1. Fan Selection Basics

2. 4 Fan Selection Basics Specific Speed Fan Features and Considerations
• Centrifugal Fan Selection
• Fan Laws
Specific Speed
• Multiple Fan Arrangements
Fan Features and Considerations

3. Fan Selection Basics Image area > Centrifugal Fan
Centrifugal Fan Selection
Centrifugal Fan
Air Enters the Impeller Axially, iiiThen Passes Through the iiiImpeller Radially
The Blades Drag the Air in a iiiCircular Motion and Centrifugal iiiForces Accelerate the Airflow iiiRadially Outward
The Airflow is Then Collected in iiiThe Volute Casing and iiiDischarged at Right Angles to iiithe Inlet Flow
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4. Fan Selection Basics Image area Motion of Air
Centrifugal Fan Selection
Motion of Air
The Increase of Centrifugal iiiForce With Radius Produces a iiiPressure Gradient, Whereby the iiiStatic Pressure in the Blade iiiIncreases With Radius
The Blades Drag the Air in a iiiCircular Motion and Centrifugal iiiForces Accelerate the Airflow iiiRadially Outward
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5. Fan Selection Basics Image area Motion of Impeller
Centrifugal Fan Selection
Motion of Impeller
The Motion of the Rotating iiiBlades Adds Rotational iiiMomentum to the Flow, iiiIncreasing the Velocity of Flow iiiin the Tangential Direction
As the Air Moves Radially iiiThrough the Impeller, the iiiAbsolute Velocity of the Flow iiiWill Increase, With the Absolute iiiMaximum Velocity at the iiiImpeller Outlet
The Increase in the Absolute iiiVelocity of the Air Leads to an iiiIncrease in the Kinetic Energy iiiand Dynamic Pressure Across iiithe Impeller
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6. Fan Selection Basics Image area Air Flow Through The Casing
Centrifugal Fan Selection
Air Flow Through The Casing
A Proportion of the Dynamic iiiPressure From the Air Leaving iiithe Impeller is Transferred Into iiiMore Useful Static Pressure
The Fan Casing is Usually iiiVolute Shaped, Allowing iiiDiffusion of the Air Leaving the iiiImpeller to Take Place
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7. Fan Selection Basics “The Fan Laws”
It is not practical to test every fan at every variable which may be encountered. Fortunately, by use of a series of equations, commonly referred to as the “Fan Laws” it is possible to predict with good accuracy the performance of a fan at other variables.
The variables include : Fan Size – D Fan Speed – N
Fan Air Density - Fan Flow Rate -
Fan Total Pressure -
Fan Velocity Pressure –
Fan Static Pressure –
Fan Input Power –
Fan Total Efficiency –
Fan Static Efficiency –
Compressibility Coefficient –
Sound Power Level - 7

8. Fan Selection Basics
Fan Laws - Volume 8

9. Fan Selection Basics
Fan Laws - Pressure 9

10. Fan Selection Basics
Fan Laws - Power 10

11. Fan Selection Basics
Fan Laws - Summary
Fan Law Summary 11

12. Fan Selection Basics
Fan Laws - Example 12

13. Fan Selection Basics
Fan Laws - Example 13

14. Fan Selection Basics Image area > Fan Specific Speed
The Ability of a Fan To Generate iiiPressure and Flow With Impeller iiiSpeed. It is the Speed at Which a iiiFan of Indeterminate Diameter iiiWill Run at to Produce Unit Flow iiiat Unit Pressure
Low Specific Speed Fans iiiProduce High Pressures at Low iiiFlow Volume
High Specific Speed Fans iiiProduce Lower Pressures at High iiiFlow Volumes
Specific Speed is Proportional to iiiImpeller Inlet Diameter and iiiImpeller Width for a Given (Fixed) iiiWheel Diameter
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Low Specific Speed
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High Specific Speed 14

15. Fan Selection Basics Image area Impeller Ranges
Impeller Styles and Specific Speed
Impeller Ranges
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Radial Impeller
Curved plate blades
Radial Impeller
Curved plate blades
Radial Impeller
Airfoil blades
Axial Impellers, various hub sizes
Airfoil blades 15

16. Start Up in Series or Parrallel
Fan Selection Basics
Multiple Fan Arrangements
Multiple Fan Arrangements
Fans in Series
Fans in Parallel
Start Up in Series or Parrallel 16

17. Fan Selection Basics Image area Fans in Series
Multiple Fan Arrangements
Fans in Series
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18. Fan Selection Basics Image area Fans in Parallel
Multiple Fan Arrangements
Fans in Parallel
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19. Fan Selection Basis Image area Start Up for Fans in Series
Multiple Fan Arrangements
Start Up for Fans in Series
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20. Fan Selection Basics Image area Start Up for Fans in Parallel
Multiple Fan Arrangements
Start Up for Fans in Parallel
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21. Fan Selection Basics Image area Fan Features and Considerations21

22. Fan Selection Basics Image area Fan Features and Considerations22