System effect factors for single-width single-inlet fans

From ASHRAE (1988), with permission

A11-4.gif (26555 bytes) Notes:
  • The effective duct length is the length of duct needed for a fully developed velocity profile to exist. This length is approximately 2.5 duct diameters for 2500 ft/min (13 m/s) or less. Add one duct diameter for each additional 1000 ft/min (5 m/s). For example, 5000 ft/min (25 m/s) flow requires five duct diameters. 
  • The blast area is the smallest flow area in the fan. i.e.. at the scroll cutoff.

KSEF values for single-width single-inlet fans

Ratio of blast area to outlet area

Outlet elbow position

No duct

12% effective duct length

25% effective duct length

50% effective duct length

100% effective duct length

0.4

A

3.20

2.68

1.76

0.84

 

 

No system effect factor

 

 

B

4.00

3.32

2.24

1.04

C

5.80

4.84

3.20

1.52

D

5.80

4.84

3.20

1.52

0.5

A

2.28

1.88

1.28

0.60

B

2.84

2.36

1.56

0.72

C

4.00

3.32

2.24

1.04

D

4.00

3.32

2.24

1.04

0.6

A

1.60

1.32

0.88

0.40

B

2.00

1.68

1.12

0.52

C

2.92

2.44

1.64

0.76

D

2.92

2.44

1.64

0.76

0.7

A

1.08

0.88

0.60

0.28

B

1.32

1.08

0.72

0.36

C

1.96

1.64

1.08

0.52

D

1.96

1.64

1.08

0.52

0.8

A

0.76

0.64

0.44

0.20

B

0.96

0.80

0.52

0.24

C

1.40

1.16

0.76

0.36

D

1.40

1.16

0.76

0.36

0.9

A

0.60

0.48

0.32

0.16

B

0.79

0.64

0.44

0.20

C

1.12

0.92

0.64

0.28

D

1.12

0.92

0.64

0.28

1.0

A

0.56

0.48

0.32

0.16

B

0.68

0.56

0.36

0.16

C

1.00

0.84

0.56

0.28

D

1.00

0.84

0.56

0.28