<![CDATA[Low-grade waste heat varies in thermal quality and can shift an Organic Rankine Cycle (ORC) away from favorable operating conditions. This study evaluates operating-point optimization of a single-pressure subcritical ORC using integrated energy and component-level exergy analyses. R245fa was used as the reference fluid, while R245fa/R1233zd(E) mixtures were examined for composition and temperature-matching effects. At a heat-source temperature of 150 °C, increasing evaporation pressure from 1.5 to 3.0 MPa raised thermal efficiency from 11.912% to 14.311%. A pressure of 2.8 MPa was retained as the reference near-optimal point, yielding 33.976 kW net power on a 1.0 kg/s working-fluid basis, 14.164% thermal efficiency, and 48.739% exergy efficiency. Increasing pressure to 3.0 MPa improved net power by only 0.57% while reducing the evaporator hot-end temperature difference from 10.7 to 7.0 K. At 2.8 MPa, total exergy destruction was 35.734 kW, distributed among the evaporator (54.16%), expander (23.49%), condenser (20.58%), and pump (1.77%). The 0.3/0.7 R245fa/R1233zd(E) mixture was the first feasible composition under the 5 K minimum temperature-difference constraint and gave the highest feasible thermal efficiency, 14.636%, or 0.472 percentage points above pure R245fa, with a temperature glide of 0.528 K. This modest gain is associated with composition-dependent source–fluid temperature matching under the imposed feasibility constraint rather than an unconstrained interior optimum. Under a 140-160 °C heat-source variation, operating-point adjustment limited the maximum relative net-power deviation to approximately ±1.8%. Raising condensation temperature from 30 to 40 °C reduced both thermal and exergy efficiencies by about 8.96%, while increasing expander isentropic efficiency from 0.80 to 0.88 raised exergy efficiency from 48.739% to 53.990%. The study integrates operating-point adaptation, mixture assessment, and component-level thermodynamic diagnosis within a simple ORC framework for variable waste-heat recovery.]]>
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