832r10005 (evaluation of energy conservation measures for wastewater treatment facilities)
TRANSCRIPT
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Evaluation of
Energy Conservation
Measuresfor Wastewater Treatment Facilies
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Evaluation of Energy Conservation Measures ii September 2010
U.S.EnvironmentalProtectionAgency
OfficeofWastewaterManagement
1200PennsylvaniaAvenueNW
Washington,DC20460
EPA832R10005
September2010
Coverphoto:
BucklinPointWWTF,MA. PhotocourtesyofNarragansettBayCommission.
Coverinsertphotos(lefttoright):
HighSpeedMagneticBearingTurboBlowerattheDePereWTF,WI. PhotocourtesyofGreenBay
MetropolitanSewerageDistrict.
OxidationDitchwithAerationRotorattheCityofBartlettWWTP#1,TN.PhotocourtesyofCityof
BartlettWastewaterDivision.
VariableOutletVaneDiffuser. PhotocourtesyofTurblex,Inc.
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Evaluation of Energy Conservation Measures iii September 2010
Preface
TheU.S.EnvironmentalProtectionAgency(EPA)ischargedbyCongresswithprotectingthenations
land,air,andwaterresources.Underamandateofenvironmentallaws,theAgencystrivestoformulate
andimplementactionsleadingtoabalancebetweenhumanactivitiesandtheabilityofecosystemsto
supportandsustainlife.Tomeetthismandate,theOfficeofWastewaterManagement(OWM)provides
informationandtechnicalsupporttohelpsolveenvironmentalproblemstodayandtobuildthe
knowledgebasenecessarytoprotectpublichealthandtheenvironmentwellintothefuture.This
documentwaspreparedundercontracttoEPA,byTheCadmusGroup. Thedocumentprovides
informationoncurrentstateofdevelopmentasofthepublicationdate;however,itisexpectedthat
thisdocumentwillberevisedperiodicallytoreflectadvancesinthisrapidlyevolvingarea. Exceptas
noted,information,interviews,anddatadevelopmentwereconductedbythecontractor.Whilethere
aremanyproven,costeffectiveenergyconservationpracticesandnumerousnewtechnologiesor
modificationsofexistingtechnologiesavailablefordetailedstudy,thecasestudiesinthisdocument
wereselectedonthebasisofspecificcriteria.Thecriteriaincludedtheabilitytoprovideasleastoneyearoffullscaleoperatingandperformancedata,capabilityofprovidingdetailedcapital,operations,
andmaintenancecostbreakdowns,andtheabilitytoprovidethedatawithinthetimeframeestablished
forcompletingthedocument.Itisanticipatedthatasthedocumentisupdated,additionalcasestudies
onnewtechnologiescouldbeincluded.
DisclaimerThisinformationrepresentsnew,innovativeoremergingapproaches,techniques,ortechnologiesthat
mayassistutilityownersandoperatorsreducethecapitaloroperatingcostsofwastewatertreatment.
Someoftheinformation,especiallyrelatedtoemergingtechnologies,wasprovidedbythe
manufacturer
or
vendor
of
the
equipment
or
technology,
and
could
not
be
verified
or
supported
by
a
fullscalecasestudy. Insomecases,costdatawerebasedonestimatedsavingswithoutactualfield
data. Whenevaluatingtechnologies,estimatedcosts,andstatedperformance,effortsshouldbemade
bythereadertocollectcurrentandmoreuptodateinformation.
Thementionoftradenames,specificvendors,orproductsdoesnotrepresentanactualorpresumed
endorsement,preference,oracceptancebyEPAorthefederalgovernment.Statedresults,conclusions,
usage,orpracticescontainedhereinmaybedifferentdependingonspecificsiteconditionsanddonot
necessarilyrepresenttheviewsorpoliciesofEPA.
ThisdocumenthasbeenreviewedinaccordancewithEPAspeerandadministrativereviewpoliciesand
approvedforpublication
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AcknowledgementsThisdocumentwaspreparedbyTheCadmusGroup,Inc.(Cadmus)underEPAContractNo.GS10F
0273KC/I1,TaskOrder311. TheCadmusTeamwasledbyLauraDufresneandStephenCoutureof
CadmusandDavidReardonandKennethHendersonofHDR. EPAtechnicaldirectionandoversightwereprovidedbyJamesWheelerandPhilZahreddine,EPAOfficeofWastewaterManagement.
Theprojectwassupportedbyatechnicalexpertpanelconsistingofthefollowingindividuals:
KathleenOConner,NewYorkStateEnergyResearchandDevelopmentAuthority
JoeCantwell,SAIC
MikeWilson,CH2MHill
SteveBolles,ProcessEnergyServices
AndreSchmidt,LosAngelesCountySanitationDistrictsEnergyRecoveryEngineeringServices
JessBurgess,ConsortiumforEnergyEfficiency
Aformalpeerreviewofthedraftdocumentwasconductedbythefollowingindividuals:
ThomasE.Jenkins,JenTechInc.
JuliaGass,Black&Veatch
GeorgeLawrence,EfficiencyVermont
GeorgeCrawford,CH2MHILL
AdditionalreviewwasprovidedbyDavidRedmonofRedmonEngineeringCompany,AndrewShawof
Black&Veatch,andAndrewTrumanofBlack&Veatch.
WhileeveryeffortwasmadetoaccommodateallofthePeerReviewcomments,theresultsand
conclusionsdonotindicateconsensusandmaynotrepresenttheviewsofallthereviewers.
Theauthorssincerelyappreciatethereviewandguidanceprovidedbythetechnicalexpertpanel
membersandpeerreviewers.
