Residential ground source heat pump systems in heating-dominated climates often incorporate auxiliary electric resistance heating. This is utilized for some portion of the winter heating – it could be intended only for rare, emergency use, or it could be intended to provide a significant fraction of the annual winter heating. In Sweden, where a typical ground source heat pump provides both heating via radiant panels and domestic hot water, the auxiliary electric resistance heating is activated when there are high domestic hot water loads or when ground heat exchanger temperatures fall to low values. Two design parameters have a strong effect on when and how much the electric resistance heating is used: ground heat exchanger size and heat pump capacity (i.e. of the vapor compression cycle.). In turn, the resulting pattern of electric resistance heating and electricity consumption has a significant influence on emissions associated with electric power generation. This influence may be more significant than might be inferred from simple annual emissions factors – the highest heating requirements occur when it is very cold and that is coincident with when Sweden imports electricity that may be produced with fossil fuels.

A range of system designs with different ground heat exchanger designs and heat pump capacities serving a typical renovated 1940s-era house in Stockholm are simulated to estimate hourly electricity consumptions. A range of data sets and models for estimating CO2 emissions are applied and both the effect of the system design and the various assumptions used in the emission analysis are investigated.