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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

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    • CommentTimeDec 7th 2020
    Hi what experiences have people had with ASHP? What companies have you used? Has the Heat pump kept up with demand? How about reliability What size ASHP have you had fitted? How big is your house? What is your experience of RHI for ASHP? I have a typical Highland White cottage with 2 bedrooms, well insulated.
    • CommentAuthortony
    • CommentTimeDec 7th 2020
    350% efficient, fit and forget, bit of noise, offer summer cooling if needed, outside box can freeze up in winter reducing efficiency to 100%,

    Define well insulated in terms of heat loss when it is -3C outside
    • CommentAuthorowlman
    • CommentTimeDec 7th 2020
    Air to air, or Air to water?
    • CommentAuthortony
    • CommentTimeDec 8th 2020
    Air to air
    Good questions!
    1 Good
    2 Daikin
    3 Easily
    4 Faultless, until it failed
    5 16kW
    6 4beds
    7 great
    8 part modernised Aberdeenshire Victorian farmhouse

    I posted some stuff about ours
    • CommentAuthorrevor
    • CommentTimeDec 8th 2020
    I ruled HP for various reasons but I am still interested in the subject. Does anyone know how the COP changes with ratio of space heating to DHW? If one has a highly insulated house requiring very little heating then the COP will reduce in my thinking as the heat pump requires greater assistance to produce DHW. I once had contact with someone who built social passive houses for a local authority but fitted a gas boiler as it was cheaper to install but also because it was able to deliver DHW quickly on demand which I guess a HP can't. It was part of my thinking also.
    • CommentAuthorbarney
    • CommentTimeDec 8th 2020
    Separate your DHW from your heating demand would be good advice

    I've put in an Atlantic DHWS Heat pump cylinder store and it uses the heat recovered from bathroom (and kitchen) ventilation streams - excellent system, which will allow me to ditch my oil combi shortly in favour of an ASHP for heating only - which will complement my PV array as well

    The DHWS will give me a cylinder of hot water every day, has direct immersion boost if required and was easy to fit (once you reconcile yourself to storage rather than instantaneous from a combi


    • CommentAuthorowlman
    • CommentTimeDec 8th 2020 edited
    <blockquote><cite>Posted By: barney</cite>
    Separate your DHW from your heating demand would be good advice

    I agree, and it's why I'm ambivalent regarding Air to Water. It tries to satisfy two different needs CH and DHW from one source at the expense of a lower COP. Each demand is more efficiently served from a dedicated source IMO. Different of course if your home heating wet system pipework etc. is already in situ. To do it consciously from new,---Nah! go Air to Air.
    • CommentAuthorEd Davies
    • CommentTimeDec 8th 2020
    There's a lot to be said for air-to-air from the simplicity point of view. However, there are also some things to think about:

    1) It doesn't help with DHW at all, so what do you use for that? Direct electric (immersion)? Direct electric to top up solar thermal?

    2) Heating the air means that the air will be slightly warmer than the surfaces meaning that, for a given comfort level, the air will need to be warmer than it would be with heating that uses a significant amount of radiant heat, particularly UFH, so the ventilation heat losses will be greater, though the conduction heat losses will be slightly less.

    I think there's a lot to be said for using an air-to-water HP for both space heating and DHW but keeping those operations quite separate: the HP is either doing space heating at a decent CoP or DHW at a lower but > 1 CoP (which still beats an immersion) but never trying to do the two at the same time.
    Revor: >>> HP and hot water:

    Heat pump needs a TS to supply DHW, which Richy already has (mentioned on another thread), or a cylinder. Or a blingy phase change store). If your build is tight for space this can be a problem. The HP would benefit from a TS anyway so you can run it at midnight when electricity is cheaper and greener

    There was a discussion a while back, Goodevans (I think) had a very good COP heating DHW.

    The tricks were:
    -start with a completely cold (or stratified) tank each time and heat it up to DHW temperature, so for most of the heating cycle the DHW is at 10-20-30-40 DegC which is easy for the HP to heat. Don't keep topping up heat into an always-hot tank.
    -heat and use a big volume of DHW at 45-50degC, rather than use a small volume at 60-70degC which will get mixed with cold anyway.
    • CommentAuthorEd Davies
    • CommentTimeDec 8th 2020 edited
    Posted By: WillInAberdeenThere was a discussion a while back, Goodevans (I think) had a very good COP heating DHW.
    If those are the ones I'm thinking of they later posted that the initial numbers they posted were a bit bogus and that they were going to do updated ones. Don't recall see an update, though, but I might have missed it. Are you sure they one's you're referencing are valid?

    Post #6 on the linked thread - GE revised the numbers down to an implied CoP of ~2. I'll revise my description of this, from 'very good' to 'good'.

    Edit: It was actually this thread I recalled, post #11, CoP was 2.5 -3 using a different experimental method.
    I'll revise my description back again, from 'good' to 'very good' !!
    • CommentAuthorCWatters
    • CommentTimeDec 12th 2020
    Does the loop between an ASHP and a thermal store have to be pressurised?
    Posted By: CWattersDoes the loop between an ASHP and a thermal store have to be pressurised?

    No it doesn't. The Samsung EHS for example can run on an open vented system.
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