Study of a Novel Hybrid Refrigeration System, with Natural Refrigerants and Ultra-Low Carbon Emissions, for Air Conditioning

Abstract

Due to its environmental benefits, CO2 shows great potential in refrigeration systems. However, a basic CO2 transcritical (BCT) refrigeration system used for airconditioning in buildings might generate massive indirect carbon emissions for its low COP. In this study, a novel CO2 transcritical/two-stage absorption (CTTA) hybrid refrigeration system is broadly investigated, and both energy efficiency and life cycle climate performance (LCCP) are specifically engaged. The theoretical model shows that optimal parameters for the generator inlet temperature (TG2), intermediate temperature (Tm), and discharge pressure (Pc), exist to achieve maximum COPtol. Using the LCCP method, the carbon emissions of the CTTA system are compared to six typical refrigeration systems by using refrigerants, including R134a, R1234yf and R1234ze(E) etc. The LCCP value of the CTTA system is 3768 kg CO2e/kW, which is 53.6% less than the BCT system and equivalent to the R134a system. Moreover, its LCCP value could be 3.4% less than the R1234ze(E) system if the COP of the CO2 subsystem is further improved. In summary, the CTTA system achieves ultra-low carbon emissions, which provides a potential alternative to air conditioning systems in buildings that can be considered alongside R1234yf and R1234ze(E) systems.