Technical Development Program COMMERCIAL HVAC EQUIPMENT Fans: Features and Analysis PRESENTED BY: Michael Ho Version 1.2
Menu Section 1 Section 2 Section 3 Section 4 Section 5 Section 6 Section 7 Section 8 Section 9 Section 10 Introduction Fan Types Centrifugal Fans Axial Fans AMCA Fan Classes Performance Ratings and Static Efficiency Fan Laws System Curve, Fan Stability, and System Effect Miscellaneous Fan Topics Summary
SECTION 1 FANS: FEATURES AND ANALYSIS Introduction
Objectives Identify fan types and basic construction Understand the application of the types of fan impellers Construct a system curve using the fan laws Identify stable fan selections Calculate system effect for an example fan Understand fan bearings, drives and motors Section 1 Introduction
SECTION 2 FANS: FEATURES AND ANALYSIS Fan Types
Centrifugal Fans Air is discharged at a right angle to fan shaft Scroll or Fan Housing Section 2 Fan Types
Plenum Fans Single-width, single-inlet airfoil impeller design, for mounting inside a cabinet Section 2 Fan Types
Axial (In-Line) Fans Air is discharged parallel to the fan shaft Section 2 Fan Types
SECTION 3 FANS: FEATURES AND ANALYSIS Centrifugal Fans
Centrifugal Fan Construction and Terminology Double-Width Double-Inlet Wheel (DWDI) Backplate Hub Disk Hubplate Webplate Housing or Scroll Blast Area Outlet Discharge Inlet Inlet Cone Inlet Bell Inlet Flare Inlet Nozzle Venturi Bearing Support Inlet Collar Inlet Sleeve Inlet Band Rim Shroud Wheel Ring Wheel Cone Inlet Rim Wheel Rim Blades Impeller Wheel Housing Side Sheet Outlet Area for Duct Connection Section 3 Centrifugal Fans
Impeller Velocity Vectors Resulting velocity in the scroll Radial Velocity Blade Tangential Velocity (Tip Speed) Section 3 Centrifugal Fans
Static Pressure vs. Velocity Pressure Static Pressure Section 3 Centrifugal Fans Velocity Pressure
Forward-Curved Wheel Design Tip Rotation Heel Characteristics: Most commonly used wheel in HVAC Light weight low cost Operates at static pressures up to 5 in. wg max 24 to 64 blades Low rpm (800 to 1200 rpm) Section 3 Centrifugal Fans
Forward-Curved Centrifugal Fan Characteristics Static Pressure Dip Overloading type fan Horsepower will continue to rise with increased cfm and can overload the motor Fan Horsepower Typical Forward-Curved rpm Line cfm Section 3 Centrifugal Fans
Airfoil Wheel Design Rotation Characteristics: Blades are curved away from direction of rotation Static pressure up to 10 in. wg 8 to 18 blades High rpm (1500 to 3000 rpm) Section 3 Centrifugal Fans
Airfoil Centrifugal Fan Characteristics Non-overloading Horsepower will peak and begin to drop off Static Pressure Fan Horsepower Typical Airfoil rpm Line cfm Section 3 Centrifugal Fans
Plenum Fan Characteristics Fan Wheel Guard Inlet Cone Plenum fans without cabinets Characteristics: Single-Width, Single-Inlet (SWSI) Best application with limited space or Operate at static pressures up to 10 in. wg when multiple duct discharge is desired Section 3 Centrifugal Fans
Plenum Fans With Cabinets Inlet Cone SWSI Plenum Fan Wheel Fan Cabinet Section 3 Centrifugal Fans
Plenum Fans 1. Airfoil centrifugal SWSI factory installed in a plenum (cabinet) 2. Plenum fans pressurize the plenum instead of accelerate the air down the duct, so the conversion from velocity to static pressure is done already 3. A major attraction is field-connected outlet ducts in multiple directions 4. Sound attenuation or lower discharge sound levels due to plenum 5. Less turbulence/pressure fluctuations entering duct system Section 3 Centrifugal Fans
SECTION 4 FANS: FEATURES AND ANALYSIS Axial Fans
Axial (In-Line) Fans Use for high cfm applications In-line space savers with no cabinet Often used in industrial AC and ventilation applications Impeller similar to prop fans but blades are more aerodynamic Often used for return fans in AC applications Propeller Type Impeller Section 4 Axial Fans
Axial Impeller Design Axial Wheel Air discharged parallel to the shaft Air is often redirected via straightening vanes making the fan a vane axial Section 4 Axial Fans