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Acronyms and Abbreviations
ACEEE AmericanCouncilforanEnergyEfficientEconomy
APPA AmericanPublicPowerAssociation
ASCE AmericanSocietyofCivilEngineers
ASE AlliancetoSaveEnergy
AWWA AmericanWaterWorksAssociation
BEP BestEfficiencyPoint
bhp BrakeHorsepower
BNR BiologicalNutrientRemoval
BOD BiochemicalOxygenDemand
CCCSD CentralContraCostaSanitaryDistrict
CEC CaliforniaEnergyCommission
CEE ConsortiumforEnergyEfficiency
CFO CostFlowOpportunity
CHP CombinedHeatandPower
DCS DistributedControlSystem
DO DissolvedOxygen
DOE DepartmentofEnergy
DSIRE DatabaseofStateIncentivesforRenewablesandEfficiency
ECM EnergyConservationMeasure
EPACT EnergyPolicyAct
EPC EnergyPerformanceContracting
EPRI ElectricPowerResearchInstitute
ESCO EnergyServicesCompany
GBMSD GreenBay(Wisconsin)MetropolitanSewerageDistrict
gpm Gallonsperminute
hp HorsepowerI&I Inflowandinfiltration
IOA InternationalOzoneAssociation
IUVA InternationalUltravioletAssociation
kW Kilowatt
kWh Kilowatthour
LPHO LowPressureHighOutput
MBR MembraneBioreactor
mg MillionGallons
mgd MillionGallonsperDay
MLE ModifiedLudzackEttingerprocess
MPN MostProbableNumber
NAESCO NationalAssociationofEnergyServiceCompanies
NEMA NationalElectricalManufacturersAssociation
NYSERDA NewYorkStateResearchandDevelopmentAuthority
PG&E PacificGasandElectric
PLC ProgrammableLogicController
PSAT PumpSystemAssessmentTool
psi PoundsperSquareInch
psig PoundsperSquareInchGauge
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rpm RevolutionsperMinute
SRT SolidsResidenceTime
TDH TotalDynamicHead
TSS TotalSuspendedSolids
TVA TennesseeValleyAuthority
UV UltravioletLight
UVT UVtransmittance
VFD VariableFrequencyDrive
W Watt
WEF WaterEnvironmentFederation
WEFTEC WaterEnvironmentFederationTechnicalExhibitionandConference
WERF WaterEnvironmentResearchFoundation
WMARSS WacoMetropolitanAreaRegionalSewerSystem
WPCP WaterPollutionControlPlant
WRF WaterResearchFoundation
WSU WashingtonStateUniversity
WWTP WastewaterTreatmentPlant
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Contents1. Introduction ............................................................................................................... 11
1.1
Background
.........................................................................................................
1
1
1.2 PurposeandAudience........................................................................................ 12
1.3 ReportOrganization............................................................................................ 13
1.4 SummaryofInnovativeandEmergingECMS..................................................... 14
1.5 References.......................................................................................................... 16
2. RecommendedApproachtoEnergyManagement ........................................................ 21
2.1 Introduction........................................................................................................ 21
2.2 RecommendedApproach................................................................................... 21
2.3 ToolsforEnergyManagement........................................................................... 24
2.4 FinancingResources............................................................................................ 24
2.5 OtherECMsandResources................................................................................. 26
2.6 References.......................................................................................................... 27
3. EnergyConservationMeasuresforPumpingSystems.................................................... 31
3.1 Introduction........................................................................................................ 31
3.2 PumpingSystemDesign...................................................................................... 33
3.3 Motors ............................................................................................................... 35
3.3.1 MotorEfficiencyandEfficiencyStandards............................................ 36
3.3.2 MotorManagementPrograms.............................................................. 37
3.3.3 InnovativeandEmergingTechnologies................................................. 38
3.4
Power
Factor
.......................................................................................................
3
9
3.5 VariableFrequencyDrives(VFDs)..................................................................... 310
3.5.1 EnergySavings..................................................................................... 311
3.5.2 Applications......................................................................................... 311
3.5.3 VFDStrategiesforWastewaterPumpingStations.............................. 312
3.6 References........................................................................................................ 313
4. DesignandControlofAerationSystems......................................................................... 41
4.1 Introduction........................................................................................................ 41
4.2 ECMsforAerationSystems................................................................................ 41
4.2.1 ECMsforDiffusedAerationSystems..................................................... 42
4.2.2 ECMsforMechanicalAerators.............................................................. 45
4.3 ControloftheAerationProcess......................................................................... 47
4.3.1 AutomatedDOControl.......................................................................... 47
4.3.1.1DOMeasurementEquipment.................................................. 410
4.3.1.2AdvancesinDOControlStrategies.......................................... 413
4.3.2 EmergingTechnologiesUsingControlParametersotherthanDO.....415
4.4 InnovativeandEmergingControlStrategiesforBiological
NutrientRemoval.............................................................................................. 418
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4.5 References........................................................................................................ 420
5. BlowerandDiffuserTechnologyforAerationSystems................................................... 51
5.1 IntroductionandComparisonofBlowerTypes.................................................. 51
5.2 HighSpeedGearless(Turbo)Blowers................................................................ 55
5.3 SingleStageCentrifugalBlowerswithInletGuideVanesandVariable
DiffuserVanes................................................................................................... 511
5.4 NewDiffuserTechnology.................................................................................. 515
5.5 References........................................................................................................ 519
6. InnovativeandEmergingEnergyConservationMeasuresforSelected
TreatmentProcesses....................................................................................................... 61
6.1 Introduction........................................................................................................ 61
6.2 UVDisinfection................................................................................................... 61
6.2.1 Design.................................................................................................... 63
6.2.2 OperationandMaintenance.................................................................. 65
6.3 MembraneBioreactors(MBRs).......................................................................... 66
6.4 AnoxicandAnaerobicZoneMixing.................................................................... 68
6.4.1 HyperbolicMixer.................................................................................... 68
6.4.2 PulsedLargeBubbleMixing................................................................. 612
6.5 References........................................................................................................ 613
7. EnergyConservationMeasuresforSolidsProcessing..................................................... 71
7.1 Introduction........................................................................................................ 71
7.2 Digestion............................................................................................................. 71
7.3
Incineration
.........................................................................................................
7
4
7.4 ThermalDrying................................................................................................... 76
7.5 References.......................................................................................................... 79
8. SummaryofFacilityCaseStudies.................................................................................... 81
8.1 Introduction........................................................................................................ 81
8.2 Approach............................................................................................................. 81
8.3 SummaryofResults............................................................................................ 83
AppendixA: FacilityCaseStudies
AppendixB: WebResources
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ListofTablesTable11. InnovativeandEmergingECMs.......................................................................... 15
Table31. PumpSystemEfficiency...................................................................................... 32
Table51. OverviewofBlowerTypesofAerationofWastewater...................................... 52
Table52. ManufacturerCostRangesforSelectBlowerTypes........................................... 53Table53. TypicalBlowerEfficiencies.................................................................................. 54
Table53. ExamplesofTurboBlowerManufacturersintheNorthAmericanMarket.......58
Table54. NetPresentWorthofBlowerSelectionsfortheCityofOneida(2003$).........514
Table61. DisinfectionEquipmentPowerandCostEstimates(55mgdPeakFlow,
38mgdAverageFlow,65%DesignUVT)............................................................ 64
Table81. SummaryofFacilityCaseStudies....................................................................... 84
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ListofFiguresFigure11. TypicalEnergyUseProfilefor10mgdSecondaryTreatmentProcesses...........12
Figure21. StepsinthePlanDoCheckActManagementSystemsApproach..................... 22
Figure31. VectorRelationshipofACPower........................................................................ 39
Figure32. WastedEnergyinAlternativeControlSchemesComparedto ...............................
