Experimental study on indoor thermal and daylighting performance of different thermotropic window systems in subtropical climate

Thermotropic (TT) glazing can dynamically regulate solar radiation and visible light in response to temperature changes without the input of additional energy, making it a promising component for smart building windows. Meanwhile, double clear glazing and low-emissivity (low-e) glazing are widely used as high-performance transparent building envelopes. In this study, the thermal and daylighting performance of single, double, and low-e double TT windows were experimentally evaluated and compared to those without TT materials. The results indicated that the TT glazing could significantly reduce indoor air temperature by up to 3.0 degrees C in single windows, 3.1 degrees C in double windows, and 4.1 degrees C in low-e double windows. When incorporated with TT materials, there shown an increase in inner surface temperature for single windows, minimal change for double windows, and a decrease for low-e double window. Additionally, daylighting performance was also improved across all window types. The epUDI300 similar to 3000lx was increased by 15 % and the epUDI>3000lx was reduced by 17 % for single glazing. The epUDI300 similar to 3000lx at window proximity was enhanced by 21 % for double and low-e double windows. These findings highlight the effectiveness of thermotropic glazing in enhancing both thermal and daylighting performance in buildings and are expected to support sustainable building practices.