General "Cooling Fan Manufacturer" use AC fan, the choice of the rated air volume, usually exceed the amount of wind actual needs, but also because the process is necessary to change the amount of wind in operation, and the current "Cooling Fan Manufacturer" using baffles to regulate the amount of wind adjustment method is more common, although the method is simple, but in fact is to achieve the purpose of regulation by artificially increasing the resistance of the way, "Cooling Fan Manufacturer" this throttle method wasting a lot of energy, recycling which will receive a portion of the power loss large energy savings.