​Methods for Adjusting Airflow in Coaxial Duct Centrifugal Fans

Methods for Adjusting Airflow in Coaxial Duct Centrifugal FansHow is the airflow of a coaxial duct centrifugal fan adjusted? There are various methods for adjusting the airflow of a coaxial duct centrifugal fan, such as adjusting the air inlet and air valves, adjusting the vortex air valve, adjusting the inlet vanes, adjusting the movable blades, and adjusting the speed. Since adjustment methods vary depending on the type of coaxial duct centrifugal fan, energy-saving effects also differ significantly. 1. Adjusting the air valve on a coaxial duct centrifugal fan is not intended to alter the fan’s characteristics but rather to modify the characteristics of the ductwork system. The airflow adjustment range typically covers all operating conditions below the fan’s rated performance curve. To alter the characteristics of the ductwork, the resistance of the ductwork is artificially increased. When the air valve is closed, the additional resistance generated by the valve consumes pressure drop, resulting in reduced adjustment efficiency. When adjusting the inlet valve—in cases where ductwork is configured on the fan’s suction side—the adjustment principle is the same as that of the air valve; however, when ductwork is configured on the fan’s discharge side, the adjustment is more efficient because it changes the inlet pressure of the coaxial duct centrifugal fan by altering its performance curve. Adjustment using a volume damper alters the fan’s characteristics by changing the fan’s cross-sectional area. Compared to reducing airflow, the change in power consumption is minimal, and the energy-saving effect is also limited. In principle, both of these adjustment methods can be used under all operating conditions below the rated curve and can shift the surge point toward lower flow rates. Therefore, they are widely used in coaxial duct centrifugal fans. 2. Adjustment of coaxial duct centrifugal fans is achieved by adjusting the vanes to change the direction of airflow into the impeller, thereby altering the fan’s performance curve. By sequentially adjusting the air intake flow, all operating conditions below the performance curve can be achieved when the angle of the inlet guide vanes is zero. Adjusting the inlet airflow through negative deflection may increase the fan’s pressure and flow rate, but the adjustment range is limited. Because the inlet vane offers a wide adjustment range, high economic efficiency, and the ability to adjust automatically, it is widely used in coaxial duct centrifugal fans. The adjustment characteristics of the inlet vane and coaxial duct centrifugal fans are superior to those of rear-flow fans or rear-axial duct centrifugal fans. The single-point efficiency of coaxial duct centrifugal fans is lower than that of rear-flat fans or coaxial duct centrifugal fans; however, in variable air volume (VAV) systems, coaxial duct centrifugal fans consume nearly the same amount of power. They offer excellent energy-saving characteristics. Furthermore, coaxial duct centrifugal fans are compact, lightweight, and operate at low speeds, making them widely used in VAV systems.