Performance comparison of liquid, vapor, and liquid–vapor injection of single-screw compressor for an air-source heat pump

Refrigerant injection techniques are usually proposed to improve the performance and reliability of compressors when a single-screw compressor applied to an air-source heat pump works at low temperatures in winter. In this study, an experimental study was conducted to present the performance comparison of the single-screw compressor in the air-source heat pump under liquid, vapor, and liquid–vapor refrigerant injection at evaporation temperatures between −19 and −8 °C. The results indicate that, when the evaporation temperature decreases from −8 to −19 °C, the heating capacity under liquid–vapor and vapor injection increases by 16.7% and 12.7%, respectively, compared with that under liquid injection and that the COPh increment under liquid–vapor injection and vapor injection is, respectively, from 11.23% to 39.21% and from 17.18% to 30.82% compared with that under liquid injection. Therefore, the liquid–vapor injection method is conducive to the operation of the air-source heat pump at a lower ambient temperature. The experimental results can provide the basis for the future design of single-screw compressors applied to air-source heat pumps.