commercial hvac equipment fans: features and...

Copyright © Carrier Corp. 2005

COMMERCIAL HVAC EQUIPMENT

Fans:Features and

AnalysisPRESENTED BY:

Michael Ho

Technical Development Program

Version 1.2


Menu

Section 2 Fan Types

Section 3 Centrifugal Fans

Section 1 Introduction

Section 8 System Curve, Fan Stability,and System Effect

Section 4 Axial Fans

Section 5 AMCA Fan Classes

Section 6 Performance Ratingsand Static Efficiency

Section 7 Fan Laws

Section 9 Miscellaneous Fan Topics

Section 10 Summary


SECTION 1

Introduction

FANS: FEATURES AND ANALYSIS


Objectives

• Identify fan types and basic construction

• Understand the application of the types offan 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

Fan Types



Centrifugal FansAir is discharged at a right angle to fan shaft

Scroll or Fan Housing

Section 2 – Fan Types


Plenum FansSingle-width, single-inlet airfoil impeller design,

for mounting inside a cabinet



Axial (In-Line) FansAir is discharged parallel to the fan shaft



SECTION 3

Centrifugal Fans



Centrifugal Fan Construction and TerminologyBlast Area Outlet

Discharge

ImpellerWheel

RimShroudWheel RingWheel ConeInlet RimWheel Rim

Inlet CollarInlet SleeveInlet Band

BearingSupport

InletInlet ConeInlet BellInlet FlareInlet NozzleVenturi

Blades

BackplateHub DiskHubplateWebplate

Double-WidthDouble-Inlet Wheel(DWDI)

Outlet Areafor DuctConnection

Housingor Scroll

HousingSide Sheet

Section 3 – Centrifugal Fans


Impeller Velocity Vectors

Blade

Tangential Velocity(Tip Speed)

Radial VelocityResulting velocity in the scroll



Static Pressure vs. Velocity Pressure

StaticPressure

VelocityPressure



Forward-Curved Wheel Design

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)

Rotation

Tip

Heel



• Overloading type fan– Horsepower will continue to

rise with increased cfm andcan overload the motor

Forward-Curved Centrifugal Fan CharacteristicsS

tatic

Pre

ssur

e

cfm

TypicalForward-Curvedrpm Line

Fan Horsepower

Dip



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)

Airfoil Wheel Design

Rotation



Airfoil Centrifugal Fan Characteristics

• Non-overloading– Horsepower will peak and

begin to drop off

Typical Airfoil rpmLine

Fan Horsepower

Sta

ticP

ress

ure

cfm



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

Fan WheelGuard

Inlet Cone

Plenum Fan Characteristics

Plenum fans without cabinets



Plenum Fans With CabinetsInlet 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 already3. A major attraction is field-connected outlet ducts in multiple directions4. Sound attenuation or lower discharge sound levels due to plenum5. Less turbulence/pressure fluctuations entering duct system

Plenum Fans



SECTION 4

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

Axial (In-Line) Fans

PropellerType 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



Tubular Centrifugal In-Line Fan• Efficient because of centrifugal wheels

• Air is discharged from the wheel, then isredirected through straightening vanesas shown here

Straightening Vanes



In-Line Fan Types



• Air discharged at an angleinstead of perpendicular

• Good efficiency and low sound

• Long bearing life due to lowspeed wheel design

• Compact size

• High volume characteristicsof axial fans

Mixed FlowImpeller

Mixed Flow Fans



Direct Drive

Impeller Motor



Belt Drive

Impeller

Motor

Belt Drive



SECTION 5

AMCA Fan Classes



Air Movement and Control AssociationAMCA 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



AMCA Fan Classes

AMCA Class Maximum SystemStatic Pressure

I 4 in. wgII 7 in. wgIII 12 in. wg



AMCA Centrifugal Fan Construction Class

If the fan discharge velocity is3000 fpm and the total systemstatic pressure is 6 in. wg, theoperating conditions fall withinthe AMCA Class II range anda Class II fan should beconsidered for this application.

If the fan discharge velocity is2500 fpm and the total systemstatic pressure is 3 in. wg, theoperating conditions fall withinthe AMCA Class I range and aClass I fan could be used forthis application.

Outlet Velocity (fpm)

Tota

lSys

tem

Stat

icPr

essu

re(in

.wg)



AMCA Classes

• 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 higherspeeds must be accommodated in the design.

• If you run a Class II wheel in a Class I condition it shouldlast longer than a Class I wheel in the Class I conditions.

