Fans &

Blowers
Training Agenda: Fans & Blowers

Introduction
Types of fans and blowers
Assessment of fans and blowers
Energy efficiency opportunities
Introduction

1. Fan components
2. System resistance
3. Fan curve
4. Operating point
5. Fan laws
Fan components
1. Drive motor (constant speed , variable speed
& multiple speed )
2. Motor pulley
3. Power transmission tool (belt , gear box &
coupling )
4. Fan pulley
5. Fan shaft
6. Lower & upper bearing (bearing assembly )
7-Fan blades or impeller with accessories
8-Structure and vibration switch or transmitter
9-Variable pitch mechanism
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System Resistance

• Sum of static pressure losses in

system
• Configuration of ducts ,elbows
• Pressure drop across equipment

• Increases with square of air volume

• Long narrow ducts, many bends: more
resistance
• Large ducts, few bends: less resistance
System Resistance

System resistance curve for various

flows

Actual with
system
resistance

calculated
Fan Curve

Performance curve of fan under

specific conditions
• Fan volume
• System static
pressure
• Fan speed
• Brake
horsepower

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Operating Point

Fan curve and system curve intersect

Flow Q1 at
pressure P1 and
fan speed N1

Move to flow Q2 by
closing damper
(increase system Move to flow Q2
resistance) by reducing fan
speed
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Fan Laws

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Types of Fans & Blowers

Types of fans
• Centrifugal
• Axial

Types of blowers
• Centrifugal
• Positive displacement
Difference between Fan & Blower
-Fans : Just air moving device
Divided to axial and centrifugal , the axial fans
low pressure and large volumes but centrifugal
sometimes high pressure , move less air but
high pressure
-Blower
When fan centrifugal is integrated with housing
and motor and air inlet in center and outlet
from the opening of the shell at edge of scroll
toward the application , the housing direct the
air (duct )
Types of Fans

Centrifugal Fans
• Rotating impeller increases air velocity
• Air speed is converted to pressure
• High pressures for harsh conditions
• High temperatures
• Moist/dirty air streams

• Categorized by blade shapes

• Radial
• Forward curved
• Backward inclined 16
Types of Fans

Centrifugal Fans – Radial fans

• Advantages
• High pressure and temp
• Simple design
• High durability
• Efficiency up to 75%
• Large running clearances

• Disadvantages (Canadian Blower)

• Suited for low/medium

airflow rates only 17
Types of Fans

Centrifugal Fans – Forward curved

• Advantages
• Large air volumes against
low pressure
• Relative small size
• Low noise level

• Disadvantages
• Not high pressure / harsh
( Canadian Blower)
service
• Difficult to adjust fan output
• Careful driver selection
• Low energy efficiency 55-65%
Types of Fans

Centrifugal Fans - Backward-inclined

• Advantages
• Operates with changing
static pressure
• Suited for high flow and
forced draft services
• Efficiency >85%

• Disadvantages ( Canadian Blower)

• Not suited for dirty airstreams
• Instability and erosion risk
Types of Fans

Axial Fans
• Work like airplane propeller:
• Blades create aerodynamic lift
• Air is pressurized
• Air moves along fan axis

• Popular with industry: compact, low

cost and light weight
• Applications
• Ventilation (requires reverse airflow)
• Exhausts (dust, smoke, steam)
Types of Fans

Axial Fans – Propeller fans

• Advantages
• High airflow at low pressure
• Little ductwork
• Inexpensive
• Suited for rooftop
ventilation
• Reverse flow

• Disadvantages
• Low energy efficiency
• Noisy
Types of Fans & Blowers

Axial Fans – Tube axial fans

• Advantages
• High pressures to overcome
duct losses
• Suited for medium-pressure,
high airflow rates
• Quick acceleration
• Space efficient

• Disadvantages
• Expensive
• Moderate noise
• Low energy efficiency 65%
Types of Fans & Blowers

Axial Fans – Vane axial fans

• Advantages
• Suited for medium/high
pressures
• Quick acceleration
• Suited for direct motor shaft
connection
• Most energy efficient 85%

• Disadvantages
• Expensive
Fans layout or Draft
I. Induced draft fane
• The blades or impeller located above the tube bundles

