Cooling Tower Applications - LOWE - 11-16-2009

7/28/2019 Cooling Tower Applications - LOWE - 11-16-2009

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StephenLowe

ASHRAEHamptonRoadsChapterPastPresident

AECOM

Design

Mechanical

Engineering

Discipline

Manager,VirginiaBeachDivision

,NCEES

BSME University

of

Virginia,

2002

Sheetmetalfabricator,equipmentinstaller,refrigerationservicetechnicianduringhighschoolandcollege

onsu t ng

ng neer

rom2003

resent


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Introduction CoolingTowerBasics

PrinciplesofOperation TypesofCoolingTowers Common

Applications

DesignConsiderations SelectionCriteria

OpenPipingandPumpingSystems WaterQuality

TowerLocation

ConstructionIssues Constructability,QualityControlandStartup RatingandCertification

essons

earne Conclusion

Resources QuestionsandDiscussion


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CoolingTowerBasics

Principles

of

Operation CoolingViaEvaporation dependsonWetBulb

DesignDryBulbTemperaturescommonlyexceed95deg

F:poor

delta

Tfor

cooling

processes

DesignWet u muc ess:~80 egF

UseaprocessthatdependsonWBtotakeadvantageofreaterdeltaT

Evaporativeeffect

is

achange

of

state

and

thus

alarge

transferofenergyoccursrelativetotherequiredmass


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OpenCoolingTowerose

rcu t

CoolingTower


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CrossFlowArrangement CounterFlowArrangement


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CoolingTowerBasics

Common

Applications PowerPlantSteamCondensation

ProcessCooling

HVAC

Heat

Rejection

WSHPLoopHeat

*Wewillbefocusingonopen,crossflowcoolingtowersforchillercondenserheatre ectionfortheremainderofthepresentation.


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as c

oo ng

ower

pp ca on


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DesignConsiderations

Design

Considerations SelectionCriteria

OpenPipingandPumpingSystems

Water

Qualityower oca on

AncillarySystems


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Selection

Criteria Process(ChillerCondenser)TemperatureRequirements

HotWaterTem erature HWT :Tem eratureofwaterenterin thetower

ColdWaterTemperature(CWT):Temperatureofwaterleavingthe

tower TowerRange:HWT CWT

LowerCWTgenerallyresultsinhigherChillerEfficiency

FlowRateorCapacity

AmbientConditions

Evaporation(orEntering)DesignWetBulb(EWB)

Approach:CWT EWB

Lowerapproachgenerallyresultsinalargertower


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NO


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DesignConditions

Use

Evaporation

Design

WB

for

selection

of

evaporativeequipment

Useo 0.4%,1%,or2%con itionisuptot e esignerbasedonspecificapplicationanddesignfirmpractice

accountforrecirculation(ruleofthumb furtheranalysisisrequiredforthespecificapplication)

Condenserwater

delta

Tdepends

on

many

factors

suchastheprocessthatiscooledandoptimizationoft epumpingsystem


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Open

Piping

and

Pumping

Systems Coolingtowerpumpingapplicationtroublesare

genera yre ate tooneo t e o owingissues:

Incorrect

Pump

Head

Estimation

AirIntroductiontoPumpSuction


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Open

Piping

and

Pumping

Systems PumpHeadEstimation

Determineactualstaticliftheight

Determineimpactofsiphondraw:eitherbreakthesiphonor

designto

maintain

it.

Determinefrictionhead

Pipe

, , .

Components(valves,strainers,etc.)


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Open

Piping

and

Pumping

Systems Pumpheadestimationerrorscancause:

Unstablepumpoperation

Unstablecondenserflowatthechiller

Admissionof

air

into

the

um

inlet

Energywasteduetoneedforextensivethrottling

Manywastedhoursandheadachesfindingtheproblem!


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DesignConsiderations OpenPipingandPumpingSystems

Pumpcavitation is

the

flashing

(boiling)

of

the

working

fluid(water)intoavaporduetoexcessivelylowsuctionpressurean so encon use w a r n ro uc on n o epumpsuction.

Net

Positive

Suction

Head

(NPSH)

is

the

measure

of

suction

. Therequiredsuctionpressureforaparticularpumpis

indicatedNPSHRandispublishedasacurveonthepumpselectionchart.

Thesuction

pressure

available to

the

pump

in

aparticular

systemisindicatedNPSHAandmustbecalculatedbytheengineer.


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NPSHAExampleCalculation


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Open

Piping

and

Pumping

Systems B&GCoolingTowerPumpingandPipingManualhas4

ru esconcern ng epumpsuc onp p ng:

1. LeavethesuctionLineAlone!

2. Placethe

um

below

tower

an

water

level

3. Avoidabovethepumpairtrapsinthesuctionline

4. Avoidfinemesh,highpressuredropstrainersinthesuction


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Open

Piping

and

Pumping

Systems Airadmittancetothepumpinletistypicallycausedby:

Towerpanvortexing

Towerpandraindown

Incorrectb ass

arran ement


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Open

Piping

and

Pumping

Systems Towerpanvortexing iscausedbyexcessivevelocityin

e owerex p p ngan can econ ro e y:

Donotexcessivelyoversizethepump

Maintainin

towerexit

i e

size

for

aminimum

of

10

i e

diameters

Increasepandepth

Installtowerontheequator


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Open

Piping

and

Pumping

Systems Towerpandraindowniscausedbyinsufficientwater

ep o oo e owerex p p ngan can eavo e by:

Correctlysizin

the

makeup

water

line

EvaporationRate

Blowdown Rate

pumpshut

down

Properlyisolatingtowercellsinmultiplecellinstallations


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Condenserandasignificantportionofthepipingsystemwilldrainpacktopanonpumpshutdown.Panma floodandchillercouldstartwithadry

condenser.

