FAN SYSTEMS
&
FAN AUDIT
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Fan Systems & Fan Audit
LEARNING OBJECTIVES
At the end of the day the trainee shall be able to :
- Measure and qualify fan performance
• Revise fan curves
• Determine system curves
• Estimate power savings potential
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Fan Systems & Fan Audit
FAN BASICS
&
FAN SYSTEMS
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Fan Systems & Fan Audit
FAN SYSTEMS - CONCEPTS OF PRESSURE
pt
TP
pSP
s
p
VP
d
Air flow
pt = ps + pd
• Static pressure (ps):
• pressure exerted in all directions by a fluid at rest
• Dynamic pressure (pd):
• pressure exerted by the velocity of a fluid : pd = ½ρv2
• Total pressure (pt):
• the sum of static and velocity pressures
20/01/2009 - 4
Fan Systems & Fan Audit
FAN SYSTEMS – SYSTEM RESISTANCE
∆p = k ρ Q2
k = Constant characteristic
ρ = Gas density
Q = Volume flow
Q
Q
p1
∆p
p2
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Fan Systems & Fan Audit
FAN SYSTEMS – SYSTEM RESISTANCE
• Each component in a system offers resistance to the
gas flow.
• System resistance :
The sum of all resistances to the flow
The system resistance varies with air flow rate
• System curve :
The relation between system resistance and flow rate
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Fan Systems & Fan Audit
• Constant static head
• Airflow through a liquid pool
• Fluidized bed
System resistance ∆P
FAN SYSTEMS – SYSTEM CURVES
∆p = k
• Complete turbulent flow
• Standard fan systems
System resistance ∆P
Airflow rate Q
∆p = kQ 2
Airflow rate Q
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Fan Systems & Fan Audit
FAN SYSTEMS – SYSTEM CURVES
• Limit discussion to the completely turbulent
system curve
12
10
∆p
∆ p = kρ Q
2
8
6
4
2
0
0
20
40
60
80
100
Q (m³/s)
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Fan Systems & Fan Audit
Pressure
Pressure vs Volumetric flow
rate given by the fan
• Defined for fixed specific
operating conditions :
• gas density
(T, p, composition)
• fan speed
• Usually, power curve is given
• Sometimes, efficiency curve
Power/Efficiency
FAN SYSTEMS – PERFORMANCE CURVES
Flow rate
blue = pressure
red = power
green = efficiency
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Fan Systems & Fan Audit
FAN SYSTEMS – FTP / FSP CONCEPT
• Fan Total Pressure (FTP)
The European way
FTP
= TP2 - TP1
= (SP2 + VP2)–(SP1 - VP1)
2
• Fan Static Pressure (FSP)
The American way
FSP
= TP2 - TP1 - VP2
= (SP2 - SP1)- VP1
1
• Static Pressure Rise(Good way!)
