7/23/2019 Ashrae - seleccion basica (ventilador Ingles)

1/22

1

Fan Selection Basics

7/23/2019 Ashrae - seleccion basica (ventilador Ingles)

2/22

2

Centrifugal Fan Selection

Fan Laws

Specific Speed

Multiple Fan Arrangements

Fan Features and Considerations

Fan Selection Basics4

7/23/2019 Ashrae - seleccion basica (ventilador Ingles)

3/22

3

Fan Selection BasicsCentrifugal Fan Selection

Image area

Centrifugal Fan

Air Enters the Impeller Axially,iiiThen Passes Through theiiiImpeller Radially

The Blades Drag the Air in a

iiiCircular Motion andCentrifugal iiiorces Acceleratethe Airflo! iiiRadially "ut!ard

The Airflo! is Then Collectedin iiiThe #olute Casing andiiiDischarged at Right Angles toiiithe Inlet lo!$$$$$$%

7/23/2019 Ashrae - seleccion basica (ventilador Ingles)

4/22

4

Fan Selection BasicsCentrifugal Fan Selection

Image area

Motion of Air

The Increase of Centrifugaliiiorce &ith Radius Producesa iiiPressure 'radient, &here(ythe iii)tatic Pressure in theBlade iiiIncreases &ith Radius

The Blades Drag the Air in aiiiCircular Motion andCentrifugal iiiorces Acceleratethe Airflo! iiiRadially "ut!ard

7/23/2019 Ashrae - seleccion basica (ventilador Ingles)

5/22

Fan Selection BasicsCentrifugal Fan Selection

Image area

Motion of Impeller

The Motion of the RotatingiiiBlades Adds RotationaliiiMomentum to the lo!,iiiIncreasing the #elocity of lo!iiiin the Tangential Direction

As the Air Mo*es RadiallyiiiThrough the Impeller, theiiiA(solute #elocity of the lo!iii&ill Increase, &ith the

A(solute iiiMaximum #elocity atthe iiiImpeller "utlet

The Increase in the A(soluteiii#elocity of the Air +eads to aniiiIncrease in the inetic Energyiiiand Dynamic Pressure Acrossiiithe Impeller

7/23/2019 Ashrae - seleccion basica (ventilador Ingles)

6/22

!

Fan Selection BasicsCentrifugal Fan Selection

Image area

Air Flow "#roug# "#e

Casing

A Proportion of the DynamiciiiPressure rom the Air +ea*ingiiithe Impeller is TransferredInto iiiMore -seful )taticPressure

The an Casing is -suallyiii#olute )haped, Allo!ingiiiDiffusion of the Air +ea*ingthe iiiImpeller to Ta.e Place

7/23/2019 Ashrae - seleccion basica (ventilador Ingles)

7/22$

Fan Selection BasicsFan Laws

%"#e Fan Laws&

It is not practical to test e*ery fan at e*ery *aria(le !hich may (e

encountered/ ortunately, (y use of a series of e0uations,

commonly referred to as the 1an +a!s2 it is possi(le to predict

!ith good accuracy the performance of a fan at other *aria(les/

The *aria(les include 3 Fan Size4 D Fan Speed 4 N

Fan Air Density - Fan Flow Rate -

Fan Total Pressure5

Fan Velocity Pressure

Fan Static Pressure

Fan Input Power Fan Total Efficiency

Fan Static Efficiency

o!pressi"ility oefficient

Sound Power #e$el -

7/23/2019 Ashrae - seleccion basica (ventilador Ingles)

8/22'

Fan Selection BasicsFan Laws ( )olume

7/23/2019 Ashrae - seleccion basica (ventilador Ingles)

9/22*

Fan Selection BasicsFan Laws ( +ressure

7/23/2019 Ashrae - seleccion basica (ventilador Ingles)

10/221,

Fan Selection BasicsFan Laws ( +ower

7/23/2019 Ashrae - seleccion basica (ventilador Ingles)

11/2211

Fan Selection BasicsFan Laws ( Summar-

Fan Law Summar-

7/23/2019 Ashrae - seleccion basica (ventilador Ingles)

12/2212

Fan Selection BasicsFan Laws ( ./ample

7/23/2019 Ashrae - seleccion basica (ventilador Ingles)

13/22

13

Fan Selection BasicsFan Laws ( ./ample

7/23/2019 Ashrae - seleccion basica (ventilador Ingles)

14/22

14

Fan Selection BasicsSpecific Speed

Image area

Fan Specific Speed

The A(ility of a an To 'enerateiiiPressure and lo! &ithImpeller iii)peed/ It is the )peedat &hich a iiian of IndeterminateDiameter iii&ill Run at to Produce

-nit lo! iiiat -nit Pressure +o! )pecific )peed ans

iiiProduce 6igh Pressures at +o!iiilo! #olume

6igh )pecific )peed ans

iiiProduce +o!er Pressures at6igh iiilo! #olumes

)pecific )peed is Proportional toiiiImpeller Inlet Diameter andiiiImpeller &idth for a 'i*en7ixed8 iii&heel Diameter

+o! )pecific )peed 6igh )pecific )peed$$$$$$%

7/23/2019 Ashrae - seleccion basica (ventilador Ingles)

15/22

1

Impeller 0anges

Fan Selection BasicsImpeller St-les and Specific Speed

Image area

Radial Impeller

Curved plate blades

Radial Impeller

Curved plate blades

Radial Impeller

Airfoil blades

Axial Impellers, various hub sizes

Airfoil blades

A1ridged Fan 0ange

9

:

;

?

@

A

B

9 > :9 :> ;9 ;>

)olume m32s

+

ressure

3

CsD;999

CsD:>99CsD@>9

CsD999

CsD@>99

I Metre dia/ fans

:B:9 rpm

: .gEm