Heat pumps, geothermal and AC
Heat Pump Efficiency explained - The definitive guide to SEER vs HSPF vs (S) COP Heat Pump Ratings
...highest COP a heat pump can achieve is about 4.5, and any heat pump with a COP of above 3 is said to have a very high energy efficiency. However, the COP rating on it's own isn't that meaningful, as it doesn't allow the easy comparison of heat pumps under very cold, or very hot conditions - for all the kind of reasons ...