A study on bidirectional coupling simulation methods for thermal comfort in cabin environments under solar radiation conditions

Accurate thermal comfort simulation methods can significantly enhance both the effectiveness and efficiency of cabin thermal comfort design. However, current thermal comfort simulation methods often overlook the interaction between environmental factors and human physiological responses, particularly in the context of cabin thermal comfort simulations under solar radiation conditions, where there is a lack of standardized approaches. This study establishes a bidirectional coupling simulation framework that incorporates the interaction between environmental factors and human physiological regulation. The proposed method integrates CFD, thermophysiological models, and thermal psychological models. Specifically, the thermophysiological component of the framework compares three models: the JOS-3 model, the Fiala model, and the TCM model. The thermal psychological model utilizes the Berkeley model. The computational accuracy of the proposed bidirectional coupling simulation framework is evaluated under both steady-state office environments and transient outdoor parking cases. Furthermore, the simulation results are compared with those obtained from three uncoupled thermal comfort evaluation models—PMV, DTS, and Lai's model—under transient environmental conditions. The results demonstrate that the CFD-JOS3-Berkeley bidirectional coupling simulation method achieves the lowest prediction error for both local and mean skin temperatures. Its overall thermal sensation prediction accuracy is superior to other thermal comfort evaluation methods, improving by 5.16, 3.91 and 3.75 times compared to non-coupled thermal comfort evaluation models PMV, DTS, and Lai's. The study further highlights that coupled simulation calculations should prioritize the use of local thermal insulation values as inputs to human thermophysiological models, with special emphasis on core body regions and exposed skin areas such as the head, hands, and lower legs in summer conditions. This research establishes a high-precision thermal comfort simulation method suitable for transient cabin environments under solar radiation, offering a reliable tool for evaluating cabin thermal comfort.