52nd North Carolina Industrial Ventilation...

52nd North Carolina Industrial Ventilation Conference

Module MM-1-1 1

Monitoring & Maintenance of Monitoring & Maintenance of Ventilation Systems,Ventilation Systems,

P t I (MMP t I (MM 11 1)1)

NC Industrial Ventilation ConferenceNC Industrial Ventilation ConferenceRaleigh, NC Raleigh, NC –– April April 20102010

Part I (MMPart I (MM--11--1)1)

11MMMM--11--11

Have you ever heard this from Have you ever heard this from plant operations?plant operations?

“The new local exhaust “The new local exhaust ventilation system we started up ventilation system we started up a month ago doesn’t work!a month ago doesn’t work!EngineeringEngineering didn’t design it didn’t design it right!”right!”

MMMM--11--11 22

Tips to Prevent this Problem Tips to Prevent this Problem at Your Siteat Your Site

Where do you start?Where do you start? Why IVS failWhy IVS fail

Common failure modes forCommon failure modes for Common failure modes forCommon failure modes for HoodsHoods DuctsDucts FansFans Collectors Collectors –– TuesdayTuesday

Ventilation System MeasurementsVentilation System MeasurementsMMMM--11--11 33

Where Do You Start?Where Do You Start?

Broadly, are system problems due toBroadly, are system problems due to Original design?Original design? System modified without redesign?System modified without redesign? Poor operating practice? (Poor operating practice? (ieie, adjusting blast , adjusting blast

MMMM--11--11 44

p g p (p g p ( , j g, j ggates)gates)

Little or no system monitoring & Little or no system monitoring & maintenance?maintenance?

Getting startedGetting started Define the problem areas & symptomsDefine the problem areas & symptoms Gather visual and measurement data on Gather visual and measurement data on

systemsystem

Defining the ProblemDefining the Problem

Observable Symptoms?Observable Symptoms? Qualitative (visible, olfactory, etc.)Qualitative (visible, olfactory, etc.) Quantitative symptoms (air samples)Quantitative symptoms (air samples)

MMMM--11--11 55

Operator complaintsOperator complaints

Specific locations affected?Specific locations affected? Reasons, frequency of equipment entry?Reasons, frequency of equipment entry? One hood/enclosure?One hood/enclosure? Multiple hoods/enclosures?Multiple hoods/enclosures? Nowhere near a hood/enclosure?Nowhere near a hood/enclosure?

Data Gathering Data Gathering -- QualitativeQualitative

Original system design work as intended?Original system design work as intended? Design basis for each hood/enclosureDesign basis for each hood/enclosure System layout and schematicSystem layout and schematic

MMMM--11--11 66

System Baseline airflows and static pressuresSystem Baseline airflows and static pressures System IH Evaluation at startupSystem IH Evaluation at startup Problem area data today?Problem area data today?


Module MM-1-1 2

Data Gathering Data Gathering –– Qualitative, 2Qualitative, 2

System modification without redesign?System modification without redesign? Site have a Change Management System with Site have a Change Management System with

IVS knowledgeable people part of the IVS knowledgeable people part of the ??

MMMM--11--11 77

process?process? Compare original schematic to as installedCompare original schematic to as installed Visual clues if no documentationVisual clues if no documentation Problem area data todayProblem area data today

Data Gathering Data Gathering –– Qualitative, 3Qualitative, 3

Operating practices?Operating practices? Designated system ownerDesignated system owner Operators (line and IVS) trainedOperators (line and IVS) trained Blast gates locked or adjusted whenever anyone Blast gates locked or adjusted whenever anyone

wantswants

MMMM--11--11 88

wantswants Monitoring & Maintenance?Monitoring & Maintenance?

System Baseline Documentation available as System Baseline Documentation available as reference for M&Mreference for M&M

Installed monitoring devices or routine system Installed monitoring devices or routine system wide data gatheringwide data gathering

Breakdown or predictive maintenanceBreakdown or predictive maintenance Recent maintenance on systemRecent maintenance on system

Data Gathering Data Gathering -- QuantitativeQuantitative

Hoods/enclosuresHoods/enclosuresMeasure area of openingMeasure area of opening

M f l itM f l it

MMMM--11--11 99

Measure average face velocity across Measure average face velocity across openingopening

Process at hood cause interference?Process at hood cause interference? External air currents?External air currents?

