Energy and exergy assessment of internal heat exchanger integration in refrigeration systems with alternative refrigerants

The efficiency of vapor compression refrigeration systems can be enhanced by incorporating an internal heat exchanger to subcool the liquid refrigerant exiting the condenser. This integration reduces flash vapor generation through the expansion valve, thereby increasing the refrigeration effect. However, it also introduces thermodynamic trade-offs, such as higher suction specific volume due to additional superheating, which can reduce the refrigerant mass flow rate and elevate the compressor discharge temperature. This study investigates the thermodynamic performance impact of internal heat exchanger integration for 17 refrigerants at two evaporation temperatures (0 and −20°C) under consistent modeling assumptions. The results show that the internal heat exchanger benefit is strongly dependent on the refrigerant type, and significant improvements are obtained with refrigerants such as R600a, R290, R404A, R450A, and R1234yf, with COP and cooling capacity typically increasing by 5–8%. However, performance degradation is observed for R32, R452B, and R454B. For R32, the COP decreases by up to about 4%, and the discharge temperature can reach 175°C. In addition to the first-law assessment, a second law (exergy) analysis is included for representative refrigerants to quantify how internal heat exchanger effectiveness influences total irreversibility, second-law efficiency, and the relative contribution of throttling losses. The exergy results show that, at an evaporation temperature of 0°C, the total exergy destruction rate slightly decreases with increasing internal heat exchanger effectiveness for R600a (from about 0.95 to 0.90 kW) and R1234yf (from about 1.08 to 1.01 kW), whereas it increases for R32 (from about 1.17 to 1.21 kW). Under the more demanding condition of −20°C, the total exergy destruction rate becomes significantly higher, reaching approximately 2.33 kW for R32 at the highest effectiveness, while decreasing from about 1.93 to 1.73 kW for R600a and from about 2.28 to 2.01 kW for R1234yf. Consistently, the second-law efficiency increases with internal heat exchanger effectiveness for R600a and R1234yf, whereas it decreases for R32, confirming that the exergetic benefit of internal heat exchanger integration remains refrigerant-dependent.