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

12357…44

Comments

  • michaels
    michaels Posts: 27,991 Forumite
    Photogenic Name Dropper First Anniversary First Post
    Cardew wrote: »
    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

    The advantage of air-to-water in a PV context is that it could replace iBoost diversion at hopefully a higher efficiency factor and hot water is in a way a time-shifter / energy storage solution, where as for us at least I suspect air-air is not that useful as we heat 24/7, obviously mostly in the evening/night/early morning in winter when it is dark. Thus the capital expenditure to cover a narrow window of shoulder demand seems unlikely to be cost effective. Perhaps if we also switched to economy 7 during the shoulder months it might make a difference?
    I think....
  • zeupater
    zeupater Posts: 5,355 Forumite
    First Anniversary Name Dropper First Post Combo Breaker
    edited 4 June 2016 at 8:32PM
    michaels wrote: »
    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
    Hi

    That's not what I'm doing ... when the pv is generating a spare ~300W February or November the idea is to use heat-pump technology to multiply this up to a reasonable amount of heat to supplement the log burner - for September, October, March, April and early May the heat-pump/pv combination will provide all of the heat we need, effectively for free.

    It's not an illogical fantasy ... we've had our pv for years and have used the combination of an 800/1600W fan heater and a 400/600/1100W oil-radiator to do what we plan to continue, it's just that we'll be able to extend the period far further into the winter period, from both sides and be far more comfortable too ....

    Anyway, as of this afternoon it's in, it's working and, from tests so far, it's even performing above the manufacturer's engineering data book specifications for today's outside temperature ... this is probably due to the short tube-run, but certainly means that if a COP of over 6.0 is achievable today, the published data is probably not too far out and, in our case, may even be a little conservative .... Early days, but time will tell ....

    On the gas side, we pay a higher unit rate with no standing charge, but normally using around 1000kWh/year the lower tariffs available with standing charges effectively becomes irrelevant .... Gas to us is effectively used as a backup for the DHW when it's been cloudy for a number of consecutive days and for boiling my blood when elderly relatives stay with us over Christmas ... not kidding, I'm usually melting at 27C around 7 metres from the log-burner and a couple of ~90year-olds are hogging my seat by the inglenook ... apart from that, it takes almost a week of temperatures well below freezing to even need the GCH ...

    HTH
    Z
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
    B)
  • zeupater
    zeupater Posts: 5,355 Forumite
    First Anniversary Name Dropper First Post Combo Breaker
    edited 3 June 2016 at 10:45PM
    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
    Hi

    Based on an air pressure of 1016millibars, the measured airflow, the input temperature, the output temperature and the measured power ... the 'real world' COP here today was ~3x the results of the study .... of course, this does not in any way represent the expected SCOP, but as we're not looking to utilise the heat-pump in unfavourable conditions and will only be multiplying the value of our own generation, why would even an abysmal COP of 2.0 be considered a failure? .... for every 1kWh of pv generation used by the heat-pump, you'd be getting 2kWh.t of heat !! ....

    HTH
    Z
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
    B)
  • zeupater
    zeupater Posts: 5,355 Forumite
    First Anniversary Name Dropper First Post Combo Breaker
    edited 5 June 2016 at 1:17PM
    Cardew wrote: »
    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
    Hi Cardew

    Running ours today and forcing it to 'High Power' on heating with an external/internal temperature difference of >10C the outdoor unit certainly was pretty noisy for a few minutes before settling down, nearly as noisy as the birds in the garden, or a car at 30mph about 50 metres away (well that's what I compared it to) .... but this is a setting to force the system to perform at the absolute maximum .... so far under normal conditions the unit seems to be more akin to a desk fan crossed with a pretty quiet fridge than a helicopter ... and we get plenty of helicopters around here so no-one would probably notice even if it was ! ...

    Anyway, we don't intend to use the 'High Power' setting much, so it shouldn't be an issue ...

