Indoor airflow and contaminant transport in a room with coupled displacement ventilation and passive-chilled-beam systems

Displacement ventilation (DV) is now widely used in enclosed environments such as office buildings. Although DV can provide good indoor air quality, its ability to remove heat is limited. On the other hand, passive chilled beams (PCBs) can have a high heat-removal capability. Therefore, this investigation evaluated a coupled DV and PCB system in terms of air quality and thermal comfort. This study first conducted experiments in a full-scale environmental chamber with the DV-PCB system to obtain airflow velocity, temperature and contaminant concentration data. A computational fluid dynamics (CFD) model was developed to simulate air distribution in an enclosed environment with the DV-PCB system, which was then validated by the measured data. The validated CFD model was employed to analyze thermal comfort and indoor air quality in the enclosed environment with the DV-PCB coupled system using four indices: vertical temperature gradient, draft rate, normalized contaminant concentration and age of air. The results indicate that PCBs were quite effective in reducing the temperature gradient created by DV. However, the cold downward jet generated by the PCBs created a "zone with high draft" under the PCBs, and the magnitude of the draft was strongly correlated with the cooling load removed by the PCBs and the size of the PCBs. In addition, the downward air jet generated by the PCBs could disrupt the contaminant stratification and increase the mean age of air in the occupied zone.