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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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Energy Assessment: Exhaust Air Heat Pumps and EPCs

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    • CommentAuthordavvac
    • CommentTimeJul 9th 2008
     
    Can anyone explain to me why EAHP in flats gives a Energy Efficiency rating of 'C', whereas a gas fired boiler (over 90% effieciency) is almost always giving us a 'B' rating?

    All other variables are the same - u values, LE lighting, air permeability etc.

    Thanks

    Dave
    • CommentAuthorLizM
    • CommentTimeJul 9th 2008
     
    Electricity has a higher carbon factor than gas, which is proportionally similar to the differences in efficiency of the EASHP and gas boiler. I'm guessing the C is at the top end of the band and the B is at the bottom end? If you are using exhaust air, I presume that you have a fan which also may not be being included in the gas calc?
    •  
      CommentAuthorOlly
    • CommentTimeJul 9th 2008
     
    Grid electricity - 0.422 kg/kWh
    Mains Gas - 0.192 kG/kWh
    Source: SAP2005 Table 12

    So depending on your heat pumps COP (Coefficient Of Performance) it could perform better or worse than gas in terms of emissions.

    I think there was a thread on here recently with graphs showing the cross over point.

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