Fans: Features and Analysis

Technical Development Program

COMMERCIAL HVAC EQUIPMENT Fans: Features and Analysis

PRESENTED BY: Michael Ho

Version 1.2

Section 1 Introduction Section 2 Fan Types Section 3 Centrifugal Fans Section 4 Axial Fans Section 5 AMCA Fan Classes Section 6 Performance Ratings and Static Efficiency Section 7 Fan Laws Section 8 System Curve, Fan Stability, and System Effect Section 9 Miscellaneous Fan Topics Section 10 Summary

FANS: FEATURES AND ANALYSIS

Introduction

• 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

FANS: FEATURES AND ANALYSIS

Fan Types

Scroll or Fan Housing

Air is discharged parallel to the fan shaft

FANS: FEATURES AND ANALYSIS

Centrifugal Fans

Housing Blast Area Backplate or Scroll Outlet Double-Width Discharge Double-Inlet Wheel Hub Disk (DWDI) Hubplate Webplate

Inlet Inlet Cone Inlet Bell Inlet Flare Inlet Nozzle Venturi

Blades Housing Outlet Area Side Sheet for Duct Connection Rim Impeller Shroud Wheel Bearing Wheel Ring Support Inlet Collar Wheel Cone Inlet Sleeve Inlet Rim Inlet Band Wheel Rim

Resulting velocity in the scroll Radial Velocity Blade

Tangential Velocity (Tip Speed)

Static Pressure

Velocity Pressure

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)

• Overloading type fan – Horsepower will continue to rise with increased cfm and can overload the motor e r u s

s Dip e r

P Fan Horsepower c i t Typical a t

S Forward-Curved rpm Line

cfm

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)

• Non-overloading – Horsepower will peak and begin to drop off e r u s s e r P

c Fan Horsepower i t a t Typical Airfoil rpm S Line

cfm

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

Inlet Cone SWSI Plenum Fan Wheel

Fan Cabinet

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

FANS: FEATURES AND ANALYSIS

Axial 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

• Axial Wheel – Air discharged parallel to the shaft – Air is often redirected via straightening vanes making the fan a vane axial

• Efficient because of centrifugal wheels • Air is discharged from the wheel, then is redirected through straightening vanes as shown here

Straightening Vanes

• 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

Motor Impeller

Motor

Impeller Belt Drive

FANS: FEATURES AND ANALYSIS

AMCA Fan Classes

• 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

Maximum System AMCA Class Static Pressure I 4 in. wg II 7 in. wg III 12 in. wg

g If the fan discharge velocity is w

. 3000 fpm and the total system n i

( static pressure is 6 in. wg, the e

r operating conditions fall within u

s the AMCA Class II range and s

e a Class II fan should be r

P considered for this application. c i t a

t If the fan discharge velocity is S 2500 fpm and the total system

m static pressure is 3 in. wg, the e t

s operating conditions fall within y

S the AMCA Class I range and a l

a Class I fan could be used for t

o this application. T

Outlet Velocity (fpm)

Section 5 – AMCA Fan Classes Copyright © Carrier Corp. 2005 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.

FANS: FEATURES AND ANALYSIS

Performance Ratings and Static Efficiency

. Static

n Typical i

( Efficiency Speed e Line r Curve u s

s (rpm) e r P c i t 6 in. wg a t S l a t o T 26,000 cfm

Airflow (cfm)

FANS: FEATURES AND ANALYSIS

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.

The most commonly used fan laws in simplified form are:

cfm varies DIRECTLY with rpm

PS varies with the SQUARE of the rpm

bhp varies with the CUBE of the rpm

cfm varies DIRECTLY with rpm cfm rpm 1 = 1 cfm2 rpm2

Static pressure varies with the SQUARE of the rpm 2 PS1 æ rpm1 ö = ç ÷ PS2 è rpm2 ø

Horsepower varies with the CUBE of the rpm 3 bhp1 æ rpm1 ö = ç ÷ bhp2 èrpm2 ø

Air Density Factors

FANS: FEATURES AND ANALYSIS

System Curve, Fan Stability, and System Effect

1. Filter 2. Coil 3. Duct Elbows 4. Supply Duct 5. Supply Diffuser 6. Return Grille 7. Return Duct

w 110% . n i ( e r u

s 100% s e r P c i

t 75% a

t 50% S

l 25% a t o T cfm (1000) Known: Fan delivers 10,000 cfm at 4 in. wg total static pressure

Estimated System Curve

Peak Fan Pressure

RP (Rated Point) e r

u Fan Pressure s

s Airflow Curve e r P

Greater resistance means less cfm

Estimated System Curve

Less resistance means more cfm

Constant rpm line e r u s s e r P

( Shaded Area = e

r Recommended u

s Operating Range s e r P c i t a t S l a t o T Airflow (1000 cfm) Legend - rpm - bhp MSE - Max. Static Eff. SC -System Curve RP - Rated Point

s far to the left of e r MSE P c i t a t S l a t o T Airflow (1000 cfm) Legend - rpm - bhp MSE - Max. Static Eff. SC -System Curve RP - Rated Point

System effect is a “pseudo” static pressure increase resulting from an improper duct connection on the fan inlet or discharge.