Tubular Centrifugal In-Line Fan Efficient because of centrifugal wheels Air is discharged from the wheel, then is redirected through straightening vanes as shown here Straightening Vanes Section 4 Axial Fans
In-Line Fan Types Section 4 Axial Fans
Mixed Flow Fans Air discharged at an angle instead of perpendicular Good efficiency and low sound Long bearing life due to low speed wheel design Compact size High volume characteristics of axial fans Mixed Flow Impeller Section 4 Axial Fans
Direct Drive Impeller Motor Section 4 Axial Fans
Belt Drive Motor Impeller Belt Drive Section 4 Axial Fans
SECTION 5 FANS: FEATURES AND ANALYSIS AMCA Fan Classes
Air Movement and Control Association AMCA is a trade association for the fan industry Section 5 AMCA Fan Classes
AMCA The Air Movement and Control Association is a trade association for the fan industry Providing assurance and reliability of manufacturer s published performance Providing buyers with information on testing procedures Verifying manufacturers performance ratings Standardizing test methods Manufacturers operate in accordance with AMCA Certified test lab Wide line of certified products Section 5 AMCA Fan Classes
AMCA Fan Classes AMCA Class I II III Maximum System Static Pressure 4 in. wg 7 in. wg 12 in. wg Section 5 AMCA Fan Classes
AMCA Centrifugal Fan Construction Class Total System Static Pressure (in. wg) If the fan discharge velocity is 3000 fpm and the total system static pressure is 6 in. wg, the operating conditions fall within the AMCA Class II range and a Class II fan should be considered for this application. If the fan discharge velocity is 2500 fpm and the total system static pressure is 3 in. wg, the operating conditions fall within the AMCA Class I range and a Class I fan could be used for this application. Outlet Velocity (fpm) Section 5 AMCA Fan Classes
AMCA Classes What Is Actually Different? Some manufacturers increase metal gauge, shaft diameter, add tip material, change to a higher strength material, etc. The bottom line is that the added loads of the higher speeds must be accommodated in the design. If you run a Class II wheel in a Class I condition it should last longer than a Class I wheel in the Class I conditions. A Class II wheel running in Class II conditions will not necessarily last longer than a Class I wheel in Class I conditions. The cost of Class III construction is usually prohibitive to be used for Class I conditions. Section 5 AMCA Fan Classes
SECTION 6 FANS: FEATURES AND ANALYSIS Performance Ratings and Static Efficiency
Centrifugal Fan Multi-Rating Table Section 6 Performance Ratings and Static Efficiency
Fan Curve Example Total Static Pressure (in. wg) Typical Speed Curve (rpm) 6 in. wg 26,000 cfm Static Efficiency Line Airflow (cfm) Section 6 Performance Ratings and Static Efficiency
SECTION 7 FANS: FEATURES AND ANALYSIS Fan Laws
The Fan Laws It is not practical to test a fan at every speed at which it may be applied. Fortunately, by the series of equations commonly referred to as the fan laws, it is possible to predict with good accuracy the performance of a fan at conditions other than those of the original rating. Section 7 Fan Laws
The Three Main Fan Laws The most commonly used fan laws in simplified form are: cfm varies DIRECTLY with rpm P S varies with the SQUARE of the rpm bhp varies with the CUBE of the rpm Section 7 Fan Laws
Fan Law 1 cfm varies DIRECTLY with rpm cfm 1 = cfm2 rpm rpm 1 2 Section 7 Fan Laws
Fan Law 2 Static pressure varies with the SQUARE of the rpm P P S1 S2 = æ ç è rpm rpm 1 2 ö ø 2 Section 7 Fan Laws
Fan Law 3 Horsepower varies with the CUBE of the rpm 3 bhp bhp 1 2 = æ ç è rpm rpm 1 2 ö ø Section 7 Fan Laws
The Fan Laws: Air Density Air Density Factors Section 7 Fan Laws
SECTION 8 FANS: FEATURES AND ANALYSIS System Curve, Fan Stability, and System Effect
System Resistance Components 1. Filter 2. Coil 3. Duct Elbows 4. Supply Duct 5. Supply Diffuser 6. Return Grille 7. Return Duct Section 8 System Curve, System Stability, and System Effect
System Curve Total Static Pressure (in. wg) 25% 50% 75% 110% 100% cfm (1000) Known: Fan delivers 10,000 cfm at 4 in. wg total static pressure Section 8 System Curve, System Stability, and System Effect
