & other specifications here ... http://www.solar-klima.com/DAISEIKAI_EN.pdf

    ... download a copy to browse through, it's much more interesting than the sales-brochures which most manufacturers limit themselves to!

    HTH
    Z
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
    B)
  • ASavvyBuyer
    ASavvyBuyer Posts: 1,737 Forumite
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    zeupater wrote: »
    Hi

    Engineering data book for performance & other specifications here ... http://www.solar-klima.com/DAISEIKAI_EN.pdf

    ... download a copy to browse through, it's much more interesting than the sales-brochures which most manufacturers limit themselves to!

    HTH
    Z

    That's a useful document. Certainly shows how efficient that model is.

    From using the info from this site for boiler efficiencies I have done a comparison between using our combi boiler and the Toshiba Unit.

    Our combi boiler is recorded as having an efficiency of 70% when used for central heating and just under 50% when heating water. Pipe losses are estimated at 5%.

    Therefore, at -10 degrees C the Toshiba is 6.15 times more efficent than the boiler.

    At +15 degrees C it works out as being 9.23 times more efficient.

    Quite impressive figures, which means that it is more cost effective to use the Air Conditioner even when having to pay for the electricity it is using. However, by matching the output to the Solar Panel generation, makes it even cheaper to run to the point of zero.

    Thanks Z for the link to the Technical Spec.
  • zeupater
    zeupater Posts: 5,358 Forumite
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    edited 14 November 2016 at 12:39PM
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    That's a useful document. Certainly shows how efficient that model is.

    From using the info from this site for boiler efficiencies I have done a comparison between using our combi boiler and the Toshiba Unit.

    Our combi boiler is recorded as having an efficiency of 70% when used for central heating and just under 50% when heating water. Pipe losses are estimated at 5%.

    Therefore, at -10 degrees C the Toshiba is 6.15 times more efficent than the boiler.

    At +15 degrees C it works out as being 9.23 times more efficient.

    Quite impressive figures, which means that it is more cost effective to use the Air Conditioner even when having to pay for the electricity it is using. However, by matching the output to the Solar Panel generation, makes it even cheaper to run to the point of zero.

    Thanks Z for the link to the Technical Spec.
    Hi

    ... yes, sort of, but for direct efficiency comparison you'd logically need to consider centralised generation and transmission losses, so allowance for closed cycle gas generation plant (~48% efficient) and transmission (~8% total losses) means that the thermal efficiency of the electricity entering the heat-pump is only ~44% before the COP multiplier kicks in ..... of course, when using your own generation there are (arguably) no generation efficiency or transmission losses ...

    On the 'cost effective' side just remember that the efficiencies you mention are energy, not cost, related so the relative costs of energy need to be applied ... on our current tariff (zero standing charge) heat provision from the heat-pump using grid supply (cold evening) works out to be around half the cost of using gas.

    HTH
    Z
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
    B)
  • ASavvyBuyer
    ASavvyBuyer Posts: 1,737 Forumite
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    zeupater wrote: »
    On the 'cost effective' side just remember that the efficiencies you mention are energy, not cost, related so the relative costs of energy need to be applied ... on our current tariff (zero standing charge) heat provision from the heat-pump using grid supply (cold evening) works out to be around half the cost of using gas.

    HTH
    Z

    Toshiba Unit installed today and working a treat. The outside unit is a lot quieter than we expected; in fact quieter than having the combi boiler running! And the inside unit is nicely humming away with the fan on low, so hardly noticeable :j
    With our current tarriffs, it also works out about half the cost of using gas compared with imported electric to provide the same level of heating in the evening. :)

    However, good to have it pre-heating the room during the day on PV power.

    Now to get used to all the programming facilities to make best use of it. :think:

    Thanks Z for the inspiration :beer:
  • zeupater
    zeupater Posts: 5,358 Forumite
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    Toshiba Unit installed today and working a treat. The outside unit is a lot quieter than we expected; in fact quieter than having the combi boiler running! And the inside unit is nicely humming away with the fan on low, so hardly noticeable :j
    With our current tarriffs, it also works out about half the cost of using gas compared with imported electric to provide the same level of heating in the evening. :)

    However, good to have it pre-heating the room during the day on PV power.

    Now to get used to all the programming facilities to make best use of it. :think:

    Thanks Z for the inspiration :beer:
    Hi

    Good to 'hear' and hope you will become as pleased with the decision as we have been so far.

    You'll obviously still be playing with optimising the airflow for the room but when you've got that sorted for both heating & cooling then the rest becomes pretty straightforward.

    Key to matching performance to pv generation (if that's what you want to do) is fan-speed and temperature set-point relative to room temperature ... have a look at the difference above & below a ~4C differential relative to the average room heating time and you can use this as a basis to play with the timer schedules to ramp the heat up to better match an average generation curve and simply over-ride manually if required ...

    HTH
    Z
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
    B)
  • ASavvyBuyer
    ASavvyBuyer Posts: 1,737 Forumite
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    edited 25 November 2016 at 1:26PM
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    First full week after having the Toshiba unit installed, so now able to do a comparison of electric & gas used compared to the same week last year. By co-incidence, the weather for this week last year was very similar with a cold snap in the middle. House at about the same temperature, but warmer during the day with the pre-heating from the Toshiba Unit.

    Electric Import up by 11.3 kWh :(
    Gas use down by 292.89 kWh :j
    So by using 11.3 kWh extra of imported electric we have saved the equivalent of nearly 26 times the amount of gas. Be good in the early spring when it will just use supplus PV power, with no extra import.

    That's not a bad saving seeing our electric is just over 4 times the price of gas per kWh.

    Humidity level has gone down too.

    Very pleased so far.
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