Exploration of non-linear influence mechanisms of traditional courtyard forms on thermal comfort in winter and summer: A case study of Beijing, China

Traditional courtyard architecture offers superior climate regulation function through its unique enclosed spatial form, which is significant in mitigating global warming, urban heat islands, and promoting sustainable urban development. However, existing research has not thoroughly explored the comprehensiveness of climate zones, the systematicity of morphological elements, and the non-linear mechanisms. This study investigates traditional courtyards in Beijing using an integrated approach combining field survey, ENVI-met numerical simulation, machine learning, and SHAP interpretation methods to reveal the non-linear influence mechanisms of courtyard morphology on thermal comfort. The results show that: 1) The XGBoost model achieves high accuracy in fitting study data, with R2 values of 0.99 and 0.85 for training and test sets, respectively; 2) The contribution of the built environment to thermal comfort in winter and summer (70 % and 52 %, respectively) is significantly higher than that of the natural environment, especially in winter; 3) Morphological features affect thermal comfort in winter and summer in a mostly synergistic way, but there are differences in the curve trend, threshold distribution, and the range of benefits, e.g., the benefits of Sky View Factor (SVF) on thermal comfort in winter and summer can be up to 2.0 degrees C and 1.5 degrees C, respectively; (4) The enhancement of thermal comfort of traditional courtyards in Beijing can be achieved through parameters such as aspect ratio (HAR), shape index (SI), and building coverage (BDG), but the implementation process is susceptible to limitations such as cultural values. The conclusions of this study make up for the shortcomings of current research areas, influencing elements, and research methods and help promote the sustainable development of courtyards in similar climatic and cultural contexts.