heat pump, variable speed compressor, control
A variable capacity heat pump, with variable speed drives on the secondary circuits, needs an adequate control for gaining the maximum energy efficiency. In the present paper, a model of a ground-source heat pump with variable speed compressor, variable speed water pumps and variable speed fans in the coils is presented. This model is used to develop a control strategy which is implemented in the GSHP (Ground Source Heat Pump) system installed at HirefSpA (Italy) in the framework of the European Project Ground-Med. The goal is to maximize the overall coefficient of performance, accounting for energy inputs to the compressor and the auxiliary components. The control parameters of the model that can be varied are the followings: frequency of compressor, frequency of water pump to the borehole heat exchangers, frequency of the water pump to the user, velocity of the fans, water temperature to the user. The present model allows to evaluate the operating conditions that lead to the maximum seasonal coefficient of performance of the system. The present model is also the baseline for the development of the strategy control, with the final objective of maximizing the seasonal coefficient of performance of the system. In order to make the system operate at optimal conditions when the load varies, a primary and secondary control has been implemented. The temperature of the tank is used in a primary controller to vary the heat output of the heat pump, depending on the difference between the measured temperature of the tank and the setpoint value. The ambient temperature is used in a secondary controller to vary the heat capacity of the fancoil unit as a function of the difference between the measured and ambient setpoint temperature.