=
SP2 - SP1
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Fan Systems & Fan Audit
FAN SYSTEMS – FTP / FSP EFFICIENCY
•
•
Q × FTP
3600 × P
Total efficiency (η
ηt)
: ηt =
Static efficiency (η
ηs)
FSP Q × FSP
=
: η s = ηt
FTP 3600× P
where
Q
:
fan flow (m³/h)
FTP
FSP
P
:
:
:
fan total pressure (Pa)
fan static pressure (Pa)
fan power (W)
Fan Total Efficiency
Fan Static Efficiency
Fan “Static Rise” Efficiency
83%
80%
85%
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Fan Systems & Fan Audit
FAN SYSTEMS – FTP vs FSP
Pe rformance Curve for IE 250 F an
25
140
120
BHP
20
100
15
80
Total
Efficiency
10
FTP
FSP
Static
Efficiency
5
5000
10000
15000
20000
25000
40
20
0
0
60
30000
0
35000
Flow R a te (cfm)
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Fan Systems & Fan Audit
FAN SYSTEMS – FAN PERFORMANCE
Performance Curve for IE 250 Fan
103
62
50
r
we
BHP
Operating Point
88
74
37
60
Effic
ienc
y
25
Fa
n
To
tal
Pr
es
su
r
45
e
12
30
Power [kW] / %efficiency
Fan Total Pressure [mbar]
Po
15
0
0
2,5
5
7,5
10
12,5
15
0
17,5
Flow Rate [m³/s]
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Fan Systems & Fan Audit
FAN SYSTEMS – FAN + SYSTEM CURVES
Performance Curve for IE 250 Fan
50
103
88
74
35
30
60
25
Effi
cien
cy
20
15
45
FT
P
Fan Pressure [mbar]
40
10
30
Power [kW] / % efficiency
r
we
o
P
45
15
5
0
0
2,5
5
7,5
10
12,5
15
0
17,5
Flow Rate [m³/s]
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Fan Systems & Fan Audit
FAN SYSTEMS – REALITY
• Measured operating
35
442
Fan Total Pressure [mbar]
30
Operating
point
368
25
Power [kW]
point may not fall on
the fan curve
• Due to measurement
errors and fan system
effects
• In Fan Curves
spreadsheet, the flow
rate is assumed
correct
Actual fan curve (XYZ-200)
295
20
221
15
10
5
0
147
Operating point :
6,12 m³/s
28,62 mbar
249,9 kW
0
2,5
5
7,5
10
74
12,5
0
15
Flow Rate [m³/s]
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Fan Systems & Fan Audit
FAN SYSTEMS – OPERATING RANGES
Unstable
Stable
Peak
Flow Rate
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Fan Systems & Fan Audit
FAN SYSTEMS – FAN TYPES
Two large classes
• Centrifugal Fans
• Extensively used in cement plants
• Clinker cooler fans
• ID fan
• Mill ventilation fans
• Dust collector fans
• Axial Fans
• Kiln shell cooling fans
• Airplane’s propeller
20/01/2009 - 17
Fan Systems & Fan Audit
FAN SYSTEMS – FAN TYPES
Exploded View of a Centrifugal Fan
Inlet
Outlet
Cutoff
Hub
Flange
Side Sheet
Scroll
Inlet Guide Vanes
Backplate
Inlet Bell
Blades
Impeller
Stationary Inlet
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Fan Systems & Fan Audit
FAN SYSTEMS – FAN TYPES
Cutaway of a Vane-Axial Fan
Inlet
Discharge Vanes
Inner Cylinder
Outlet
Belt Fairing
Tailpiece
(sometimes omitted)
Blades
Impeller
Hub
Inlet Bell
Outer Cylinder Diffuser
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Fan Systems & Fan Audit
FAN SYSTEMS – FAN PRINCIPLES
Centrifugal Fan Principles
vr : radial velocity
v
vr
vt
vt : tangential velocity
v : fluid velocity
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Fan Systems & Fan Audit
FAN SYSTEMS – FAN BLADES
• Different types of fans characterized by their
blade type:
• Straight radial
• Forward curve
• Radial tip
• Backward inclined - flat blade
• Airfoil
• Different applications require different blade type
• Each type has different fan performance curves
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Fan Systems & Fan Audit
FAN SYSTEMS – FAN BLADES
Airfoil (AF) : 85 - 90 %
Backward-curved (BC) : 85 %
Backward-inclined (BI) : 75 - 80 %
Radial-tip (RT) : < 71 %
Forward-curved (FC) : 65 %
Radial blade (RB) : 60 - 63 %
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Fan Systems & Fan Audit
FAN SYSTEMS – FAN LAWS
• Fan performance curve made for specific
conditions:
• fan speed
• air density (temperature, pressure)
• Always AT INLET CONDITIONS
• What happens in other conditions?
