York ZT SERIES, Техническое руководство

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5167821-YTG-K-1118
Johnson Controls Ducted Systems 75
Altitude and temperature correction for CFM, static pressure, and power
Use the information below to assist in the application of the product at altitudes at or exceeding 1000 feet above sea level.
The air flow rates listed in the standard blower performance tables are based on standard air at sea level. As the altitude or
temperature increases, the density of air decreases. In order to use the indoor blower tables for high altitude applications, certain
corrections are necessary.
A centrifugal fan is a constant volume device. This means that, if the RPM remains constant, the CFM delivered is the same
regardless of the density of the air. However, since the air at high altitude is less dense, less static pressure is generated and less
power is required than a similar application at sea level. Air density correction factors are shown in the
Altitude and temperature
correction factors table on page 75 and the following figure.
Use the examples below to 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, you must use the
airflow performance tables to determine the static pressure and BHP. We assume an air temperature of 70°F because no temperature data is
given. The
Altitude and temperature correction factors table on page 75 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 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 = 1.5 / .832 = 1.80 in.
Enter the blower table at 6000 CFM and static pressure of 1.8 in. The RPM listed is 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
BHP at 5,000 ft. = 0.7 x .832 = 0.58
Altitude and temperature correction factors
Air temp.
Altitude (ft.)
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
40 1.060 1.022 0.986 0.950 0.916 0.882 0.849 0.818 0.788 0.758 0.729
50 1.039 1.002 0.966 0.931 0.898 0.864 0.832 0.802 0.772 0.743 0.715
60 1.019 0.982 0.948 0.913 0.880 0.848 0.816 0.787 0.757 0.729 0.701
70 1.000 0.964 0.930 0.896 0.864 0.832 0.801 0.772 0.743 0.715 0.688
80 0.982 0.947 0.913 0.880 0.848 0.817 0.787 0.758 0.730 0.702 0.676
90 0.964 0.929 0.897 0.864 0.833 0.802 0.772 0.744 0.716 0.689 0.663
100 0.946 0.912 0.880 0.848 0.817 0.787 0.758 0.730 0.703 0.676 0.651
0.600
0.650
0.700
0.750
0.800
0.850
0.900
0.950
1.000
1.050
1.100
40 50 60 70 80 90 100
Air Temperature (ºF)
Correction Factor
Sea Level
1000 ft
2000 ft
3000 ft
4000 ft
6000 ft
7000 ft
8000 ft
9000 ft
10000 ft
5000 ft