Avoid Over size Motors and Fans

1. A Presentation
By
ENGR. WASIULLAH
Energy Auditor
BLOWERS & FANS
Dated : 11-07-2017

2. Instruments Used
1: Power Quality Analyzer Fluke 43 B
2: Strobo Scope
3: Air Flow Meter
4: Anemometer

3. 1. An apparatus with rotating blades that creates a current
of air for cooling or ventilation.
2. A handheld device, typically folding and shaped like a
segment of a circle when spread out, that is waved so as
to cool the person holding it.
What is Fan ?
A blower is a machine used for moving gas with a
moderate increase of pressure: a more powerful fan, if
you will. By changing the angle of the blades, a blower
will be able to push air in any direction you want it.
What is Blower ?

4. Introduction
1. Fan components
2. System resistance
3. Fan curve
4. Operating point
5. Fan laws

5. Equipment Specific Ratio Pressure rise (mmWg)
Fans Up to 1.11 1136
Blowers 1.11 to 1.20 1136 –2066
Comparison Between Fans and
Blowers

6. Fan Components
Provide air for ventilation and industrial
processes that need air flow

7. System Resistance
• Sum of static pressure losses in system
• Configuration of ducts, pickups, elbows
• Pressure drop across equipment
• Increases with square of air volume
• Long narrow ducts, many bends: more
resistance
• Large ducts, few bends: less resistance

8. Types of Fans
FANS
Axial Fans Centrifugal Fans
Propeller
fans
Tube axial
fans
Vane axial
fans
Backward
inclined
Radial
impellers
Forward
curved
impellers
Special Types of Fans
Inline centrifugal fans Power roof ventilators
Fan and dust collector
combination
Disc blade
Propeller
blade

9. Types of Blowers
Blowers
Centrifugal Positive Displacement

10. Types of Fans & Blowers
• Rotating impeller increases air velocity
• Air speed is converted to pressure
• High pressures for harsh conditions
• High temperatures
• Moist/dirty air streams
• Material handling
• Categorized by blade shapes
• Radial
• Forward curved
• Backward inclined
Centrifugal Fans

11. Types of Fans & Blowers
Centrifugal Fans – Radial fans
• Advantages
• High pressure and temp
• Simple design
• High durability
• Efficiency up to 75%
• Large running clearances
• Disadvantages
• Suited for low/medium
airflow rates only

12. Centrifugal Fans – Forward curved
•Advantages
• Large air volumes against low
pressure
• Relative small size
• Low noise level
•Disadvantages
• Not high pressure / harsh service
• Difficult to adjust fan output
• Careful driver selection
• Low energy efficiency 55-65%

13. Centrifugal Fans - Backward-inclined
• Advantages
• Operates with changing
static pressure
• Suited for high flow and forced
draft services
• Efficiency >85%
• Disadvantages
• Not suited for dirty airstreams
• Instability and erosion risk

14. • 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)
Axial Fans

15. Axial Fans – Propeller fans
• Advantages
• High airflow at low pressure
• Little ductwork
• Inexpensive
• Suited for rooftop
ventilation
• Reverse flow
• Disadvantages
• Low energy efficiency
• Noisy

16. 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%

17. 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

18. 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

19. 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

20. Positive Displacement Blowers
• Rotors trap air and push it through housing
• Constant air volume regardless of system
pressure
• Suited for applications prone to blockage
• Turn slower than centrifugal blowers
• Belt-driven for speed changes

21. Assessment of fans and blowers
• 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
Fan Efficiency and Performance

22. Peak efficiency or Best Efficiency Point
(BEP)
Airfoil
Tubular
Forward
Efficiency
Flow rate
Backward
Radial
Airfoil
Tubular
Forward
Efficiency
Flow rate
Backward
Radial
Type of Fan
Peak
Efficiency
Range
Centrifugal fans:
Airfoil, Backward
curved/inclined
79-83
Modified radial 72-79
Radial 69-75
Pressure blower 58-68
Forward curved 60-65
Axial fans:
Vane axial 78-85
Tube axial 67-72
Propeller 45-50

23. 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
Methodology – fan efficiency

24. Step 1: Calculate air/gas
density
Step 2: Measure air velocity
and calculate average
Step 3: Calculate the
volumetric flow in the
duct
Methodology – fan efficiency
t = Temperature of air/gas at
site condition
Cp = Pitot tube constant, 0.85
(or) as given by the
manufacturer
p = Average differential
pressure
γ = Density of air or gas at
test condition

