Performance of a Two-Phase Injection Heat Pump with the Variation of Injection Quality and Pressure

Heat pumps are becoming more commonly and widely used due to their advantages in efficiency and versatile applications in both cooling and heating. However, the reliability of its compressor is being compromised due to high discharge temperatures caused by harsh operating conditions. Among the numerous studies conducted in improving the discharge temperature and performance of the heat pump, two-phase injection is receiving great interest. In this study, the performance of the two-phase injection heat pump was measured with a variation of operating parameters. The experiment results were used to study the performance change according to the operating parameter such as injection quality and pressure. It was found that the performance of the heat pump using the two-phase injection was better in terms of COP by up to 5.8% compared to that using the vapor injection. Furthermore, the two-phase injection was effective in reducing the discharge temperature to improve the compressor reliability. Two types of optimum injection qualities were suggested through this study: discharge temperature optimum injection quality (TIQ), and performance optimum injection quality (PIQ). It was found that in most conditions PIQ was sufficient in satisfying the compressor reliability, but in harsh operating conditions, where the compression ratio was high, TIQ was required in order to maintain the compressor reliability.