SystemEffect (1)

7/27/2019 SystemEffect (1)

1/41

and

1


2/41

Fan Testing Types


3/41


4/41

yp ca ns a a on ype

Free inlet Free outlet


5/41

yp ca ns a a on ype

Free inlet Ducted outlet


6/41

yp ca ns a a on ype

Ducted inlet Free outlet

Office


7/41

yp ca ns a a on ype

Ducted inlet Ducted outlet


8/41

Fan and System Curves


9/41

Fan Performance Curve

0.6

.

700 RPM

0.5

0.4

P

re

ssure

0.2

.

0.1

0

0 2 4 6 8 10 12 14 16 18

Airfl ow


10/41

Fan Laws for Fan Speed

NCC

N

,

PC =NC

N

( )P P

, Fan Pressure

3

HC =

C

NH H

, Fan Power


11/41

with Fan Speed0.7

750 RPM

0.5

.

700 RPM

650 RPM

0.4

ss

ure

0.2

0.3Pr

0.1

0

0 2 4 6 8 10 12 14 16 18


12/41

System Curves

, ystem r ow ate

PC =QC

Q

( )P

,


13/41

ys em es s ance urve

1.2

.

1B

0.8

Pre

ssure

0.4

.

0.2

0

0 5 10 15 20 25 30 35 40 45

Airfl ow


14/41

ang ng ys em es s ance urve

1.2

1.4

1

0.8

Pressure

Curve B

0.4

.

Curve A

0.2

0

0 2 4 6 8 10 12 14 16 18

Airfl ow


15/41

ys em pera ng o n

0.6

0.7

0.5

Fan Performance

Curve

0.4

Pressure

0.2

.

Operating Point

0.1

System Resistance

Curve

0

0 2 4 6 8 10 12 14 16 18

Airfl ow


16/41

ang ng e ys em pera ng o n

Chan in Fan S eed

3.5

3

2

.

ur

e

1400 RPM

1.5Press

Operating Point

0.5

1

700 RPM

O eratin Point

0

0 5 10 15 20 25 30 35 40 45

at 700 RPM

Airfl ow


17/41

Chan in the S stem

ang ng e ys em pera ng o n

3.5

2.5

3

2

su

re

Curve B

1.5Pre

Operating Point

on Curve B

Curve A

0.5

1

Operating Pointon Curve A

0

0 5 10 15 20 25 30 35 40 45

Airfl ow


18/41


19/41

Common cause of deficient

per ormance o a an sys em

Improper inlet or outlet conditions

Non-uniform inlet or outlet flow

Swirl at the inlet


20/41

System Effect

Detrimental effect on fan air

performance due to airflow disturbances

in close proximity to the fan either

.


21/41

Can decrease performance

an cause excess v ra on

Can cause excess noise Can require more energy to achieve rated

erformance

Takes time to determine and understand


22/41

FGH IJ K L M N O

System 3.04.0

.P

Q

R

Effect

Curve2.0

2.5

S

0.91.0

.

T

U

0.5

0.6

0.7.

V

0.25

0.3

.

X

0.15

0.2

0.15 6 7 8 910 15 20 25 30 35 40 45

,(AirDensity =0.075 lbm/ft

3)


23/41

Exam le

Given:

Centrifu al Fan

3,000 cfm at 1 inch static pressure

13 by 13 inch fan discharge / duct size

9 by 13 inch blast area

3 000 cfm / 13 x 13 / 144 = 2556 f m

u v u x x . . .

Effective duct length = 2.5 (2,500 FPM or less) + 1 duct for

ever additional 1 000 f m

Effective duct length = 2.5 + 1 = 3.5 diameters = 3.5 x 14.5 in. = 4 ft

Blast Area / Outlet Area = (9 x 13) / (13 x 13) = 0.7


24/41

Exam le Continued

BlastArea DischargeDuct

OutletArea

100%Effective DuctLength

No 12% 25% 50% 100%

t

Blast Area

Duct Duct Duc Duct

U W --U W --

U-V W-X --

0.4

OutletA ea

0.5

0.6

P R-SP R-S

R-S S-T

W-X -- --

X -- --

-- -- --

0.7

0.8

0.9

S U

T-U VW

W-W W-X

1.0 -- -- ---- --


25/41

4.0

5.0P

Q

2.0

2.5

.

S S

0.91.0

.

T

U

0.5

0.6

0.7.