    HTH
    Z
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
    B)
  • zeupater
    zeupater Posts: 5,355 Forumite
    First Anniversary Name Dropper First Post Combo Breaker
    michaels wrote: »
    The advantage of air-to-water in a PV context is that it could replace iBoost diversion at hopefully a higher efficiency factor and hot water is in a way a time-shifter / energy storage solution, where as for us at least I suspect air-air is not that useful as we heat 24/7, obviously mostly in the evening/night/early morning in winter when it is dark. Thus the capital expenditure to cover a narrow window of shoulder demand seems unlikely to be cost effective. Perhaps if we also switched to economy 7 during the shoulder months it might make a difference?
    Hi

    The issue with Air to Water heat-pumps is the the COP reduces as the water temperature increases, There are some pretty reasonable high temperature units available which have a potential to achieve a decent COP, but the overall performance is very much aligned to the particular installation, the user settings and how the householder wants to use what they've got. With DHW you're normally targeting 50C+ even in <7C average winter conditions, which usually means a relatively poor overall performance.

    As Cardew raised earlier, split unit air to air technology is pretty mature ... what's changing now is the high-pressure related performance and, importantly, both the range of operation available through high-performance inverters and the 'power saving' settings which are being built into the control systems ....

    I find it interesting, but then again, I've always questioned the relevance of 'crowd think' and find many obscure ideas interesting ....

    HTH
    Z
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
    B)
  • Martyn1981
    Martyn1981 Posts: 14,752 Forumite
    Name Dropper Photogenic First Anniversary First Post
    zeupater wrote: »
    it's even performing above the manufacturer's engineering data book specifications for today's outside temperature ... this is probably due to the short tube-run,

    HTH
    Z

    Hiya Z, loads of questions, so thanks for all the data so far, but I'll limit my start to - what is a short tube-run?

    My preferred location for the two units would be approx 3m apart, plus a ceiling to floor drop of about 2m more?

    I'd hope to position the outside unit under my PV canopy on the ESE wall. That way it should get some shading during the summer (cooling), but some direct sunlight in the shoulder months (heating).

    May I ask what unit you went for so I can start revising some specs, and get back into this.

    Thanks.

    Mart.
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
  • zeupater
    zeupater Posts: 5,355 Forumite
    First Anniversary Name Dropper First Post Combo Breaker
    edited 4 June 2016 at 10:32PM
    Martyn1981 wrote: »
    Hiya Z, loads of questions, so thanks for all the data so far, but I'll limit my start to - what is a short tube-run?

    My preferred location for the two units would be approx 3m apart, plus a ceiling to floor drop of about 2m more?

    I'd hope to position the outside unit under my PV canopy on the ESE wall. That way it should get some shading during the summer (cooling), but some direct sunlight in the shoulder months (heating).

    May I ask what unit you went for so I can start revising some specs, and get back into this.

    Thanks.

    Mart.
    Hi

    Like an excited kid with a new toy, I was up and ready to play quite early this morning, well as soon as I'd had a coffee and breakfast ... :) ... in reality that means that the unit has been running on pure pv for about 3.5 Hrs so far today ...

    Our indoor unit is mounted a couple of inches from the ceiling on the inside and the outdoor unit is on wall brackets about 12" off the ground so that we can sweep and weed the patio below it (with a block paved patio fighting weeds is a full time job!) ... the tube runs (feed&return) go through the wall and drop to the outdoor unit in plastic trunking, have a couple of alignment bends and that's about it ... probably somewhere in the region of 2.5 metres of separation. Of course the tubes are individually insulated with Armaflex (same as our solar thermal runs), but with opportunity for heat loss over distance, my preference was to keep the run short.

    Regarding two units ... I looked at that too, still might consider a second unit but decided that one may actually deliver the majority of what I wanted to achieve so I'd try a single unit first and keep my options open. If we went for a second unit at the same time I'd already decided that two outdoor units would provide some form of redundancy if there was an issue. Other considerations on a multi-split revolved around the indoor units being around 10m apart, there being little cost advantage, a loss of power restriction flexibility and no readily available data on multi-split performance when only one indoor unit is required ....

