Analysis of map-based models for reciprocating compressors and optimum selection of rating points

Abstract

The present work includes an in-depth performance analysis in fixed-speed reciprocating compressors. The industry standard for compressor characterization is the AHRI-540, which uses a 10-term and third-degree polynomial to characterize mass flow rate and energy consumption. However, the suitability of such a high-degree polynomial is unclear, and the potential for overfitting and extrapolation errors cannot be ignored. This work analyzes the response surfaces of mass flow rate and energy consumption in reciprocating compressors to determine if more concise models with lower degrees are more suitable. For that purpose, a massive experimental dataset with multiple compressors using different refrigerant and suction conditions was analyzed to obtain overall conclusions in the compressor field. The results of the present work showed that mass flow rate modeling requires lower-degree polynomials. However, the energy consumption characterization is more complex, and the model reported in the standard may be justified. Additionally, it was found that, if the specific energy consumption is selected as the modeling variable, it is possible to use a compact polynomial expression, which can also be extended to scroll compressors and also has the advantage of reducing the experimental data necessary for the model fit. Finally, by selecting the mass flow rate and the specific energy consumption as response variables, this work also explores other critical issues related to the experimental points’ location and minimum sample sizes required in order to minimize the experimental costs and increase the model accuracy.