• A Class II wheel running in Class II conditions will notnecessarily last longer than a Class I wheel inClass I conditions.

• The cost of Class III construction is usuallyprohibitive to be used for Class I conditions.

What Is Actually Different?



SECTION 6

Performance Ratings and Static Efficiency



Centrifugal Fan Multi-Rating Table

Section 6 – Performance Ratingsand Static Efficiency


Fan Curve Example

StaticEfficiencyLine

26,000 cfm

6 in. wg

Airflow (cfm)

Tota

lSta

ticPr

essu

re(in

.wg)

TypicalSpeedCurve(rpm)

Section 6 – Performance Ratingsand Static Efficiency


SECTION 7

Fan Laws



The Fan Laws

It is not practical to test a fan at everyspeed at which it may be applied.

Fortunately, by the series of equationscommonly referred to as the “fan laws,” itis possible to predict with good accuracythe performance of a fan at conditionsother than those of the original rating.

Section 7 – Fan Laws


The Three Main Fan Laws

The most commonly used fan laws insimplified form are:

cfm varies DIRECTLY with rpm

PS varies with the SQUARE of therpm

bhp varies with the CUBE of the rpm



Fan Law 1

2

1

2

1rpmrpm

cfmcfm =

cfm varies DIRECTLY with rpm



2

2

1

2S

1S

rpmrpm

PP

÷÷ø

öççè

æ=

Static pressure varies with theSQUARE of the rpm

Fan Law 2



3

2

1

2

1rpmrpm

bhpbhp

÷÷ø

öççè

æ=

Horsepower varies with theCUBE of the rpm

Fan Law 3



Air Density Factors

The Fan Laws: Air Density



SECTION 8

System Curve, Fan Stability,and System Effect



System Resistance Components

1. Filter2. Coil3. Duct Elbows4. Supply Duct5. Supply Diffuser6. Return Grille7. Return Duct

Section 8 – System Curve, System Stability,and System Effect


System Curve

100%

110%

75%50%

25%

Known: Fan delivers 10,000 cfm at 4 in. wg total static pressure

cfm (1000)

Tota

lSta

ticP

ress

ure

(in.w

g)



Intersection of System Curve and Fan rpmEstimated System Curve

cfm

Pre

ssu

re

RP (Rated Point)

Peak Fan Pressure

Fan PressureAirflow Curve



Variation from Estimated System Curve

cfm

Pre

ssu

re

Constant rpm line

Less resistancemeans more cfm

Estimated System Curve

Greater resistancemeans less cfm



Airflow (1000 cfm)

Tota

lSta

ticP

ress

ure

(in.w

g)

Legend- rpm - bhp MSE - Max. Static Eff. SC -System Curve RP - Rated Point

Fan Stability – Good Selection

Shaded Area =RecommendedOperating Range



Airflow (1000 cfm)

Tota

lSta

ticP

ress

ure

(in.w

g)

Fan Stability – Poor Selection

Legend- rpm - bhp MSE - Max. Static Eff. SC -System Curve RP - Rated Point

Rated Point toofar to the left ofMSE



Fan Stability – Other Factors



System Effect

System effect is a “pseudo”static pressure increase resultingfrom an improper duct connection

on the fan inlet or discharge.



1. Manufacturers test their fans accordingto AMCA’s latest standards

2. The test duct connection is idealized3. Installations not meeting this ideal connection

will have lower fan performance

PILOT TUBETRAVERSE OPTIONAL

TRANSFORMATIONPIECEELEMENTSCONVERGING – 15°MAX.DIVERGING – 7° MAX

Idealized Fan Test Station

STRAIGHTENER

VP3r

SP3r

A3 = A1+12½% A1

-7½% A1

SYMMETRICALTHROTTLING DEVICE

TEST FAN



System Effect

Fans are testedunder ideal conditions

BUTthey are rarely, if ever,

installed underthese 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 dimensionsa and b, the equivalent duct diameter is equal to

4abp

Desired Fan Discharge Velocity Profile



Step 1- Determine Fan Outlet Arrangement

Cut-Off Plate

Inlet ConeFanHousing

Find the Blast Area ÷ Outlet Area Ratio

Blast AreaHeight

FanRotation

Outlet AreaHeight



NoDuct

12%Effective

Duct

25%Effective

Duct

50%Effective

Duct

100%Effective

Duct

PressureRecovery 0% 50% 80% 90% 100%

Blast AreaOutlet Area System Effect Curve

0.40.50.60.70.80.91.0

PP

R-SS

T-UV-W-

R-SR-SS-TU

V-WW-X-

UU

U-VW-X

X-

-

WW

W-X-

-

-

-

-

-

-

-

-

-

-

Step 2 Losses - Outlet Duct Factors

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

Air Velocity (fpm * 100)