VariableFrequencyDrives................................................................................ 311
Figure41. EimcoWaterTechnologiesCarrouselSystemExcellAeratorII........................ 46
Figure42. CommonCascadeSystemforAutomatedDOControl..................................... 410
Figure43. OpticalDOSensorOperation............................................................................ 412
Figure44. IntegratedAirFlowControlSystemforAutomatedDOControl...................... 414
Figure45. FlowThroughRespirometryCell...................................................................... 416
Figure46. RepresentationofBIOSProcess....................................................................... 417
Figure47. RepresentationoftheBiosProcess.................................................................. 419
Figure51. ExampleofHighSpeedTurboBlowerwithAirBearings(HIS)........................... 56
Figure52. ExampleofHighSpeedTurboBlowerwithMechanicalBearings
(Atlas
Copco)
.......................................................................................................
5
6
Figure53. ComparisonofPowerDrawforOldandNewBloweratBurlington,VT..........511
Figure54. ExampleofSingleStageCentrifugalBlowerwithInletGuideVanesand
VariableDiffuserVanesbyTurblex................................................................. 511
Figure55. ExampleofSingleStageCentrifugalBlowerwithInletGuideVanesand
VariableDiffuserVanesbyDresserRoots........................................................ 511
Figure56. VariableOutletVaneDiffuserfromTurblex................................................... 512
Figure57. UltrafinePoreMembraneAerationPanel....................................................... 515
Figure58. AeroStripDiffuserbytheAerostripCorporation............................................ 516
Figure61. ExampleUVLampConfigurationsforWastewaterTreatment.......................... 62
Figure62. TypicalInstallationofaHyperboloidMixer........................................................ 69
Figure63. ConventionalHydrofoilMixer........................................................................... 611
Figure64. TypicalBioMixTMInstallation............................................................................. 612
Figure71. VerticalLinearMotionMixerbyEnersaveFluidMixers,Inc.............................. 73
Figure72. SchematicRepresentationofMultipleHearthIncineratorEnergyEfficiency
ImprovementsatWSSCWesternBranchWWTP............................................... 76
Figure73. ExampleofSolarDryerbyParkson..................................................................... 78
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1.Introduction
1.1 Background
Providingreliablewastewaterservicesandsafedrinkingwaterisahighlyenergyintensive
activity
in
the
United
States.
A
report
prepared
for
the
Electric
Power
Research
Institute
(EPRI)
in
1996
estimatedthatbytheendofthatyear,theenergydemandforthewaterandwastewaterindustry
wouldbeapproximately75billionkilowatthours(kWh)peryear,orabout3percentoftheelectricity
consumedintheU.S.(Burton1996). TheConsortiumforEnergyEfficiency(CEE)nowestimatesthe
annualenergyusageatapproximately100billionkWhperyear(Burton1996,extrapolatedbyCEE). At
anaverageenergycostof$0.075perkWh,thecostforprovidingsafedrinkingwaterandproviding
effectivewastewatertreatmentisapproximately$7.5billionperyear.
Energyisusedthroughoutthewastewatertreatmentprocess;however,pumpingandaeration
operationsaretypicallythelargestenergyusers(seeFigure11foratypicalenergyuseprofilefora
mediumsizedwastewatertreatmentplant). Energycostsinthewastewaterindustryarerisingdueto
manyfactors,including:
Implementationofmorestringenteffluentrequirements,includingenhancedremovalofnutrientsandotheremergingcontaminantsofconcernthatmay,insomecases,leadtotheuse
ofmoreenergyintensivetechnologies.
Enhancedtreatmentofbiosolidsincludingdrying/pelletizing. Agingwastewatercollectionsystemsthatresultinadditionalinflowandinfiltration,leadingto
higherpumpingandtreatmentcosts.
Increaseinelectricityrates.Asaconsequenceoftheserisingcosts,manywastewaterfacilitieshavedevelopedenergymanagement
strategiesandimplementedenergyconservationmeasures(ECMs).Usingthefiguresprovidedearlierin
thissection,improvingtheenergyefficiencyofAmerica'sdrinkingwaterandwastewatersystemsby10
percentcouldsavemorethan10billionkWheachyear,representingacostsavingsofapproximately
$750millionannually.
Chapter1covers:
1.1 Background
1.2 PurposeandAudience
1.3 ReportOrganization
1.4 SummaryofInnovativeandEmergingECMs
1.5 References
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Figure11.TypicalEnergyUseProfilefor10mgdSecondaryTreatmentProcesses.
Source:WEF2009,Figure7.1.Usedwithpermission.
Note:energyuseforvarioustreatmentprocesseswillvarygreatlyfromplanttoplant. Advancedtreatment
processesmayrequiremoreenergythanconventionaltreatmentprocessesandmaynotberepresentedinthis
figure.
1.2 PurposeandAudienceThepurposeofthisreportistoencouragetheimplementationofECMsatpubliclyowned
treatmentworks(POTWs)byprovidingaccurateperformanceandcost/benefitinformationforsuch
projects.Thereportsfocusismainlyonenergyefficientequipmentreplacement,operational
modifications,andprocesscontrolenhancementsthatleadtoimprovedenergyefficiencyandcost
savingswithreasonablepaybackperiods(10yearsorless). Thescopeofthereportdoesnotinclude
cogenerationtechnologies(alsoknownascombinedheatandpower,orCHP)oralternative/renewable
energytechnologies,astheinformationonthesetopicsisbeingdevelopedbyEPAunderseparate
projects.ThemainaudiencesforthisreportarePOTWmanagers,owners,andoperatorswhomaybe
consideringtheimplementationofECMsandstatesorotheragencieswhomaybeinterestedin
supportingsuchprojects.
ThisreportincludessummaryinformationonconventionalECMsthatareinuseintheU.S.and
haveastrongtrackrecordofsuccesswithrespecttoenergyconservation;however,thefocusis
identificationofinnovativeandemergingECMs. Forthepurposesofthisdocument,innovativeand
emergingaredefinedasfollows:
Innovative: technologiesthatmaybeestablishedoverseasandhaveeitherbeentestedintheU.S.asafullscaledemonstrationprojectorinstalledataU.S.wastewatertreatmentplant
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(WWTP)foratleastoneyearbutnotmorethan5years. Foratechnologythatmeetstheabove
criteriatobeconsideredinnovativeratherthanemerging,independenttestdatashowing
energysavingsmustbepresentedintheliteratureordocumentedinthisreportinoneofthe
facilitycasestudies.Innovativetechnologiesincludemodificationsandnewapplicationsfor
establishedtechnologies.
Emerging:technologiesinthedevelopmentortestingstageintheU.S.andthatshowpotentialforenergysavingsandrelativelyshortpaybackperiods,butforwhichindependentfullscale
demonstrationoroperatingdataarenotyetavailable.
SeeSection1.4forasummaryofinnovativeandemergingECMsidentifiedinthisreport.