Ducts & FansDucts & Fans Duct layout Duct layout –– diameters, lengths, types of transitions diameters, lengths, types of transitions

at junctionsat junctionsD t i l it d t tiD t i l it d t ti

Data Gathering Data Gathering –– Quantitative, 2Quantitative, 2

MMMM--11--11 1010

Duct conveying velocity and static pressuresDuct conveying velocity and static pressures Fan shaft speed, motor ampsFan shaft speed, motor amps

Air cleaning deviceAir cleaning device Differential pressureDifferential pressure Operating at base condition?Operating at base condition?

Causes of IVS FailuresCauses of IVS FailuresSudden Failure ModesSudden Failure Modes –– major airflow reductionmajor airflow reduction

Broken fan beltBroken fan belt Water in baghouse Water in baghouse

cleaning compressed aircleaning compressed air Bag sucked into ductBag sucked into duct

MMMM--11--11 1111

Bag sucked into ductBag sucked into duct Baghouse dust removal Baghouse dust removal

system backs up into system backs up into baghousebaghouse

Explosion vent opensExplosion vent opens

Causes of IVS Failures Causes of IVS Failures Gradual Failure ModesGradual Failure Modes

Dust buildup in elbowsDust buildup in elbows Dust erodes holes in ductsDust erodes holes in ducts Increasing filter differential Increasing filter differential

pressurepressure Bag cleaning systemBag cleaning system

MMMM--11--11 1212

Bag cleaning systemBag cleaning system Moisture sensitive dustMoisture sensitive dust

Slipping fan beltsSlipping fan belts Dust visible in exhaustDust visible in exhaust Duct gaskets or access door seals Duct gaskets or access door seals

leaking audiblyleaking audibly


Module MM-1-1 3

Causes of IVS Failures Causes of IVS Failures –– Gradual Gradual FailureFailureCollector High Differential PressureCollector High Differential Pressure

High bag differential pressure due to improper bag conditioning (seeding) at startup of new bags

MMMM--11--11 1313

at startup of new bags

Scrubber venturi plugging another example

Causes of IVS Failures Causes of IVS Failures –– where where in the system?in the system?Branch versus System failure?Branch versus System failure?

Branches Branches -- Localized impactLocalized impact Dusting at some hoodsDusting at some hoods Poor suction some hoods, harder suction at Poor suction some hoods, harder suction at

th h dth h d

MMMM--11--11 1414

other hoodsother hoods Filter and fan not obviously affectedFilter and fan not obviously affected

SystemSystem--widewide No or low airflowNo or low airflow Similar effects seen at all branchesSimilar effects seen at all branches

Causes of IVS FailuresCauses of IVS FailuresChange Change -- Add a duct branch/hoodAdd a duct branch/hood

AA

IDID D,inches

Q,CFM

V,fpm

VP/ 100’

AA 88 1500 4200 3.4

BB 88 3000 8400 13

MMMM--11--11 1515

BB

CC

BB 88

CC 88 4500 16800 350

Impossible conveying velocity Impossible conveying velocity requirements that fans cannot requirements that fans cannot deliver. Only option with this deliver. Only option with this duct is branch ON/OFF duct is branch ON/OFF procedure procedure –– good luck!good luck!

Rough Rule of Thumb:

Downstream duct diameter2 ~ sum of squares of upstream duct diameters

82+82 = 128 ~ 112 or 121

112+82 = 185 ~ 142 or 196, ~ 132 or 169

Causes of IVS FailuresCauses of IVS FailuresChange Change –– Remove Remove a duct branch/hooda duct branch/hood

MMMM--11--11 1616

Don’t blank a branch like these. It starves airflow and velocity downstream causing dust dropout.

Unless duct changed, bleed air equivalent on removed branch.