• What if I change the speed of the fan? (N)
• What if the gas density changes? (ρρ)
• What if I change the size of the fan? (D)
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Fan Systems & Fan Audit
FAN SYSTEMS – FAN LAWS
• Geometrically similar (impeller) fans
• Volume is directly proportional to fan speed
Q2 N 2
=
Q1 N1
• Pressure is proportional to the square of the speed
TP2
N2
=
TP1
N1
2
• Power is proportional to the speed cubed
P2
=
P1
N2
N1
3
20/01/2009 - 24
Fan Systems & Fan Audit
Exercise 5.1 – FAN LAWS
Question :
• Fan Details :
n = 1305 [min-1]
v (1) = 7,1 [m³/s]
dpT = 7,6 [kPa]
P = 66,5 [kW]
Increased flow (2)
v (2) = 8,5 [m³/s]
n, dp , P =?
20/01/2009 - 25
Fan Systems & Fan Audit
Exercise 5.1 – FAN LAWS
Solution :
Q 2 N1 8.5 ×1305
=
= 1562 min −1
N2 =
Q1
7.1
N2
TP2 = TP1
N1
P2 = P1
N2
N1
2
1562
= 7,6 ×
1305
3
= 66.5 ×
1562
1305
2
= 10.89 kPa
3
= 114.0 kW
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Fan Systems & Fan Audit
20/01/2009 - 27
Fan Systems & Fan Audit
FAN SYSTEMS – FAN LAWS - SPEED
Performance Curve for IE 250 Fan
185
75
182
2m
i n -1
150
167
0m
in -1
151
8m
in -1
50
37,5
110
75
Power [kW]
Fan Pressure [mbar]
62,5
25
40
12,5
0
0
2,5
5
7,5
10
12,5
15
17,5
20
0
Flow Rate [m³/s]
20/01/2009 - 28
Fan Systems & Fan Audit
FAN SYSTEMS – FAN LAWS - DENSITY
• Fans are constant volume machines
• Affects the pressure generated and
power consumed
• A change in density affects the
system curve
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Fan Systems & Fan Audit
FAN SYSTEMS – FAN LAWS - DENSITY
Performance Curve for IE 250 Fan
50
120
45
105
90
1.13 kg/m³
35
30
75
25
60
20
45
0.56 kg/m³
15
30
10
15
5
0
Power [kW]
Fan Pressure [mbar]
40
0
0
2,5
5
7,5
10
12,5
15
17,5
Flow Rate [m³/s]
20/01/2009 - 30
Fan Systems & Fan Audit
FAN SYSTEMS – FAN LAWS - DENSITY
Dust collector on inlet side
of fan
• total pressure drop: 20
mbar
• inlet of fan - 20 mbar
Clinker cooler fan
• total pressure drop: 20
mbar
• inlet of fan: atmosphere
For same air flow, fan selection would be different
due to density change at fan inlet
20/01/2009 - 31
Fan Systems & Fan Audit
FAN SYSTEMS – FAN LAWS (SIZE)
• Used mostly to compare two similar
fans of same type
• Some examples of “tipping out” fans
• Casing often has to be redesigned
20/01/2009 - 32
Fan Systems & Fan Audit
FAN SYSTEMS – FAN LAWS (SIZE)
40
75
35
67,5
60
30
52,5
25
45
20
37,5
+10% D
30
15
22,5
D
10
15
5
0
Power [kW]
Fan Pressure [mbar]
Performance Curve for IE 250 Fan
7,5
0
2,5
5
7,5
10
Flow Rate [m³/s]
12,5
15
17,5
0
D = Diameter
20/01/2009 - 33
Fan Systems & Fan Audit
FAN SYSTEMS – FAN CONTROL
•
•
Requirement to control the air flow from a fan
The system resistance curve governs the fan
output
• Air flow can be changed by changing :
• The fan curve
• The system resistance curve
• Available methods:
• Discharge dampers
