ENGINEERING MANUAL OF AUTOMATIC CONTROL
GENERAL ENGINEERING DATA
489
AIRFLOW DATA
FAN RATINGS
Fans are rated at standard conditions of air: 0.075 lb/ft
3
and 70F at sea level. Therefore, pressures corrected to standard conditions
must be used when selecting fans from fan rating tables or curves. Table 29 gives correction factors.
Pressure at operating conditions x factor = pressure at standard conditions.
Horsepower at standard conditions ÷ factor = horsepower required at operating conditions
CAUTION: Size motor for highest density (lowest factor) condition at which it is expected to operate.
Table 29. Altitude and Temperature Correction Factors.
EXAMPLE:
Air at 1000 ft and 140F: 28.86 in. Hg x 1.17 = 33.77 in. Hg
Altitude with Barometric Pressure
Temp Ft 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
F in. Hg 29.92 29.38 28.86 28.33 27.82 27.31 26.82 26.32 25.84 25.36 24.90
–40 0.79 0.81 0.82 0.84 0.85 0.87 0.88 0.90 0.92 0.93 0.95
0 0.87 0.88 0.90 0.92 0.93 0.95 0.97 0.99 1.00 1.02 1.04
40 0.94 0.96 0.98 1.00 1.01 1.03 1.05 1.07 1.09 1.11 1.13
70 1.00 1.02 1.04 1.06 1.08 1.10 1.12 1.14 1.16 1.18 1.20
80 1.02 1.04 1.06 1.08 1.10 1.12 1.14 1.16 1.18 1.20 1.22
100 1.06 1.08 1.10 1.12 1.14 1.16 1.18 1.20 1.22 1.25 1.27
120 1.09 1.11 1.13 1.16 1.18 1.20 1.22 1.24 1.27 1.29 1.31
140 1.13 1.15 1.17 1.20 1.22 1.24 1.26 1.29 1.31 1.34 1.36
160 1.17 1.19 1.21 1.24 1.26 1.28 1.31 1.33 1.35 1.38 1.41
180 1.21 1.23 1.25 1.28 1.30 1.32 1.35 1.37 1.40 1.42 1.45
200 1.25 1.27 1.29 1.32 1.34 1.36 1.39 1.42 1.44 1.47 1.50
250 1.36 1.36 1.39 1.41 1.44 1.47 1.49 1.52 1.55 1.58 1.61
300 1.43 1.46 1.49 1.51 1.54 1.57 1.60 1.63 1.66 1.69 1.72
350 1.53 1.56 1.58 1.61 1.64 1.67 1.70 1.74 1.77 1.80 1.84
400 1.62 1.65 1.68 1.71 1.75 1.78 1.81 1.84 1.88 1.91 1.95
450 1.72 1.75 1.78 1.81 1.85 1.88 1.92 1.95 1.99 2.03 2.06
500 1.81 1.84 1.88 1.91 1.95 1.98 2.02 2.06 2.10 2.14 2.18
550 1.91 1.94 1.98 2.01 2.05 2.09 2.13 2.17` 2.21 2.25 2.29
600 2.00 2.04 2.07 2.11 2.15 2.19 2.23 2.27` 2.32 2.36 2.40
650 2.09 2.13 2.17 2.21 2.25 2.29 2.34 2.38 2.43 2.47 2.52
700 2.19 2.23 2.27 2.31 2.35 2.40 2.44 2.49 2.53 2.58 2.63
750 2.28 2.32 2.37 2.41 2.46 2.50 2.55 2.60 2.64 2.69 2.74
800 2.38 2.42 2.46 2.51 2.56 2.60 2.65 2.70 2.75 2.80 2.86
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