Numerical simulation of hybrid ventilation for underground subway depot with superstructures

This study proposed a hybrid ventilation mode for underground subway depot with superstructures and described the construction of a calculation model for estimating the smoke-exhaust efficiency of ventilation systems in such buildings. The hybrid ventilation system consisted of natural ventilation, a flow deflector, and mechanical fans. The smoke-layer height, smoke temperature, gas-flow routes, and velocity distribution under the ceiling were recorded, and the smoke-exhaust efficiencies of the three ventilation modes were calculated and compared. The results revealed a lower ceiling temperature in hybrid ventilation than in mechanical ventilation or natural ventilation systems, with no smoke accumulation in the bottom layer or interlayer. Therefore, the thickness and stability of the smoke layer was determined to be more desirable in hybrid ventilation than in the other two ventilation systems. Gas-flow routes demonstrated that air from outside flowed in through the side window along the ceiling of the bottom layer to the exhaust fan. The dispersion of hot smoke was thus impeded, and smoke was entrained into the fan. The smoke-exhaust efficiencies of hybrid ventilation and mechanical ventilation systems were similar, and both were higher than that of natural ventilation.