• Advantages :
1. Better distribution of air across the bundle
2. Less possibility of hot air flow recirculating into the intake.
The hot air is discharged upward at approximately 2.5 times
the intake velocity, or about 1,500 feet per minute.
3. Better process control and stability because the plenum
covers 60% of the bundle face area, reducing the effects of
sun, rain, and hall.
4. Increased capacity in the fan-off or fan failure condition, since
the natural draft stack effect is much greater.
I. Induced draft fane
• Disadvantages :
1. Possibly higher horsepower requirements if the air flow is very
hot.
2. Air flow temperature should be limited to 220°F to prevent
damage to fan blades, bearings, or other mechanical
equipment in the hot air stream. When the process inlet
temperature exceeds 350°F, forced draft design should be
considered because high effluent air temperatures may occur
during fan-off or low air flow operation.
3. Fans are less accessible for maintenance, and maintenance
may have to be done in the hot air generated by natural
convection.
4. Plenums must be removed to replace bundles.
II- Forced Draft :
• The blades or impeller located below the tube bundle

• Advantages :
I. Possibly lower horsepower requirements if the effluent air is
very hot. (Horsepower varies inversely with the absolute
temperature.)
II. Better accessibility of fans and upper bearings for
maintenance.
III. Better accessibility of bundles for replacement.
IV. Accommodates higher process inlet temperatures
II- Forced Draft :
• Disadvantages
I. Less uniform distribution of air over the bundle.
II. Increased possibility of hot air recirculation, resulting from low
discharge velocity from the bundles, high intake velocity to the
fan ring, and no stack.
III. Low natural draft capability on fan failure.
IV. Complete exposure of the finned tubes to sun, rain, and hail,
which results in poor process control and stability.
AIR
COOLERS

COLD AIR PASS

THROUGH THE FAN

HOT AIR PASS

THROUGH THE FAN
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Types of Fans & Blowers

Blowers
• Difference with fans
• Much higher pressures <1.20 kg/cm2
• Used to produce negative pressures for
industrial vacuum systems

• Types
• Centrifugal blower
• Positive displacement
Types of Blowers

Centrifugal Blowers
• Gear-driven impeller
that accelerates air
• Single and multi-stage
blowers
• Operate at 0.35-0.70
kg/cm2 pressure
• Airflow drops if system
pressure rises
Types of Blowers

Positive Displacement Blowers

• Rotors trap air and push it through
housing
• Constant air volume regardless of
system pressure
• Suited for applications prone to
clogging
• Turn slower than centrifugal blowers
• Belt-driven for speed changes
Assessment of fans and blowers

Fan Efficiency and Performance

• Fan efficiency:
• Ratio of the power conveyed to air stream
and power delivered by the motor to the fan
• Depends on type of fan and impeller

• Fan performance curve

• Graph of different pressures and
corresponding required power
• Supplier by manufacturers
Assessment of fans and blowers

Peak efficiency or Best Efficiency

Point (BEP)
Airfoil Peak
Type of Fan Efficiency
Backward Range
Centrifugal fans:
Efficiency

Radial
Airfoil, Backward 79-83
curved/inclined

Modified radial 72-79

Radial 69-75
Tubular
Pressure blower 58-68
Forward curved 60-65
Axial fans:
Forward
Vane axial 78-85
Tube axial 67-72
Flow rate
Propeller 45-50
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Assessment of fans and blowers

Methodology – fan efficiency

Before calculating fan efficiency
• Measure operating parameters
• Air velocity, pressure head, air stream temp,
electrical motor input

• Ensure that
• Fan is operating at rated speed
• Operations are at stable condition
Assessment of fans and blowers

Methodology – fan efficiency

Step 1: Calculate air/gas density
t = Temperature of air/gas
at site condition

Cp = Pitot tube constant,

0.85 (or) as given by the
Step 2: Measure air velocity and manufacturer
calculate average
p = Average differential
pressure

γ = Density of air or gas at

test condition

Step 3: Calculate the volumetric

flow in the duct
Assessment of fans and blowers

Methodology – fan efficiency

Step 4: Measure the power drive of the motor

Step 5: Calculate fan efficiency

• Fan mechanical efficiency

• Fan static efficiency

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© UNEP 2006
Assessment of fans and blowers

