AMCA In Motion - Fall 2016 - 10
THE AMCA INDUSTRIAL PROCESS/
POWER GENERATION MARKET GROUP
Control of Industrial Process
and Power Generation Fans
Fans often serve over a wide range of
operating conditions. For example, many
industrial fan systems see variable loads
because of changes in ambient conditions
and production demands. To accommodate
demand changes, flow is controlled in four
principal ways: with resistance control
devices, spin control devices, variable pitch
blades and speed control.
T
his article outlines the four control methods as a guide
to help consulting, process and facility engineers consider which might be the best approach for their applications
on a project-by-project basis.
mechanism that are complicated to retrofit if the fan was not
originally designed for pitch adjustment.
Many fans are sized to handle the largest expected operating
or peak condition (frequently referred to as test block conditions). Because normal operating conditions are often well
below these design conditions, air-moving equipment is often
oversized, operating below its most efficient point and creating
problems that include high energy costs; high system pressures
and noise; and, in systems with high particulate matter contents,
erosion of impeller and casing surfaces.
Consequently, the combination of extended operating times
and the tendency to oversize the air-moving equipment to
meet test block conditions creates a need for efficient flow
control. Often, the flow control devices are selected on initial
cost, yet the costs associated with their performance are not
recognized.
Each of the four control approaches are now described in turn.
100
AMCA
80
70
Design HP (%)
Each of the four control methods has a set of advantages and
drawbacks in terms of initial cost, flow-control effectiveness
and energy efficiency. In fan systems that are used relatively
infrequently (for example, less than 500 hours annually),
initial cost may be the dominant factor. In high runtime applications, flow control effectiveness and energy efficiency may
be the key determinants.
In many industrial applications, fans must operate for
extended periods. They are often used directly to support
production or to maintain safe working conditions. In either
case, fan system operating efficiency is a high priority. The
relative efficiencies of the flow control options are shown in
Figure 1.
Of these flow control options, only controllable pitch
blades are typically not considered for retrofits. This is
because there are many elements of a pitch adjustment
Summer 2016
Outlet damper
Inlet box damper
Variable inlet vane
Variable pitch
Variable speed
90
BASIC PRINCIPLE
10
Relative efficiency of various fan controls
60
50
40
30
20
10
0
0
10
20
30
40
50
60
Design flow (%)
70
80
90
100
Figure 1. Efficiency of various fan controls.
Image courtesy of Howden.
inmotion
W W W. A M C A . O R G
http://WWW.AMCA.ORG
Table of Contents for the Digital Edition of AMCA In Motion - Fall 2016
Contents
AMCA In Motion - Fall 2016 - BB1
AMCA In Motion - Fall 2016 - BB2
AMCA In Motion - Fall 2016 - Cover1
AMCA In Motion - Fall 2016 - Cover2
AMCA In Motion - Fall 2016 - Contents
AMCA In Motion - Fall 2016 - 2
AMCA In Motion - Fall 2016 - 3
AMCA In Motion - Fall 2016 - 4
AMCA In Motion - Fall 2016 - 5
AMCA In Motion - Fall 2016 - 6
AMCA In Motion - Fall 2016 - 7
AMCA In Motion - Fall 2016 - 8
AMCA In Motion - Fall 2016 - 9
AMCA In Motion - Fall 2016 - 10
AMCA In Motion - Fall 2016 - 11
AMCA In Motion - Fall 2016 - 12
AMCA In Motion - Fall 2016 - 13
AMCA In Motion - Fall 2016 - 14
AMCA In Motion - Fall 2016 - 15
AMCA In Motion - Fall 2016 - 16
AMCA In Motion - Fall 2016 - 17
AMCA In Motion - Fall 2016 - 18
AMCA In Motion - Fall 2016 - 19
AMCA In Motion - Fall 2016 - 20
AMCA In Motion - Fall 2016 - 21
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AMCA In Motion - Fall 2016 - 23
AMCA In Motion - Fall 2016 - 24
AMCA In Motion - Fall 2016 - 25
AMCA In Motion - Fall 2016 - 26
AMCA In Motion - Fall 2016 - 27
AMCA In Motion - Fall 2016 - 28
AMCA In Motion - Fall 2016 - 29
AMCA In Motion - Fall 2016 - 30
AMCA In Motion - Fall 2016 - 31
AMCA In Motion - Fall 2016 - 32
AMCA In Motion - Fall 2016 - 33
AMCA In Motion - Fall 2016 - 34
AMCA In Motion - Fall 2016 - 35
AMCA In Motion - Fall 2016 - 36
AMCA In Motion - Fall 2016 - Cover3
AMCA In Motion - Fall 2016 - Cover4
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