Source: Coming in from the cold: Heat pump efficiency at low temperatures, Duncan Gibb et al. 2023
This graph from a recent European academic paper shows air-source heat pump performance in mild cold climates in Canada, China, Germany, Switzerland, the United States and the UK.
The red dashed line showing average COP is not the important takeaway from this graph. Rather, look at the large range of the data. At 0C, heat pump COP ranged significantly, from just over one to over four!
This is a meta study of both the normal air-to-air heat pumps we love to use for space heating here in New Zealand but it also includes air-to-water systems. These are still fairly unusual in this country, but one features in the Kapiti expoHaus, which we have case studied here.
This graph tells me that selecting the right equipment is almost more important than selecting a heat pump in the first place. What’s in the box is important.
Full paper available here: