Optimization of the boundary condition treatment for coupled BES–CFD simulation

The coupling of building energy simulation (BES) and computational fluid dynamics (CFD) is a powerful approach for the accurate prediction of indoor thermal environments. However, the high computational cost and complexity of CFD often limit its application in routine design workflows. To address these limitations, this study proposes and validates a lightweight yet accurate BES–CFD coupling method that minimizes dependence on CFD while maintaining high predictive reliability. The core contribution lies in the optimization of the boundary condition treatment within the CFD–BES co-simulation process. Specifically, this involves the dynamic calculation of the convective heat transfer coefficient (CHTC) using CFD-derived free-stream velocities and a semi-empirical correlation model based on dimensionless numbers. Such an approach avoids direct CHTC extraction from CFD and reduces data exchange requirements while preserving key physical interactions. The performance of this method is rigorously validated under both free-running and air-conditioned conditions. The results demonstrate that omitting the near-wall air temperature difference, a variable used in previous coupling frameworks, has negligible impact on accuracy. In periods or environments characterized by rapid temperature fluctuations, increasing the coupling frequency is necessary to maintain predictive accuracy. In addition, the method enables the BES to produce results comparable to those of the BES–CFD coupling in thermal environments dominated by natural convection. These findings highlight the potential of the proposed approach as a reliable and computationally efficient tool for high-fidelity BESs.