Thermodynamic assessment of R1234yf + R1243zf + R600a ternary mixture for domestic heat pumps

Mixtures of hydrofluoroolefins (HFOs) and hydrocarbons (HCs) are increasingly recognized as promising substitutes for hydrofluorocarbon (HFC) refrigerants in residential heating systems due to their favorable environmental profiles and thermodynamic properties. This study investigates the ternary refrigerant mixture comprising 2,3,3,3-tetrafluoropropene (R1234yf), 3,3,3-trifluoropropene (R1243zf), and isobutane (R600a) as a potential drop-in replacement for R410A, widely used in domestic heat pump applications. Firstly, to verify the accuracy of the available thermodynamic property models, experimental measurements of pvTz properties for the ternary mixture were conducted across two-phase and superheated vapor regions using an isochoric apparatus at three isochores between temperatures of 260.15 K and 373.15 K. An excellent agreement between experimental results and calculations derived from multi-fluid Helmholtz-energy explicit models with model parameters recently determined for the binary subsystems was found, achieving average absolute relative deviations (AARD) below 1 %. Additionally, heat pump cycle simulations employing these thermodynamic property models revealed key performance indicators including coefficient of performance (COP), volumetric heating effect (VHE), temperature glide, and flammability index. Simulations indicated that no single pure fluid simultaneously optimizes COP and VHE, thereby emphasizing the importance of optimized mixture compositions. An optimal ternary composition was identified, delivering COP deviations up to +2 % compared to R410A, while highlighting environmental advantages and outlining necessary design adjustments for practical residential heat pump integration.