User's Manual

1068152-YTG-L-0815
Johnson Controls Unitary Products 77
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 airflow performance data
is 3,000 CFM, 1.4 IWC and 2.0 BHP?
Solution: At an elevation of 5,000 ft. the 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". 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" 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" / .832 = 1.68"
Enter the Supply Air Blower Performance Table at 3,000 CFM
and static pressure of 1.68". 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