ThisreportbuildsuponanextensiveliteraturereviewoftheeffectivenessandcostsofECMsfor
municipalwastewatertreatmentandsolidsprocessing.Additionally,apaneloftechnicalexperts
providedinputontheimplementationofvariousECMs.Detailedfacilityassessmentsofninewastewater
treatmentfacilitiesareprovided,includingdetailedinformationonECMimplementation,energy
savings,andcostdata.
1.3 ReportOrganization
Thereportisorganizedintoninechaptersandtwoappendicesasfollows:
Chapter1,Introduction,presentsbackground,purpose,audience,andorganizationforthereport.
Chapter2,RecommendedApproachtoEnergyManagement,presentsacomprehensiveapproachtoenergymanagementatawastewatertreatmentutility,includingdevelopingan
energymanagementprogram.Itlistsavailabletoolsandfinancingresourcesthatcanhelp
utilitiesimplementtheirprograms.ItalsolistsotherECMsthatshouldbeconsideredby
wastewaterutilitiesbutarenotthefocusofthisreport.
Chapter3,EnergyConservationMeasuresforPumpingSystemsprovidesanoverviewofconventionalECMsrelatedtopumpingdesign,variablefrequencydrives(VFDs),andmotorsand
refersthereadertoindustrystandardsandweblinksforadditionalguidance.
Chapter4,DesignandControlofAerationSystems,providesdetailedinformationonECMsrelatedtothedesignofaerationsystemsandautomatedaerationcontrol,including
conventionalcontrolbasedondissolvedoxygen(DO)measurementsandemergingcontrol
strategies.Innovativeandemergingtechnologiesforautomatedcontrolofbiologicalnitrogen
removalarealsodiscussed.
Chapter5,BlowerandDiffuserTechnologyforAerationSystems,describesinnovativeECMsrelatedtobloweranddiffuserequipment.Itincludesasummaryofvariousblowertypessuchas
singlestagecentrifugal,highspeedturbo,andscrewcompressorsinadditiontonewdiffuser
technology.
Chapter6,InnovativeandEmergingEnergyConservationMeasuresforSelectedTreatmentProcesses,providesadiscussionofECMsforadvancedtechnologies(UVdisinfection,
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membranes,andanoxiczonemixing)andpresentsfullscaleplanttestresultswhereavailable.
ForECMsthataretechnicallyfeasibleandpromisingfortheindustrybutwhereoperatingdata
arenotavailable,manufacturersinformationisprovided.
Chapter7EnergyConservationMeasuresforSolidsProcessing,describesinnovativeEMSfordigestion,incineration,andthermaldryingandprovidessupportingdatafromcasehistories.
Chapter8,SummaryofFacilityCaseStudies,describestheapproachusedtoselecttheninefacilitycasestudiesandsummarizescasestudyfindingsinnarrativeformandinsummary
tables.
AppendixA,FacilityCaseStudies,containsdetailedinformationandresultsfromninefacilitycasestudies.
AppendixB,WebResources,providesresourcesforfurtherinformation.Categoriesofwebresourcesincludebooksavailablefromonlineretailers;governmentpublicationsthroughU.S.
DepartmentofEnergy(DOE)andU.S.EnvironmentalProtectionAgency(EPA);information
availablefromnonprofitorganizations,stateprograms,WaterEnvironmentResearch
Foundation(WERF)andWaterResearchFoundation(WaterRF);andonlinejournalsand
conferenceproceedings.
1.4 SummaryofInnovativeandEmergingECMs
Table11liststheinnovativeandemergingECMsidentifiedinthisreportandreferencesthe
specificreportsectionformoreinformation. AsstatedinSection1.2,independentdemonstrationor
fullscaleoperatingdatadocumentingenergysavingsarerequiredforanewtechnologytobe
consideredinnovative;otherwise,itwasclassifiedasemerginginthisreport. Notethatthisreport
describesmanyotherconventionalECMsthatcanachievesignificantenergysavings.
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Table11. InnovativeandEmergingECMs
Chapter ECMName ECMCategorization
andReportSection
4DesignandControl
ofAerationSystems
IntermittentAeration Emerging4.2.1
DualImpellerAerator(mechanicalmixing) Emerging4.2.2
Integratedairflowcontrol Innovative4.3.1
AutomatedSRT/DOControl Innovative 4.3.1
Respirometryforaerationcontrol Emerging4.3.2
Criticaloxygenpointcontrol Emerging4.3.2
Offgasmonitoringandcontrol Emerging4.3.2
Onlinemonitoringandcontrolofnitrification
usingnicotinamideadeninedinucleotide(NADH)
(Symbioprocess)
Emerging4.4
BioprocessIntelligentOptimizationSystem(BIOS) Emerging4.4
5 BlowerandDiffuser
Technologyfor
AerationSystems
Highspeedgearless(Turbo)blowers Innovative5.2
Singlestagecentrifugalblowerswithinletguide
vanesandvariablediffuservanes
Innovative5.3
Ultrafinebubblediffusers Emerging5.4
Newdiffusercleaningtechnology Emerging5.5
6Innovativeand
EmergingEnergy
ConservationMeasures
forSelectedTreatment
Processes
LowpressurehighoutputlampsforUV
disinfection
Emerging6.2.1
AutomatedchannelroutingforUVdisinfection Emerging6.2.2
Membraneairscouralternatives Emerging6.3
Hyperbolicmixers Innovative6.4.1
PulsedLargeBubbleMixing(e.g.,BioMx) Innovative6.4.2
7EnergyConservation
MeasuresforSolids
Processing
Verticallinearmotionmixer Innovative7.2
Upgradingmultiplehearthfurnacesto
incorporatewasteheatrecovery/combustionair
preheating
Innovative7.3
Solardrying Emerging7.4
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1.5 References
Burton,FranklinL.1996.WaterandWastewaterIndustries:CharacteristicsandEnergyManagement
Opportunities.BurtonEnvironmentalEngineering,LosAltos,CA.PreparedfortheElectricPower
ResearchInstitute.PaloAlto,California.ReportCR106941.September,1996.
Carns,K.,2005.BringingEnergyEfficiencytotheWater&WastewaterIndustry:HowDoWeGetThere?
InWEFTEC2005Proceedings.
WaterEnvironmentFederation(WEF).2009.ManualofPractice(MOP)No.32:EnergyConservationin
WaterandWastewaterFacilities.PreparedbytheEnergyConservationinWaterandWastewater
TreatmentFacilitiesTaskForceoftheWaterEnvironmentFederation.McGrawHill,NewYork.
USEPA.2008.EnsuringaSustainableFuture:AnEnergyManagementGuidebookforWastewaterand
WaterUtilities.January2008.Availableonline:
http://www.epa.gov/waterinfrastructure/pdfs/guidebook_si_energymanagement.pdf
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2.RecommendedApproachtoEnergyManagement
2.1 Introduction
Equipmentupgradesandoperationalmodificationstoreduceenergyuseshouldnotbeone
timeevents,butshouldbeincorporatedintoacomprehensiveenergyreviewandmanagementstrategy.
