More and more modern buildings are using glass curtain walls as their building envelope. The large area of window leads to a significant increase in solar heat gain, resulting in an increase in the cooling load and energy consumption of the building envelope. In the calculation of building cooling load, the thermal performance parameter of windows, the solar heat gain coefficient, is used to calculate the solar radiation heat gain of the windows. The window-to-wall ratio of buildings with glazing facades is large, and the phenomenon of escape of incident solar radiation cannot be ignored. In order to calculate the solar radiation escape rate, a dynamic model of solar radiation escape rate incorporating the solar path tracking model is developed in this research, which can achieve big data simulation analysis based on actual meteorological conditions. The model is programmed and simulated using MATLAB R2024a software. Five representative cities from different climate regions in China are selected and the variation rule of solar radiation escape rate are analyzed on three different time scales: day, month, and year. The influence of building orientation was also calculated and analyzed. The numerical calculation results indicate that the escape solar radiation rate varies with the incident angle of solar radiation at different times. It was found that the smaller the solar azimuth angle and solar altitude angle, the smaller the escape rate of solar radiation. The latitude of a city has a significant impact on the solar radiation escape rate. The weighted average of the solar radiation escape rates for each city were calculated for both summer and winter. Regardless of the season, the city’s location, and the orientation of the room, the value of solar radiation escape rate varies from 8.64% to 10.33%, which indicates that the solar radiation escape phenomenon cannot be ignored in glass curtain wall buildings. The results can be used as a reference value of solar radiation escape rate for the correction of actual solar heat gain of buildings in different climate regions.

The solar heat gain is an important component of building cooling load, and its magnitude affects building energy consumption directly. In buildings with glass curtain walls, the window to wall rate is close to 1, so the amount of solar heat gain is huge, which directly determines the energy consumption level of a building’s air conditioning system. In fact, incident solar radiation can escape to the exterior through the transparent envelope, which cannot be ignored in buildings with glass curtain walls. This will cause changes in solar heat gain, so the solar heat gain coefficient (SHGC) needs to be corrected. In this paper, the heat transfer process of solar radiation in window shading systems is analyzed, and an amended calculation model for the SHGC is established. Multiple forms of windows and shading systems are selected and their SHGC-amended factor for rooms with different orientations under different standard calculation conditions in various countries is calculated. As the number of glass layers increases, the transmittance of the window gradually decreases, the reflectance and absorbance gradually increase, and the SHGC value decreases. The SHGC-amended factor decreases with an increasing escape rate, and the two can be approximated as a linear correlation. The weakening effect of shading on the solar heat gain of the buildings is overestimated. The SHGC-amended factor proposed in this paper can calculate building solar heat gain more accurately.