1061903-XIM-A-0713
Johnson Controls Unitary Products 27
Corrected static pressure = 1.5 x 0.832 = 1.248 IWC
Corrected BHP = 4.0 x 0.832 = 3.328
Example 2: A system, located at 5,000 feet of elevation, is to
deliver 6,000 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 = 1.5 / .832 = 1.80"
Enter the blower table at 6000 sCFM and static pressure of
1.8". The rpm listed will be the same rpm needed at 5,000 ft.
Suppose that the corresponding BHP listed in the table is 3.2.
This value must be corrected for elevation.
BHP at 5,000 ft. = 3.2 x .832 = 2.66
Drive Selection
1. Determine side or bottom supply 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. 6800 CFM
2. 2.0 iwg
3. Using the supply air blower performance table below, the following data point was located: 1020 RPM & 5.92 BHP.
4. Using the RPM selection table below, Size X and Model Y is found.
5. 5.92 BHP exceeds the maximum continuous BHP rating of the 5.0 HP motor. The 7.5 HP motor is required.
6. 1020 RPM is within the range of the 7.5 HP drives.
7. Using the 7.5 HP motor and drive, 3.5 turns open will achieve 1020 RPM.
Example Supply Air Blower Performance
Air Flow
(CFM)
Available External Static Pressure - IWG
0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6
RPM BHP RPM BHP RPM BHP RPM BHP RPM BHP RPM BHP RPM BHP RPM BHP RPM BHP RPM BHP RPM BHP RPM BHP
Standard
5 HP & Field
Supplied
Drive
Standard 5 HP & Drive High Static 7.5 HP & Drive
6400 719 2.55 756 3.03 792 3.49 828 3.92 864 4.32 899 4.67 933 4.98 966 5.24 998 5.45 1028 5.59 1056 5.67 1083 5.68
6800 742 3.02 778 3.51 814 3.97 850 4.40 886 4.79 921 5.15 955 5.46 988 5.72 1020 5.92 1050 6.07 1078 6.15 1105 6.16
7200 765 3.54 802 4.03 838 4.49 874 4.92 910 5.32 945 5.67 979 5.98 1012 6.24 1044 6.44 1074 6.59 1102 6.67 1129 6.68
7600 790 4.11 827 4.60 863 5.06 899 5.49 935 5.88 970 6.24 1004 6.55 1037 6.81 1069 7.01 1099 7.16 1127 7.24 1154 7.25
7.5 HP & Field
Supplied Drive
Table X: RPM Selection
Size
(Tons)
Model HP
Max
BHP
Motor
Sheave
Blower
Sheave
6 Turns
Open
5 Turns
Open
4 Turns
Open
3 Turns
Open
2 Turns
Open
1 Turn
Open
Fully
Closed
XY
5 5.75 1VP60 BK110 730 765 800 835 870 905 N/A
7.5 8.63 1VP60 BK090 905 950 990 1035 1075 1120 N/A
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