Section2.2presentsEPAsrecommendedapproachtoenergymanagementforwastewaterutilities. On
linetoolsandfinancingresourcesareavailabletoutilitiesinterestedindevelopinganenergy
managementstrategyandaredescribedinSections2.3and2.4respectively.
AsexplainedinChapter1,thescopeofthisdocumentisenergyconservationmeasures(ECMs)
relatedtoequipmentupgradesandoperationsstrategies,withafocusoninnovativeandemerging
technologies.Theseareonlyasubset,however,oftheECMsavailabletowastewaterutilities.Section
2.5listsothertypesofECMs(mainlyconventional)andprovidesreferencesforadditionalinformation.
2.2 RecommendedApproach
Tooptimizeenergysavingsatawastewatertreatmentplant(WWTP)nowandinthefuture,
ECMsshouldbeevaluatedandimplementedaspartofacomprehensiveenergymanagementprogram.
Inordertoassistutilitiesindevelopingsuchaprogram,theEPAOfficeofWastewaterManagement
developedaguidebookentitledEnsuringaSustainableFuture: AnEnergyManagementGuidebookfor
WastewaterandWaterUtilities(USEPA,2008a)
http://www.epa.gov/waterinfrastructure/pdfs/guidebook_si_energymanagement.pdf,whichnotesthat:
Moreandmoreutilitiesarerealizingthatasystematicapproachformanagingthefullrangeof
energychallengestheyfaceisthebestwaytoensurethattheseissuesareaddressedonan
ongoingbasisinordertoreduceclimateimpacts,savemoney,andremainsustainable(EPA
2008,p.3).
ThisEPAguidebookrecommendstheplandocheckactmanagementsystemapproachforenergy
conservationandmanagementasshowninFigure2.1. Thisbasicapproachisapplicabletoallutility
operationsandnotsolelytoenergymanagementactivities.However,theapproachhasbeenexpanded
andtailoredtowaterandwastewaterutilitiesinasimple9stepapproachshowninthetextbox
followingFigure2.1. Thesekeystepsforsuccessarebasedonexperienceofwaterandwastewater
utilitiesthathavegonethroughtheprocessofidentifyingandimplementingECMs. Notethatinthe9
stepapproach,identifyingECMsdoesnotcomeintoplayuntilStep6,DeviseaPlan.
Chapter2covers:
2.1 Introduction2.2 RecommendedApproach2.3 ToolsforEnergyManagement2.4 FinancingResources2.5 OtherECMsandResources2.6 References
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Figure21.StepsinthePlanDoCheckActManagementSystemsApproach
Source: USEPA2008b
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Recommended9StepApproachtoEnergyManagement
1. CreateanEnergySustainabilityTeam. Identifyanenergyprogrammanagementteamwithresponsibilityforimplementingtheimprovementprogramfromstarttofinish. Createacore
teamwithrepresentativesfromallaspectsofoperations,maintenanceandmanagement.
ConsiderappointinganEnergyManagerwhoseonlyresponsibilityisenergyconservation(andpossiblyrecovery)foryourfacility.
2. GatherData. Gatherdataonenergyuse(e.g.,fromgas,fueloilandelectricitybills). Makethisdataavailabletotheteam.
3. BenchmarkPerformance. Createabaselineofenergyperformanceagainstwhichyoucanmeasureimprovementsovertime. YoucandothisusingENERGYSTARsPortfolioManagerfor
wastewatertreatmentplants,availableonlineat
http://www.energystar.gov/index.cfm?c=water.wastewater_drinking_water.Portfolio
Managerhasthebenefitofconvertingalltypesofenergyuse(e.g.,naturalgas,fueloil,and
electricity)
to
a
common
unit
so
that
they
can
be
added
together,
and
provides
an
estimate
of
greenhousegasemissions. Youmayalsobeabletocompareyourutilitysperformanceto
similarutilitiesifyoumeetcertaincriteria.
4. ConductanEnergyAudit. Determinetheenergyuseofvariousprocessesandidentifyopportunitiesforenergyusereduction.
5. DevelopGoals. Identifyquantifiableenergyimprovementgoalsthatcomplementyourutilitysmission,goals,andstrategicdirection.
6. DeviseaPlan. IdentifyEnergyConservationMeasures(ECMs)anddevelopaplanforimplementing
them.
Start
with
low
hanging
fruit
and
focus
on
energy
intensive
operations
suchasaerationandpumping. Considerrenewableenergyoptionsandopportunitiesfor
energygenerationusingalternativemethods. Determinecostsandpaybackperiodsfor
variousoptions.
7. ImplementImprovements. Assignresponsibilitiesandestablishdeadlines. Consideralternativefinancingapproaches. Fullyengageandtrainyouroperationsstaff.
8. MonitorandMeasureResults. Trackperformance,reviewprogresstowardsenergygoals,anddevelopaplanformaintainingenergyefficientequipment. Reevaluateyourgoalsinlightof
newinformationandpriorities,andmakechangestoyourprogramasnecessary.
9. CommunicateSuccess. Communicatethesuccessesofyourenergymanagementprogramtoemployees,utilitymanagement,andyourcommunity.
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2.3 ToolsforEnergyManagement
Anumberoftoolshavebeendevelopedtohelpwastewaterutilitiesimplementanenergy
managementprogram. Datamanagementtoolsthatareavailableonlineinclude:
The
ENERGY
STAR
benchmarking
tool
Portfolio
Manager
provides
a
way
for
utilities
to
track
theirenergyuseaswellascomparetheirperformancetoutilitieswithsimilarsizeand
treatmentgoals.Itisavailablefreeonlineat
http://www.energystar.gov/index.cfm?c=water.wastewater_drinking_water.See
http://www.energystar.gov/index.cfm?c=business.bus_internet_presentationsfordetails
regardingregularwebbasedtraining.
Pumpandmotormanagementtools(seeChapter3formoreinformation):- ThePumpingSystemAssessmentTool(PSAT),developedbytheDepartmentofEnergy
(DOE)andavailablefreeonlineat
http://www1.eere.energy.gov/industry/bestpractices/software_psat.html
can
help
users
determinetheefficiencyoftheirexistingpumpingsystemsandcalculateenergyandcost
savingsforupgrades.
- MotorMaster+isamotorselectionandmanagementtool,availableforfreeonlineathttp://www.motorsmatter.org/.Itincludesinventorymanagementfeatures,maintenance
logging,efficiencyanalysis,savingsevaluation,andenergyaccounting.Itincludesacatalog
of17,000motorsfrom14manufacturers,includingNEMAPremiumefficiencymotors,and
motorpurchasinginformation.
