I am running a SAP calculation on a proposed building which will be utilising a 8.5 kW ASHP for space and water heating. I am also running a comparative analysis against a mains gas boiler to show the reduction in dwelling emission rate (DER).

I have noticed that when specing the heat pump in my model the TER shoots up from 14.49 kgCO2/yr/m2 (in the gas powered model) to 21.5 kgCO2/yr/m2. This is having a pretty massive impact on the percentage improvement of DER over TER between models.

Can any one explain why this happens? I cannot find an explanation elsewhere and I would hate to overstate the potential improvement the heat pump brings.


  • $\begingroup$ If you don't get an answer here, you may want to try Unmet Hours -- it's a building energy modeling group, very similar to SE (actually they had an Area 51 proposal at one point, but not enough momentum back then). $\endgroup$ – LShaver Mar 19 at 19:46
  • $\begingroup$ Those look like CO2 factor proportions for heating oil vs coal fired base load. Are you sure the heat pump's coefficient of performance is included in those numbers? Please post your entire comparative analysis. $\endgroup$ – Phil Sweet Mar 20 at 19:48

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