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7/30/2019 Understanding Fan Operation and Performance - W. Hilbish
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Understanding Fan Operation andPerformance
Walter Hilbish
Perry Nuclear Power Plant
FirstEnergy
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Fan Definition
What is a fan? Defined by ASHRAE
A fan is an air pump that creates a pressure
difference and causes airflow. The impeller
does work on the air, imparting to it both
static and kinetic energy, which vary in
proportion, depending on the fan type.2000 ASHRAE Systems and Equipment Handbook Chapter 18
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FansA fan is a constant volume machine. For a fixed
speed, the fan will move the same volume of gas
irregardless of gas density.
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Fans
Most manufacturers
rate the fan based
upon tests conducted
using AMCA 210. Testing uses ideal
configurations (i.e
straight duct runs, 10
duct diameters, no
obstructions, etc.).
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AMCA Installation Types
Four basic test
installations are defined.
AMCA Certified Ratings
require that the testinstallation be identified.
Example:Performance certified is forinstallation Type A: Free inlet, Freeoutlet. Performance ratings do not
include the effects of appurtenances(accessories). Performance ratingsdo not include the effects of crosswinds.
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Fan Performance Tables
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Fan CurvesGraphical depiction
of pressure-volume
performance of given
fan size and speed
operating at variouspoints from shutoff
to free delivery.
Graph may also
include power,efficiency, system,
and stall curves.
STP - standard temperature (70 F) and pressure (29.92 in Hg) with gas
density of 0.075 lb/ft3.
Unless otherwise specified the curve is
at STP .
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Fan Testing
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Fan Laws
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Fan Laws
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Fan Laws
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Types of Fan
Two basic types of fan are:
Centrifugal - rotating impeller to increasevelocity of an airstream.
Axial - air is pressurized by the aerodynamiclift of the fan blade.
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Centrifugal Fan Components
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Axial Fan Components
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Axial Fan Components
Vaneaxial fanshown
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Centrifugal Fans - Blade Designs
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Centrifugal - Airfoil
Blade curves away from direction ofrotation
Highest efficiency
Relatively low noise
High structural strength
Power reaches max near peak
efficiency, then reduces twoards free
delivery (self-limiting).
For given duty, has highest speed of
centrifugal design
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Centrifugal - Backward Inclined
Efficiency slightly less than
airfoil design
Pronounced region of instability
where low efficiency andpulsations (stall, surge, bi-stable
flow)
Power reaches max near peak
efficiency, then reduces t0wards
free delivery (self-limiting). Consideration for use in
applications where airfoil blade
erosion concern
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Centrifugal - Backward Curved
Power reduces towards free
delivery (self-limiting).
Promote smoother flow than BI
fan Operate at higher speeds and
therefore require sturdier
construction than FC
Less susceptible to flow/fan
instabilities due to lesspronounced instability region
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Centrifugal - Radial
Rugged blade design, self-cleaning
Lowest efficiency centrifugal
Used for material handling due to
blade strength
Moderate to high pressure industrialapplications
Power rises continually to free
delivery (overloading).
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Centrifugal - Radial Tip
Blade is radial at outer edge of wheel,
curved in direction of flow as it
moves inward
More efficient than Radial blade
Used for mildly erosive environments
Higher pressure than Airfoil
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Centrifugal - Forward Curved
Also called Squirrel Cage Blade curved forward in direction of
rotation
Low pressure HVAC applications
(residential, etc.)
Lower speed than other centrifugals
Single thickness blade, lightweight
construction
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Axial Fans - Types
Propeller - generally operate at< 1/2 inch water gauge,
inefficient, steeply rising power
curve (overloading).
Tubeaxial - propeller mountedin cylindrical tube, ranges up to
~ 4 inches water gauge,
overloading.
Vaneaxial - utilizes guidevanes to recover rotational
energy, up to 10 inches (single
stage), overloading.
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Axial Fans - Curves
Propeller Tubeaxial
Vaneaxial
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Axial Fan - Guide Vanes
Function - reduce thehelical flow pattern ofthe fan.
Inlet - vanes guide airflowinto a rotational pattern oppositeto fan rotation to provideneutralize deflection by bladesand result in axial flow
Outlet - vanes takerotational pattern from bladesand redirects it to an axial flow,converting some rotationalvelocity into static pressure.
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AMCA Class
Definition AMCA 99 -An establishedminimumperformance level for
fan aerodynamicperformance in termsof pressure and
airflow rate.
Simply put in general terms - the higherthe Class, the greater mechanical
strength (and price).
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Gaps/Clearances
Ensure gaps andclearances setper VendorManual
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Gaps/ Clearances continued
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Centrifugal Fan Volume Control
Generally 3 methods:
Variable speedchanging fan speed results in achange in fan flow.
Outlet damperfunctions by changing systemresistance, forcing the fan to operate againsthigher backpressure and reducing the flow.
Inlet dampercombination of resistance changeand potential flow characterisitic change (spin,reduced turbulence) at fan inlet.
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Centrifugal Fan Vortex
The inlet box damper(positioned properly) and
both types of inlet vane
dampers pre-spin the air
in the direction of fanrotation. By creating spin
in the direction of fan
rotation, the airflow,
pressure and horsepower
of the fan are reduced,resulting in a new fan
performance curve.
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Recognition
Following references were used in thegeneration of this presentation for technical
or pictorial support:
CML Northern Blower Fanfacts (1991)
Improving Fan System Performance: A
Sourcebook for Industry - DOE/AMCA
(2003)Engineering Papers - Moore Fans
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Recognition (continued)
CML Northern Blower Fanfacts (1991)
Fan Handbook: Selection, Application,
and Design - Frank P. Bleier (1997)
ASHRAE Systems and Equipment
Handbook Chapter 18, Fans (2000)
AMCA Fan Application Manual,
Publications 200-98 & 201-2002
AMCA Standards Handbook Publication
99
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Recognition (continued)
Fan Engineering, 9th Edition - Howden
Buffalo
Value in the Air: Why Direct DriveBackward Curved Plenum Fans? - AAON
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Additional Information may be found at the following websites:
http://www.moorefans.com/http://www.aaon.com/literature.aspx?id=1
http://www.chicagoblower.com/service/default.asphttp://www.cincinnatifan.com/catalogs/EngData-203-internet.pdfhttp://www.northernblower.com/download/fanfacts.pdfhttp://www.nyb.com/eng_letters.asphttp://www.greenheck.com/library/articles?c=2
http://www.hartzellfan.com/lib_pdf/Bulletin%20A-108-N.pdfhttp://www.tcf.com/TCFBlower/literature.asphttp://www.howden.com/en/Library/HowThingsWork/http://www.lorencook.com/PDFs/cookbook.pdf
For some history of fans, see the following:Benjamin Franklin Sturtevant
http://www.sturtevantfan.com/index.html
History of the Vaneaxial Fan
http://www.jba-1.com/HistoryOfVaneaxialFan.htm
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