Understanding Fan Operation and Performance Walter Hilbish Perry Nuclear Power Plant FirstEnergy

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

Fans A fan is a constant volume machine. For a fixed speed, the fan will move the same volume of gas irregardless of gas density.

Fans Most manufacturer’s 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.).

AMCA Installation Types Four basic test installations are defined. AMCA Certified Ratings require that the test installation be identified. Example: “Performance certified is for installation Type A: Free inlet, Free outlet. Performance ratings do not include the effects of appurtenances (accessories). Performance ratings do not include the effects of cross winds.”

Fan Performance Tables

Fan Curves Graphical depiction of pressure-volume performance of given fan size and speed operating at various points from shutoff to free delivery. Graph may also include power, efficiency, system, and stall curves. Unless otherwise specified the curve is at STP . STP - standard temperature (70° F) and pressure (29.92 in Hg) with gas density of 0.075 lb/ft3.

Fan Testing

Fan Laws

Fan Laws

Fan Laws

Types of Fan Two basic types of fan are: Centrifugal - rotating impeller to increase velocity of an airstream. Axial - air is pressurized by the aerodynamic lift of the fan blade.

Centrifugal Fan Components

Axial Fan Components

Axial Fan Components Vaneaxial fan shown

Centrifugal Fans - Blade Designs

Centrifugal - Airfoil Blade curves away from direction of rotation 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

Centrifugal - Backward Inclined Efficiency slightly less than airfoil design Pronounced region of instability where low efficiency and pulsations (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

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 less pronounced instability region

Centrifugal - Radial Rugged blade design, self-cleaning Lowest efficiency centrifugal Used for material handling due to blade strength Moderate to high pressure industrial applications Power rises continually to free delivery (overloading).

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

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

Axial Fans - Types Propeller - generally operate at < 1/2 inch water gauge, inefficient, steeply rising power curve (overloading). Tubeaxial - propeller mounted in cylindrical tube, ranges up to ~ 4 inches water gauge, overloading. Vaneaxial - utilizes guide vanes to recover rotational energy, up to 10 inches (single stage), overloading.

Axial Fans - Curves Tubeaxial Propeller Vaneaxial

Axial Fan - Guide Vanes Function - reduce the helical flow pattern of the fan. Inlet - vanes guide airflow into a rotational pattern opposite to fan rotation to provide neutralize deflection by blades and result in axial flow Outlet - vanes take rotational pattern from blades and redirects it to an axial flow, converting some rotational velocity into static pressure.

AMCA Class Definition AMCA 99 - An established minimum performance level for fan aerodynamic performance in terms of pressure and airflow rate. Simply put in general terms - the higher the Class, the greater mechanical strength (and price).

Gaps/Clearances Ensure gaps and clearances set per Vendor Manual

Gaps/ Clearances continued

Centrifugal Fan Volume Control Generally 3 methods: Variable speed – changing fan speed results in a change in fan flow. Outlet damper – functions by changing system resistance, forcing the fan to operate against higher backpressure and reducing the flow. Inlet damper – combination of resistance change and potential flow characterisitic change (spin, reduced turbulence) at fan inlet.

Centrifugal Fan Vortex The inlet box damper (positioned properly) and both types of inlet vane dampers pre-spin the air in the direction of fan rotation. 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.

Recognition Following references were used in the generation 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

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

Recognition (continued) Fan Engineering, 9th Edition - Howden Buffalo Value in the Air: Why Direct Drive Backward Curved Plenum Fans? - AAON

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.asp http://www.cincinnatifan.com/catalogs/EngData-203-internet.pdf http://www.northernblower.com/download/fanfacts.pdf http://www.nyb.com/eng_letters.asp http://www.greenheck.com/library/articles?c=2 http://www.hartzellfan.com/lib_pdf/Bulletin%20A-108-N.pdf http://www.tcf.com/TCFBlower/literature.asp http://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