2.4 FinancingResources
Fundingenergyconservationprojectsisanimportantcomponentofanenergymanagement
program,particularlyduetolimitedresourcesavailabletoutilitiesandtheneedtomeetmultiple
environmentalobjectivesandregulatoryrequirements. Anumberoffundingoptions,however,are
availabletoautility. TheCaliforniaEnergyCommission(CEC)notesthat:
Ashortageofinternalfundsneednotbeabarriertoimplementingenergyefficiencyprojects.
Thereareplentyoffinancingsources,programsandoptionsavailabletoserveyou.Realbarriers
areduetothelackofawarenessorunderstandingofthe:
1) manybenefitsofinvestinginenergyefficiencyprojects.Thesebenefitsincludeenergycostsavings,increasedrevenues,improvedworkercomfortandproductivity,
reducedmaintenancecostofold,inefficientequipment,andreductionof
environmentaldegradationand
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2)manyprogramsforfinancingenergyefficiencyprojects(CEC2000)1.
Capitalprojectsforpublicallyownedwastewaterutilitieshavehistoricallyreceivedfundingfrom
grantsandloans;however,thirdpartyfinancing(e.g.,stateenergyoffices,energyservicescompanies)is
becomingmorecommon.InmanypartsoftheU.S.,energyperformancecontracting(EPC)hasbeen
usedtofinanceenergyefficiencyimprovements(Zobler2009).Properlystructuredperformance
contractscanbeconsideredintheutilitysoperatingbudgetinsteadofasacapitalexpense.Examples
includeenergyserviceproviderbasedfinancingandtaxexemptleasepurchaseagreements.
Oneoptiontostreamlinetheaudit,financing,andimplementationstepsofanenergy
managementprogramistohireanEnergyServicesCompany(ESCO).ESCOsusuallydevelopandmanage
EPCs,manageawiderangeoftasks,andassumesomeormostofthetechnicalandperformancerisk
associatedwiththeproject.SeetheNationalAssociationofEnergyServiceCompanies(NAESCO)
websiteathttp://www.naesco.org/formoreinformationandalistofserviceprovidersinyourarea.
AdditionalguidanceisavailableintheCECsHandbook,HowtoHireanEnergyServicesCompany(CEC
2000),availableonlineathttp://www.energy.ca.gov/reports/efficiency_handbooks/40000001D.PDF.
Inadditiontotheaboveresources,otherfreetoolsandresourcesareavailabletohelp
wastewaterutilitiesfinanceECMs.Examplesareprovidedbelow.
TheCleanWaterStateRevolvingFund(CWSRF),offeringlowinterestloans(average2.2percent)forwastewatertreatmentimprovements.Theprogramisadministeredbyindividual
statesAlistofregionalandstatecontactsisavailableonlineat
http://www.epa.gov/owm/cwfinance/cwsrf/contacts.htm.
FinancingguidancefromENERGYSTAR,availableonlineathttp://www.energystar.gov/index.cfm?c=business.bus_financing.Includesaspreadsheetbased
CashFlowOpportunity(CFO)Calculatorthatcanhelpplantmanagerscalculatesimplepayback
aswellascostofdelay,whichisthelostopportunitycostiftheprojectisdelayed12monthsormore.
DatabaseofStateIncentivesforRenewablesandEfficiency(DSIRE),availableonlineathttp://www.dsireusa.org/isacomprehensivesourceofinformationonstate,local,utility,and
federalincentivesandpoliciesthatpromoterenewableenergyandenergyefficiency.
Establishedin1995,DSIREisanongoingprojectoftheNorthCarolinaSolarCenterandthe
InterstateRenewableEnergyCouncil,whichisfundedbytheU.S.DepartmentofEnergy(DOE).
ReportbytheCECtitledHowtoFinancePublicSectorEnergyEfficiencyProjects(CEC2000),availableonlineathttp://www.energy.ca.gov/reports/efficiency_handbooks/40000001A.PDF.
Includesadescriptionofcosteffectivenesscriteriaandoptionsforfinancingenergyefficiency
projects.
1Formoreinformation,seetheCECreport,HowtoFinancePublicSectorEnergyEfficiencyProjects.January2000.
Availableonlineathttp://www.energy.ca.gov/reports/efficiency_handbooks/40000001A.PDF
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2.5 OtherECMsandResources
Althoughthefocusofthisdocumentistoreportoninnovativeandemergingequipmentand
operationsrelatedECMs,otherECMs(bothinnovativeandconventional),havebeenusedsuccessfully
atWWTPstosaveenergyandassociatedcosts,suchas:
Lighting,HVAC,andotherbuildingimprovements. ReducingtheloadingtotheWWTPsby:
- Collectionsystemimprovementstoreduceinfiltrationandinflowtoreducestormrelatedpeaks
- Waterconservation- Useofequalizationbasinstoattenuatepeakflowsandloadings
UseofSupervisoryControlandDataAcquisition(SCADA)softwareforprocessmonitoringandoperationalcontrol. SCADAhasmanyoperationalbenefits,including:
- Itcanprovidedataforprocessmodelingandenergyuseoptimization- Itcanprovideimmediatedetectionofproblemsthroughdiagnosticdisplays,enabling
quickinterventionforfastresolutions
- Itcanallowoperatorstocompensateforseasonalflowandwetweatherbyautomaticallyadjustingsetpoints(USEPA2006).
Implementingcogenerationtechnologytogenerateelectricityandrecoverableheatonsiteusingmethaneoffgasfromanaerobicdigesters.
Implementingenergymanagementstrategiessuchas- Hiringanenergymanager- Realtimepowermonitoring- Peakelectricdemandreduction- Submeteringtoidentifythemostenergyintensiveprocesses
OtherECMsthatcanoffermodestimprovementsandmaybeeasyforasystemtoimplementinclude
pumpcoatingstoreducefrictionorinstallingavortexgritremovalsysteminsteadofonethatuses
aeration.
ECMsshouldalwaysbeconsideredwhenaplantisfacingamajor20or30yearupgrade. Atthis
time,thereareopportunitiestoreconfiguretheplantforenergysavings. NotedinChapters3and4of
thisdocumentbutworthreiteratingistheimportanceofproperlydesigningforenergyefficiency.
Maximizingequipment(blowerandpump)turndowncapacityanddesigningforplantupgradesinstages
(i.e.,rightsizing)cangoalongwaytomeetenergyefficiencygoals. Anotherimportantdesign
conceptistousehydraulicheadwheneverpossibletoreducetheneedtopump. TheConsortiumfor
EnergyEfficiency(CEE)hasrecentlyissuedguidanceonhowtoincludeenergyefficiencyinrequestsfor
qualifications(RFQs)andRequestsforProposals(RFPs). Thisguidanceisavailablefreeonlineat
http://www.cee1.org/ind/motsys/ww/rfp/index.php3.
