Energy, Exergy, and Environmental Assessment of R-152a as a Low-GWP Alternative for R-134a in Domestic Heat Pump Water Heaters for Tropical Countries

Domestic heat pump water heaters offer an energy-efficient solution for hot water production in tropical countries. This study evaluates the energy and exergy performance as well as the environmental impact of R-152a as a replacement for R-134a in a domestic heat pump water heater. The evaluation uses a thermodynamic modelling approach under fixed operating conditions, with an evaporator temperature of 10°C, a condenser temperature of 50°C, and a water heating capacity of 1.6 m³. The results indicate that R-152a achieved an actual coefficient of performance (COP) of 6.25, which was 4.3% higher than that of R-134a at 5.99. R-152a also required a lower refrigerant mass flow rate. The mass flow rate decreased from 7.595 g/s for R-134a to 4.555 g/s for R-152a, which represents a reduction of approximately 40%. The exergy analysis further showed that R-152a consistently exhibited higher exergy efficiency than R-134a across the investigated ranges of evaporator temperature and compressor efficiency. This result indicates that R-152a has a lower thermodynamic irreversibility. From an environmental perspective, R-152a also showed a much lower direct Total Equivalent Warming Impact (TEWI). Its direct TEWI was 195.3 kg CO2-eq, which was 91.3% lower than that of R-134a at 2252.25 kg CO2-eq. This reduction is mainly related to the lower Global Warming Potential (GWP) of R-152a, which is 124, compared with 1430 for R-134a. The results demonstrate that R-152a is a promising low-GWP alternative to R-134a for domestic heat pump water heaters, offering improved thermodynamic performance, higher exergy efficiency, and substantially reduced environmental impact. However, its flammability must be carefully addressed through proper safety measures before practical implementation.