Climate-responsive roof design: phase-change materials and cool-roof coatings across Türkiye's six climate zones

Roof material and coating decisions are typically finalized early in design, yet climate-specific evidence for choosing among roof-integrated phase-change materials (PCMs), high-reflectance cool roofs (CR), and their combination remains limited. This study evaluates all three strategies via annual EnergyPlus simulations of a standardized office model across Türkiye's six TS 825 climate zones (Mersin, Şanlıurfa, İstanbul, Ankara, Van, and Erzurum). Five inorganic PCM products with nominal melting temperatures of 21, 23, 25, 27, and 29 °C were tested individually before the best-performing temperature in each city was paired with the cool-roof finish. Performance was assessed from annual ideal-load heating and cooling demand, with total demand defined as their sum. The optimal PCM reduced total demand by 4.24–10.15%, with the preferred melting temperature shifting from 25 °C in cooling-dominated Mersin to 21 °C in cold Erzurum; 23 °C was optimal in the other four cities. The cool roof reduced cooling demand in every city but increased heating demand, producing net annual savings of only 0.22% in Erzurum and up to 5.86% in Mersin. The combined strategy achieved the lowest total demand in five cities, with savings of 8.00–11.92%. Van was the exception: its optimal PCM alone saved 10.01%, whereas the combined case saved 6.33%, indicating that the coating and PCM were not universally additive. The findings show that PCM transition temperature should be matched to local operating conditions and that cool roofs require an annual heating–cooling assessment rather than a cooling-only evaluation.

Keywords: Phase-change material (PCM), cool-roof coating, climate zones, energy efficiency, office building.