Airflow Balancing - Lennox BAC020SNM 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 figure11).
Min
Pulley
Pulley Dia /
External
type
Min
Diameter
Dist
95
8450 /
120
D8450
20.2
110
8550 /
136
D8550
20.6
Table_2
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 (2) the motor pulley actual diameter can be
estimated
BALTIC R410A-IOM-0708-E
Max Nb of turns
Actual diameter (DM) or distance between faces for a given number of turns
Dia / from fully
Max closed to
0.5
Dist fully open
116 5 114
28 5 21
131 5 129
31.2 5 21.6 22.7 23.8 24.8 25.9 26.9
from fully closed with SPA belt in (mm)
1 1.5 2 2.5
112 110 108 106
21.8 22.5 23.3 24.1 24.9
127 125 123 121
3 3.5 4 4.5
101.3 99.2 97.1
103
25.7
26.4 27.2
118 116 114 112 110
28 29.1 30.1
Fig. 41
5 5.5
95 -
28 -
-
31 -
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