Intersection of System Curve and Fan rpm Estimated System Curve Peak Fan Pressure RP (Rated Point) Pressure Fan Pressure Airflow Curve Section 8 System Curve, System Stability, and System Effect cfm
Variation from Estimated System Curve Greater resistance means less cfm Estimated System Curve Less resistance means more cfm Pressure Constant rpm line Section 8 System Curve, System Stability, and System Effect cfm
Fan Stability Good Selection Total Static Pressure (in. wg) Shaded Area = Recommended Operating Range Airflow (1000 cfm) Legend - rpm - bhp MSE - Max. Static Eff. SC -System Curve RP - Rated Point Section 8 System Curve, System Stability, and System Effect
Fan Stability Poor Selection Total Static Pressure (in. wg) Rated Point too far to the left of MSE Airflow (1000 cfm) Legend - rpm - bhp MSE - Max. Static Eff. SC -System Curve RP - Rated Point Section 8 System Curve, System Stability, and System Effect
Fan Stability Other Factors Section 8 System Curve, System Stability, and System Effect
Fan Stability Other Factors Section 8 System Curve, System Stability, and System Effect
System Effect System effect is a pseudo static pressure increase resulting from an improper duct connection on the fan inlet or discharge. Section 8 System Curve, System Stability, and System Effect
Idealized Fan Test Station SYMMETRICAL THROTTLING DEVICE STRAIGHTENER 1. Manufacturers test their fans according to AMCA s latest standards 2. The test duct connection is idealized 3. Installations not meeting this ideal connection will have lower fan performance Section 8 System Curve, System Stability, and System Effect PILOT TUBE TRAVERSE VP 3r SP 3r TEST FAN OPTIONAL TRANSFORMATION PIECE ELEMENTS CONVERGING 15 MAX. DIVERGING 7 MAX A 3 = A 1 +12½% A 1-7½% A 1
System Effect Fans are tested under ideal conditions BUT they are rarely, if ever, installed under these conditions. Section 8 System Curve, System Stability, and System Effect
Desired Fan Discharge Velocity Profile To calculate 100% effective duct length, assume a minimum of 2½ duct diameters, for 2500 fpm or less. Add 1 duct diameter for each additional 1000 fpm. Example: 5000 fpm = 5 equivalent duct diameters. If duct is rectangular with side dimensions a and b, the equivalent duct diameter is equal to Section 8 System Curve, System Stability, and System Effect 4ab p
Step 1- Determine Fan Outlet Arrangement Find the Blast Area Outlet Area Ratio Fan Rotation Blast Area Height Outlet Area Height Cut-Off Plate Inlet Cone Fan Housing Section 8 System Curve, System Stability, and System Effect
Step 2 Losses - Outlet Duct Factors No Duct 12% Effective Duct 25% Effective Duct 50% Effective Duct 100% Effective Duct Pressure Recovery Blast Area Outlet Area 0% 50% 80% 90% 100% System Effect Curve Section 8 System Curve, System Stability, and System Effect 0.4 0.5 0.6 0.7 0.8 0.9 1.0 P P R-S S T-U V-W - R-S R-S S-T U V-W W-X - U U U-V W-X X - - W W W-X - - - - - - - - - - - Determining system effect Find blast area/outlet area from Step 1 or use 0.6 if not known Determine effective duct length Enter table above to find appropriate letter for system effect Example: 0.6 and 25% effective duct (use curve U or V)
Step 3- System Effect Curves Pressure Add System Effect Factor Pressure ( in. wg) 0.15 in. wg U 2500 fpm Given: 2500 fpm duct velocity and the U curve Air Velocity (fpm * 100) Air Density = 0.075 lb per cu ft Section 8 System Curve, System Stability, and System Effect
Discharge Elbows What if we had put a sideways turning elbow (Position B) right off the fan? What is the penalty in system effect? Section 8 System Curve, System Stability, and System Effect
