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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.

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    • CommentAuthorcjard
    • CommentTimeJan 18th 2016 edited
    SWMBO has decided an ASHP is a good idea, mainly because it's ideally fit n forget and I have enough on my plate with everything else.

    She asks pointy questions like "why is this Chinese one a grand and that other one with the same rating is 5 grand"

    At best I can explain that the performance of the jap one holds out a lot longer as air temps fall and that it has an inverter driven compressor so it shouldn't cycle as much, but I have no answer for the follow ups like "does it matter?"

    I dunno.. Does it? With a big enou buffer, who cares about the inverter or lack thereof? And when one can buy a new Chinese ASHP every year and it be a long time before the outlay reaches that of a Japanese one, does it make sense to get a Japanese one?

    I have he tluxury of living next door to a house that is broadly similar to mine, and I watch it's development. A Certain Supplier from every building mag going, has specked a 14kw ecodan for that property. Interestingly they tell me the final bits of paperwork (which I presume includes a decision about which ASHP to go for) will be done when the as-built configuration is given, which is done after the pump is installed. This seems arse about face to me, but who am o to judge?

    So right now I'm looking at one of 2 options:

    * Diy.a cheap non inverter one, mate it to a big heat pump cylinder and let it cycle if needs be, sod the RHI
    * MCS install of a high end one, add umpteen thousands to the mortgage, use the RHI

    There is also the option of buying a high end one for cheaper than RRP and not using the RHI, though financially there might be a limited circumstance where that's viable..

    Prices wise, a DIY job would be around 1k plus the unit price I think
    Ecodan is just shy of 7k commissioned (note, that doesn't mean installed) and rhi'd
    Calor guesstimated 9k for a daikin altherma hybrid, RHI compliant
    Samsung ones have been floating around for circa 4k as a second hand system, no RHI

    I don't doubt my technical ability to do the DIY route, I just can't decide (with everything else on my plate from second fix, plasterboarding, flooring, kitchening, stairing, decorating and landscaping whether this is just one of those jobs where it's worth handing off to someone else. Essentially it looks like the expensive option, plus the extra mortgage, minus the RHI comes to about the same cost of buying a cheap pump and not using the RHI.. I just have to front the cash, which is a bind.. In essence my query is (I think):

    Are inverter driven HPs worth the premium or is a somewhat agricultural Chinese pump that simply cycles on and off for a quarter of the price a better bet for a user who is prepared to have a large tank of hot water sitting there wi the aim of smoothing things out?
    • CommentAuthortony
    • CommentTimeJan 18th 2016
    • CommentAuthorTriassic
    • CommentTimeJan 19th 2016 edited
    Have you built as air tight ad as well insulated as you can, fabric first approach will save you money.

    Have you done a heat loss calculation? What sort if heating will you have?

    The house next door does not sound like an example of best practice, so done follow his lead.

    Are you aiming to do both the heating and hot water from the same ashp, if so the higher ashp output temperatures will lower efficiency. It may be better to keep the thermal store temperature lower to match hour heating temperature requirements and instal an in line water heater to boost dhw as you use it.

    Do more research, there is quite a debate on thus subject going on in the other place. This may be worth a read http://www.ebuild.co.uk/topic/18157-towards-a-heating-checklist-please-comment/
    • CommentAuthorcjard
    • CommentTimeJan 19th 2016 edited
    Won't know the AT results until it's tested but I've done most of the work myself and I've even gone to the extent of lining the back of the service void battens with guttersealant (forever gooey) before nailing em to the wall through the vcl. Everything will be orconned and unitaped so I'll be disappointed if the test result is low, though I'm doing a conversion and do have to work around some intricate original features i.e. Roof trusses, that pierce e new structure. Hence, in some cases I've had to accept a best effort (read:membranes, tapes and then spraying joints with a closed cell urethane foam). Insulation is good, though the slight killer is that windows are larger than average, being an industrial conversion. Walls are maybe 0.12ish, roof similar, floor sub 0.1.

    I do have some heat loss calcs for the place (done by various others) but I think there's some error in all of them. Most recently I found an online one provided by Samsung that seems to be used by installers of heat pumps, as it asks very specific questions about heat emitters, areas, roof and glazing sizes etc. come the end of it it said the heat loss is 6.5 to 7.5kw (260sqm, ~. How this relates to mwh per annum or gas boiler size (for example)I'm not sure. One thing I am surprised at, with the level of insulation, the heat loss is higher than I was expecting. I guess it's the glazing, particularly in the roof(gotta keep the industrial look)

    Amenable to having a cylinder temp of 45, I don't use hotter anyway
    • CommentTimeJan 20th 2016
    That does sound a bit high for the level of insulation you've described. What type of windows are they? (apologies if you've posted before) You should be able to work a simplistic heat loss calc just for the rooflights if you think they're a problem.

    You might be in the low-energy region where many models give dubious answers. It would be interesting to know what PHPP comes up with.
    • CommentAuthorcjard
    • CommentTimeJan 20th 2016 edited
    By "walls are 0.12ish" that's what thermalcalconline gave me for my wall buildup, but it naturally doesn't take into account the glazing. As this is an industrial conversion, it has industrial size openings. The roof windows on the front are 1.7 x 7.3 metres. On the back a bit smaller, 1.7 x 4.8 ish I think, but then there's a plan to create a roof terrace, and that will have a glazed door 3 x 2.1 in where the previous roof lights were removed. The master bed sits under an arch window that's is a perfect semicircle 4m wide and most of the other rooms have some form of bi folding door as their light, not least because the house is inside another building and getting a good amount of light in is a challenge

    I'm planning on making insulated shutters for much of he glazing, and I might have to use them during the day to keep the sun out too.. Such is the problem of converting.. Some problems can't be designed out because you're hamstrung by the existing features.
    • CommentTimeJan 20th 2016
    But your model presumably includes the sizes of the windows and what type of glazing and frame do they have?
    • CommentAuthorcjard
    • CommentTimeJan 26th 2016 edited
    It does. Glazing is double with alu frames, it's supposed to be to latest regs so 1.5 u I think. Certainly the biggest loser hence the thinking to have additional heat barriers eg curtains or shutters if it works out cold
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