Air Flow Balancing - Lennox ROOFTOP FLEXY FCA Series Installation Operating & Maintenance Manual

AIR FLOW BALANCING

AIR FLOW BALANCING AIR FLOW BALANCING AIR FLOW BALANCING AIR FLOW BALANCING
The actual resistance of ductwork systems is not always the
same as the calculated theoretical values. To rectify this, it
may be necessary to modify the pulley and belt setting. To
this effect, the motors are fitted with variable pulleys.
TEST
You should already have measured the + ve pressure
experienced on fan discharge, as well as the pressure
experienced in the return duct to the fan.
Measure the motor absorbed power.
If the absorbed power is greater and the pressure lower than
the rated values, your system has a lower pressure drop than
anticipated. Reduce the flow. If the system resistence is
significantly lower than design, there is a risk that the motor
will overheat resulting in an emergency cut out.
If the absorbed power is lower and the pressure greater than
the rated values, your system has a higher pressure drop than
anticipated. Increase the flow. At the same time you will
increase the absorbed power which may result in having to fit
a larger motor.
To carry out the adjustment and to avoid a time-consuming
re-start, stop the machine and if necessary lock the main
switch.
First unscrew the 4 Allen screw(s) on the pulley (see figure
11).
Figure 12
Slacken the belts, then remove then (see § "BELT TENSION").
The flow can now be increased by turning the flange(s) to
move them closer (or alternatively, move them apart to reduce
the flow).
For two-groove pulleys, turn the flanges the same number of
turns.
If necessary, check the pulley diameter by measuring the outer
diameter of a belt positioned in the groove (figure 12).
Finally, replace and tension the belts before carrying out a
test. Re-check the absorbed power levels. Repeat the
operation until a satisfactory result has been achieved.
To minimise the number of operations, refer to the flow /
pressure charts on the following pages for the type of fans
used. With reference to the following example, you can
estimate your flow and thus calculate the necessary
adjustment.
ALLEN wrench 4
IOM / ROOF-TOP FLEXY™ Series - Page 15
Figure 11