Thermotropic glass vs. vertical shading: Evaluation of building energy, daylighting and thermal comfort performance

Thermotropic (TT) glazing has been demonstrated that can achieve comparable energy-saving performance to external horizontal shading devices by dynamically modulating solar heat gain through windows in response to ambient climatic variations. The aim of this work is to identify whether TT glazing can replace external vertical shading devices considering building energy consumption, daylighting performance, and thermal comfort. A comparative study was conducted by using an experimentally validated model. The model was used to evaluate the building energy consumption, daylighting performance, and thermal comfort of a reference office room equipped with TT glazing and the room equipped with the vertical shading devices considering different building orientations and 5 climates of China. The results indicated that across the five climate zones, in the east- and west-facing reference office rooms, as well as in the south-facing office rooms of Nanjing and Xiamen, the application of TT glazing led to lower EUIs than both the double-clear glazing with all vertical shading and the baseline double-clear glazing without shading. This use of TT glazing reduced building energy use by 0.1%-11.1% compared both with vertical shading and the baseline condition. On the north-facing façades across the five climate zones, the application of external shading devices resulted in the lowest EUIs. TT glazing and vertical shading devices with equivalent shading lengths showed similar daylighting performance for the 0-100 lx and 300-3000 lx ranges. Compared with vertical shading, TT glazing provided comparable or superior thermal comfort, reducing PPD_overheating by up to 2.0% and PPD_overcooling by up to 0.5%.