Impact of heat pump controller in the performance: experimental comparison of EN14825/EN14511 and compensation method of four different air-to-water heat pumps
In this study, we present the impact of the controller on the performance of various heat pumps by comparing the results evaluated using two distinct test methods: the first is the standard EN14825:2022+EN14511:2022 and the second is the two-mass model of the compensation method. The standard prescribes the test method and the calculation procedure of the seasonal performance factors. With this method, the laboratory controls the temperature supply according to the tables defined for the test cases, and the controller of the heat pump is not included in the test boundary. Instead, the controller is included in the test boundary of the two-mass model of the compensation method, which emulates the load: the return temperature depends on the emulation result, and the unit controls the supply temperature. The laboratory adjusts the heating curve to obtain the same average supply temperature as foreseen in the standard. The standard method considers steady-state performance (with the only exception of defrost) while the second method considers dynamic working conditions. Four different heat pumps were tested under different part load points considering the design capacity declared by the manufacturer. The test considered average climate conditions and low- and medium-temperature applications. The comparison done with the two methods reveals that the influence of the controller is different between the tested units and the test points. Those differences can be seen in the defrost control and the capacity control in part-load conditions. The results indicate a COP difference in the test points ranging from 0% to 10% for one unit and up to 30% for another unit. The implications of these findings demonstrate the importance of including the control in the test boundary for the development of heat pumps.