Airflow Balancing - Lennox FCM 85 Installation, Operating And Maintenance

VENTILATION : AIRFLOW BALANCING
The actual resistance of ductwork systems is not always identical to 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.
SITE TEST AND MAINTENANCE
Measure the motor absorbed power.
If the absorbed power is greater and the pressure lower than the rated values, the ventilation system has a lower pressure
drop than anticipated. Reduce the flow by reducing the rpm. If the system resistance 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 by increasing the rpm. At the same time you will increase the absorbed power which may result
in having to increase the motor size.
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 13).
Min
Pulley
Pulley
Dia /
External
type
Min
Diameter
Dist
8450 /
120
D8450
20.2
110
8550 /
136
D8550
20.6
Table_1
The easiest way to determine the fan rotation speed is to
use a Tachometer. If not available the fan rpm can be
estimated using the following two methods.
st
1 Method with the pulley secured in place:
L
Measure the distance between the two outside faces of the
pulley.
Using table (1) the motor pulley actual diameter can be
estimated.
FLEXYII-IOM-0409-E
Max Nb of turns
Dia / from fully
Max closed to
Dist fully open
95 116 5
28 5
131 5
31.2 5
Actual diameter (DM) or distance between faces for a given number of
turns from fully closed with SPA belt in (mm)
0.5 1 1.5 2
114 112 110 108
21 21.8 22.5 23.3
129 127 125 123
21.6 22.7 23.8 24.8
2.5 3 3.5 4
106 103 101.3 99.2
24.1 24.9 25.7 26.4
121 118 116 114
25.9 26.9 28 29.1
Fig. 13
4.5 5 5.5
97.1 95 -
27.2 28 -
112 110 -
30.1 31 -
Page 36