Material matching and optimization for passive operational condition of buildings in transitional seasons: Coupled radiation regulation and latent heat storage for minimizing equivalent energy consumption

Buildings often operate under passive conditions during transitional seasons, making accurate evaluation of the indoor thermal environment particularly important. In this work, equivalent energy consumption (EEC) was used to assess the deviation of indoor air temperature from ideal thermal comfort range. For autumn in two studied cities, the building thermal environment was enhanced through cool paint (CP) and phase change material (PCM). The optimal CP for Shanghai was identified as ultra-high solar reflectivity (SR = 0.95) and thermal emissivity (TE = 0.95), while that for Beijing was high SR (0.93) and low TE (0.08), achieving total EEC reductions of 68.0% and 26.2%. Based on the fixed total latent heat constraint, PCM with lower specific latent heat demonstrated superior spatial thermal regulation potential. The optimal PCM mass distribution between the roof and the south wall was determined as 1:17 for Shanghai and 13:5 for Beijing, further reducing EEC to 1.537 and 2.874 kWh·m−2. The customized optimization of phase change temperature for PCM on the roof was 20 or 22 °C, while that on the south wall was 28.0 °C for Shanghai and 22.0 °C for Beijing, achieving EEC of 1.505 and 2.827 kWh·m−2. This work provided theoretical guidance for material selection in sustainable building design.