The Effects of Window Geometry Parameters on Indoor Thermal and Visual Comfort of Thermochromic Windows in Office Building

Thermochromic windows can dynamically modulate solar radiation to optimize indoor thermal and visual comfort. However, their performance is strongly influenced by window geometry parameters, while the optimal geometrical conditions for evaluating their performance remain unclear. This study aims to investigate how window geometry parameters, namely orientation, window-to-wall ratio (WWR), and sill height, influence thermochromic windows’ performance, as well as to identify the proper geometry parameters for performance evaluation. The improved HNU Solar model and EnergyPlus were employed for the simulation of an office building located in Changsha in south China, to assess indoor thermal and visual comfort with thermochromic windows under different conditions of window orientations, WWRs (30–60%), and sill heights (0–1.5 m). The results reveal that on a typical summer day, with thermochromic windows, the solar-induced thermal discomfort duration was lowered by 60.9%, 82.4%, 63.7%, and 96.4% for east, south, west, and north windows, respectively; visual discomfort duration is also mitigated by 28.6%, 37.4%, and 45.4% with east, south, and west windows. As the WWR increases from 30% to 60%, with thermochromic windows, indoor thermal comfort decreases, whereas indoor visual comfort increases; as the sill height increases from 0 to 1.5 m, both thermal and visual discomfort time ratios first increase and then decrease, while the reduction in the thermal or visual discomfort duration by thermochromic windows gradually diminishes. In addition, the proper WWR range for evaluating the performance of thermochromic windows is from 40% to 50%, and the corresponding sill height range is from 0.5 to 1 m. These findings provide practical guidance for identifying the feasibility of thermochromic windows under different window geometries, as well as the selection of window geometry parameters for the performance evaluation.