High-resolution urban-scale impact of retro-reflective façade materials on building thermal load

This paper presents a high-resolution urban-scale evaluation of the impact of retro-reflective (RR) façade materials on building thermal load. Unlike earlier studies limited to isolated buildings or simplified geometries, we integrate LiDAR-derived 3D city models, local meteorological data, and per-triangle thermal load simulation to quantify seasonal thermal load impacts on an urban scale. The triangle-based framework enables detailed estimation of shading, orientation, and vegetation effects under realistic urban configurations. The methodology was applied to 914 buildings in Celje, Slovenia, represented by more than seven million building surface triangles. Results show that Prism RR material increased annual heating demands by 2.1% and reduced cooling demands by 0.76%, while Glass bead material increased heating by 1.6% and reduced cooling by 0.65%. On the days of maximum city-aggregate cooling demand reduction, Prism and Glass bead materials reduced cooling demands by up to 19.31% and 15.39%, respectively. These location-specific results demonstrate a seasonal trade-off, where reduced summer cooling demand is counterbalanced by increased heating demand. The analysis also identifies a previously underreported seasonal asymmetry, with the highest heating demand increases occurring in spring when solar irradiation is high yet heating demand remains.