Experimental study on air extraction performance of novel rooftop natural ventilators

Abstract

The air extraction performance of novel rooftop natural ventilators was experimentally investigated and compared to the conventional turbine ventilator. The newly developed ventilator integrates a vertical-axis wind turbine with a static ventilator, where the wind turbine, equipped with 8C-type rotors and six rotor guide vanes, serves to drive the rotation of the static ventilator. The static ventilator is an exhaust cowl with curved guide vanes inside. The wind turbine, including 8C-rotors and 6 flat guide vanes, is 10 cm in height with a diameter of 21 cm. The dimensions of static ventilation are 7 cm in height, and 26 cm and 21 cm in bottom and top diameters, respectively, with curved guide vanes inside. Various heights of guide vanes (0.5 and 3 cm) and numbers of guide vanes (0, 6 and 12) were investigated. An open wind tunnel system was used to simulate the condition where the wind blows over the rooftop ventilator. The ventilator air extraction rates were determined using the mean air velocities, measured using a hot-wire anemometer at an open slot in a ventilation pipe connected to the ventilator. The results indicated that the rotating and non-rotating novel ventilators exhibited superior air extraction rates at most tested wind speeds compared to the rotating conventional turbine ventilator. The curved guide vanes inside the static ventilator played the most important role in the air extraction rate. This study suggests that a static ventilator with an adequate guide-vane design may be more suitable for rooftop ventilation than a conventional turbine ventilator.