cooling tower applications - lowe - 11-16-2009
TRANSCRIPT
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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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DesignConsiderations
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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DesignConsiderations
Open
Piping
and
Pumping
Systems Coolingtowerpumpingapplicationtroublesare
genera yre ate tooneo t e o owingissues:
Incorrect
Pump
Head
Estimation
AirIntroductiontoPumpSuction
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DesignConsiderations
Open
Piping
and
Pumping
Systems PumpHeadEstimation
Determineactualstaticliftheight
Determineimpactofsiphondraw:eitherbreakthesiphonor
designto
maintain
it.
Determinefrictionhead
Pipe
, , .
Components(valves,strainers,etc.)
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DesignConsiderations
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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DesignConsiderations
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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DesignConsiderations
Open
Piping
and
Pumping
Systems Airadmittancetothepumpinletistypicallycausedby:
Towerpanvortexing
Towerpandraindown
Incorrectb ass
arran ement
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DesignConsiderations
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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DesignConsiderations
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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DesignConsiderations WaterQuality
Removalof
Solids
Whatsthatfloatin inthebasin????
Whateveritis,ithasagoodshotatendingupinsideyourchiller!!!!
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DesignConsiderations WaterQuality
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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ConstructionIssues LessonsLearned
VerticalLoopinSuctionPiping
Towermountedongradeadjacenttomechanicalroom
Coldwaterpipeexitsbottomofbasinandpassesthrough
mechanicalroom
wall
Pipeistherunupthewalltotheroofstructuretogetthepipeacrosstheroomtothepump
,
rooflevel
becomes
air
locked
Thepumpwillrequiremanualpriminginordertostart
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ConstructionIssues LessonsLearned
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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ConstructionIssues LessonsLearned
Airintroducedtopumpsuctionviabypass
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ConstructionIssues LessonsLearned
Airintroducedtopumpsuctionviabypass
AIRCANBEDRAWNINTOPUMPSUCTION
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ConstructionIssues LessonsLearned
Airintroducedtopumpsuctionviatowerdischargeman o
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ConstructionIssues LessonsLearned
Airintroducedtopumpsuctionviatowerdischargeman o
MUSTISOLATETOWERDISCHARGE
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ConstructionIssues LessonsLearned
Floodinghotwaterpansonmanifolded towers
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ConstructionIssues LessonsLearned
Floodinghotwaterpansonmanifolded towers
AUTOFLOWVALVE
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ConstructionIssues LessonsLearned
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?