Johnson Controls ZZ Series, Installation Manual

Page: 37 / 69

5834853-YIM-B-0320
Johnson Controls Ducted Systems 37
Figure 20: Belt Adjustment
Altitude and Temperature Correction for CFM, Static
Pressure and Power.
The information below should be used to assist in application of
product when being applied at altitudes at or exceeding 1000
feet above sea level.
The air flow rates listed in the standard blower performance
tables are based on standard air at sea level. As the altitude or
temperature increases, the density of air decreases. In order to
use the indoor blower tables for high altitude applications,
certain corrections are necessary.
A centrifugal fan is a "constant volume" device. This means
that, if the rpm remains constant, the CFM delivered is the
same regardless of the density of the air. However, since the air
at high altitude is less dense, less static pressure will be
generated and less power will be required than a similar
application at sea level. Air density correction factors are shown
in Table 11 and Figure 21.
Belt Tightening
Slots
(1/4” X 1/2”)
Span Length
Defl. Force
Motor Mount
Slide Plate
Motor Mounting
Plate
Motor
Removed
C
A B
A
B
Motor Mounting
Plate
Motor Mounting
Slide Plate
Procedure for adjusting belt tension:
1. Loosen the three nuts (A and B on side and C on
back) of motor mount slide plate.
2. Adjust tension by placing a flat heat screwdriver into
the belt tightening slots (1/4" X 1/2") in the motor
mount slide plate and applying pressure against the
motor mounting plate. See Figure 21.
3. Tighten the three loosened nuts (A, B and C).
4. Determine the deflection distance from normal
position, use a straight edge from sheave to sheave
as reference line. Use belt tension checker to apply a
perpendicular force to the belt at the midpoint of the
span as shown. Deflection distance of 4mm (5/32") is
obtained.
5. After adjustments are completed re-tighten nuts (A, B
and C).