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Fan Fundamentals

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Vic McCauley

on 29 April 2013

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Transcript of Fan Fundamentals

BASICS of...
Fan Design and Selection Applications
Common fan terms
Fan blade types
Fan types
Bacon
Fan arrangements
Fan selection
Fan curve types
Fan performance control Coming Up Applications BASICS ...
to insure requirements are met Volume is the amount of gas required by application or system.
Standard air is type of gas most commonly used for calculations.

Requirements based on application
Ventilation
Changes of air per specific period of time
Material Handling
Minimum velocity required to keep material moving through pipe or duct
Dust/Mist/Vapor Collection
Maintain minimum velocity at collection point to catch the fumes, mist or dust

Combustion Applications
Require proper mass of components per specific period of time to insure proper combustion
Specify requirement of Weight Flow Rate in pounds of volume
The pounds per hour of gas required for combustion divided by the density equals volume (ACFM).

Common Units
cfm (cubic feet per minute)
m3/s (cubic meters per second)
l/s (liters per second) BASICS of Volume Fan vs. System
Pressure is the energy the fan imparts to the gas to overcome system resistance, in order to deliver required volume

Types of Pressure
Static Pressure -- SP is the potential energy to overcome system resistance
Velocity Pressure -- VP is the kinetic Energy associated with motion – movement of gas
VP usually negligible compared to SP with centrifugal fans and may be ignored
VP important with Axial Fans
Total Pressure -- TP is the sum of SP and VP
TP is the basis of Vane Axial selections

Sources of Resistance
Duct Walls and Duct Length
Filters
Control devices -- dampers
System effects due to design or jobsite limitations

Common Units
''WG (inches water gauge)
PSI (pounds per square inch)
mm Hg (millimeters mercury)
"Hg (inches mercury)
mm WG (millimeters H20) BASICS of Pressure Power required by the fan to deliver a specified volume and overcome a specified system resistance (TSP).

The motor must be selected to be equal to or greater than the BHP (kW)
Important factors in motor selection
RPM
Environment
= the weight of the object in pounds and the square of the radius of gyration in feet and expressed in terms of pound- feet squared.
Formula to calculate motor requirement:
(Nf)2
Motor = Fan X (Nm)2 + Sheave
Nf = Fan RPM
Nm = Full Load Motor RPM

Note:
1) Speed Up Drives - Motor must put out more than the fan.
2) Speed Down Drives - Motor must put out less than the fan.
3) Direct Drive - Motor and fan will be the same.

Common units
Brake Horsepower or BHP (English)
Kilowatts or kW (SI Units -- metric) Revolutions per minute is the impeller rotation rate required to deliver the required performance.

How to calculate the effect the change in RPM has on flow rate, pressure and power when everything else stays the same. Velocity is the speed the gas is moving at a specific point
Inlet velocity
Outlet velocity
Duct Velocity

Critical Velocity Applications
Conveying
Dust collection
Air knife

Controlling Air Velocity
Outlet Cone and Evasé
Slows gas down leaving the fan
Has a controlled expansion of the gas
Lessens resistance in the system
Increases efficient static regain

Inlet cone and Inlet Bell
Controls gas into fan
Minimizes losses

Common units: ft/min, m/hr, ft/sec, m/sec Density is the mass of gas per specified volume.

Factors affecting Density (D)
Temperature (T) -- if the T increases the D decreases
Elevation (E) -- the higher the E the lower the D
Humidity (H) -- if the H increases the D decreases
Gas makeup -- D will vary depending on the composition

Standard air is defined as 0.075 pounds per cubic foot, 70 degrees F, bone dry and measured at sea level. If the density of the gas is more or less than 5% from standard then corrections to the fan selection should be made.

Common Units: pounds per cubic foot, kilograms per cubic meter What is the sound data as stated by fan manufacturers?
Measured according to AMCA Standards 300/301
Tested in near perfect environment
Sound from all other sources taken out
These conditions do not exist on any job site
Fan noise data are only necessary for comparison of fans
System designer must be aware of job site conditions including the fan's location in relationship to other equipment, walls, surroundings, etc.

Fans generate two sources of sound that are measured
Sound from the inlet or the outlet of fan
This sound can be controlled with silencers or by extending the ductwork to a different location
Sound radiating from the fan housing
This can be controlled by varying housing material thickness, wrapping the fan with insulation, or installing a sound enclosure over the fan. A mechanical device designed to move a specified amount of gas by overcoming system resistance.

