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Green Building Bible, Fourth Edition
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Energy Assessment: solid fuel boiler SAP failure

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    • CommentAuthorGreenPaddy
    • CommentTimeSep 20th 2012 edited
     
    I've just received the SAP assessment for a client's house I've designed.

    SAP rating=97%
    EI rating=95%
    DER=5kgCO2/m2

    Pretty good I'd have thought....."computer says no". It fails as the 'multifuel' log boiler stove has an efficiency of 71%, below some magical figure, and also the TER is 4kgCO2/m2.

    Re-working the fuels sorces (primary now electric) it passes;

    SAP rating=93%
    EI rating=92%
    DER=12kgCO2/m2

    Ignoring the bonkers system that fails a more efficient house, producing 1/3 of the CO2, can anyone point me to the regs which state a minimum value for the boiler efficiency. I'm familiar with SAP2009 9.90 procedure document, and I can't find a minimum there (infact the default values are 60-65%).

    Help???
    • CommentAuthorneilu
    • CommentTimeSep 20th 2012
     
    Minimum efficiencies for heating systems are given in the Domestic Building Services Compliance Guide, a document that is referred to in the building regulations approved document L1A.
    Its easy to find using an internet search, and can be downloaded from the government's planning portal website.
    • CommentAuthorDarylP
    • CommentTimeSep 20th 2012
     
    • CommentAuthorDarylP
    • CommentTimeSep 20th 2012
     
    GreenPaddy,

    SAP compares the DER with the TER. In order to 'pass' your Dwelling Emission Rate (DER) must be less than the Target Emission Rate (TER).

    You have to improve over 2006 Build Regs' standards, for the same sized 'notional' building. If the TER is low, you have to go even lower in terms of the DER.

    If you want any help or pointers, feel free to email me...

    Cheers..
    :smile:
    • CommentAuthorGreenPaddy
    • CommentTimeSep 22nd 2012
     
    Thanks guys. The Domestic Bld Serv Guide shows 70% as the minimum, so there must be some other source that SAP limits are drawn from. The number was something over 80%. I'll keep looking, maybe write to BRE or the Scottish Govt office.

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