403134-YIM-E-0311
36
Johnson Controls Unitary Products
The examples below will assist in determining the airflow
performance of the product at altitude.
Example 1:
What are the corrected CFM, static pressure, and
BHP at an elevation of 5,000 ft. if the blower performance data
is 1,400 CFM, 0.6 IWC and 0.67 BHP?
Solution:
At an elevation of 5,000 ft. the indoor blower will still
deliver 1,400 CFM if the rpm is unchanged. However, Table 13
must be used to determine the static pressure and BHP. Since
no temperature data is given, we will assume an air temperature
of 70°F. Table 12 shows the correction factor to be 0.832.
Corrected static pressure = 0.6 x 0.832 = 0.499 IWC
Corrected BHP = 0.67 x 0.832 = 0.56
Example 2:
A system, located at 5,000 feet of elevation, is to
deliver 1,400 CFM at a static pressure of 1.5". Use the unit
blower tables to select the blower speed and the BHP
requirement.
Solution:
As in the example above, no temperature
information is given so 70°F is assumed.
The 1.5" static pressure given is at an elevation of 5,000 ft. The
first step is to convert this static pressure to equivalent sea level
conditions.
Sea level static pressure = 0.6 / .832 = 0.72"
Enter the blower table at 1,400 sCFM and static pressure of
0.72". The rpm listed will be the same rpm needed at 5,000 ft.
Suppose that the corresponding BHP listed in the table is 0.7.
This value must be corrected for elevation.
BHP at 5,000 ft. = 0.7 x .832 = 0.58
Drive Selection
1.
Determine side or bottom supply air duct application.
2.
Determine desired airflow.
3.
Calculate or measure the amount of external static pressure.
4.
Using the operating point determined from steps 1, 2 & 3, locate this point on the appropriate supply air blower performance
table. (Linear interpolation may be necessary.)
5.
Noting the RPM and BHP from step 4, locate the appropriate motor and/or drive on the RPM selection table.
6.
Review the BHP compared to the motor options available. Select the appropriate motor and/or drive.
7.
Review the RPM range for the motor options available. Select the appropriate drive if multiple drives are available for the
chosen motor.
8.
Determine turns open to obtain the desired operation point.
Example
1.
2200 CFM
2.
1.6 iwg
3.
Using the supply air blower performance table below, the following data point was located: 1478 RPM & 1.82 BHP.
4.
Using the RPM selection table below, Size X and Model Y is found.
5.
1.82 BHP exceeds the maximum continuous BHP rating of the 1.5 HP motor. The 2 HP motor is required.
6.
1478 RPM is within the range of the 2 HP drive.
7.
Using the 2 HP motor and drive, 2.5 turns open will achieve 1478 RPM.
Example Supply Air Blower Performance
Air Flow
(CFM)
Available External Static Pressure - IWG
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
RPM BHP RPM BHP RPM BHP RPM BHP RPM BHP RPM BHP RPM BHP RPM BHP RPM BHP RPM BHP
Field Supplied
Drive
Standard Drive Option
HIgh Static Drive Option
2000
907
1.00
990
1.07
1070
1.15
1146
1.23
1220
1.31
1291
1.40
1359
1.49
1425
1.58
1488
1.68
1550
1.77
2200
960
1.24
1043
1.31
1123
1.39
1199
1.47
1273
1.55
1344
1.64
1412
1.73
1478
1.82
1541
1.92
1602
2.01
2400
1015
1.51
1099
1.59
1178
1.66
1255
1.74
1329
1.83
1400
1.92
1468
2.01
1534
2.10
1597
2.19
1658
2.29
2600
1074
1.83
1157
1.90
1237
1.98
1314
2.06
1387
2.14
1458
2.23
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Table X: RPM Selection
Size
(Tons)
Model
HP
Max
BHP
Motor
Sheave
Blower
Sheave
5 Turns
Open
4 Turns
Open
3 Turns
Open
2 Turns
Open
1 Turn
Open
Fully
Closed
X
Y
1.5
1.73
1VL44
AK56
930
995
1060
1130
1195
1260
2
2.3
1VP56
AK56
1325
1395
1460
1525
1590
1660