Typical Systems: Centrifugal
90 degree turn in direction of airflow
Differentiated by wheel types Axial
Airflow straight through fan
Differentiated by casing styles Paddle wheel design for dirty gas applications
Least efficient of all fan blade types
Noisiest
Used for material handling
Used for low velocity - high pressure applications Slightly less efficient than Airfoil (AF)
Handles light dust loading and moisture Combines radial and curved blades
Efficiency of curved design
Material handling and pressure capabilities of radial design
Common usage is for exhaust from kiln ovens and large dust collection systems Propeller Fan are Axial Fans
High volume, low pressure, low efficiency
Airfoil shaped blades improve efficiency and sound
Common Applications
Wall/ceiling ventilation
Machine/control panel cooling

Tube axial (TAX)
Axial wheel in a “tube” housing
Higher efficiency and pressure capabilities than PROP fan, but still relatively low
General exhaust, ventilation

Vane axial
Heavier construction than TAX, addition of straightening vanes
High Efficiency
Common Applications
Ventilation
Combustion
Energy recovery

Inline Centrifugal
Centrifugal wheel in a vane axial casing
medium efficiency
low pressure return air ventilation applications
Mixed Flow Fan -- Variation
Rules of Thumb:
If you could breath the air through the fan
Typically Air Foil (AF), Backward Inclined (BI), or Axial
If the airstream is dusty or moist or has the potential to be
Typically BI
If the airstream is dirty or has material going through the airstream
Typically Radial Blade (RB) or Radial Tip (RT)

Exceptions…
Performance outside normal range
Burner may require 1,000 CFM at 28”SP and it is a clean airstream, but AF will not operate under those conditions. A RB will.
If there is an applications when the airstream is dirty a special custom built airfoil can be built for efficiency and a dirty air stream. Arrangement 10 -- A/10
A/1 type fan with motor located under bearing pedestal
Common arrangement known as a Vent Set fan Two Entities in Selection
The Fan
The System
Each Entity represented by characteristic “Fingerprint”
The Fan Curve
The System Curve
Operating Point is at the intersection of these curves System curve
The only place a system can operate
Change in system changes curve
Characteristic of V and P Relationship through system Select to the right of peak pressure
10% between design and peak pressure
Allows for unforeseen system variation

For the same duty, select:
Smaller fan to move right on the fan curve
Larger fan to move left on the fan curve Non-overloading
Non-overloading fans have a point on the speed curve that the BHP max’s out at
Typical Impellers:
Air Foil (AF), Backward Inclined (BI), Axial Overloading fans
BHP continues to increase to full open flow
Caution must be used not to overload the motor
Typically requires damper or similar control on fan or in system
Typical Impellers:
Radial Blade (RB), Forward Curved (FC) Ratings based on standard air -- 0.075 lb/ft3, 70° F, Sea Level, 0% humidity
You have to interpolate between the catalog and the design condition
If selection is …
Above listed values -- point is left of peak and try a smaller size or different type
At the bottom of the table or below the table values that is an inefficient selection and/or over-speed for that fan. It would be better to choose a larger size or different wheel type.
The most efficient point is two or three values from the top value in each column.





Typical Performance Table showing comparison to a family of fan speed curves The computer will calculate the exact performance information
Be careful, fan selecting takes practice
AMCA allows variation in performance
There are performance losses not accounted for -- belt loss, system effects as oversights, uncertain job site conditions
System designers normally use varying amounts of safety factors in their designs -- know the application

Computer selects what you tell it to
Understand what your asking the fan to do and the conditions it will operate in including density, temperature, elevation, etc. Parallel blade inlet dampers
On inlet box or nested vanes
Pre-spins air in the same rotation as the wheel
Keeps pressure capabilities
Opposed blade outlet damper
Bolts to outlet of fan or Evasé
Adds pressure to system -- needs to stay right of peak Speed control
Generally most efficient way to control flow
Does not maintain pressure capabilities



Changing the blade pitch of an axial fans is also an efficient means to control performance Efficiency
The most efficient fan may be too close to peak pressure
More efficient fans cost less to operate for the same performance

Sound
Does the end user have any restrictions for the location?
A larger fan is quieter or consider a smaller fan with noise attenuation Speed
Can the fan handle the required speed? At maximum temperature?
Allow for future Conditions?

