Document 6RXvY83J9JqYao21nDwDewrX1

590 CHAPTER 32 1948 Guide FAN DESIGNATIONS Fig. 5 shows the names and definitions of types of fans recently dis tributed by the National Association of Fan Manufacturers 2. In order, to prevent misunderstandings, which , may cause delays and losses, the arrangements, and designations adopted by the National Association of Fan Manufacturers8 and indicated in Figs. 6 and 7 should be"used. FAN CONTROL In some heating and ventilating systems it is desirable to vary the volume of air handled by the fan, and this may be accomplished by a number of methods. Where the change is made infrequently, the pulley or sheave on the driving motor, or fan, may be changed to vary the speed of the fan and alter the air volume. Dampers may be placed in the duct system to vary the volume. Variable speed pulleys or transmissions, such as fan belt change boxes, electric or hydraulic couplings, may be used to vary the fan speed. Variable speed motors and variable fan inlet vanes may also be used to adjust the fan volume. All of these methods will give control. From a power consumption standpoint, a reduction of the fan speed is most efficient. Inlet vanes save some power and dampers save the least. From the standpoint of first cost, dampers usually are the lowest in cost. In some installations adjustments of volume are desirable Fig. 5. Names and Definitions of Types of Fans Propeller Fan A propeller fan consists of a propeller or disc type wheel within a mounting ring or plate and including driving mecha nism supports either for belt drive or direct connection. Tubeaxial Fan A tubeaxial fan consists of a propeller or disc type wheel within a cylinder and including driving mechanism supports either for belt drive or direct connection. Vaneaxial Fan A vaneaxial fan consists of a disc type wheel within a cylinder, a set of air guide vanes located either before or after the wheel and including driving mechanism supports either for belt drive or direct connection. Centrifugal Fan A centrifugal fan consists of a fan rotor or wheel within a scroll type of housing and including driving mechanism sup ports either for belt drive or direct connection; Fans 591