Specifications
267233-YIM-B-0507
32 Unitary Products Group
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 6,000 CFM, 1.5 IWC and 4.0 BHP?
Solution: At an elevation of 5,000 ft. the indoor blower will still
deliver 6,000 CFM if the rpm is unchanged. However, Table 10
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 = 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 desired airflow.
2. Calculate or measure the amount of external static pressure.
3. Using the operating point determined from steps 1 & 2, locate this point on the appropriate supply air blower performance table.
(Linear interpolation may be necessary.)
4. Noting the RPM and BHP from step 3, locate the appropriate model and drive on the RPM selection table.
5. Review the BHP compared to the motor options available. Select the appropriate motor.
6. Review the RPM range for the motor options available. Select the appropriate drive if multiple drives are available for the
chosen motor.
7. Determine turns open to obtain the desired operation point.
Example
1. 19000 CFM
2. 5.4 iwg
3. Using the supply air blower performance table below, the following data point was located: 1150 RPM & 36 BHP.
4. Using the RPM selection table below, Size X and Model Y is found.
5. 36 BHP exceeds the maximum continuous BHP rating of the 30 HP motor. The 40 HP motor is required.
6. 1150 RPM is within the range of the 30 & 40 HP drives, but step 5 requires the 40 HP motor.
7. Using the 40 HP motor and drive, 5.5 turns open will achieve 1150 RPM.
Example Supply Air Blower Performance
Air Flow
(CFM)
Available External Static Pressure - IWG
3.0 3.4 3.8 4.2 4.6 5.0 5.4 5.8 6.2 6.6
RPM BHP RPM BHP RPM BHP RPM BHP RPM BHP RPM BHP RPM BHP RPM BHP RPM BHP RPM BHP
30 HP & Field Supplied Drive Standard 30 HP & Drive Alternate 40 HP & Drive
18000 800 10.00 850 14.00 900 18.00 950 22.00 1000 26.00 1050 30.00 1100 34.00 1150 38.00 1200 42.00 1250 46.00
19000 850 12.00 900 16.00 950 20.00 1000 24.00 1050 28.00 1100 32.00 1150 36.00 1200 40.00 1250 44.00 1300 48.00
20000 900 14.00 950 18.00 1000 22.00 1050 26.00 1100 30.00 1150 34.00 1200 38.00 1250 42.00 1300 46.00 1350 50.00
21000 950 16.00 1000 20.00 1050 24.00 1100 28.00 1150 32.00 1200 36.00 1250 40.00 1300 44.00 1350 48.00 1400 52.00
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
30 34.50 1VL51 BK99 1000 1025 1045 1060 1110 1150 N/A
40 46.00 1VL63 BK67 1125 1175 1250 1325 1400 1475 N/A