Multi-objective optimization and TOPSIS-based comprehensive evaluation of low-GWP refrigerant mixtures for high-temperature heat pumps

Selecting low global warming potential (GWP) refrigerant mixtures for high-temperature heat pumps requires balancing cycle efficiency, volumetric capacity, temperature matching, environmental impact, and cost. This study integrates multi-objective optimization with multi-criteria decision-making to screen binary and ternary mixtures formulated from 19 pure refrigerants under large temperature lifts. NSGA-III is coupled with a single-stage vapor compression cycle model to optimize the coefficient of performance (COP), volumetric heating capacity (VHC), and overall temperature matching index ( π glide,overall ). Pareto solutions satisfying π glide,overall < 2 are ranked using TOPSIS based on COP, VHC, total equivalent warming impact (TEWI), and total annual cost rate ( Z total ). Heat-sink inlet/outlet temperatures of 80/90, 90/100, and 100/110 °C are investigated at fixed heat-source inlet/outlet temperatures of 25/15 °C. Ternary mixtures broaden the attainable trade-off space, although no single composition simultaneously optimizes all three objectives. Increasing heat-sink temperature reduces attainable COP and VHC and worsens the best achievable temperature matching. At 80/90 °C, R170/RE170 ranks first with mass fractions of 0.11/0.89. At 90/100 °C, R1224yd(Z)/R161/RE170 ranks first with mass fractions of 0.27/0.13/0.60. At 100/110 °C, R600/R601a/RE170 ranks first with mass fractions of 0.32/0.06/0.62. The latter achieves a TOPSIS score of 0.8991 and ranks first under four of five weighting schemes. Detailed analysis at 100/110 °C identifies compression and throttling as the principal sources of exergy destruction. Electricity-related indirect emissions dominate TEWI, whereas annualized capital and maintenance costs dominate Z total .