Belt, rope and chain drives
In the interest of energy efficiency, it would be preferable for all fans to be arranged for direct drive. There are however, many reasons for incorporating an indirect drive through vee belts, ropes or chains etc. A degree of flexibility can be introduced which will cater for a system resistance which has been imprecisely calculated or which may vary through the lifetime of the fan.
These drives may allow the use of standard motors and also enable the manufacturer to cover the duty envelope with a reduced number of models.
It might be thought desirable to arrange all fans to be directly driven, i. e. with the fan impeller mounted directly on the shaft extension of the driving motor. There are however, a number of reasons for arranging for an indirect drive through belts, ropes or chains and suitable pulleys or sprockets.
From a user viewpoint, such drives give a degree of flexibility to the fan installation, permitting easy changes in the fan speed. If the system resistance as calculated proves to be incorrect, it is a relatively simple matter to make a change to the pulleys and/or belts. Thus a new fan speed to give the required duty can be arranged. Provided that the fan is mechanically suitable for any such increases then it is also possible to upgrade the performance over time. This might be necessary with extensions to a building and its associated HVAC system. In a mine ventilating plant for example, the duty could be increased as the mine working lengthened. There are many other reasons for changing the fan duty and the reader will be able to identify these for his particular industry.
From a manufacturer’s viewpoint, indirectly driven fans enable him to reduce the number of models, which he has to produce in order to provide an adequate cover of the duty range at a reasonable efficiency. Theoretically, provided it could be driven fast enough, one fan model could meet all fan duties, albeit in many cases at low energy efficiency.
Posted in Fans Ventilation A Practical Guide