Evaluation of binary and ternary refrigerant blends as replacements for R134a in an air-conditioning system
mixtures, R134a, refrigeration, thermodynamics, screening
We investigated refrigerant blends as possible low-GWP (global warming potential) alternatives for R134a in an air-conditioning application. We carried out an extensive screening of the binary and ternary blends possible among a list of 10 pure refrigerants comprising three hydrofluoroolefins (HFOs), six hydrofluorocarbons (HFCs), and carbon dioxide. The screening was based on a simplified cycle model, but with the inclusion of pressure drops in the evaporator and condenser. The metrics for the evaluation were nonflammability, low-GWP, high COP (coefficient of performance), and a volumetric capacity similar to the R134a baseline system. While no mixture was ideal in all regards, we identified 12 "best" blends that were nonflammable (based on a new estimation method by Linteris, et al., presented in a companion paper at this conference) and with COP and capacity similar to the R134a baseline; the tradeoff, however, was a reduction in GWP of, at most, 56% compared to R134a. An additional seven blends that were estimated to be "marginally flammable" (ASHRAE Standard 34 classification of A2L) were identified with GWP reductions of as much as 90%. These 19 "best" blends were then simulated in a more detailed cycle model.