Flexible dynamic model of PHEX for transient simulations in Matlab/Simulink using finite control volume method

Abstract

In order to improve the energy efficiency and control of heat pump systems, it is necessary to develop dynamic models that accurately simulate their real performance. In addition, these models will help to carry out future works of research, such as new low carbon refrigerant testing. Physics-based models follow a set of physics laws that characterize the model as the most accurate, versatile and robust to simulate different heat pump systems. Taking into account the fact that the dynamics of the elements that regulate mass flow (compressors and valves) are much faster than the dynamics of the components that regulate heat transfer (heat exchangers), the model complexity usually resides in the latter. This paper provides a detailed explanation of the physics-based dynamic model in Matlab/Simulink using the finite-control volume approach applied to a refrigerant-to-liquid plate heat exchanger. Dynamic experimental tests were developed to validate the model under four possible situations: condenser and evaporator heat exchangers working in both counter- and parallel-flow. In addition, an approximation of the number of finite control volumes required to reach a good accuracy, while maintaining a reasonable simulation time is presented. Simulation results show great accuracy when compared to experimental tests. It was proved by calculating the Normalized Residual Error, which is between 1.1 E-04 and 1.0 E-03 in all cases. It was also concluded that using twenty finite control volumes, there is good agreement between the accuracy of the results and the computational time.