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AppendixBofthisreportprovidesacomprehensivelistofwebreferencesforenergy
conservation.OtherimportanttechnicalreferencesincludetheWaterEnvironmentFederation(WEF)
ManualofPractice(MOP)No.32:EnergyConservationinWaterandWastewaterFacilities(WEF2009)
andthereportbytheElectricPowerResearchInstitute(EPRI),QualityEnergyEfficiencyRetrofitsfor
WastewaterSystems(EPRI1998).TheWEFMOP8,DesignofMunicipalWastewaterTreatmentPlants
(WEFandASCE2010)providesguidanceondesigningenergyefficientwastewatertreatmentplant
components.TheWERFreport,EnergyEfficiencyinWastewaterTreatmentinNorthAmerica:A
CompendiumofBestPracticesandCaseStudiesofNovelApproaches,providesrecommendationson
energyefficiencyimprovementsboththroughoptimizationofcurrentprocessesandthroughadoption
ofnovelapproaches.ThereportisscheduledtobepublishedinJanuary2011.Lastly,theWERFreport,
BestPracticesforSustainableWastewaterTreatment:InitialCaseStudyIncorporatingEuropean
ExperienceandEvaluationToolConcept(2009),highlightsEuropeancasestudiesrelatedtoenergy
efficiencyinwastewatertreatment.
Additionalonlineresourcesforcomprehensiveenergymanagementinclude:
EnsuringaSustainableFuture: AnEnergyManagementGuidebookforWastewaterandWaterUtilities(USEPA2008a). Thisdocumentprovidesastepbystepmethodforenergyconservation
basedonthePlanDoCheckActmanagementapproach.Itisavailableonlineat:
http://www.epa.gov/waterinfrastructure/pdfs/guidebook_si_energymanagement.pdf
EPAsWastewaterManagementFactSheet:EnergyConservation(USEPA2006),availableonlineat:http://www.epa.gov/owm/mtb/energycon_fasht_final.pdf. This7pagefactsheetdescribes
possiblepracticesthatcanbeimplementedtoconserveenergyataWWTP.
TheFlexYourPowerBestPracticesGuideforLocalGovernments,WastewaterSector,availableonlineat: http://www.fypower.org/bpg/module.html?b=institutional&m=Water_Use. This
guidecontainsa4stepapproachtoreducingenergyuseataWWTPandincludeslinksto
additionalonlineresources.
WisconsinFocusonEnergysWaterandWastewaterEnergyBestPracticeGuidebook(FocusonEnergy2006),availableonlineat:
http://www.werf.org/AM/Template.cfm?Section=Home&TEMPLATE=/CM/ContentDisplay.cfm&
CONTENTID=10245. ThisguidebookcontainsbenchmarkingresultsfromselectedWisconsin
wastewaterfacilities,bestpracticeapproachestoongoingmanagementofenergyuse,best
practicefundingandfinancingopportunities,andreferencesforfurtheropportunitiesin
water/wastewatersystemenergyefficiencyandpowerdemandreduction.
2.6 References
CaliforniaEnergyCommission(CEC).2000.HowtoFinancePublicSectorEnergyEfficiencyProjects.
January2000.Availableonlineathttp://www.energy.ca.gov/reports/efficiency_handbooks/40000
001A.PDF
Cantwell,J.,J.Newton,T.Jenkins,P.Cavagnaro,andC.Kalwara.2009.RunninganEnergyEfficient
WastewaterUtilityModificationsThatCanImproveYourBottomLine.WEFWebcast.June19,2009.
-
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EvaluationofEnergyConservationMeasures 28 September2010
EnergyStar.2010.EnergyStarGuidelinesforEnergyManagement.U.S.EnvironmentalProtection
AgencyandtheU.S.DepartmentofEnergy.Accessed1March2010.
http://www.energystar.gov/index.cfm?c=guidelines.guidelines_index
EPRI.1998.QualityEnergyEfficiencyRetrofitsforWastewaterSystems.ElectricPowerResearch
Institute.ProjectManager:KeithCarns.CR109081.
FocusonEnergy.2006.WaterandWastewaterEnergyBestPracticeGuidebook.Reportpreparedby
ScienceApplicationsInternationalCorporation.Availableonlineifrequestedat
http://www.focusonenergy.com/Business/IndustrialBusiness/Guidebooks/
Ishida,C.,E.Garvey,S.Dent,S.Deslauriers,andH.S.McDonald.2008.Optimo:AnInnovative
WastewaterMasterPlanOptimizationModelThatImprovesSystemEfficiency,ReducesRisks,andSaves
CapitalandO&MCosts.PresentedatUtilityandManagement2008.Tampa,FL.WEF.
USDOE.2007. MotorMaster+:MotorDrivenSystems,version4.0.6.U.S.DepartmentofEnergy.
http://www1.eere.energy.gov/industry/bestpractices/software_motormaster.html
USDOE.2008.PumpingSystemAssessmentTool(PSAT).U.S.DepartmentofEnergy.
http://www1.eere.energy.gov/industry/bestpractices/software_psat.html
USEPA.2006.WastewaterManagementFactSheet:EnergyConservation.July2006.EPAOfficeofWater
832F06024.Availableonline:http://www.epa.gov/owm/mtb/energycon_fasht_final.pdf
USEPA.2008a.EnsuringaSustainableFuture:AnEnergyManagementGuidebookforWastewaterand
WaterUtilities.January2008.Availableonline:
http://www.epa.gov/waterinfrastructure/pdfs/guidebook_si_energymanagement.pdf
USEPA.2008b.EPAEnvironmentalManagementSystems:BasicInformation. Lastupdated17June
2008.Availableonline:http://www.peercenter.net/toolkit/
WEFandASCE.2010.DesignofMunicipalWastewaterTreatmentPlantsWEFManualofPractice8and
ASCEManualsandReportsonEngineeringPracticeNo.76,5thEd.WaterEnvironmentFederation,
Alexandria,VA,andAmericanSocietyofCivilEngineersEnvironment&WaterResourcesInstitute,
Reston,Va.
WEF.2009.MOPNo.32:EnergyConservationinWaterandWastewaterFacilities.Preparedbythe
EnergyConservationinWaterandWastewaterTreatmentFacilitiesTaskForceoftheWater
EnvironmentFederation.McGrawHill,NewYork.
WERF.2009.BestPracticesforSustainableWastewaterTreatment:InitialCaseStudyIncorporating
EuropeanExperienceandEvaluationToolConcept.Alexandria,VA:WERF.Availableonline:http://www.werf.org/AM/Template.cfm?Section=Search&Template=/CustomSource/Research/Publicati
onProfile.cfm&id=OWSO4R07a
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3.EnergyConservationMeasuresforPumpingSystems
3.1 Introduction
Pumpingoperationscanbeasignificantenergydrawatwastewatertreatmentplants(WWTPs),
inmanycasesaresecondonlytoaeration.Pumpsareusedformanyapplications. Attheplant
headworks,theymaybeusedtoprovidehydraulicheadforthetreatmentprocesses.Withintheplant,
theyareusedtorecycleandconveywasteflows,solids,andtreatedeffluenttoandfromavarietyof
treatmentprocesses.Pumpsarealsofoundinremotelocationsinthecollectionsystemtohelpconvey
wastewatertotheplant.
