5. Fans and Blowers

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5. Fans and Blowers
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Difference between fans, blowers and compressors
As per ASME the specific pressure, i.e, the ratio
of the discharge pressure over the suction
pressure is used for defining the fans, blowers
and compressors as highlighted below
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Fan types
Axial fan
Centrifugal fan
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Centrifugal Fan Types
Paddle Blade (Radial blade)
Forward Curved (Multi vane)
Backward Curved
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Axial Flow Fan Types
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Fan Types and Efficiencies
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System characteristic curve
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System curve
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Fan Laws
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Fan static pressure
Fan Static Pressure r SP SP (Fan outlet) SP
(Fan outlet)
SP (Fan outlet) Static pressure at fan outlet,
inches WC
SP (Fan outlet) Static pressure at fan inlet,
inches WC
r SP 0.05 (-10) 10.05 in W.C.
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Static Pressure Profile of the System
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Static pressure drop and rise across entire system
Fan behaviour
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• Flow control
• Damper - Most Popular
• Variable Speed Drive

Recirculation
Damper
100
VFC
Power
75
50
VFD
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Ideal
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75
50
100
Flow
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Impact of speed reduction
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Use of VSD Boiler ID fan case study
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Use of VSD Boiler ID fan case study(contd.)
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Energy audit of fan

• Collect fan and motor specifications with ducting
  network
• Measure motor power input
• Measure fan and motor speed
• Measure static pressure at various points in the
  duct
• Measure total and static pressure and compute
  flow
• Estimate the system efficiency and check fan
  operating point

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What to Look for in the Field

• Overall system efficiency will be determined by
  the type of fan or blower, its interaction with
  the air distribution system, and the method of
  control.
• Determine whether the right type of fan or blower
  is used for an application. Is your fan or blower
  is providing the best efficiency and performance
  in a given application.
• The efficiency of a system depends on the number
  and type of bends and restrictions. Sharp bends,
  especially, increase the resistance the fan or
  blower must overcome. Bends and restrictions near
  the inlet or outlet seriously degrade capacity
  and efficiency.
• With a properly selected fan or blower and
  well-designed air distribution system, the method
  of control is the main thing determining energy
  efficiency. In systems requiring constant air
  volume, the speed of a belt-driven fan or blower
  should be adjusted by proper selection of pulley
  sizes, and equipment should operate only when
  needed. In systems requiring variable airflow, an
  adjustable-speed control is most efficient.

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Energy conservation in fans

• Match fan capacity to demand
• downsizing, pulley change, VSD..
• Avoid unnecessary demand
• excess air reduction
• idling
• Reduce pressure drops
• Remove redundant ducts
• Modify ducting with minimum bends
• Drive system
• Provide direct drive where possible
• Replace V-belt by flat belt
• Replace with energy efficient fans
• Regular preventive maintenance

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Energy saving in Boiler ID fan by speed reduction
through pulley change
10
26 kW
8
1470 RPM
1181 RPM
14 kW
10
6
1470 RPM
882RPM