York International ZQ Series Installation Manual page 45

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 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 25 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 21 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 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 1.5 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 = 0.6 / .832 = 0.72 in.
Enter the blower table at 1,400 sCFM and static
pressure of 0.72 in. 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 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.
6. Review the BHP compared to the motor
options available. Select the appropriate
motor and, or drive.
INSTALLATION MANUAL ZQ SERIES 3 - 5 ton 60 Hertz R-410A
Johnson Controls Ducted Systems
- Add or deduct any additional static
resistance from Table 38.
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