AMCA International Technical
Seminar 2009
System Effects
Presented by:
Joe Brooks, AMCA International, Inc.
The Air Movement and Control Association
International (AMCA), has met the standards and
requirements of the Registered Continuing
Education Providers Program. Credit earned on
completion of this program will be reported to the
RCEPP. A certificate of completion will be issued to
each participant. As such, it does not include
content that may be deemed or construed to be an
approval or endorsement by NCEES or RCEPP.
System Effects, Slide 2
Learning Objectives
 Describe system resistance of components
 Know how a fan interacts with the system
 Define System Effect and System Effect Factor
(SEF)
 Know how to avoid system effect factors
System Effects, Slide 3
Two Components of System Design
 Calculate flow resistance losses for each
component in the system
 Select and position fan to avoid system
effect loss
 If loss cannot be avoided, estimate loss and
select fan for higher pressure
System Effects, Slide 4
Ductwork Example
System Effect Controlled by Inlet and Outlet Conditions
System Resistance
System Effects, Slide 5
Causes of Non-Performing Systems
 System resistance miscalculated.
 Fan not properly selected.
 Defective fan (or fan rating).
 There is a system effect loss.
System Effects, Slide 6
Fan Manufacturer’s Responsibility
 Provide accurate fan performance ratings.
 Provide a fan built within tolerance so that
it is capable of meeting its rating.
System Effects, Slide 7
What is System Effect?
 A factor used to correct for system
induced installation effects.
 The difference in performance between a
fan tested in the laboratory and one
tested in a real installation.
System Effects, Slide 8
Inlet Connections
ASHRAE Guidelines
System Effects, Slide 9
Outlet Connections
ASHRAE Guidelines
System Effects, Slide 10
Outlet Connections
ASHRAE Guidelines
System Effects, Slide 11
What is Missing?
 Only guidelines to avoid losses.
 No way to quantify losses.
System Effects, Slide 12
AMCA Publication 201-02
 The bible of
system effects
 Generated from
ASHRAE funded
research
System Effects, Slide 13
Credibility Gap
 Are system effects just fudge factors that
the fan manufacturers made up?
 System effect video.
System Effects, Slide 14
Definition of System Effect
 Fan ratings are established using AMCA
210 test codes that are close to ideal
conditions.
 Fans in actual systems are often less than
ideal.
 The difference in performance for the
same fan tested in both conditions is the
“System Effect”.
System Effects, Slide 15
Purpose of Discussion
 Aimed primarily at the fan system
designer
There are two goals:
 Avoid poor fan system configurations
 When optimum conditions cannot be met,
use the “system effect” factors to
estimate any losses during system
design.
System Effects, Slide 16
Why System Effect is Important
 May have to accept deficient performance,
or...
 Speed up the fan (if possible)
 May require more energy to meet performance
 May exceed motor horsepower limit
 Many cause excessive noise
 Many cause excessive vibration
System Effects, Slide 17
Normal System Performance
D e s ig n p re s s u re
1
Calculated duct system curve
Fan curve
Design volume
System Effects, Slide 18
Deficient Performance With System Effect
System effect at actual
flow volume
 Operating point is at
point 3
 Operating point is not
on fan curve!
4
D e s ig n p re s s u re
1
3
Calculated duct system
with no allowance for
system effect
Original fan curve
Design volume
Deficient volume
System Effects, Slide 19
Correcting For System Effect
System effect at actual
flow volume
2
Actual duct system with
system effect
Calculated duct system
with no allowance for
system effect
System effect loss at
design volume
4
D e s ig n p re s s u re
1
3
New fan curve
Original fan curve
Design volume
Deficient volume
System Effects, Slide 20
With System Effects Added:
 The fan will be selected for the higher
pressure (no need to speed up).
 The motor will be selected to include the
anticipated loss.
System Effects, Slide 21
What are the Causes of the Losses?
 Inlet losses are caused by:
 Unequal loading of the fan blades (eccentric
flow).
 Improper fan blade attack angle.
 Turbulence which disrupts the flow.
 Outlet losses are caused by:
 Loss of conversion of local high velocity into
pressure.
System Effects, Slide 22
Inlet vs. Outlet Losses
 Inlet induced losses tend to be higher
than outlet losses.
 Losses induced on the inlet can often
exceed 20%.
 Losses as high as 50% have been
reported.