25. Step 4: Measure the power drive of the motor
Step 5: Calculate fan efficiency
• Fan mechanical efficiency
• Fan static efficiency
Methodology – fan efficiency

26. • Non-availability of fan specification data
• Difficulty in velocity measurement
• Improper calibration of instruments
• Variation of process parameters during
tests
Difficulties in Performance Assessment

27. Energy Efficiency Opportunities
1. Choose the right fan
2. Reduce the system resistance
3. Operate close to Best Efficiency Point (BEP)
4. Maintain fans regularly
5. Control the fan air flow

28. • 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!
• 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
1. Choose the Right Fan

29. • Increased system resistance
reduces fan efficiency
2. Reduce the System Resistance
• Check periodically
• Check after system
modifications
• Reduce where
possible

30. • Best Efficiency Point = maximum
efficiency
• Normally close to rated fan capacity
• Deviation from BEP results in inefficiency
and energy loss
3. Operate Close to BEP

31. • Periodic inspection of all system
components
• Bearing lubrication and replacement
• Belt tightening and replacement
• Motor repair or replacement
• Fan cleaning
4. Maintain Fans Regularly

32. 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
5. Control the Fan Air flow

33. a) Pulley change: reduce motor/drive pulley
size
• Advantages
• Permanent speed
decrease
• Real energy reduction
• Disadvantages
• Fan must handle capacity change
• Only applicable if V-belt system or motor
5. Control the Fan Air flow

34. 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
5. Control the Fan Air flow

35. 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
5. Control the Fan Air flow

36. 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
5. Control the Fan Air flow

37. 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
5. Control the Fan Air flow

38. 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
5. Control the Fan Air flow

39. g) Disc throttle:
Sliding throttle that changes width of
impeller exposed to air stream
• Advantages
• Simple design
• Disadvantages
• Feasible in some applications only
5. Control the Fan Air flow

40. 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
5. Control the Fan Air flow

41. i) Operate fans in series
• Advantages
• Lower average duct pressure
• Less noise
• Lower structural / electrical support required
• Disadvantages
• Not suited for low resistance systems
5. Control the Fan Air flow

42. Effects of Over Size Motors
Installment of Oversized Motors
If the load is 7.5 KW and we select higher size motor, there
is loss of efficiency and so extra power consumption.

43. Benchmark
OK
Under Load
Over Load
Graphs Colors Coding

44. Department Fan No. Load%
D/S
RF#1 57
RF#2 76
Ring AC#1
RF#1 71
RF#2 61
Ring AC#2
RF#1 53
RF#2 70
Benchmark
80
Avoid Over Sized Motors
Actual Data

45. Avoid Over Sized Motors

46. Department Fan No. Load%
Ring AC#3
RF#1 30
RF#2 37
RF#3 43
Ring AC#4
RF#1 38
RF#2 40
Autocone
RF#1 46
RF#2 90
Benchmark 80
Avoid Over Sized Motors

47. Avoid Over Sized Motors

48. Department Return Fan# Load %
B.R/Card Return Fan# 1 49.87
D/S
Return Fan#1 50.82
Return Fan#2 43.45
Ring A.C 1
Return Fan#1 58.57
Return Fan#2 59.77
Ring A.C 2
Return Fan#1 66.80
Return Fan#2 66.57
Auto Cone
Return Fan#1 43.09
Return Fan#2 42.36
Benchmark 80
Avoid Over Sized Motors

49. Avoid Over Sized Motors

50. Fan Installation and Maintenance
 Fan rating tests are conducted under ideal conditions i.e. uniform straight
air flow .
 In practice duct connections cause non-uniform air flow.
 Location and installation of fan must consider the location of duct
components to minimize losses.
System Effect:
 This is the estimated loss in fan performance due to non-uniform air flow.
 System effect factor is obtained from resulting fan performance curve and
actual system curve.
A vortex or spin may be created by non-uniform flow conditions.
 This may be caused due to poor inlet box, multiple elbows or ducts near
the inlet.
 If vortex or spin cannot be avoided, the use of turning vanes, splitter
sheets will reduce the effect.

51. Inspection and Maintenance:
 Wear or accumulation on an impeller will cause weakening of the
impeller structure .
 Severe vibrations may cause damage or failure at the bearings or fan
structure.
Scheduled inspection of following items of fans is recommended:
 Bearings for proper operating temperature
 Excessive vibration of bearings or housing
 Belt drives for proper tension and minimum wear
 Correct coupling alignment
 Fan impeller for proper alignment and rotation
 Impeller free from excess wear or material accumulation

52. Thank You