Thermal Comfort Analysis of Displacement Ventilation System Coupled with Passive Chilled Beams
Thermal comfort, displacement ventilation, passive chilled beam, coupled system
Displacement ventilation (DV) has been widely studied in literature, and is currently used in enclosed environments like office buildings. Although DV has been shown to be able to provide better indoor air quality in the occupied zone than conventional mixing ventilation (MV), its capability of removing heat is usually limited. Since it supplies air directly to occupied zone, the temperature of supply air is inevitably higher than that in MV. Meanwhile, passive chilled beams (PCB), which cool occupied space by running chilled water through beams at ceiling level, has been reported to have a high heat removal capability, and can save energy. Thus, a coupled system that combines both DV and PCB has the potential of keeping the advantages of both systems, and was explored in detailed by using experimental and simulation methods. This study focused on investigating the thermal performance of a coupled system of DV and PCB, and compared it with a corresponding DV-only system. Experiment was carried out in a full-scale environmental chamber to measure air velocity and temperature at various locations in the chamber. Moreover, a computational fluid dynamics (CFD) model was used to simulate the air velocity and temperature distributions, which were then validated by the measured data. With the validated CFD model, thermal comfort in the occupied zone were analyzed with the coupled system and the DV-only system. Thermal comfort level was presented by the predicted mean vote (PMV), and percentage dissatisfied people due to draft (PD). The results indicated that the PCB can help to cool down the temperature in the room, and the air temperature stratification was still maintained in most regions. However, due to the cold downward jet generated by the PCB, the region under the PCB had a higher air velocity and lower temperature than that with DV-only system. This resulted in a local zone with less thermal comfort. Based on reported results, this study provided preliminary guidelines for designing of the coupled system with acceptable thermal comfort in occupied zone.