• Variable inlet vanes
• Box-vane control
• Variable speed drives
20/01/2009 - 34
Fan Systems & Fan Audit
FAN SYSTEMS – FAN CONTROL
Discharge Dampers
Parallel Blades
• More flow on one side of duct
• Not very linear response
Opposed Blades
Yields more uniform profile
More linear response
The discharge dampers change
the system resistance curve
Power wasting devices
20/01/2009 - 35
Fan Systems & Fan Audit
FAN SYSTEMS – FAN CONTROL
Discharge Dampers
90
20% open
40% open
Fan Pressure [mbar]
75
60
60% open
45
80% open
30
Wide open
15
0
0
5
10
15
20
25
30
35
40
Flow rate [m³/s]
20/01/2009 - 36
Fan Systems & Fan Audit
FAN SYSTEMS – FAN CONTROL
Variable Inlet Vanes
• Installed at the inlet of the fan
• Controls volume and direction
of air flow
• Designed to give a spin to the
air in the direction of the
impeller
• Pre-spin unload the impeller
reducing the pressure
• Less pressure implies less
power
Closed Position
Open Position
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Fan Systems & Fan Audit
FAN SYSTEMS – FAN CONTROL
Variable Inlet Vanes
75
90
67,5
80
60
70
52,5
60
45
50
37,5
40
30
30
22,5
20
15
10
7,5
0
25% open
0
5
10
15
20
50%
25
75% 100%
30
35
40
Power [kW]
Pressure
100
0
Flow rate [m³/s]
20/01/2009 - 38
Fan Systems & Fan Audit
FAN SYSTEMS – FAN CONTROL
Box Vane Control
• Similar to inlet vanes: pre-spin
effect
• Blades always parallel
• Must be used with an inlet box
• Power efficiency: a little less
than inlet vanes.
• Easier to maintain than inlet
vanes (hot and dusty
applications)
20/01/2009 - 39
Fan Systems & Fan Audit
FAN SYSTEMS – FAN CONTROL
Box Vane Control
Box vane controls
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Fan Systems & Fan Audit
FAN SYSTEMS – FAN CONTROL
Box Vane Control
20/01/2009 - 41
Fan Systems & Fan Audit
FAN SYSTEMS – FAN CONTROL
Variable Speed Fans
• Direct application of the fan laws:
Q2 N 2
=
Q1 N1
TP2
N
= 2
TP1
N1
2
P2
N2
=
P1
N1
3
• Maintain same efficiency at different speeds
• The most efficient method of controlling fans
• Higher initial cost
20/01/2009 - 42
Fan Systems & Fan Audit
FAN SYSTEMS – FAN CONTROL
Variable Speed Fans
Efficiency :
η1 =
Q1 × TP1
P1
Fan Laws :
N
Q2 = Q1 2
N1
η2 =
Q 2 × TP2
=
P2
N
TP2 = TP1 2
N1
N2
Q1
N1
2
N2
× TP1
N1
N2
P1
N1
3
N
P2 = P1 2
N1
3
2
=
Q1 × TP1
P1
20/01/2009 - 43
Fan Systems & Fan Audit
FAN SYSTEMS – FAN CONTROL
Power Savings
100
90
80
% Power
70
Discharge
damper
60
Bo
ne
a
xv
co
e
I nl
50
ol
r
t
n
ne
a
tv
s
40
30
Variable
speed
20
10
0
0
10
20
30
40
50
60
70
80
90
100
110
% Flow
20/01/2009 - 44
Fan Systems & Fan Audit
Exercise 5.2 – VARIABLE SPEED ID FAN
Question :
100%
open
Fan Inlet
P = -70mbar
T = 350C
Fan Outlet
P = -2mbar
T = 350C
Flow = 144.4m3/s
• (a) Plot the operating point on the fan curve
• (b) What is the speed of the fan?
• (c) What is the shaft power of the fan?
• (d) Is the fan selection good? Why?