No Documented Proof of No Documented Proof of PerformancePerformance

BaselinePerformance Criteria:•Airflow: + 10 % design•Pressure: + 20% baseline•All duct branches

MMMM--11--11 1717

Turnover document -engineering to operations along with air monitoring results

ISOMETRIC VIEW - OPERATOR FRIENDLY

Causes of IVS Failures Causes of IVS Failures -- Changes to Changes to Calculated System Resistance :Calculated System Resistance :

Dust plugs ducts, elbows first - more resistance Baghouse filter media blinds - poor startup seeding Bags bridge in filter - dust removal failure or filter design

incorrect for particulate collectedA d l ft b d t t k

MMMM--11--11 1818

Access door left open – bypass duct network Fan belts wear and slip Balancing orifices or blast gates removed/changed Unauthorized changes to system Design not robust enough to minimize duct plugging Proof of performance not measured or documented


Module MM-1-1 4

Lack of management ownership and support No one accountable for system operation No trained personnel on site

C t t d ti t l / i t i t

Causes of IVS Failures Causes of IVS Failures –– Lack of Lack of Management SupportManagement Support

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Cannot get downtime to clean/maintain system No system in place to ensure changes done by

competent resources Breakdown rather than predictive maintenance –

Working Harder, Not Smarter

IVS Operating Skills IVS Operating Skills NeededNeeded

5 functional levels of increasing skill General Awareness User Operator

MMMM--11--11 2020

p Troubleshooter Change Reviewer

Site complexity and risk assessment determines job description and number of people trained at each level

SummarySummary

IV Systems degrade and stop performing without maintenance due to Physical reasons Management reasons

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Management reasons Predictive M&M is “Before the Fact” control of

exposures Staff for success, but keep looking for the best

value Best to work with Baselined IVS

Hood/Enclosure Failure Hood/Enclosure Failure ModesModes

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Open Faced HoodsOpen Faced HoodsOBJECTIVE: CAPTURE Dust source between

person and hood Protection is general air

movement into hood Low air velocity must pull

MMMM--11--11 2323

Low air velocity must pull dust into hood

Airflow requirement increases with distance

Welding hoods, simple “elephant trunk” hoods

Key Principle for Open HoodsKey Principle for Open HoodsFlow Rate as Distance from HoodFlow Rate as Distance from Hood

X ti 2 Q ti 4

MMMM--11--11 2424

X times 2 Q times 4

(move hood away and performance drops)


Module MM-1-1 5

Capture VelocitiesCapture Velocities

Dispersion Conditions

Example Capture Velocity, ft/min

Release with practically no velocity into quiet air

Evaporation from tanks; degreasing, etc.

50 -100

Released at low velocity Spray booths; intermittent 100 - 200

MMMM--11--11 2525

yinto moderately still air

p y ;container filling; welding; plating; pickling

Active generation into zone of rapid air motion

Spray painting in shallow booths; barrel filling; conveyor loading

200 – 500

Released at high initial velocity into zone of very rapid air motion

Grinding; abrasive blasting; tumbling

500 - 2000

Table 6-1: From American Conference of Governmental Industrial Hygienists (ACGIH®), Industrial Ventilation: A Manual of Recommended Practice for Design, 26th Edition. Copyright 2007. Reprinted with permission.

Capture Velocities Capture Velocities –– factors to factors to decide upper or lower end of rangedecide upper or lower end of range

Lower End of Range Upper End of Range Room air currents minimal

or favorable to capture Disturbing room air

currents

Contaminants of low toxicity or of nuisance

Contaminants of high toxicity

MMMM--11--11 2626

toxicity or of nuisance value only

toxicity

Intermittent, low production

High production, heavy use

Large hood-large air mass in motion

Small hood-local control only

Table 6-1: From American Conference of Governmental Industrial Hygienists (ACGIH®), Industrial Ventilation: A Manual of Recommended Practice for Design, 26th Edition. Copyright 2007. Reprinted with permission.

Hood Shape and Distance Hood Shape and Distance Determine Required AirflowDetermine Required Airflow

MMMM--11--11 2727

Fig. 6-11: From American Conference of Governmental Industrial Hygienists (ACGIH®), Industrial Ventilation: A Manual of Recommended Practice, 26th Edition. Copyright 2007. Reprinted with permission."

Hood Calculations Hood Calculations -- Math Math ReviewReview

Continuity Equation: Q = VxA = V1xA1 = V2xA2Q-ft3/min, V-ft/min, A-ft2

Duct Area:

MMMM--11--11 2828

A = pi x radius2 = pi x (diameter/2)2

A=3.14x(D/2)2x(1 ft/12in)2 = pi x D2/576

Velocity-Velocity Pressure:V = 1096x(VP/df)1/2 = 4005x(VP)1/2 (sea level)or VP = (V/4005)2 (VP-inches water column)

Calculate Hood Face VelocityCalculate Hood Face Velocity

MMMM--11--11 2929

Hood Face Velocity SolutionHood Face Velocity Solution

Find VductVd = 4005x(1.1)1/2 = 4200 ft/min

Find AductAd = pi x (4)2/576 = 0.087 sq.ft.

