5168274-BIM-I-1121
34
Johnson Controls Ducted Systems
Air Balance
Start the supply air blower motor. Adjust the resistances in both
the supply and the return air duct systems to balance the air
distribution throughout the conditioned space. The job
specifications may require that this balancing be done by
someone other than the equipment installer.
To check the supply air CFM after the initial balancing has been
completed:
1.
Remove the two 5/16” dot plugs from the blower motor and
the filter access panels shown in the Unit Dimensions Front
View (Figures 7 and 8) and Unit Dimensions Rear View
(Figure 9), respectively.
2.
Insert at least 8" of 1/4 inch tubing into each of these holes
for sufficient penetration into the air flow on both sides of
the indoor coil.
NOTE:
The tubes must be inserted and held in a position
perpendicular to the air flow so that velocity pressure
will not affect the static pressure readings.
3.
Using an inclined manometer, determine the pressure drop
across a dry evaporator coil. Since the moisture on an
evaporator coil may vary greatly, measuring the pressure
drop across a wet coil under field conditions would be
inaccurate. To assure a dry coil, the compressors should
be deactivated while the test is being run.
Figure 19: Pressure Drop Across A Dry Indoor Coil Vs.
Supply Air CFM For All Unit Tonnages
4.
Knowing the pressure drop across a dry coil, the actual
CFM through the unit can be determined from the curve in
Pressure Drop vs. Supply Air CFM Figure 19.
After readings have been obtained, remove the tubes and
reinstall the two 5/16” dot plugs that were removed in Step 1.
Table 13: RPM Selection
Size
(Tons)
Model
HP
Motor
Sheave
Blower
Sheave
6 Turns
Open
5 Turns
4 Turns
3 Turns
2 Turns
1 Turns
Fully
Open
Open
Open
Open
Open
Closed
-15
XA
5
1VP60
BK120
700
730
760
790
820
850
880
(15)
7.5
1VP60
BK100
845
885
925
960
1000
1035
1070
-20
XA
7.5
1VP60
BK110
765
800
835
870
900
935
965
(20)
10
1VP60
BK090
930
970
1010
1050
1090
1130
1170
Table 14: Indoor Blower Specifications
Size
(Tons)
Model
Motor
Motor Sheave
Blower Sheave
Belt
HP
RPM
Eff.
SF
Frame Datum Dia. Bore (in)
Model
Datum Dia. Bore (in)
Model
-15
(15)
XA
5
1750
0.895
1.15
184T
4.5 - 5.7
1-1/8
1VP60
11.4
1-3/16
BK120
BX81
7.5
1750
0.91
1.15
213T
4.5 - 5.7
1-3/8
1VP60
9.4
1-3/16
BK100
BX78
-20
(20)
XA
7.5
1750
0.91
1.15
213T
4.5 - 5.7
1-3/8
1VP60
10.4
1-3/16
BK110
BX78
10
1760
0.895
1.15
215T
4.5 - 5.7
1-3/8
1VP60
8.4
1-3/16
BK090
BX75
Table 15: Power Exhaust Specifications
Voltage
Motor
Motor
CFM @
0.1 ESP
HP
RPM
1
1. Motors are multi-tapped and factory wired for high speed.
QTY
LRA
FLA
MCA
208/230-1-60
3/4
1075
1
7.7
5.0
6.25
5250
460-1-60
3/4
1075
1
4.1
2.2
2.75
5250
575-1-60
3/4
1050
1
2.84
1.5
1.875
5250
Failure to properly adjust the total system air quantity
can result in extensive blower damage.
0.00
0.10
0.20
0.30
0.40
0.50
0.60
3000
4000
5000
6000
7000
8000
9000
10000
Pressure Drop
(IW
G)
Nominal Air Flow (CFM)
Pressure Drop Across a Dry Coil vs Supply Air CFM
XA-15
XA-20
