DFOS-103 - page 6

Selecting Fans at Non-
Standard Conditions
1.00
.99
.93
.89
.88
.86
.84
.82
.81
.79
.78
.77
.68
1.00
1.00
1,00
.99
.98
.98
.97
.97
.96
.96
.95
.94
.93
Steel
Wheel
Steel
Shaft
70
100
200
300
350
400
450
500
550
600
650
700
800
Temp.
(F°)
Temp./ DerationFactors
135
150
165
182
200
222
245
270
300
330
365
402
445
490
542
600
660
730
807
890
5288
4657
4083
4071
3592
3225
2852
2638
2359
2089
1885
1703
1145
1027
938
839
776
699
626
564
3542
3246
2886
2653
2355
2205
1991
1809
1663
1433
1318
1141
1043
939
858
775
695
637
576
518
5288
4657
4083
4071
3592
3225
2852
2638
2359
2089
1885
1703
1493
1312
1228
1078
1052
924
809
718
4607
4221
3753
3437
3063
2868
2590
2353
2163
1863
1715
1483
1360
1224
1120
1011
906
831
751
675
6207
6134
5408
4778
4216
3786
3347
3096
2768
2452
2213
1999
1709
1558
1418
1403
1235
R/F
R/F
R/F
R/F
R/F
4721
4323
3853
3607
3258
2959
2720
2344
2157
1866
1706
1535
1404
1268
1136
R/F
R/F
R/F
FAN
SIZE
Max.
Wheel
Max.
Shaft
Max.
Wheel
Max.
Shaft
Max.
Wheel
Max.
Shaft
CLASS I
CLASS II
CLASS III
TABLE I
Temperature andAltitude Correction
TABLE II
MaximumRPMat 70°F
TABLE III
Temperature/
SpeedDeration
Correction factors for temperature (F) and altitude (above sea level):
standard air = .075 lbs. per cubic foot at sea level, 29.92” Hg barometric pressure and 70° F
-15
0
70
100
150
200
250
300
350
400
500
600
650
700
800
.84
.87
1.00
1.06
1.15
1.25
1.34
1.43
1.53
1.62
1.81
2.00
2.09
2.19
2.38
.86
.88
1.02
1.08
1.17
1.27
1.36
1.46
1.56
1.65
1.84
2.04
2.13
2.23
2.42
.87
.90
1.04
1.10
1.19
1.29
1.39
1.49
1.58
1.68
1.88
2.07
2.17
2.27
2.48
.89
.92
1.06
1.12
1.22
1.32
1.41
1.51
1.61
1.71
1.91
2.11
2.21
2.31
2.51
.90
.93
1.08
1.14
1.24
1.34
1.44
1.54
1.64
1.75
1.95
2.15
2.25
2.35
2.56
.92
.95
1.10
1.16
1.26
1.36
1.47
1.57
1.67
1.78
1.98
2.19
2.29
2.40
2.60
.
94
.97
1.12
1.18
1.28
1.39
1.49
1.60
1.70
1.81
2.02
2.23
2.34
2.44
2.65
.95
.99
1.14
1.20
1.31
1.42
1.52
1.63
1.74
1.84
2.06
2.27
2.38
2.49
2.70
.97
1.00
1.16
1.22
1.33
1.44
1.55
1.66
1.77
1.88
2.10
2.32
2.43
2.53
2.75
1.01
1.04
1.20
1.27
1.38
1.50
1.61
1.72
1.84
1.95
2.18
2.40
2.52
2.63
2.86
AIR
TEMP
(F°)
29.92
500´
29.38
1000´
28.86
1500´
28.33
2000´
27.82
2500´
27.31
3000´
26.82
3500´
26.32
4000´
25.84
5000´
24.90
ALTITUDE (feet) withBAROMETRICPRESSURE (In. Hg)
Note: For deratingmax. speeds due to high temperature, not
operational capabilities.R/F: Refer to Factory.
Fan capacity tables are based on the fan
handling standard air at 70°F and sea level.
For operating conditions other than these,
correct the HP of the fan and check the
speed derating limits.
EXAMPLE:
Select a fan to handle 5500 CFM at 2" SP at
400°F and at 2000 feet above sea level.
1. Refer to Table 1. At 2000 feet altitude
and 400° F, the correction factor is 1.75.
2.Corrected SP is 1.75 X 2" = 3.5" SP at
70°F and sea level.
3. Using the fan rating tables, selection of
the proper size fan is nowbased on 5500
CFMat 3.5" SP. These specifications
indicate that one selection available is
the size 222 Class I fanwhich shows a
performance of 5500 CFMat 3.5" SP,
requiring 4.19 BHP at 1749 RPM.
4. To correct the BHP, divide 4.19 by 1.75 =
2.39 BHP, which is the corrected BHP at
400°F and 2000 feet altitude.
5. Verify thewheel and shaft maximum
speeds using Table II and Table III.
a.Multiply the class maximumwheel
speed from Table II by the Class I Wheel
Deration Factor from Table III. Thewheel
maximum speed@400°F is 3225 RPM x
.86 = 2774 RPM. Thenmultiply themaxi-
mum shaft speed from Table II by the
Shaft Deration Factor from Table III. The
shaft maximum speed@400°F is 2205
x .98 = 2161. Thus, themaximumallow-
able fan speed is 2161 RPM.
b.Check the abovemaximumallowable
fan speed against the selected fan RPM.
Since the fan operating speed of 1749
RPM is within safe limits of themaximum
allowable of 2161 RPM, the size 222
Class I fanwill deliver 5500 CFMat 2" SP,
400°F and 2000 feet altitude requiring
2.39 HP.
Chicago’s RA Design 51
Whenworkingwith lower pressure, typically below5" SP, and space
and initial cost are primary considerations, the alternate Design 51RA
fan in smaller sizes may offer a better selection. The RA fanwas
specifically engineered for both improved efficiency and lower
sound levels in lowpressure, high volume applications. A typical
comparison of the twodesigns follows.
EXAMPLE:
Size 300 fanwith 15,900 CFMat 1-1/2 " SP, 70°F and sea level.
StandardDesign 51 = 1529 RPM at 10.78 BHP
RADesign 51 = 1376 RPM at 8.7 BHP
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