Johnson Controls ZL Series Installation Manual page 47

Figure 24: Altitude/temperature correction factors
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 ftif the
airflow performance data is 3,000 cfm, 1.4 IWC and
2.0 bhp?
Solution: At an elevation of 5,000 ftthe indoor
blower will still deliver 3,000 cfm if the rpm is
unchanged. However, the Altitude correction 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. The Altitude/
Temperature Factors show the correction factor to
be 0.832.
Corrected static pressure = 1.4 x 0.832 = 1.16 IWC
Corrected bhp = 2.0 x 0.832 = 1.66
Example 2: A system, located at 5,000 feet of
elevation, is to deliver 3,000 cfm at a static pressure
of 1.4 in. 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 1.4 in. 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 = 1.4 in. / .832 = 1.68 in.
Enter the Supply Air Blower Performance Table at
3,000 cfm and static pressure of 1.68 in. The rpm
listed will be the same rpm needed at 5,000 ft.
Suppose that the corresponding bhp listed in
the table is 2.0. This value must be corrected for
elevation.
bhp at 5,000 ft = 2.0 x .832 = 1.66
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, and 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.
6. Review the bhp compared to the motor
options available. Select the appropriate
motor and, or drive.
Installation Manual ZL Series 7.5- 12.5 Ton 60 Hertz R-410A
Johnson Controls Ducted Systems
- Add or deduct any additional static
resistance from .
47