Compressor Heat Pump Model Based on Refrigerant Enthalpy and Flow Rate

Abstract

This paper introduces a compressor heat pump model using flow rate and enthalpy values for the calculation of heat pump control parameters. The aim of in this article presented research work was to develop an universal model of a compressor heat pump which will enable simulation tests for compressors of any volumetric efficiency with variable operating parameters (e.g. temperature of the lower source and condensation temperature) worked with any refrigerant. An additional assumption was the possibility of conducting simulation tests continuously. The model was developed on the basis of equations describing the thermodynamic transformations taking place in the refrigeration system. The data needed for the model are the input signals of saturation and condensation temperatures and the refrigerant mass flow rate entered as a time series. The output signals are heating capacity, cooling capacity, power consumed by the compressor, and the temperature at the second point of the thermodynamic cycle of the refrigerant. The paper presents equations for examples of the frequently used refrigerants R410a and R290 and practical verification of the presented algorithm in the laboratory made for refrigerant R410a. A description of the laboratory stand is also included. Comparison of the capacity provided by the condenser and the coefficient of performance with the values simulated using the proposed model confirms the correctness of the applied model and its practicality. The results obtained by simulation and measurements show very good convergence. The developed model makes it possible to calculate the operational parameters of the device, e.g. such as COP and SCOP for given boundary conditions, which then enables to estimate the coverage degree of the heat load of the building by the heat pump due to central heating and to estimate momentary and seasonal operating costs of the heat pump.