A "real-time" dynamic model of an air-air heat pump.

The work deals with the development of a model of a heat pump, to be used within studies referring to Distributed Generation Systems and Efficient Energy Conversion Systems carried out by the authors. The heat pump considered is an air-air type: the model is developed in the Simulink® environment and features a volumetric electric driven compressor, an expansion valve and heat exchangers to evaporate and condense the refrigerating fluid. Compressor and valve are not considered as state-determined components, and they are modeled according to a quasi steady approach; compressor rotational speed and expansion valve coefficient of discharge can be varied during operation. Condenser and evaporator are considered to be state determined components. The mathematical model of the heat exchangers considers the phase change of the refrigerating fluid. Mass and energy conservation equations (the last applied to both the fluid and the steel pipe) for all the fluid phase zones are defined and solved for both condenser and evaporator. This leads to a system of differential equations for each heat exchanger, solved in matrix form. The validation has been carried out by comparing the performances of the model to the experimental data gathered from a real air-air heat pump system; theoretical results and experimental data were compared under unsteady operating conditions.