Difficulties in Performance
Assessment
• Non-availability of fan specification
data
• Difficulty in velocity measurement
• Improper calibration of instruments
• Variation of process parameters
during tests
Training Agenda: Fans & Blowers

Introduction
Types of fans and blowers
Assessment of fans and blowers
Energy efficiency opportunities
Energy Efficiency Opportunities

1. Choose the right fan

2. Reduce the system resistance
3. Operate close to BEP
4. Maintain fans regularly
5. Control the fan air flow

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Energy Efficiency Opportunities

1. Choose the Right Fan

• Considerations for fan selection
• Noise
• Rotational speed
• Air stream characteristics
• Temperature range
• Variations in operating conditions
• Space constraints and system layout
• Purchase/operating costs and operating life

• “Systems approach” most important!

Energy Efficiency Opportunities

1. Choose the Right Fan

• Avoid buying oversized fans
• Do not operate at Best Efficiency Point
• Risk of unstable operation
• Excess flow energy
• High airflow noise
• Stress on fan and system
Energy Efficiency Opportunities

2. Reduce the System Resistance

• Increased system resistance
reduces fan efficiency

• Check periodically
• Check after system
modifications
• Reduce where
possible
Energy Efficiency Opportunities

3. Operate Close to BEP

• Best Efficiency Point = maximum

efficiency
• Normally close to rated fan capacity
• Deviation from BEP results in
inefficiency and energy loss
Energy Efficiency Opportunities

4. Maintain Fans Regularly

• Periodic inspection of all system
components
• Bearing lubrication and replacement
• Belt tightening and replacement
• Motor repair or replacement
• Fan cleaning
Energy Efficiency Opportunities

5. Control the Fan Air flow

a) Pulley change
b) Dampers
c) Inlet guide vanes
d) Variable pitch fans
e) Variable speed drives (VSD)
f) Multiple speed drive
g) Disc throttle
h) Operating fans in parallel
i) Operating fans in series
Energy Efficiency Opportunities

5. Control the Fan Air flow

a) Pulley change: reduce motor/drive
pulley size
• Advantages
• Permanent speed
decrease
• Real energy reduction
(BEE India, 2004)
• Disadvantages
• Fan must handle capacity change
• Only applicable if V-belt system or motor
Energy Efficiency Opportunities

5. Control the Fan Air flow

b) Dampers: reduce flow and increase
upstream pressure
• Advantages
• Inexpensive
• Easy to install

• Disadvantages
• Limited adjustment
• Reduce flow but not energy consumption
• Higher operating and maintenance costs
Energy Efficiency Opportunities

5. Control the Fan Air flow

c) Inlet guide vanes
• Create swirls in fan direction
• Reduce angle air and fan blades
• Lowering fan load, pressure, air flow

• Advantages
• Improve efficiency: reduced load and airflow
• Cost effective at 80-100% of full air flow

• Disadvantage
• Less efficient at <80% of full air flow
Energy Efficiency Opportunities

5. Control the Fan Air flow

d) Variable pitch fans: changes angle
incoming airflow and blades
• Advantages
• High efficiency at range of operating
conditions
• No resonance problems
• No stall problems at different flows

• Disadvantages
• Applicable to axial fans only
• Risk of fouling problems
• Reduced efficiency at low loads
Energy Efficiency Opportunities

5. Control the Fan Air flow

e) Variable speed drives (VSDs): reduce
fan speed and air flow
• Two types
• Mechanical VSDs
• Electrical VSDs (including VFDs)

• Advantages
• Most improved and efficient speed control
• Speed adjustments over continuous range

• Disadvantage: high costs

Energy Efficiency Opportunities

5. Control the Fan Air flow

e) Variable frequency drives
• Change motor’s rotational speed by
adjusting electrical frequency of power
• Advantages
• Effective and easy flow control
• Improved efficiency over wide operating range
• Can be retrofitted to existing motors
• Compactness
• No fouling problems
• Reduced energy losses and costs
Energy Efficiency Opportunities

