The COP (Coefficient of Performance) is given in relation to the efficiency level of a heat pump. It defines the ratio between the usable heating output delivered (kW) and the electrical power input supplied. It also reflects the power consumption of auxiliary drives, the defrost energy and the proportional pump output for heating, brine and groundwater feed pumps. The COP is calculated under test conditions using standardised methods (EN 145II), i.e. at specific temperatures and times. It is therefore a useful and accurate indicator of the quality of a heat pump.