Centrifugal fans are usually available in several arrangements, which is the position of the motor against the fan. The three main criteria may influence your choice in determining the optimal type of arrangement for your fan:
1. Fan performance, including temperature, airstream contents and so on,
2. Drive type, including belt or direct drive,
3. Size/location, including the space the unit takes up, access to various components on the fan and so on.
Among the three criteria, the first criterion shall be taken the most seriously, as the performance is what the fan aims to deliver in the end. Without desired performance, nothing is obtained. Fan performance shall come first before trying every possible means to put it in the required space.
Belt Drive Arrangement
From the perspective of fan performance, the fan with arrangement 1 has the greatest flexibility. As the bearings are located outside the airstream, motor frame size is unlimited. It means that the motor choice will be restricted only by the fan’s highest speed and motor service factor to be desired. Arrangement 1 enables the customer to choose among four motor locations as shown below: W, X, Y, and Z. It can be put in a desired position that makes inspection and maintenance easy and the discharge ductwork will not be interfered with.
There is a drawback of arrangement 1. It is the largest space required for the unit to be installed. This may entail more investment with the growing square footage for the ventilation equipment. As the motor is installed independent of the fan, arrangement 1 requires a structural base or some other elements to connect them. It is something that may be forgotten on fan applications. So it is necessary to check again the equipment package to make sure one is provided.
Both arrangement 3 fans and arrangement 1 fans need a structural base as the motor is installed independent of the fan. Also, there are flexible motor locations as well as unlimited motor frame size. One of the drawbacks of arrangement 3 fans is the position of the bearings.
For arrangement 3 fans, one bearing is placed on each wheel side. It creates a stable mount for the wheel and produces the narrowest fan design for a given wheel size. If used with a split housing, arrangement 3 is very suitable for retrofit applications when the fan needs to be moved about in narrow hallways, tight stairwells, or smaller personnel elevators.
The drawback of the arrangement 3 is that there is at least one bearing located in the airstream. It means the ability of the fan to be used in applications handling clean air below 180 degrees F is limited. For an arrangement 3 fan of a single width that has usually a ducted inlet, it may be a problem for the maintenance or replacement of the bearing located in the airstream.