Condenserwillremainfloodedonpumpshutdown.Minimalsystemvolumewilldraintopanonshutdown,thereforepan

should

not

flood.


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WRONGBypassconnectedtopumpsuctionpipingcancauseairintroductiontopumpinletandunstable

pump

operation.

CORRECTypass sc arg ng o as nw

balancingvalve

set

equal

to

dischargenozzlepressuredropwillresultinconstantpumpheadandfloodedpumpsuction.


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CORRECTSeparateoperatorsallowvalvestomaintain

WRONGLinkedvalveswillresultinunstableflow.

aconstanttotalflowasbothvalvesmodulate.


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BypassConfiguration

Example


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DesignConsiderations WaterQuality

RemovalofSolids

ChemicalTreatment

Consultachemicaltreatmentprofessionalforyourspecific

a lication

BiologicalContamination

Minimizedrift

Site

towers

away

from

air

intakes Avoidpipingdesignsthatresultinstagnantwater

Chemicall treat


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Removalof

Solids

Whatsthatfloatin inthebasin????

Whateveritis,ithasagoodshotatendingupinsideyourchiller!!!!


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RemovalofSolids

Guywithshovelandbucket

Inlinestrainers

Sidestream

filters

Basinsweepingsystem


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DesignConsiderations TowerLocation

Visibility

Sound

Drift


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GettingtheproperRealEstate Location,location,location

CoolingTowersarehighlyvisibleduetophysicalsizean p ume

Needampleclearancetominimizerecirculationand

Lowfrequencysoundemittedfromlargefanstravelsr atdistanc

Driftcan

mark

windows

and

paint

jobs


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DesignConsiderations AncillarySystems

FreezeProtection

TowerSumpBasin Electric SteamInjection

Recirculation

WaterTreatmentSystems ChemicalSystems

ControlSystems

Pneumaticoperators willrequirefreezeprotectioninsomeclimates

Largevalvesrequirelotsoftorque electricoperatorsmayneedtobeindustrialgrade


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ConstructionIssues Constructability,Startup,QualityControl

Thereislotsoflargepipingunderneaththetower,make

Considerlayingoutallofthepipingbasedona

manufacturers

particular

tower Uset emanu acturer sstartupc ec istonyoursite

visit

Readtheinstallationando erationmanualdurin

design;there

are

lots

of

options

that

affect

the

cost

of

thetower.Youneedtospecifythemifyourapplicationneedsthem.


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ConstructionIssues RatingsandCertification

ManufacturersRatedPerformance

CTICertification

PerformanceBasedCommissioning


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ConstructionIssues LessonsLearned

TowerBasinFreezeProtection

DirectsteaminjectionispopularinindustrialandlargescaleHVACapplications.

Chemicalused

for

boiler

feedwater may

react

with

condenser

waterchemicaltreatmentresultinginthereleaseofnoxiousgases.

Ahotwatercirculator um cou ledtoaheatsourcecanbe

usedinstead.


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VerticalLoopinSuctionPiping

Towermountedongradeadjacenttomechanicalroom

Coldwaterpipeexitsbottomofbasinandpassesthrough

mechanicalroom

wall

Pipeistherunupthewalltotheroofstructuretogetthepipeacrosstheroomtothepump

,

rooflevel

becomes

air

locked

Thepumpwillrequiremanualpriminginordertostart


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FloodingTower

on

Pump

Shutdown

.

Thereisasignificantvolumeofwaterlocatedabovethetowerbasinduetoalonghorizontalrunofhotcondenserwaterpipe

. Thedivertingvalveisinstalledinthehorizontalwiththe

bypassconnectionfacingdown.

,

horizontalpipe

runs

through

the

diverting

valve

and

back

to

thebasin.

Thebasinoverflowsinthe arkin lotresultin inanunsightlypuddleandwastedchemicaltreatment


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Airintroducedtopumpsuctionviabypass


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Airintroducedtopumpsuctionviabypass

AIRCANBEDRAWNINTOPUMPSUCTION


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Airintroducedtopumpsuctionviatowerdischargeman o


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Airintroducedtopumpsuctionviatowerdischargeman o

MUSTISOLATETOWERDISCHARGE


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Floodinghotwaterpansonmanifolded towers


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Floodinghotwaterpansonmanifolded towers

AUTOFLOWVALVE


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Multipleconnectedtowersshouldhaveanequalizationne.

Whenaddingorreplacingtowersconnectedthroughan

e ualizationline

desi n

the

tower

and

framin

to

ensurethattheexistingoperatingwaterlevelismatchedwiththenewtower.

t snecessarytoprov ev rat on so at on ort etower,thepipingsystemmust beisolatedfromthetower.


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Resources B&GCoolingTowerPumpingandPipingManual

MarleyCoolingTowerCompany CoolingTowerFun amenta s

BaltimoreAirCoilProductandApplicationHandbook

vapco qu pment ayout anua

www.CTI.org

an oo 200 ys emsan Equipment,Chapter39


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Questions?

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Cooling Tower Applications - LOWE - 11-16-2009