The influence of roof obstacles on the performance of natural smoke ventilators in wind conditions

This paper examines the performance of natural ventilators shielded with either external aerodynamic elements or obstacles, that are found on most of modern rooftops. In past studies the effect of shielding on the performance of natural vents was not investigated in depth. In this study, after a calibration of the numerical model, ten series of CFD simulations were performed. Nine types of obstacles (plus one reference case), four wind velocities and seven wind attack angles (280 simulations) were considered. The aerodynamic elements placed close to the vent significantly improved the ventilator performance described with the discharge coefficient Cv. In contrary, the roof obstacles such as ducts or large ventilation units had neutral or negative effect on the performance of vents. It was also found, that a natural ventilator may have a positive shielding effect on the next natural ventilator located on the roof, which could lead to the increase of the whole system performance in the building. The results of this study show, that the external aerodynamic elements, and in some cases even natural roof obstacles, may be used to shield the natural vents from the possible negative influence of wind.