Energy and exergy analysis of an air-source heat pump water heater system using CO2/R170 mixture as an azeotropy refrigerant for sustainable development.
Abstract In this paper, the azeotropic mixture of CO2/R170 (0.78/0.22, mass fraction) is presented as a refrigerant to replace R134a in an ASHPWH system. On the basis of the first and second laws of thermodynamics, system performance and the exergy efficiency analysis are carried out for the system using both refrigerants. The results show that both the COPheat (coefficient of heating performance) and exergy efficiency of the system using the CO2/R170 mixture refrigerant are higher than that using the R134a, and the values can be increased by 31.3% and 30.6%, respectively. Moreover, the compressor discharge temperature for CO2/R170 is about 34.3–49.8 °C lower and the compression ratio of compressor also has a significant reduction (from 12.0417 to 3.2734), which leads to a higher lifetime for the compressors. So, the CO2/R170 mixture may be a good choice to substitute for R134a in ASHPWH systems. Also, a CO2/R170 ASHPWH system may be more suitable in cold region.