Altitude and Temperature Corrections

FORM 100.50-EG5 (108)

The information below should be used to assist in application of product when being applied at altitudes at or exceeding 1000 feet above sea level.

The airﬂow rates listed in the standard blower perfor- mance 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.

TABLE 7 – ALTITUDE-CORRECTION FACTORS

A centrifugal fan is a “constant-volume” device. This means that if the RPM remains constant, the CFM de- livered is the same regardless of the density of the air. However, since the air at high altitude is less dense, less static pressure will be generated and less power will be required than a similar application at sea level. Air-density-correction factors are shown in Table 7 and Figure 2.

Air						Altitude (feet)
Temp	0	1000	2000	3000	4000		5000	6000	7000	8000	9000	10000
40	1.060	1.022	0.986	0.95	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	0.73	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	0.88	0.848	0.817		0.787	0.758	0.730	0.703	0.676	0.651

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 7 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 7 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 / 0.832 = 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 blower table is 3.2.

This value must be corrected for elevation.

BHP at 5,000 ft = 3.2 x .832 = 2.66

JOHNSON CONTROLS

Altitude and Temperature Corrections

Air

Altitude (feet)

Temp