Influence of Microclimate on Human Thermal and Visual Comfort in Urban Semi-Underground Spaces

Semi-underground spaces are integral to urban infrastructure yet their impact on human comfort, particularly in cold regions, remains inadequately investigated. The purpose of this study is to evaluate the comprehensive environmental quality of semi-underground spaces and its impact on human comfort in the cold-climate context of China. Representative transportation and workspace types, including underpasses, libraries, laboratories, and photography studios, were examined during winter and summer. An integrated methodology comprising field measurements, questionnaires, and numerical simulations was employed to analyze thermal, visual, and air quality conditions. Results reveal compounded environmental challenges: elevated temperature-humidity levels and equipment heat gains cause thermal discomfort; CO2 and TVOC accumulation deteriorates air quality; and lighting is often insufficient or imbalanced. Furthermore, distinct functional spaces require tailored management strategies, such as balanced ventilation for transit areas and intelligent thermal control for laboratories. These findings provide a theoretical foundation and practical guidance for the performance-oriented design and optimization of semi-underground spaces in high-density urban environments.