The Effects of Hybrid Refrigerant Injection on the Heating Performance of an Inverter-Driven Heat Pump System

This study experimentally investigates the effects of hybrid refrigerant injection on the heating performance of an inverter-driven heat pump system operating with R410A as the primary refrigerant and R32 as the injection refrigerant. The objective is to evaluate the influence of injection on heating capacity, coefficient of performance (COP), compressor power consumption, exergy efficiency, and exergy destruction under different operating conditions. The experiments were conducted at outdoor temperatures of 0, 3, 5, and 10 °C, compressor frequencies of 30, 50, 70, and 90 Hz, and injection ratios ranging from 0 to 30%. The results demonstrate that hybrid refrigerant injection significantly affects the thermodynamic and operational characteristics of the heat pump. Increasing the injection ratio generally enhances the refrigerant mass flow rate and improves the heat transfer and compression processes, resulting in increased heating capacity. The improvement is particularly important under lower outdoor-temperature conditions, where the heat pump experiences a greater heating demand. The injection process also influences compressor power consumption; therefore, the improvement in heating capacity does not necessarily correspond to a proportional increase in COP at all operating conditions. The results further indicate that compressor frequency and outdoor temperature strongly interact with the injection ratio, with the optimum operating condition depending on the combined effects of these parameters. Exergy analysis shows that appropriate injection can improve exergy efficiency and reduce the relative thermodynamic losses of the system, although excessive injection may increase irreversible losses in some operating conditions. Finally, the findings demonstrate the potential of hybrid refrigerant injection as an effective approach for improving the heating performance and thermodynamic utilization of inverter-driven heat pump systems over a wide range of outdoor operating conditions.