Thermal-economic-carbon trilemma optimization for BIPV facades in cold-climate public buildings: A hybrid NSGA-II-TOPSIS framework based on validated thermal network modeling

Building-Integrated Photovoltaics (BIPV) represent an effective solution for energy conservation and carbon emission reduction in office buildings located in cold regions. However, the traditional single-target BIPV facade design faces the dilemma of balancing insulation performance, energy economy, and carbon footprint reduction. This study proposes an innovative hybrid optimization framework, which combines the thermal resistance network modeling with the NSGA-II-TOPSIS algorithm to systematically resolve these contradictions. The effects of inclination angle, cavity spacing, and window-to-wall ratio (WWR) on heat load and PV efficiency are analyzed by establishing a steady-state heat transfer model. The NSGA-II algorithm is used to generate a Pareto optimal solution set, and is combined with the TOPSIS method to realize the optimal scheme decision under different priority scenarios. The results indicate that the enclosed cavity BIPV facade (5#) demonstrates the best overall performance, with an energy payback period (EPP) of 11.33 years, annual operational carbon emission reduction of 28.51 tCO2, and initial carbon emissions of 192.16 tCO2.Finally, the CFD simulation results verify the accuracy of the thermal model, and the temperature error is controlled within 4 °C. This research method provides a reliable decision support tool for the optimized design of BIPV facades in cold regions, taking into account the thermal performance, economy, and carbon emission reduction benefits.