PILOT TUBE TEST FAN TRAVERSE OPTIONAL STRAIGHTENER TRANSFORMATION SYMMETRICAL PIECE THROTTLING DEVICE ELEMENTS CONVERGING – 15° VP 3r MAX. SP DIVERGING – 7° MAX 1. Manufacturers test their fans according 3r +12½% A1 A3 = A1 to AMCA’s latest standards -7½% A1 2. The test duct connection is idealized 3. Installations not meeting this ideal connection will have lower fan performance

Fans are tested under ideal conditions BUT they are rarely, if ever, installed under these conditions.

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 4ab a and b, the equivalent duct diameter is equal to p Section 8 – System Curve, System Stability, and System Effect Copyright © Carrier Corp. 2005 Step 1- Determine Fan Outlet Arrangement Find the Blast Area ÷ Outlet Area Ratio

Fan Rotation Blast Area Height Outlet Area Height

Cut-Off Plate

Fan Housing Inlet Cone

12% 25% 50% 100% No Effective Effective Effective Effective Duct Duct Duct Duct Duct

Pressure 0% 50% 80% 90% 100% Recovery Blast Area System Effect Curve Outlet Area

0.4 P R-S U W - 0.5 P R-S U W - 0.6 R-S S-T U-V W-X - 0.7 S U W-X - - 0.8 T-U V-W X - - 0.9 V-W W-X - - - 1.0 - - - - - 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)

. Given: n i ( e r

u 2500 fpm duct velocity s s e r “U” and the “U” curve P – r o t c a F t c e f f E m e t

s 0.15 in. wg y S 2500 fpm

Air Velocity (fpm * 100) Air Density = 0.075 lb per cu ft

Section 8 – System Curve, System Stability, and System Effect Copyright © Carrier Corp. 2005 Discharge Elbows What if we had put a sideways turning elbow (Position B) right off the fan? What is the penalty in system effect?

Outlet No 12% 25% 50% 100% Blast Area System Effect Factor Elbow Outlet Effective Effective Effective Effective Outlet Area Curves for SWSI fans Position Duct Duct Duct Duct Duct A N O P-Q S B M M-N O R 0.4 C L-M M N Q Impact of elbows: D L-M M N Q • Enter table at 0.6 A P Q R T 0.5 B N-O O-P P-Q S C M-N N-O O-P R-S blast area ratio D M-N N-O O-P R-S R O

A Q Q-R R-S U T P Q T C • Enter at 25% 0.6 B R A C N-O O-P P-Q S F effective duct D O P Q-R S-T T C

A S-T T U W E F

0.7 B R-S S T V F • With elbow “B” find C Q-R R S U-V E

D R R-S S-T U-V M

curve “R” E A S S-T T-U V-W T B R R-S S-T U-V S 0.8 Y

C Q Q-R R-S U S • Now go to system D Q-R R S U-V O effect curves to A S-T T U W N 0.9 B R-S S T V C R R-S S-T U-V find loss D R-S S T V

A R-S S T V Multipliers For DWDI Fans B S-T T U W 1.0 C R-S S T V D R-S S T V Elbow Position B = DPS * 1.25 Elbow Position D = DPS * 0.85 Elbow Positions A and C = DPS * 1.00 Section 8 – System Curve, System Stability, and System Effect Copyright © Carrier Corp. 2005 Elbow Loss ) g w

. “R” Elbow “B” n i ( e r

u added pressure loss s s e r P – r o t c

a 0.42 in. wg F t c e f f E m e t s y

S 2500 fpm

Air Velocity (fpm * 100) Air Density = 0.075 lb per cu ft

Avoid non-uniform airflow at fan discharge

Avoid Avoid

24” Min.

System effect caused by non-uniform airflow into the vortex of the plenum fan

FANS: FEATURES AND ANALYSIS

Miscellaneous Fan Topics

Hours and Years

How long is 200,000 hours? The following table converts hours to years based on different daily usage. Grease (Zerk) Fitting YEARS Hours 8 hours 16 hours Continuous per day per day 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

L10 Life

• L10 life is defined as the number of cycles that 90% of a group of identical bearings will last before fatigue failure occurs

• L10 life assumes ideal conditions where factors affecting life, other than load, are present

• L10 = B10

L50 = B50

• L10 life of 40,000 hours, means that after 40,000 hours at design load and rpm, 10% of the bearings will have failed

• L50 life of 200,000 hours means that after 200,000 hours at design load and rpm, 50% of the bearings will have failed

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.

Totally Enclosed Open Drip Proof Fan-Cooled (ODP) Motor (TEFC) Motor

• 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

Drive Losses 3% to 5%

V-Belts

Motor Sheave hp * .746 = kW Required Motor Output = (Fan bhp) + (Drive Losses) Drive Losses increase required motor output by 3 to 5%

Standard 2-inch 2-inch Steel Spring Isolator Seismic Rated Isolator

FANS: FEATURES AND ANALYSIS

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

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