System Effect Factors for Outlet Elbows System Effect Factor Curves for SWSI fans Impact of elbows: Enter table at 0.6 blast area ratio Enter at 25% effective duct With elbow B find curve R Now go to system effect curves to find loss Blast Area Outlet Area Multipliers For DWDI Fans Elbow Position B = DP S * 1.25 Elbow Position D = DP S * 0.85 Elbow Positions A and C = DP S * 1.00 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Outlet Elbow Position A B C D A B C D A B C D A B C D A B C D A B C D A B C D No Outlet Duct N M L-M L-M P N-O M-N M-N Q P N-O O S-T R-S Q-R R S R Q Q-R S-T R-S R R-S R-S S-T R-S R-S 12% Effective Duct O M-N M M Q O-P N-O N-O Q-R Q O-P P T S R R-S S-T R-S Q-R R T S R-S S S T S S 25% Effective Duct P-Q O N N R P-Q O-P O-P R-S R P-Q Q-R U T S S-T T-U S-T R-S S U T S-T T T U T T 50% Effective Duct S R Q Q T S R-S R-S U T S S-T W V U-V U-V V-W U-V U U-V W V U-V V V W V V 100% Effective Duct NO SYSTEM EFFECT FACTOR Section 8 System Curve, System Stability, and System Effect
Elbow Loss System Effect Factor Pressure (in. wg) 0.42 in. wg R 2500 fpm Elbow B added pressure loss Air Velocity (fpm * 100) Air Density = 0.075 lb per cu ft Section 8 System Curve, System Stability, and System Effect
System Effect Conclusion - Discharge Avoid non-uniform airflow at fan discharge Avoid Avoid Section 8 System Curve, System Stability, and System Effect
Non-Uniform Inlet Flow 24 Min. System effect caused by non-uniform airflow into the vortex of the plenum fan Section 8 System Curve, System Stability, and System Effect
SECTION 9 FANS: FEATURES AND ANALYSIS Miscellaneous Fan Topics
Bearings Hours and Years Grease (Zerk) Fitting How long is 200,000 hours? The following table converts hours to years based on different daily usage. Hours 8 hours per day YEARS 16 hours per day Continuous duty 40,000 13.7 6.8 4.6 100,000 34.2 17.1 11.4 200,000 68.4 34.2 22.8 400,000 137 68.4 45.8 500,000 171 85.6 57.0 1,000,000 342 171 114 Typical Pillow Block Bearing Section 9 Miscellaneous Fan Topics
L 10 Life ABMA Life Ratings ABMA American Bearing Manufacturers Association L 10 life is defined as the number of cycles that 90% of a group of identical bearings will last before fatigue failure occurs L 10 life assumes ideal conditions where factors affecting life, other than load, are present Section 9 Miscellaneous Fan Topics
Bearings Bearing Life: L 10 = B 10 L 50 = B 50 L 10 life of 40,000 hours, means that after 40,000 hours at design load and rpm, 10% of the bearings will have failed L 50 life of 200,000 hours means that after 200,000 hours at design load and rpm, 50% of the bearings will have failed Section 9 Miscellaneous Fan Topics
Bearing Life Bearing life is the length of time (or number of revolutions) until failure occurs Bearing life depends on: 1. Loading 2. Speed 3. Operating temperature 4. Maintenance 5. Contamination level Individual bearing life is impossible to predict accurately. Also, bearings that appear identical can exhibit considerable life differences. For instance, reducing the speed by ½ can double the life. Reducing the load by ½ may increase life by ~10. Section 9 Miscellaneous Fan Topics
Common HVAC Fan Motor Types Totally Enclosed Fan-Cooled (TEFC) Motor Open Drip Proof (ODP) Motor Section 9 Miscellaneous Fan Topics
Fan Drive Packages Characteristics: Classic V-Belt design Constructed of tough malleable iron High torque carrying capacities Fixed or adjustable based on motor size Variable Sheave Variable (adjustable) allowing the balancer to fine tune the specified airflow Industry often provides fixed sheaves (pulleys) on 25 hp or larger motors, as standard Section 9 Miscellaneous Fan Topics
Motor and Drive Terminology Motor Input kw = Motor Output/Motor Efficiency Fan bhp (Fan Shaft bhp) Fan Sheave hp *.746 = kw Drive Losses 3% to 5% V-Belts Motor Sheave Required Motor Output = (Fan bhp) + (Drive Losses) Drive Losses increase required motor output by 3 to 5% Section 9 Miscellaneous Fan Topics
Fan Spring Isolation Standard 2-inch Steel Spring Isolator 2-inch Seismic Rated Isolator Section 9 Miscellaneous Fan Topics
SECTION 10 FANS: FEATURES AND ANALYSIS Summary
Summary Identified fan types and basic construction Discussed the application of the various types of fans Constructed a system curve using the fan laws Identified stable fan selections Calculated system effect for an example fan Discussed fan bearings, drives and motors Section 10 Summary
Technical Development Program Thank You This completes the presentation. TDP-612 Fans: Features and Analysis Artwork from Symbol Library used by permission of Software Toolbox www.softwaretoolbox.com/symbols