System Effects, Slide 23
Good Flow Conditions for a Fan:
 Straight uniform flow directed only in the
axial direction--on the fan inlet
 For Ducted fans - a straight length of
outlet ductwork
System Effects, Slide 24
AMCA Publication 210-07
Defines standard
methods of testing
fans for rating
purposes
System Effects, Slide 26
How are the Losses Quantified?
 AMCA 201 publishes data for a variety of
configurations
 Most identify a “Loss Curve” which is
based on the configuration and identified
by a letter
 Most also need the air velocity as a parameter.
System Effects, Slide 27
System
Effect Curves
Curve T
Add 0.55 to
Static
Pressure
4000 FPM
System Effects, Slide 28
Outlet System Effects
 In addition to the flow velocity, may need
to know:
 effective duct length
 blast area
System Effects, Slide 29
System Effect Curves for Outlet Ducts Axial Fans
System Effects, Slide 30
Fan Outlet Velocity Profile - Centrifugal
System Effects, Slide 31
System Effect Curves for Outlet Ducts Centrifugal Fans
System Effects, Slide 32
Outlet Duct Elbows - Centrifugal Fans
WORSE
BAD
System Effects, Slide 33
S. E. Curves for Outlet Elbows on Centrif.
System Effects, Slide 34
System Effects, Slide 35
S. E. Curves for Outlet Elbows - Axial
System Effects, Slide 36
S. E. Curves for Inlet Elbows - Axial
System Effects, Slide 37
Percentage of Unobstructed Inlet Area
System Effects, Slide 38
Fans and Plenum – Two Losses
Distance L / (Inlet Dia.) gives one loss
Loss factors given for 0.3 to 0.75
clearance
Keep inlet
centerline on
centerline of unit
Note: Spacing for two fans is
important
No loss factors
given
System Effects, Slide 39
Elbows Change the Velocity Profile
Fan inlet here will
create a system effect
loss for any type of
fan
System Effects, Slide 40
Right Angle Turns At Fan Inlet
Inlet with 3-piece
elbow
Inlet with rectangular
inlet Duct
(POOR)
Inlet with special
designed inlet box
All methods will induce some system effect loss.
Some methods are better than others
System Effects, Slide 41
System Effect - Round Inlet Ducts
System Effect Curves
R/D
System Effect Curves
R/D
No
2D
Duct Duct
--
N
P
No
2D
Duct Duct
0.5
O
Q
S
R/D
No
2D
Duct Duct
5D
Duct
0.5
P-Q
R-S
T
U
0.75
Q
R-S T-U
0.75
Q-R
S
5D
Du ct
1.0
R
S-T U-V
1.0
R
S-T U-V
R-S
2.0
R-S
T
U-V
2.0
R-S
T
U-V
3.0
S
T-U
V
3.0
S-T
U
V-
D
Length
of Duct
5D
Duct
System Effect Curves
D
Length
of Duct
D
Length
of Duct
R
R
R
2 piece mitered
round section
3 piece mitered
round section
4 or more piece
mitered round section
System Effects, Slide 42
Forced Inlet Vortex (Inlet Spin or Swirl)
Pre-Rotating
Inlet Swirl
Counter-Rotating
Inlet Swirl
System Effects, Slide 43
Corrections for Inlet Spin
System Effects, Slide 44
Normalized Pressure-Volume Curve
Note that this is
similar to a variable
system effect.
A new curve is
generated at each
vane setting
System Effects, Slide 46
Pressure Drop Multipliers for Volume
Control Dampers on a Fan Outlet
System Effects, Slide 47
Measured Inlet Sound Power
Vaneaxial Fan System Effect
110
Blade Pass - 135 Hz
100
90
80
70
63
Fan Only
125
250
500 1000 2000 4000 8000
2 PC Elbow on Inlet
2 PC Elbow 3 De
System Effects, Slide 48
System Effect Factors are Real
 When designing your fan/system, do
everything possible to avoid a “system
effect” for efficient use of energy
 When conditions leading to system effect
cannot be avoided, add the calculated
loss to the fan pressure requirement at
the system design stage.
System Effects, Slide 49
Thumb Rules
 Minimum of 2-1/2 Duct Diameters on
Outlet,
 Minimum 3 to 5 Duct Diameters on Inlet,
and
 Avoid Inlet Swirl
System Effects, Slide 50
System Effects, Slide 57
Questions?
System Effects, Slide 59
System Effects, Slide 60