A critical analysis of the AHRI polynomials for scroll compressor characterization

Abstract

• Scroll compressor energy and mass flow surfaces with evaporating and condensing conditions. • ARHI polynomials overfit scroll compressor behavior. • Two-degree polynomials are more indicated to scroll compressors. • Less experimental points are required to characterize scroll compressor. • Pressure as polynomial variable is more suitable than temperature. This paper presents the analysis of the energy consumption and mass flow rate of scroll-type compressors. The study has included the data of several AHRI reports (especially AHRI 11 and AHRI 21) and data from other sources. A total of 7 different scroll compressors of different sizes have been considered in the study, some of them tested with various refrigerants (R134a, R32, R410A, R404a…). For all the studied compressors and refrigerants, the compressor energy consumption and mass flow rate values have been analyzed. The main objective is to better understand the dependence of these variables on the operating conditions and the refrigerant used. The analyzed data include tests following different superheat control, i.e., constant superheat or constant return temperature, so the effect of the inlet temperature on these variables is also discussed. As the main novelty of this study, the analysis of the response surfaces has allowed the authors to evaluate the most suitable correlation to use, including an analysis of the necessary experimental tests and where to place them to increase the model's accuracy. It was found that using the condensing and evaporating pressure terms is more universal than the classical temperature domain. In scroll compressors, AHRI polynomials overfits the compressor performance introducing significant deviations in the interpolation and extrapolation capabilities if the experimental data are not properly selected. Finally, it was found that lower degree polynomials are more suitable for this kind of compressor and has also the advantage of requiring fewer experimental point measurements to characterize the compressor with the corresponding cost-savings.