349218-JIM-F-0512
44
Johnson Controls Unitary Products
Figure 20: 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 20.
After readings have been obtained, remove the tubes and
reinstall the two 5/16” dot plugs that were removed in Step 1.
NOTE:
De-energize the compressors before taking any test
measurements to assure a dry indoor coil.
Supply Air Drive Adjustment
The RPM of the supply air blower will depend on the required
CFM, the unit accessories or options and the static resistances
of both the supply and the return air duct systems. With this
information, the RPM for the supply air blower and the motor
pulley adjustment (turns open) can be determined from the
Blower Performance Data Tables.
High speed drive accessories (containing a smaller blower
pulley and a shorter belt) are available for applications requiring
the supply air blower to produce higher CFM's and/or higher
static pressures. Use Model 1LD0460 for 15 ton units, Model
1LD0417 for 17.5 and 20 ton units, and Model 1LD0435 for 25
ton units. Refer to the Blower Motor and Drive Data Table 18.
Note the following:
1.
The supply air CFM must be within the limitations shown in
the Blower Performance Tables 15 and 16.
2.
Pulleys can be adjusted in half turn increments.
3.
The tension on the belt should be adjusted as shown in the
Bet Adjustment, Figure 18.
4.
Tighten blower pulley and motor sheave set screws after
any adjustments. Re-check set screws after 10-12 hours
run time recommended.
Failure to properly adjust the total system air quantity
can result in extensive blower damage.
Pressure Drop Across A Dry Indoor Coil VS Supply Air CFM
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
4000
5000
6000
7000
8000
9000
10000
11000
12000
Nominal Air Flow (CFM)
Pressure Drop (IWG)
Belt drive blower systems MUST be adjusted to the
specific static and CFM requirements for the application.
The belt drive blowers are NOT set at the factory for any
specific static or CFM. Adjustments of the blower speed
and belt tension are REQUIRED. Tighten blower pulley
and motor sheave set screws after these adjustments.
Re-checking set screws after 10-12 hours run time is
recommended.
Additional Static Resistance
Size
(Tons)
Model
CFM
Cooling Only
1
1. Add these values to the available static resistance in the respective Blower Performance Tables.
Economizer
2
3
2. Deduct these values from the available external static pressure shown in the respective Blower Performance Tables.
3. The pressure drop through the economizer is greater for 100% outdoor air than for 100% return air. If the resistance of the
return air duct is less than 0.25 IWG, the unit will deliver less CFM during full economizer operation.
Electric Heat kW
18
36
54
72
J15
(15)
ZJ
4500
0.10
0.10
0.10
0.10
0.20
0.20
6000
0.10
0.10
0.10
0.20
0.30
0.40
7500
0.10
0.10
0.10
0.30
0.40
0.60
J18 (17.5)
J20 (20)
J25 (25)
ZJ
6000
0.10
0.10
0.10
0.10
0.20
0.20
7500
0.10
0.10
0.10
0.20
0.30
0.40
9000
0.15
0.15
0.10
0.30
0.40
0.60
10500
0.15
0.15
0.20
0.40
0.60
0.80
12000
0.20
0.20
0.30
0.50
0.70
0.90