20/01/2009 - 45
Fan Systems & Fan Audit
Exercise 5.2 – VARIABLE SPEED ID FAN
20/01/2009 - 46
Fan Systems & Fan Audit
Exercise 5.2 – VARIABLE SPEED ID FAN
20/01/2009 - 47
Fan Systems & Fan Audit
Exercise 5.2 – VARIABLE SPEED ID FAN
Solution :
• REMEMBER – ALWAYS CONVERT TO INLET
CONDITIONS !
• 144.4m3/s x 3600 = 519840m3/hr at the outlet
• Remember ‘Ideal Gas Law’
• PV = nRT or P1V1/T1 = P2V2/T2
• So, Flow at inlet Conditions,
• = 519840 x (1013-2)/(1013-70) = 557327m3/hr
• From Performance curves,
• Delta P = 68mbar => Speed is 990rpm
• Shaft Power is 2025kW
20/01/2009 - 48
Fan Systems & Fan Audit
FAN SYSTEMS – FAN CONTROL
Drive Arrangements
Belt drive
• Standard speed motors can
be used
• no need for slow speed
motors (expensive )
• Exact fan speed for
required air and volume
can be obtained
• Speed can be adjusted by
simply changing pulley
ratio
Direct drive
• Reduces initial cost if
standard speed motor
could be used
• no extra supports,
pulleys, bearings, shafts
• Elimination of power loss
by belt drive (5 to 10%)
• No maintenance required
from stretching belts
20/01/2009 - 49
Fan Systems & Fan Audit
FAN SYSTEMS
LAFARGE PREFERRED SPECIFICATIONS
•
•
Important points are :
• Safety margin : 10% on volume & 10% on pressure
• Recommended maximum fan speed
• Far enough to be from critical speed
• Variable inlet vane dampers(clean gas) or variable
speed
• V-belt drive
Often required :
• Piezometer
• Silencer
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Fan Systems & Fan Audit
FAN AUDIT
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Fan Systems & Fan Audit
FAN AUDIT
Objective :
Reduce energy consumption
Indicators:
• kWh absorbed by the motor
• Fan efficiency
• Fan reliability factor
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Fan Systems & Fan Audit
FAN AUDIT
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Fan Systems & Fan Audit
FAN AUDIT
Hardfacing was removed
Deformation
Crack
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Fan Systems & Fan Audit
FAN AUDIT PROGRAM
•
•
•
Many fans don’t operate at optimal point
• Operating conditions has changed since installation
• Bad initial selection at installation
Energy is wasted
Audits every five years or more frequently
• To check operating conditions of the fan
• Identify improvements to bring it to optimal
performance (efficiency)
• Identify solutions if fan is a process bottleneck
Coordination between Maintenance, Production and
Process departments
20/01/2009 - 55
Fan Systems & Fan Audit
FAN AUDIT - PREPARATION
• List fans that make up for 80% of power
consumption
• Operating conditions, new and future, adapted to
Process requirements
• Maintenance history of the fans
• Fan curves
• Ducting arrangement / flowsheet
• Adequate position of measuring points
• Creation of a common (Maintenance, Process) file
20/01/2009 - 56
Fan Systems & Fan Audit
FAN AUDIT - MEASUREMENT
• Flow rate
• For one operating point
• More could be required for fans with wide
ranges of operating point
• Static pressure at fan inlet
• after damper if any
• before variable inlet vane if any
• Static pressure at fan outlet
• before damper if any
• Static pressure on other side of damper
• to determine pressure drop through damper
• Damper opening
20/01/2009 - 57
Fan Systems & Fan Audit
FAN AUDIT - MEASUREMENT
• Gas temperature and composition
• For density
• Moisture content if significant
• Correction for dust load if significant
• Fan speed
• Absorbed power
• Fan elevation
• Atmospheric pressure
• Ambient air temperature
20/01/2009 - 58
Fan Systems & Fan Audit
MEASUREMENT FOR FAN STATIC PRESSURE
20/01/2009 - 59
Fan Systems & Fan Audit
FAN AUDIT – MECHANICAL EVALUATION
•
External inspection (fan running):
• Bearings temperature
• Vibrations of bearings and housing
• Noise level
• Leakage (holes in housing, ducting,…)
• Even air flow distribution at fan inlet
• Pressure drop through dust collector (if any)
20/01/2009 - 60
Fan Systems & Fan Audit
FAN AUDIT – MECHANICAL EVALUATION
•
Internal inspection (fan stopped) :
• Fan impeller alignment
• Impeller and housing: wear and material
accumulation
• Dampers: proper opening / closing, damages
and material accumulation
• Louvers: configuration of blades, functioning of
individual blade
• Turning vanes condition
20/01/2009 - 61
Fan Systems & Fan Audit
FAN AUDIT – MECHANICAL EVALUATION
•
Internal inspection (fan stopped) :
• Belt drive : tension and wear
• Coupling alignment
• Internal cone adjustment (too large a gap?)
