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    Eric Fewster
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    Hello everyone,

    Wonder if anyone can run their beady eye over this and let me know if I'm on the right track? I posted it on the iPHA forum but didn't get anywhere….

    I am using PHPP for retrofit, and part of what this entails is coming up with economic savings for various improvements. With regard to this, space heating and electricity are easy to identify via the verification & electricity sheets. However, for the question of gas saved it appeared not as straightforward.

    Adding a boiler doesn't affect the space heating demand on the verification sheet, yet it does impact carbon emissions on the PE value sheet – so it is saving money somewhere since it is operating more efficiently than an older boiler. So since the boiler has a monetary cost, I want to know what the payback period is for this item and therefore want to look at gas saved. To do that, I think the logic below is OK, but it would be good to have others just cross-check!

    – Using PHPP version 7, I take the PE Value sheet cell F71 or Boiler sheet H59 (which is the final energy used normalized to m2, after taking into account the boiler inefficiency and DHW – yet before primary energy is calculated)
    – From this value I subtract the overall space heating demand including distribution losses (PE Value G6, which is normalized to m2). This overall space heating demand is also used in the boiler sheet cell F10, which is part of the sum of the final energy in F59… tracing the F59 formulae back through the boiler sheet, although I didn’t entirely understand the ‘why’ of the calcs, I can see that they run via the % efficiency part and also pick up on the DHW kWh demand, as well as the overall space heating demand (Boiler sheet F10). So I think it's the one I should use.

    Thanks for any help on this!

    Eric

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