From reading the AHRI standard for performance rating of heat pumps (see here) the formula on page 99 seems to indicate that in the calculation of HSPF both the energy for the heat pump compressor, as well as the energy consumption for electric resistance backup heat, is included. Therefore, I would conclude that to predict savings from installing a heat pump with electric resistance backup, with a baseline of pure electric resistance heat, that the savings could be calculated using the following formula:
(Total BTU heating requirement for the heating season) * (1/HSPF_electric res - 1/HSPF_heat pump) / 1000
Where HSPF_elec res is the HSPF of pure electric resistance heating: 3.41
And HSPF_heat pump is the HSPF of the heat pump with electric resistance backup
Is this correct? Thank you very much for your time and any feedback you can provide
