Comparison of the performance of a vapor-injection scroll compressor and a two-stage scroll compressor working with high pressure ratios

This paper presents a comparative analysis of the performance of a vapor-injection scroll compressor (SCVI) and a two-stage scroll compressor (TSSC) working with high pressure ratios in heat pump applications. Semi-empirical models of the compressors are implemented. The models are adjusted with experimental data obtained in a calorimetric test bench. The optimum displacement ratio (DR) is analyzed considering two criteria, COP maximization, and discharge temperature minimization. Once defined the optimum DR, a systematic comparison of the compressors is performed in terms of compressor efficiencies, heating capacity, COP, and discharge temperature. Finally, the intermediate pressure is optimized for a high-temperature water heating application, taking into account heat sink of finite capacity. Results show that the optimum DR of TSSC is around 0.58 and the COP is 6% larger than that the SCVI at the nominal point. Considering a wide range of operating conditions, the SCVI presents better efficiency and COP for pressure ratios below 5. For higher-pressure ratios, the TSSC presents better performance and achieves lower discharge temperature. The heating capacity of the TSSC can be improved by 7% by varying the swept volume of the high-stage compressor compared with the SCVI, with a minimum effect on the COP and on the discharge temperature from the optimum conditions.