MMMM--11--11 3030

Find AhoodAh = 4”x10”x(1 ft/12”)2 = 0.278 sq.ft.

Calculate VhoodVh = Vd x (Ad/Ah)

= 4200 x (0.087/0.278) = 1315 ft/min


Module MM-1-1 6

Calculate Hood SPCalculate Hood SP

MMMM--11--11 3131

Included angle = 90o


1. Find duct VP

2 Find entry loss coefficient for shape

MMMM--11--11 3232

2. Find entry loss coefficient for shape

3. Find acceleration loss

4. Calculate Hood SP

Hood Entry Losses Hood Entry Losses –– ShapesShapes

MMMM--11--11 3333

Fig. 9-a: From American Conference of Governmental Industrial Hygienists (ACGIH®), Industrial Ventilation: A Manual of Recommended Practice for Design, 26th Edition. Copyright 2007. Reprinted with permission.

Hood Entry Losses Hood Entry Losses -- TransitionsTransitions

MMMM--11--11 3434

Fig. 9-a: From American Conference of Governmental Industrial Hygienists (ACGIH®), Industrial Ventilation: A Manual of Recommended Practice for Design, 26th Edition. Copyright 2007. Reprinted with permission.

1. Duct VP = 1.1”w.c. (diagram)2. Entry loss = 0.25 x VP3 Acceleration loss = 1 x VP


MMMM--11--11 3535

3. Acceleration loss = 1 x VP4. Hood SP

= acceleration loss + entry loss = 1VP+0.25VP=VP(1+0.25)=1.1x1.25 = 1.4”w.c.

Using Hood Static Pressure (Using Hood Static Pressure (SPSPhh) for ) for MonitoringMonitoring

Every hood has a specific SPh based on its shape and the airflow through it.

SPh values can be found in Industrial Ventilation, A Recommended Practice

MMMM--11--11 3636

A Recommended Practice SPh values can be measured in the field at

startup Local SPh indication (Magnehelic or manometer)

provides operator warning of IVS problems


Module MM-1-1 7

Open EnclosuresOpen Enclosures

OBJECTIVE: CONTAIN Person in front of cabinet, dust

inside cabinet Protection: low velocity inward

i t

MMMM--11--11 3737

air movement Avoid giving particle escape

velocity from process or manual handling procedure

Bag dumps, super sack dumps, dump cabinets

Uniform Velocity Profile Techniques to Uniform Velocity Profile Techniques to Get Equal Air Path LengthsGet Equal Air Path Lengths

Internal baffle

Bag dump open face enclosure

MMMM--11--11 3838

Air inlet from top – unequal air paths => poor face velocity profile (arrow length)

Baffle moves air inlet to back wall – equal air path lengths & velocities

Air inlet from back – equal air path lengths also possible – decide based on layout

Uniform Velocity ProfileUniform Velocity ProfileSlotsSlots

Hood opening: 60” x 60”

3 slots, 2”x 36”

Duct diameter 12”

MMMM--11--11 3939

Duct diameter 12

Rectangular to round duct transition 120 degrees

Sealed EnclosuresSealed Enclosures Contaminant totally surrounded by

enclosure Protection: negative pressure and

inward air movement Low air velocity at access openings

A id l i i

MMMM--11--11 4040

Avoid enclosure positive pressure -dusting

Examples: belt conveyor housings, bins, Loss In Weight bins

Need air bleed to maintain duct conveying velocity

Air Bleeds Air Bleeds –– Maintain Duct Conveying Maintain Duct Conveying Velocity with Sealed EnclosuresVelocity with Sealed Enclosures

Good Air Bleed Design

MMMM--11--11 4141

How does air get How does air get into the duct?into the duct?