Outlet Velocity
Is there a maximum or minimum specified outlet velocity?
Would using an Evase’ make a more efficient operation? Available Space
Will the fan arrangement fit the available space?
Sound and vibration may be an issue at that location

Cost – What is important to the end user?
Purchase price or first cost -- actual cost of entire package
Operating cost -- cost to run fan package -- this is where fan efficiency plays big role
Does the end user understand the value of what you are providing?
Are there alternate features that will provide a benefit? BASICS of Density BASICS of Velocity BASICS of RPM Q = Flow Rate
P = Presssure
PWR = Power requirement BASICS of Fan Power BASICS of Sound BASICS of Fan Types A BASIC Fan Centrifugal fan types
SWSI -- Single Width Single Inlet
DWDI -- Double Width Double Inlet BASIC fan blade types Airfoil Highest efficiency, quietest, generally runs fastest
Clean gas applications
Special custom design wheels can be built for dirty airstream when efficiency is key Radial Backward Inclined/Curved Radial Curved Sound pressure levels are usually measured in decibels (dB) using the A weighting scale.

A sound level meter using the A scale integrates the noise of all frequencies from every ambient source to give a single number.

Manufacturers usually present the fan noise data using the sound pressure levels in each octave band.

Sound can be described as similar to light from a lamp

Sound levels diminish with distance just like light intensity.

Similar to Sound Power a 75 Watt bulb is still a 75 Watt bulb whether you are next to the bulb or three miles away. BASICS of Selecting Fans BASICS of Arrangement BASICS of Fan Curves Fan curve
Only area the fan can operate
Curve is at a specific fan speed
Pressure Vs. Volume Power vs. Volume Curve
Read values on Right side
The intersection of the Fan and Power curves are arbitrary Rule of Thumb Arrangement 1 (A/1)
Overhung wheel
No motor base attached to fan
CBC models include SQA, D/51 SW Plenum Fans, Industrial Airfoil (IAF) A/3
Center-hung wheel
Used in clean ambient airstream due to having a bearing in the airstream unless custom designed inlet
CBC model include:
D/51 DW, D/55 & D/5120 Plenum Arrangement 4 -- A/4
Direct drive, fan wheel mounted on the motor shaft
Ambient duty due to location of motor in airstream
CBC models include: SQAD, D/47, PFD Arrangement 7 -- A/7
Direct drive
A/3 type fan with motor direct coupled to fan
Attached base Arrangement 8 -- A/8
Direct drive
A/1 type fan with motor direct coupled to fan
Attached base Arrangement 9 -- A/9
A/1 fan with motor base attached
Belt drive, several variations -- 9T, 9S, 9H Custom built products offer wide variety of arrangement options BASICS of Axial Fans BASICS of Centrifugal Fan Plug
90 degree turn in direction of air flow
Wheel is installed directly in oven or dryer
Can handle temperatures up to 800 degrees Plenum
Un-housed fans
Installed directly into plenum
Normally arrangement 3 Understanding basics
leads to satisfied customers,
insuring expectations are met BASICS of Catalog Selection BASICS of Computer Selection BASICS of Performance Control BASICS of an Educated Selection Use common sense! http://www.engeqpt.com http://www.chicagoblower.com Design 36A SQA Airfoil with
Inlet Damper 36A SQAD Airfoil 44 SQA Airfoil Plug Fan 34 Vane Axial 47 Vane Axial 37 DCT Tube Axial Design 37 DCP
Direct Connect Panel Fan 38 CPB Cast Aluminum
Pressure Blower, Arrg 4 53 BI Single Stage
Pressure Blower Arrg 4 52 DDI Industrial
BI Arrg 4 16A Industrial Arrg 9
WF, LS or AM Wheels 36A SQBD Arrg 4
Square Housing D51A-DWDI, A\3 10A Airfoil Arrg 1 Design 5120 Airfoil Plenum Fan Design 1807/4800/4806/4894/5000/5400
Radial Tip, Inlet Box with Damper, Arrg 8
CW-TAU 45 degrees Design 36B SQB Backward Inclined Design 39A SQI Radial Blade Design 39A SQI Radial Blade
with Inlet Fangle IAF - Industrial Airfoil ICF - Industrial Centrifugal Fan IDD - Industrial Direct Drive Design 2300B - PAF
Pressure Air Fan Design 70 - Plug Fan Design 44 - DD - Direct Drive
Airfoil Plug Fan Design 10A Airfoil/Backward Curved
Heavy Duty Fan Design 1902/3/4 PFD
Package Forced Draft
Airfoil - Direct Drive CW-TH90 Arrg 7 Design 51 Airfoil Plenum Fan Insulated Housing
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