Sys

tem

Effe

ctFa

ctor

–P

ress

ure

(in.

wg)

Air Density = 0.075 lb per cu ft

2500 fpm

0.15 in. wg

Given:2500 fpm duct velocityand the “U” curve“U”



What if we had put a sideways turning elbow (Position B) right off the fan?What is the penalty in system effect?

Discharge Elbows



Blast AreaOutlet Area

OutletElbow

Position

NoOutletDuct

12%Effective

Duct

25%Effective

Duct

50%Effective

Duct

100%Effective

Duct

0.4ABCD

NM

L-ML-M

OM-NMM

P-QONN

SRQQ

0.5ABCD

PN-OM-NM-N

QO-PN-ON-O

RP-QO-PO-P

TS

R-SR-S

0.6ABCD

QP

N-OO

Q-RQ

O-PP

R-SRP-QQ-R

UTS

S-T

0.7ABCD

S-TR-SQ-RR

TSR

R-S

UTS

S-T

WV

U-VU-V

0.8ABCD

SRQ

Q-R

S-TR-SQ-R

R

T-US-TR-S

S

V-WU-VU

U-V

0.9ABCD

S-TR-SR

R-S

TS

R-SS

UT

S-TT

WV

U-VV

1.0ABCD

R-SS-TR-SR-S

STSS

TUTT

VWVV

NOSY

STEM

EFFE

CTFA

CTO

R

System Effect Factors for Outlet ElbowsSystem Effect FactorCurves 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 tofind loss

Multipliers For DWDI FansElbow Position B = DPS * 1.25Elbow Position D = DPS * 0.85Elbow Positions A and C = DPS * 1.00



Elbow Loss

2500 fpm

0.42 in. wg

Elbow “B”added pressure loss

“R”

Air Velocity (fpm * 100)

Sys

tem

Effe

ctFa

ctor

–P

ress

ure

(in.w

g)

Air Density = 0.075 lb per cu ftSection 8 – System Curve, System Stability,

and System Effect


Avoid

Avoid

System Effect Conclusion - Discharge

Avoid non-uniform airflow at fan discharge



Non-Uniform Inlet Flow

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

24” Min.



SECTION 9

Miscellaneous Fan Topics



Hours and Years

How long is 200,000 hours? The following tableconverts hours to years based on different daily usage.

HoursYEARS

8 hoursper day

16 hoursper day

Continuousduty

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

Bearings

Typical Pillow Block Bearing

Grease (Zerk) Fitting

Section 9 – Miscellaneous Fan Topics


ABMA Life Ratings

L10 Life• L10 life is defined as the number of cycles that

90% of a group of identical bearings will lastbefore fatigue failure occurs

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

American Bearing Manufacturers AssociationABMA



Bearing Life:• L10 = B10

L50 = B50

• L10 life of 40,000 hours, means that after40,000 hours at design load and rpm,10% of the bearings will have failed

• L50 life of 200,000 hours means that after200,000 hours at design load and rpm,50% of the bearings will have failed

Bearings



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.

Bearing Life



Common HVAC Fan Motor Types

Open Drip Proof(ODP) Motor

Totally EnclosedFan-Cooled

(TEFC) Motor



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 specifiedairflow

• Industry often provides fixed sheaves(pulleys) on 25 hp or larger motors, asstandard



Motor Input kW = Motor Output/Motor EfficiencyFan bhp

(Fan Shaft bhp)

Drive Losses3% to 5%

Fan Sheave

V-Belts

Motor Sheavehp * .746 = kW

Required Motor Output = (Fan bhp) + (Drive Losses)Drive Losses increase required motor output by 3 to 5%

Motor and Drive Terminology



Standard 2-inchSteel Spring Isolator

2-inchSeismic Rated Isolator

Fan Spring Isolation



SECTION 10

Summary



Summary

• Identified fan types and basic construction

• Discussed the application of the various typesof 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 YouThis completes the presentation.

TDP-612 Fans: Features and AnalysisArtwork from Symbol Library used by permission ofSoftware Toolboxwww.softwaretoolbox.com/symbols

commercial hvac equipment fans: features and...

Documents