Biggest Hood & Enclosure FailureBiggest Hood & Enclosure FailureCause: Room Air CurrentsCause: Room Air Currents

MMMM--11--11 4242

Open windowsPedestal fans

High velocity HVAC diffusers


Module MM-1-1 8

Face Velocity Impact:Face Velocity Impact:Unauthorized ChangesUnauthorized Changes

MMMM--11--11 4343

Other Hood/Enclosure Failure Other Hood/Enclosure Failure ModesModes

Open hood moved out of position Excessive particle momentum

Face velocity too low to stop high energy particles Process design steps to slow particles

Poor face velocity profile

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Poor face velocity profile Unequal air paths External air currents

Changing hood airflow Physical changes to hood (ie, dust buildup inside, etc.) Connected IVS degrades

No air bleed on sealed enclosure HVAC Supply insufficient

Hood MaintenanceHood Maintenance

Visual Checks React to visible emissions to room Check for hood modifications

First line of defense – monitor air flow

MMMM--11--11 4545

Install Hood Static Pressure gauges with action limits (+ 20% Baseline)

OR take routine Face Velocity

measurements

Hood Maintenance, cont.Hood Maintenance, cont.

Things that can change airflow: Dirty screens Deposited

contaminants in plenum behind

MMMM--11--11 4646

plenum behind hood opening

Bypassing thru open access doors

Hood face modifications

Duct & Fan Duct & Fan Failure ModesFailure Modes

4747MMMM--11--11

Key Duct Design Key Duct Design PrinciplesPrinciples

Round ducts preferred Smooth duct interior, not spiral wound Adequate conveying velocity - ALL BRANCHES – target +

10% design

MMMM--11--11 4848

10% design Elbow radius 2.5 R/D mitered or 2.0 R/D smooth is best

to minimize duct fouling Merge two dusty streams at angle appropriate for dust

properties Balance and Baseline systems to prove you got what you

paid for


Module MM-1-1 9

Design Principles Design Principles -- Duct Duct SizingSizing

Size Ducts for Conveying Velocity Range Dust Control Systems: 3500 to 4500 fpm. Aerosol or other small particle Control Systems:

2500 to 3500 fpm.

MMMM--11--11 4949

(ft/min)duct in ty air veloci V

min)/(ft airflow Q

(inches)diameter duct D

)(ftduct of area sectional-crossA

: where 576/)144/1)(4/(

3

2

22

V

QDDA

Range of Minimum Duct Design Range of Minimum Duct Design Velocities Velocities

Nature of Contaminant

Examples Minimum Design Velocity, fpm

Vapors, gases,

k

All vapors, gases, smoke Any desired velocity (economic optimum

l it ll )

MMMM--11--11 5050

smoke velocity usually)

1000 - 2000 Fumes Welding 2000 – 2500

Very fine light dust

Fine rubber dust, Bakelite molding powder dust, jute lint, cotton dust, shavings (light,) soap dust, leather shavings

3000 – 4000

Table 3-1: From American Conference of Governmental Industrial Hygienists (ACGIH®), Industrial Ventilation: A Manual of Recommended Practice, 25th Edition. Copyright 2004. Reprinted with permission.

Nature of contaminant

Examples Minimum transport velocity, fpm

Average industrial

dust

Grinding dust, buffing lint (dry), wool jute, coffee beans, shoe dust, granite dust, general material handling, brick dust, clay dust, foundry (general,) limestone dust

3500 - 4000

Range of Minimum Duct Design Range of Minimum Duct Design VelocitiesVelocities

MMMM--11--11 5151

limestone dust

Heavy dusts Sawdust (heavy & wet,) metal turnings, foundry tumbling barrels and shake-out, sand blast dust, wood blocks, hog waste, brass turnings, cast iron boring dust, lead dust

4000-4500

Heavy or moist

Lead dusts with small chips, moist cement dust, asbestos chunks from transite pipe cutting machines, buffing lint (sticky,) quick lime dust

> 4500

Table 3-1: From American Conference of Governmental Industrial Hygienists (ACGIH®), Industrial Ventilation: A Manual of Recommended Practice, 25th Edition. Copyright 2004. Reprinted with permission.

Duct Conveying Velocity Changes with Duct Conveying Velocity Changes with Diameter Diameter

Find V & VPQ=VA=VAAA=VBAB, VB=VA(AA/AB)Remember duct area A=Pi D2/4

V =V (D /D )2 = 1000(8/4)2

MMMM--11--11 5252

VB=VA(DA/DB)2 = 1000(8/4)2

= 4000 fpmV = 4005(VP)1/2, VP=(V/4005)2

VPA = (1000/4005)2 = 0.062” w.c.