    As you know, we've considered this for a while and I've really done the research. The main consideration is matching the heat-pump to low pv generation conditions, so the main requirement is to concentrate on maximum efficiency, performance range (High/Low) and linking this to controllability ... and of course, as Cardew mentions, noise levels (both indoor & out). Looking at what's out there and comparing one make/unit against another I kept coming back to using the Toshiba Daiseikai 8 range as a benchmark, so, as I could find nothing to beat it on specification and as it's what I became most familiar with for available performance data comparison, that's what's on the wall now .... the range is by no means the cheapest option out there, but that's not the issue, my criteria is performance based value for money .....

    We're currently heating, watching a 50" TV, using a laptop, charging two mobile phones, covering all background power usage and ... wait for it ..... using a grand total of 300W - so somewhere in the region of 170-200W is heating the house with a COP multiplier in current conditions of somewhere around 6.0 (according to engineering data and our own tests yesterday) ... this is exactly the kind of performance we need for the shoulder months - all I need to learn now is how to optimise the unit to suit conditions, which means airflow patterns, setting daily temperature programs, using internal doors as heat-flow baffles etc, then look forward to Autumn (did I really say that! - :D;)) ...

    HTH
    Z
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
    B)
  • silverwhistle
    silverwhistle Posts: 3,791 Forumite
    First Anniversary Name Dropper First Post
    zeupater wrote: »
    On the gas side, we pay a higher unit rate with no standing charge, but normally using around 1000kWh/year the lower tariffs available with standing charges effectively becomes irrelevant .... Gas to us is effectively used as a backup for the DHW /SNIP/

    Effectively the same as I operate, although with a smaller terrace house and only me to keep happy, apart from visitors (as described above!). I'd like to get my gas usage under a thousand as it's just over at the moment. Repairs to my rear wall and replacing a draughty back door are all part of my incremental improvements.

    I can't afford or justify heat pumps, but I am thinking of getting a single room MHRV unit for the bathroom. I did a very bad job of retro-fitting a burnt out normal extractor but as my girlfriend is a qualified electrician she knows she's provisionally booked to fit one. :D

    Any recommendations from the experts? :-)
  • silverwhistle
    silverwhistle Posts: 3,791 Forumite
    First Anniversary Name Dropper First Post
    zeupater wrote: »
    the unit seems to be more akin to a desk fan crossed with a pretty quiet fridge than a helicopter ... and we get plenty of helicopters around here so no-one would probably notice even if it was ! ...


    Me too. Chinooks or Robinsons?
  • zeupater
    zeupater Posts: 5,355 Forumite
    First Anniversary Name Dropper First Post Combo Breaker
    silverwhistle wrote: »
    Effectively the same as I operate, although with a smaller terrace house and only me to keep happy, apart from visitors (as described above!). I'd like to get my gas usage under a thousand as it's just over at the moment. Repairs to my rear wall and replacing a draughty back door are all part of my incremental improvements.

    I can't afford or justify heat pumps, but I am thinking of getting a single room MHRV unit for the bathroom. I did a very bad job of retro-fitting a burnt out normal extractor but as my girlfriend is a qualified electrician she knows she's provisionally booked to fit one. :D

    Any recommendations from the experts? :-)
    Hi

    I know someone who fitted a 'cheap' bathroom 'trickle' heat recovery unit ... think it was about £300 from 5crewfix (so not that cheap!), but they don't seem to be in the catalogue any more ... anyway, it fixed the condensation problems they were having much better than the powerful extractor which it replaced ... from memory it was either a a Vent-Axia or Xpelair, I can't remember which so wouldn't have a clue as to the model .... have a look on the web to see what the current line-up is ....

    HTH
    Z
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
    B)
★ ★ ★ Meet your Ambassadors

Categories

  • All Categories
  • 343.1K Banking & Borrowing
  • 250.1K Reduce Debt & Boost Income
  • 449.6K Spending & Discounts
  • 235.2K Work, Benefits & Business
  • 607.8K Mortgages, Homes & Bills
  • 173K Life & Family
  • 247.8K Travel & Transport
  • 1.5M Hobbies & Leisure
  • 15.9K Discuss & Feedback
  • 15.1K Coronavirus Support Boards