Performance evaluation of low global warming potential working fluids as R134a alternatives for two-stage centrifugal chiller applications

With the increasing concern about climate change, the Kigali Amendment to the Montreal protocol requires parties to gradually reduce high global warming potential (GWP) hydrofluorocarbon (HFC) use by 80-85% by the late 2040s. The US Environmental Protection Agency (EPA) and EU Directive 517/2014 are also setting the ban on the use of such refrigerants. R134a, as a high GWP (GWP(100):1300) HFC refrigerant, is a commonly used medium pressure chiller refrigerant that will be phased out. Searching for low GWP R134a alternatives is necessary. In this study, hydrofluoroolefin blends-R513A, R513B, R515A, R515B, R516A and pure hydrofluoroolefins-R1234yf and R1234ze(E) are investigated for performance evaluation for two-stage centrifugal chiller application with a fixed cooling capacity 1,750 kW. The evaluation was conducted via a thermodynamic process model, a component sizing methodology and a life cycle environmental performance methodology R515A, R515B and R1234ze(E) show a 25% volume capacity reduction in comparison with baseline due to their low suction density. All R134a alternatives exhibit more component heat transfer area than baseline, with 5-15% increase for the evaporator and 12-38% for the condenser. The comparison for the compressor impeller diameter shows that R513A, R513B, and R516A do not require the compressor size change from baseline, while R515A, R515B and R1234ze(E) need a more than 18% larger compressor size. R134a alternatives can provide 8.4-16.7% life cycle emission reduction in China and 14.7-27.7% in South Korea. In general, R513A, R513B and R516A are more preferable R134a drop-in options for less component modification and the same compressor can be employed directly. R516A is A2L and necessary vessel safety code protection is needed. R515A and R515B can serve as the system newly design-based interim non-flammable replacement for R134a in medium-pressure chillers with a large modification for a compressor. Gradually, with more strict regulations, R1234ze(E) can be the ultimate option in the market with less/negligible modification from R515A and R515B. For R1234yf, its poor heat transfer performance and high price can impede its application in chillers. It is anticipated that the viewpoints and insights from this study can be beneficial for the engineers, policymakers, scholars, public and manufacturers to maintain the maximum sustainability and economic benefits.