Quasi-dynamic coupling method between CFD and building energy simulations for studying PCM-based radiant floor cooling systems

Although an indoor radiant floor cooling system that combines high thermal storage of phase change materials (PCMs) with underfloor nocturnal ventilation has been confirmed to be effective in the tropics, its optimal settings have not yet been clarified under naturally ventilated conditions. This study developed a quasi-dynamic coupling method between building energy simulation (BES) and computational fluid dynamics (CFD) to optimize the PCM-based floor cooling system for indoor thermal environments. The thermal hysteresis of PCMs was integrated into the quasi-coupling method to simulate the effect of PCMs on indoor temperatures. Conventional BES-based decoupling methods and the quasi-coupling method with three popular turbulent models in the Reynolds-averaged Navier-Stokes (RANS) equations for CFD were compared and validated with the measurement results in an experimental building in Indonesia. The results showed that quasi-couplings reproduced the PCM temperature (coefficient of determination: R 2 = 0.98; root mean squared error: RMSE = 0.4 °C). The shear-stress transport (SST) k − ω was the most accurate turbulence model for floor surface heat flux ( R 2 = 0.92, RMSE = 3.9 W / m 2 ). This proves that the quasi-coupling method is more accurate than the decoupling method in replicating the phase change of the PCMs, including its effects on thermal storage and hysteresis. Among the RANS models, SST k − ω was the best for solving near-floor heat convection. The quasi-dynamic coupling method showed that the PCM-based floor cooling system effectively modifies the near-floor air temperature because nocturnal heat dissipation is enhanced by underfloor ventilation and thermal storage of PCMs under naturally ventilated conditions.