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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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    • CommentAuthorCWatters
    • CommentTimeMar 13th 2013
    Any advice for this poster on another forum? In particular how to meet SAP when using the output from a turbine to drive an immersion heater. Is the SAP assessor correct?



    The SAP assessor has just informed us that the house will fail as it stands, because of using an immersion heater. It would only pass if we either installed an air source heat pump or:

    To enable the dwelling to pass using electric space/water heating the following would be required:•Electric under floor heating throughout

    •Electric instantaneous water heating

    •100% low energy light fittings

    •Pressure test at 3.8
    • CommentAuthorDarylP
    • CommentTimeMar 14th 2013

    As them to email me, I have Dip. OnConEA, and am happy to help where I can.

    • CommentAuthorEd Davies
    • CommentTimeMar 14th 2013
    I'm expecting to have similar problems. My current plan is to install the smallest possible LPG system boiler which will keep the regulators happy and probably be a good fall-back for the odd periods when my solar (plus small turbine?) aren't sufficient. Hopefully a 47 kg bottle should last a while in practice so no need for a big installed LPG tank.

    Don't understand why an immersion isn't allowed but electric UFH is. Can't be much difference if the heat leaking from the tank goes into the house.
    • CommentAuthorDarylP
    • CommentTimeMar 14th 2013
    Both are 'allowed', but electric space heating pushed the DER up massively, so the designer has to compensate with increased thermal performance to reduce the space heating load.
    SAP is primarily a CO2 reduction tool!
    Mains electricity is the most CO2 intensive fuel type.

    Good luck:smile:
    • CommentAuthorEd Davies
    • CommentTimeMar 14th 2013
    Well yes, but why does an immersion push the DER up but electric UFH not? What's the difference?
    • CommentAuthorDarylP
    • CommentTimeMar 14th 2013
    .... possibly an error in the assessment?
    It is very difficult to comment on something I have not seen?

    Perhaps the Fabric losses are so small that the electric ufh will not use that much electricity, whereas no amount of insulation can reduce the hot-water energy requirement...?

    • CommentTimeMar 14th 2013
    Really good to see JSH giving sound advise on this other forum, their gain, our loss IMO.
    • CommentAuthorEd Davies
    • CommentTimeMar 15th 2013
    Not sure but it looks to me like JSH is muddling up ACH and m³/(m²·h) over there. oz07 picks up on it further down the thread.

    <rant class="off-topic">It's more than a little irritating (to me, at least) that a) there are these two ways of measuring things, b) people don't make it clear which they're using and c) the stupid m³/(m²·h) measure exists at all as it fails to encourage designs with small outside surfaces. If it was m² of finished floor area rather than envelope area it'd make a lot more sense (to the limited extent that floor area can be taken as a proxy for occupancy). Ditto specifying element U-values rather than the building heat loss coefficient per m² of floor area.</rant>
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