The performance of a heat pump is a measure of its COP ( Coefficient of performance). Commercially available HVAC systems have COP of 3 to 4 while GHPs have greater than 6. The COP also depends on the temperature difference. When the temperature difference is small then the COP will be large. Similarly the cooling performance, measured as energy efficiency ratio (EER). The GHPs EER, depending on the seasonal temperature variation is about 80% and above.