V

S stem effect factor for

0.25

0.3

0.4W

X

no duct = 0.31 in.wg

0.15

0.2

No system effect with25% effective duct

0.15 6 7 8 910 15 20 25 30 35 40 45

AIR VELOCITY, FPM IN HUNDREDS

eng

pm (AirDensity =0.075 lbm/ft 3)


26/41

-

Axial FansAxial Fan

100% Effective Duct Length

No

Duct

Effective

Duct

Tubeaxial Fan -- -- -- -- --

Effective

Duct

Effective

Duct

Effective

Duct

aneaxa an -- --


27/41

System Effect Curves for SWSI FansOutlet No 12% 25% 50% 100%

Blas t A rea Elbow Outlet E ffec tive E ffective E ffec tive E ffective

Outlet Area P osition Duct Duct Duct Duct Duct

A N O P -Q S

0.4 B M-N N O-P R-S

C L-M M N Q

P osition C

P osi tion D

D L-M M N Q

A O-P P-Q R T

0.5 B N-O O-P Q S-T

C M-N N O-P R-S

N

O

P osition B

- - -

A Q Q-R S U

0.6 B P Q R T

C N-O O Q S

D N-O O Q S

S

Y

S

T P osi tion AInlet

A R-S S T V

0.7 B Q-R R-S S -T U-V

C P Q R-S T

D P Q R-S T

A S S-T T-U W

E

M

E

F

0.8 B R-S S T V

C Q-R R S U-V

D Q-R R S U-V

A T T-U U-V W

- -

F

E

C

T

.

C R S S-T V

D R S S-T V

A T T-U U-V W

1 B S-T T U W

F

A

C

T

-

D R-S S T V R


28/41


29/41

Inlet Conditions

Lengthof Duct

R

Inlet with 3- iece Inlet with rectan ulaelbow inlet Duct

designed inlet box


30/41

S stemEffectCurves S stemEffectCurves

R/D NoDuct

2DDuct

5DDuct

0.5 O Q S

R/D NoDuct

2DDuct

5DDuct

0.5 P-Q R-S T

R/D NoDuct

2DDuct

5DDuct

-- N P R-S

0.75 Q R-S T-U

1.0 R S-T U-V

2.0 R-S T U-V

0.75 Q-R S U

1.0 R S-T U-V

2.0 R-S T U-V

D D D

3.0 S T-U V 3.0 S-T U V-W

Lengthof Duct

Lengthof Duct

Lengthof Duct

R

2 piece miteredround section

3 piece miteredround section

4 or more piecemitered round


31/41

turning vanesR/D No

Duct2D

Duct5D

Duct

0.5 S T-U V

R/D NoDuct

2DDuct

5DDuct

0.5 O Q S

R/D NoDuct

2DDuct

5DDuct

0.5 S T-U V

1.0 T U-V W

2.0 V V-W W-X

0.75 P R S-T

1.0 R S-T U-V

-

1.0 T U-V W

2.0 V V-W W-X

.

Length

Square

Length

Square

Length

Square

of Duct

R

of Duct

R

of Duct

R

Square elbow - Square elbow - Square elbow -

ong urnng vanes


32/41

Pre-Rotation Counter-Rotation


33/41

Inlet Swirl

from inlet swirl is turning vanes


34/41

System Curve at Design Point

Calculated duct system

1

Pressure Fan pressure-volume curve

Design Volume


35/41

System Effect Ignored

with system effect

Calculated duct systemwith no allowance for

System effect at4

System effect loss

New Fan Curve at Higher Speed

1

3 a es gn vo ume

Design Pressure

Original Fan Curve

Fan Curve with System Effect

Deficient Volume Performance

Design Volume

PRESSURE GRADIENTS


36/41

PRESSURE GRADIENTS

Fan as Tested

C-D duct friction 750 Pa (duct design)

A free inlet 0 Pa (no SEF)

B-C outlet with straight duct attached for 2 or more diam. 0 Pa (no SEF)

--------------------

REQUIRED Fan PS 750 Pa


37/41

Exhaust System

A Entrance loss-shar ed e duc 100 Pa duct desi n

A-B Duct friction at 5000CMH 750 Pa (duct design)

B SEF 1 150 PaC SEF 2 50 Pa

E Fan PV 125 Pa

E SEF 3 150 Pa

------------------

REQUIRED Fan Pt 1325 Pa

Fan P = fan P fan P

Fan PS = 1325 Pa 125 Pa

Fan PS = 1200 Pa

PRESSURE GRADIENTS


38/41

PRESSURE GRADIENTS

Plenum Effect

E-F duct friction at 5000CMH (Q) 750 Pa (duct design)

E contraction loss-plenum to duct 50 Pa (part of duct system)

E PS energy required to create velocity at E 125 Pa (part of duct system)

D PV loss (also PT loss) at D as result of air velocity decrease 0 Pa

PS does not change from duct to plenum at D

C-D outlet duct on fan as tested 0 Pa

--------------------


PRESSURE GRADIENTS


39/41

PRESSURE GRADIENTS

Abrupt Expansion at Fan Outlet

D-E duct friction at 5000CMH (Q) 750 Pa (duct design)

D contraction loss-plenum to duct 50 Pa (part of duct system)

D PS energy required to create velocity at D 125 Pa (part of duct system)

B-C SEF 150 Pa

B-C PV loss (also PT loss) at C as result of air velocity decrease 0 Pa

PS does not change from duct to plenum at C

------------------



40/41

u u

Minimum 2.5 duct diameters on Outlet Minimum 5 to 8 duct diameters on Inlet

Avoid inlet swirl

If any of these general rules are broken, make sure

to take system effect into account.


41/41

Thank you

www.amca.org

Documents

SystemEffect (1)