Thermoresponsive building envelope with optical modulation and latent heat storage: Energy savings and thermal comfort evaluation under diverse climatic conditions

Thermal comfort is essential for occupant well-being, yet maintaining it consumes a substantial portion of building energy. To address this, this study proposes and fabricates an innovative thermoresponsive building envelope integrating a thermoresponsive hydrogel (TH) layer with a phase change material (PCM) layer. The TH enables optical modulation, adjusting solar absorption and reflection with temperature to reduce solar radiation during hot seasons while capturing solar heat during cold seasons. Simultaneously, the PCM provides latent heat storage, reducing daily temperature fluctuations and maintaining nighttime indoor temperatures during cold seasons, thereby lowering heating demand and improving thermal comfort. Sensitivity analysis indicated that the optimal transition temperature of the TH layer is higher in the colder regions due to greater heating demand and lower ambient temperatures, whereas the optimal phase change temperature of the PCM layer lies below the heating setpoint to compensate for the heating reduction. Based on typical meteorological year weather data, simulations across 34 provincial-level capital cities of China demonstrated that the proposed envelope can reduce annual energy consumption by 4.0-18.2% (7.8-17.1 MJ m -2 ) and increase comfort hours by 0.2-9.7% compared to a bare envelope in residential buildings with heating and cooling setpoints of 20 °C and 26 °C, respectively, depending on the region and the optimal transition temperatures of both the TH and PCM layers. These results highlight the feasibility of passive building envelope designs as an effective energy-saving and thermal comfort strategy across different climates.