Multi-objective optimisation of deep energy retrofit strategies for a school building

This study presents an integrated framework for multi-objective optimisation of deep energy retrofit strategies for an existing school building. A calibrated EnergyPlus model, hourly energy-system operation optimisation, and 15-year economic and energy assessment are combined. Calibration using 2017–2021 monthly district heat data yielded overall MBE = 0.78% and CV(RMSE) = 7.61%. The decision space includes glazing, wall and roof insulation, secondary systems, heat pumps, thermal storage, and photovoltaics. Global cost and net primary energy were used as competing objectives, with discount rates of 0%, 3%, 6%, and 8%. Maximum photovoltaic capacity was observed across all Pareto-optimal solutions, while heat pumps with fan-coil units and storage dominated the low-primary-energy region. Across the four economic scenarios, 543 unique configurations appeared on at least one GC–PE Pareto front, whereas only 20 (3.68%) retained Pareto-optimality in all four scenarios, highlighting the limited cross-scenario robustness of complete retrofit configurations.