VPB = (4000/4005)2 = 0.998” w.c.

Pressure Loss Pressure Loss ––Overcoming Straight Duct FrictionOvercoming Straight Duct Friction

Smaller ducts have greater resistance per length. They create high system pressure

MMMM--11--11 5353

create high system pressure drop on the governing leg of the system.

Maintenance Saver Maintenance Saver ––Long Radius ElbowsLong Radius Elbows

MMMM--11--11 5454


Module MM-1-1 10

Branch Entries:Branch Entries:Merge angle based on contaminant characteristicsMerge angle based on contaminant characteristics

MMMM--11--11 5555

15 degree15 degree30 degree30 degree

Branch Entries:Branch Entries:Do not use TDo not use T--ConnectionConnection

MMMM--11--11 5656

Pressure Loss Pressure Loss –– Branch EntriesBranch Entries

Very sticky

MMMM--11--11 5757

Mildly sticky

Dry, free flow

NO, don’t do this!!!!

Fig. 9-f: From American Conference of Governmental Industrial Hygienists (ACGIH®), Industrial Ventilation: A Manual of Recommended Practice for Design, 26th Edition. Copyright 2007. Reprinted with permission.

Balancing Airflows Balancing Airflows Between BranchesBetween Branches

MMMM--11--11 5858

1. w/o balancing devices, airflow takes path of least resistance

2. Change in one branch affects entire system balance

Note: 11” S.P. to fan, 7” just to get to bag

house inlet

Which Method to Balance Systems Is Which Method to Balance Systems Is Used at Your Site?Used at Your Site?

Balance by Design Size ducts to restrict flow or

add flow Adds 10-20% more airflow to

system

l b l

MMMM--11--11 5959

Balance by Blast Gate Adjustable (both advantage

and disadvantage)

Balance by Fixed Orifice Pre-calculate orifice size

based on actual duct construction – most accurate balance

At a glance, duct design At a glance, duct design principles met?principles met?

KEY PRINCIPLES1. Size duct for

conveying velocity in all branchesM i t i

1133

44

MMMM--11--11 6060

2. Maintain conveying velocity through merge of two dusty air streams

Good, Bad, & Ugly all in one photo!

22

33


Module MM-1-1 11

Duct MaintenanceDuct Maintenance

Visual Damage-dents, holes? Open duct access doors? Local gauges with action

limitsR ti it i

MMMM--11--11 6161

Routine monitoring Duct network static pressures Strategic airflows

Take Troubleshooting action > + 20% Baseline static pressure

Maintenance Access Maintenance Access

Fittings & elbows should be flanged (or have quick disconnect couplings) at both ends.

For frequently removed section or complex sections -match mark adjoining duct sections for efficient re-assembly

MMMM--11--11 6262

assembly. Provide quick opening access door in large diameter

ductwork (18” dia. and above). Consider permanent platforms for hard to reach duct

section requiring frequent cleanout.

Monitoring Monitoring -- Test Test PortsPorts

Remote sensing of duct static pressure saves climbing ladders

Use single piece of tubing

MMMM--11--11 6363

Use single piece of tubing Need to wait for reading

to equalize Check for plugging if

reading doesn’t change

Courtesy Dwyer Co.

Belts lose or worn?Pulleys aligned?Bearings lubed?Vibration?

Fan Failure Modes Fan Failure Modes -- Fan Fan Drive SystemDrive System

MMMM--11--11 6464

Fan Design PrinciplesFan Design Principles

Match the fan performance curve with the system Oversizing for possible future need may be inefficient operating

point for current need Consequence – major energy costs

For long term reliability

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o o g te e ab ty Heavy duty industrial exhausters Optimal shaft alignment and balance Don’t exceed fan mfr’s maximum shaft speed recco.

Avoid fan performance degradation (system effects) due to poor fan inlet and discharge duct design

Design Operating PointDesign Operating Point

System balance calculations determine fan requirement

Fan Performance TablesFan

Pressure

MMMM--11--11 6666

Fan Performance Tables locate the vendor’s fan that can deliver requirement

SystemSystem

OperatingPoint

Flow


Module MM-1-1 12

Fan LawsFan Laws

•First Law: Airflow

•Second Law: Static Pressure

Q QN

N3 23

2

SP SPN

N3 23

2

2

MMMM--11--11 6767

•Third Law: Power

rough approximation:

N2

PWR PWRN

N3 23

2

3

268.2)(

3

PaSPh

mairflow

kWPWR

Calculation Calculation –– Fan Capable of Fan Capable of Change?Change?

