Parametric optimisation of building envelopes for energy efficiency in Taiwan’s cooling-dominated climates

This study investigates multi-objective optimisation of building envelope insulation for office buildings in Taiwan's subtropical climates. Using EnergyPlus simulations integrated with jEPlus + EA and the NSGA-II algorithm, various insulation types (foam concrete, rockwool, and polyurethane) and thicknesses were evaluated against Taiwan's regulations (U-factor 3.5 W/m²K). Metrics analyzed included cooling electricity consumption, insulation costs, U-factors, and net present value (NPV). Results show optimised insulation strategies achieved annual cooling energy savings of 1–3% when modelled with realistic chilled-water HVAC systems. Foam concrete demonstrated superior cost-effectiveness, yielding high NPV despite higher U-factors, while advanced insulations offered lower U-factors (2.37 W/m²K) but with diminishing economic returns, particularly under Kaohsiung's hotter climate with 21% higher cooling degree days. Climate projections using SSP1-2.6 and SSP5-8.5 scenarios indicate a 5.12–11.15% increase in future cooling demands by 2080. The findings support integrated thermal-economic optimisation to inform resilient, cost-effective building codes tailored to Taiwan's regional climatic variations.