Architectural integration and thermodynamic optimization of VCC-driven single-stage ORC system for ultra low-grade waste heat recovery

Achieving carbon neutrality requires cost-effective technologies that improve energy efficiency while reducing greenhouse gas emissions. This study evaluates a vapor compression cycle integrated single-stage organic Rankine cycle (VCC-SS-ORC) that recovers the desuperheated fraction of VCC condenser waste heat through a shared heat exchanger (SHX) and converts it into electricity without external heat input. The architectural novelty lies in using the SHX as the direct thermal interface between the VCC condenser and ORC evaporator to maximize power recovery under a fixed 100 kW cooling load. A thermodynamic model is developed using R134a and R1233zdE in the VCC and zeotropic mixtures R245fa/R365mfc and R123/R236ea in the ORC. Sensitivity analyses vary the VCC condensing temperature from 313.15 to 318.15 K at fixed evaporation temperature and the VCC evaporation temperature from 273.15 to 280.15 K at fixed condensing temperature. Single-objective genetic algorithm optimization identifies the optimal ORC evaporating temperature and mixture composition for maximum net electric output. The optimized mixtures, 0.45R245fa/0.55R365mfc and 0.48R123/0.52R236ea, improve COP system over COP VCC by up to 2.24% and 1.60%, respectively. Under condensing temperature variation, the optimized R245fa/R365mfc case increases net electric output from 470.54 to 738.06 W, corresponding to a 56.85% increase. Under evaporation temperature variation, the optimized ORC reaches up to 819.78 W with a peak ORC thermal efficiency of 4.22% for 0.45R245fa/0.55R365mfc, while 0.48R123/0.52R236ea yields up to 557.23 W with 4.04% efficiency. Results confirm modest but measurable efficiency gains under steady-state fixed load conditions. Practical implementation requires experimental validation, off-design assessment, dynamic control analysis, techno-economic evaluation, and life-cycle carbon assessment.