Performance of existing fan 12,546 ACFM @ 8” FSP Fan shaft speed 875 RPM and 23.2 BHP.Increase flow at the system hoods to

MMMM--11--11 6868

Increase flow at the system hoods to 14,000 CFM without changing any of the system duct. The Determine new operating volume, pressure and horsepower if the change is made by only a fan speed increase.

Fan Laws CalculationFan Laws Calculation

1. Calculate new fan shaft speed

2 Calculate new static pressure required

MMMM--11--11 6969

2. Calculate new static pressure required

3. Calculate new brake horsepower

Fan Laws CalculationFan Laws Calculation

Speed change N2=N1(Q2/Q1)=875(14000/12546)=976 RPM

Static pressure change P2=P1(Q2/Q1)2 =8”(14000/12546)2= 9.95”

MMMM--11--11 7070

2 1(Q2/Q1) ( / )

Brake horsepower change HP2=HP1(Q2/Q1)3=23.2(14000/12546)3

=32.2 BHP (versus 25 HP motor) fan motor upgrade to next size, 40 HP MCC & wiring upgrade size 2 size 3

Effect of Fan Speed ChangeEffect of Fan Speed Change

(1.1)2=1.21

(1.1)3=1.33

MMMM--11--11 7171

(1.1)

No Fan System EffectsNo Fan System Effects

No loss stack4 x (D+1”)

Inlet duct- 5D or greater

System effects can add several inches Fan Static Pressure to overcome poor inlet conditions

MMMM--11--11 7272


Module MM-1-1 13

Stack Weather Head Stack Weather Head –– Critical to DispersionCritical to Dispersion

MMMM--11--11 7373

DON’T USE THESE!

Recommended “No Loss” Stackhead – bird’s eye view!

Fan MaintenanceFan Maintenance

Visual Overheated bearings? Unusual noises or vibrations (belts aligned?, impeller

out of balance-erosion/buildup?) Air leaks on flexible connections?

MMMM--11--11 7474

Routine Maintenance Lubricate shaft bearings – fan, motor Check mechanical components (belts, bearings, fan

impellor & housing clean) Check vibration isolators Vibration analysis Motor condition & electrical current draw

Useful Fan ReferencesUseful Fan References

AMCA Publication 201 – Fans & Systems Publication 202 – Troubleshooting Fans

ACGIH

MMMM--11--11 7575

ACGIH Industrial Ventilation, A Manual of Recommended

Practice for Design, 26th edition Industrial Ventilation, A Manual of Recommended

Practice for Operation and Maintenance, 1st edition

Your Fan Manufacturer’s literature

Key Issues for Any CollectorKey Issues for Any Collector

Meeting environmental emission permit requirements contaminant collection efficiency collected contaminant recycle or disposal

Operating the collector within its designOperating the collector within its design

MMMM--11--11 7676

Operating the collector within its design Operating the collector within its design differential pressure (DP) rangedifferential pressure (DP) range DP high DP high –– acts like a damper & reduces airflow in acts like a damper & reduces airflow in

rest of systemrest of system DP low DP low ––

bypassing of collector and DC System?bypassing of collector and DC System? cause higher than desired airflow in DC System?cause higher than desired airflow in DC System?

Types of CollectorsTypes of Collectors

Particulate Collectors (dusts/mists/fumes) Fabric Filters or

Baghouses

Vapor/Gas Collectors Absorbers Gas Scrubbers

Thermal & Catalytic

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Cyclones Particle Scrubbers Electrostatic Precipitators Mist Eliminators

Thermal & Catalytic Oxidizers

Bio Filters

SUMMARY SUMMARY ––RELIABLE IVS PERFORMANCERELIABLE IVS PERFORMANCE

Reliable Hood/Enclosure Exhaust Airflows Interference by room air currents Modifications that degrade performance

Keep duct conveying velocities within range

MMMM--11--11 7878

Keep duct conveying velocities within range Air flow balanced between all branches Design systems with maintenance in mind Fan inlets and exhausts – avoid fan system effects Keep air cleaning device differential pressures within Base

Condition range

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