5. Control the Fan Air flow

f) Multiple speed drive
• Changes fan speed from one speed to
other speed
• Advantages
• Efficient control of flow
• Suitable if only 2 speeds required

• Disadvantages
• Need to jump from speed to speed
• High investment costs
Energy Efficiency Opportunities

5. Control the Fan Air flow

g) Disc throttle:
Sliding throttle that changes width of
impeller exposed to air stream
• Advantages
• Simple design

• Disadvantages
• Feasible in some applications only
Energy Efficiency Opportunities

5. Control the Fan Air flow

h) Operate more fans in parallel (instead
of one large fan)
• Advantages
• High efficiencies at varying demand
• Risk of downtime avoided
• Less expensive and better performance than
one large fan
• Can be equipped with other flow controls

• Disadvantages
• Only suited for low resistance system
Energy Efficiency Opportunities

5. Control the Fan Air flow

i) Operate fans in series
• Advantages
• Lower average duct pressure
• Less noise
• Lower structural / electrical support required

• Disadvantages
• Not suited for low resistance systems
Energy Efficiency Opportunities

5. Controlling the Fan Air Flow

Comparing
Fans in
Parallel
and Series
Energy Efficiency Opportunities

5. Controlling the Fan Air Flow

Comparing
the impact of
different types
of flow control
on power use
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Power/torque transmission
 Chain
 Gear
 Coupling
 Belt :
I. No lubrication required
II. More flexibility
III. Economically
IV. Suitable for equipment continuously in-service
V. Good mechanical efficiency
VI. Quiet , smooth operation when aligned
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Belt

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Belt material
 To ensure adherence with pulley groove
 To reduce the belt tension
 Rubber , neoprene , urethane , similar synesthetic
material

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Belt components
 Protective cover
 Insulation section
 Tension members
 Compression section

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Types
 Flat belt : leather material , economic
 V-belts : more advance ( speed , torque ,
adherence )
 Synchronous belt (timing belt , positive belt ) :
more precision and no slippage
V-belt classifications
 Light duty /fractional horsepower v-belt
V-belt classifications
 Classical v-belt : heavy duty
V-belt classifications
 Deep wedge groove /narrow v-belt :compact
design and high speed capability
V-belt classifications
 Cogged /raw-edge v-belt : features of both
classical and narrow configuration
I. Used in heavy trucks and bused because of
longer life and reduced bending stress
II. Cut notches to increase the contact are and
adherence and reduce slippage
V-belt classifications
 Banded belt : for vertically mounted applications
I. Guide the belt inside pulley in a straight line
II. Assure lateral rigidity
III. Used in shock loads drives to avoid jump off or
roll out
V-belt classifications
 V-ribbed /poly v-belt
I. Combination of flat and v-shaped
II. More stability than flat
III. Power transmission is higher
IV. Use in diesel engines (multi pulley drive)
V. More flexibility and high effective contact area
Standard trapezoidal synchronous
 Timing belts or positive belts STS
I. Smooth engaged teeth with pulley , high speed
II. No slippage
III. Different from cogged
IV. Precision applications (machine tools , robots )
V. Suitable for back lash
High torque drive or belt HTD
Curvilinear synchronous belt HTB
I. Round shape
II. High torque and low speed
III. Reduce jump off or slippage
IV. Less tooth wear due to friction
Belt length
Pulley or sheaves material
 Gray /cast iron
 Ductile iron
 Sintered metal

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Pulley or sheaves types
 B (block) : diameter 0-6 inch
 W (web ) : 6-14 inch
 A (arm ) : over 14 inch

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Bushings types
 TL (taper lock ) :
used when excessive torque to avoid QD bolts
subjected to shear forces
 QD (quick disconnect ) : quick maintenance
 STB ( split taper bushing ) :more rigidity , dual
key

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Belts problems

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Belts equivalent

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Tools and spares

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Maintenance
 3 monthly preventive maintenance
I. Clean blades
II. Grease the bearing upper and lower
III. Check belt tension
IV. Check pulley alignment
 Annual preventive
I. Apply 3 M
II. Adjust the blade angel
III. Check pulley alignment and belt condition
Fans & Blowers

THANK YOU
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