• Accumulation of material in the duct
• Type of fan wheel –
To confirm drawings / fan curve
• Validation of existing drawings
20/01/2009 - 62
Fan Systems & Fan Audit
FAN AUDIT – ADDITIONAL INFORMATION
•
Fan system diagram showing :
• fan
• damper (position and type)
• position in relation with its environment
• elbows
• duct expansions, contractions
• turning vanes
20/01/2009 - 63
Fan Systems & Fan Audit
FAN AUDIT – ADDITIONAL INFORMATION
•
Statistics on flow, pressures and damper
opening
• Aspen / IP21
•
Fan curve
• Correct to actual conditions (elevation,
temperature, density, RPM)
•
Fan and motor name plate information
20/01/2009 - 64
Fan Systems & Fan Audit
FAN AUDIT – EVALUATION
• Position operating point on fan curve
• Does it match? Why?
• Calculate efficiency
• Is it good?
• How can we improve the efficiency?
• How can we increase flow or pressure,
if required?
20/01/2009 - 65
Fan Systems & Fan Audit
FAN AUDIT – EVALUATION
Duty Cycle :
• For fans with highly variable flow demand
such as:
• Cooler exhaust
• Kiln I.D.
• Some cooler fans
Variable Frequency Drive (VFD) ?
20/01/2009 - 66
Fan Systems & Fan Audit
FAN AUDIT – EVALUATION
Duty Cycle :
• For constant duty fans such as:
• Mill draught
• Primary air
Find most cost effective solution to
gain efficiency
• Replace belt (and motor?)
• Modify impeller?
20/01/2009 - 67
Fan Systems & Fan Audit
FAN AUDIT – EVALUATION
What Is The Damper Saying?
• If fan damper never open > 75%
then fan is oversized and wasteful
Downsizing?
Replace belts?
VFD?
20/01/2009 - 68
Fan Systems & Fan Audit
FAN AUDIT – EVALUATION
Fan Design –
•
•
Poor efficiency fan design costs all the time
Many pre-1985 fans are straight radial :
• 60-75% efficiency
•
Current technology :
• Curve radial (dirty air) : to 82% efficiency
• Airfoil (clean air)
: to 85% efficiency
20/01/2009 - 69
Fan Systems & Fan Audit
FAN AUDIT – EVALUATION
Low Cost Solutions –
• Is Hermit Crab solution possible?
• Can shaft & bearing be retained?
• Can you take advantage of the need to replace an
impeller for maintenance reason?
• Is there a retired fan that could do the job?
• Inlet turning vanes can improve efficiency by 2%
• Is there a way to modify ducting configuration to
reduce system effect?
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Fan Systems & Fan Audit
FAN AUDIT – REPORT
• Summary
• Measurements
• Mechanical observations
• Other information
• Findings
• Fan curve
• Original
• Corrected to actual conditions with
operating point and duty cycle
• Recommendations
• Follow up of actions
• Include action plan in PIP
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Fan Systems & Fan Audit
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