Theoverallefficiencyofapumpingsystem,alsocalledthewiretowaterefficiency,isthe
productoftheefficiencyofthepumpitself,themotor,andthedrivesystemormethodofflowcontrol
employed.Pumpsloseefficiencyfromturbulence,friction,andrecirculationwithinthepump(WEF
2009).Anotherlossisincurrediftheactualoperatingconditiondoesnotmatchthepumpsbest
efficiencypoint(BEP).1 Thevariousmethodsforcontrollingflowratedecreasesystemefficiency.
Throttlingvalvestoreducetheflowrateincreasesthepumpinghead,flowcontrolvalvesburnhead
producedbythepump,recirculationexpendspowerwithnousefulwork,andVFDsproduceaminor
amount
of
heat.
Of
these
methods,
VFDs
are
the
most
flexible
and
efficient
means
to
control
flow
despitetheminorheatlossincurred.Table31summarizestypicalpumpsystemefficiencyvaluesnote
thatinefficiencyinmorethanonecomponentcanaddupquickly,resultinginaveryinefficientpumping
system.
1BEPistheflowrate(typicallyingallonsperminuteorcubicmetersperday)andhead(infeetormeters)thatgivesthe
maximumefficiencyonapumpcurve. Forbasicinformationonpumpsystemdesign,seetheWEFManualofPracticeNo.32,
EnergyConservationinWaterandWastewaterFacilities(WEF2009),orthesixpartseries,UnderstandingPumpSystem
FundamentalsforanEnergyEfficientWorld(PumpZone2008and2009),availableonlineathttp://www.pump
zone.com/pumps/pumps/understandingpumpfundamentalsforanenergyefficientworld.html
Chapter3covers:
3.1 Introduction
3.2 Pumping
System
Design
3.3 Motors
3.4 PowerFactor
3.5 VariableFrequencyDrives(VFDs)
3.6 References
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Table31.PumpSystemEfficiency
Pump SystemComponent
Efficiency
Range Low Avg High
Pump 30 85 % 30 % 60 % 75 %1
Flow Control2
20 98 % 20 % 60 % 98 %Motor
385 95 % 85 % 90 % 95 %
Efficiency of System 5 % 32 % 80 %1. For pumping wastewater. Pump system efficiencies for clean water can be higher.2. Represents throttling, pump control valves, recirculation and VFDs.3. Represents nameplate efficiency and varies by horsepower. See Section 3.4 for more information
Inefficienciesinpumpingoftencomefromamismatchbetweenthepumpandthesystemit
servesduetoimproperpumpselection,changesinoperatingconditions,ortheexpectationthatthe
pumpwilloperateoverawiderangeofconditions.Signsofaninefficientpumpingsysteminclude:
Highly
or
frequently
throttled
control
valves
Bypassline(recirculation)flowcontrol
Frequenton/offcycling
Cavitationnoiseatthepumporelsewhereinthesystem
Ahotrunningmotor
Apumpsystemwithnomeansofmeasuringflow,pressure,orpowerconsumption
Inabilitytoproducemaximumdesignflow
Formoreinformation,refertothePumpSystemBasicAssessmentGuide(PumpSystemsMatterTM
2010),availableonlineathttp://www.pumpsystemsmatter.org/content_detail.aspx?id=3334.
The
literature
provides
several
examples
of
plants
reducing
pumping
energy
by
as
much
as
50
percentthroughpumpsystemimprovements(FocusonEnergy2006).Energysavingsresultfrom
loweringofpumpingcapacitytobettermatchsystemdemands,replacinginefficientpumps,selecting
moreefficientmotors,andinstallingvariablespeedcontrollers.Generallyspeaking,energyconservation
measures(ECMs)forpumpingareconventionalanddonotrepresentanareawhererecenttechnology
innovationhasplayedapartinimprovingenergyconservationandefficiency.PumpingECMsare,
however,stillextremelyimportanttoreducingandoptimizingenergyuseatwastewatertreatment
plants.ThischapterprovidesanoverviewofconventionalECMsrelatedtopumpingdesign,variable
frequencydrives(VFDs),andmotorsandrefersthereadertoindustrystandardsandweblinksfor
additionalguidance.
WastewaterutilitiesshouldconsiderimplementingpumpingECMsaspartofalongtermpump
testingandmaintenanceprogram.Pumpsshouldbetestedeverytwotothreeyearstoensurethatthey
areoperatingefficiently.Utilitiesshouldtestforflow,head,andpowerconsumptionandthencalculate
efficiencyforeachpumpsystem.Ifoverallsystemefficiencyislow(lessthan60or70percentfor
centrifugalwastewaterpumps,lessthan72percentforcleanwaterpumps2),amoredetailedevaluation
iswarranted.Thistypeofprogramcangivetheplantearlywarningwhenpumpcomponentsarefailing
andcanpreventcatastrophicfailures.Itisimportantthatallcomponentsbeevaluatedandaddressed
2EmailcommunicationfromKenHenderson,September8,2010.
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holisticallysothattheentiresystemisenergyefficient.Stateandlocalrequirementsforredundancy
(e.g.,thecommonrequirementthatapumpstationcanpumppeakflowswiththelargestpumpoutof
service)andsafetyfactorsmaylimitavailableefficienciesinsomecases.
Severaltoolsareavailablefreeonlinetoassistwastewaterutilitiesindevelopingapumptesting
andmaintenanceprogram.PumpSystemsMatterTM,aneducationprogramconceivedbytheHydraulic
Institute,providestechnicalreferences,downloadabletools,tipsheets,andwhitepapersontheir
websiteathttp://www.pumpsystemsmatter.org/default.aspx.TheDepartmentofEnergy(DOE)has
developedandsupportsthePumpSystemAssessmentTool(PSAT),availablefreeonlineat
http://www1.eere.energy.gov/industry/bestpractices/software_psat.html,tohelpusersdeterminethe
efficiencyoftheirexistingpumpingsystemsandcalculateenergyandcostsavingsforupgrades.The
WaterEnvironmentFederation(WEF)providesguidanceonlifecyclecosting,operationand
maintenancepractices,andmeasurementequipmentintheirMOPNo.32(WEF2009).
3.2 PumpingSystemDesign
Appropriatesizingofpumpsiskeytoefficientoperationofwastewatertreatmentplants.Pumps
sizedforpeakflowconditionsthatoccurinfrequentlyor,worse,inthefuturetowardstheendofthe
pumpsservicelifeoperatethemajorityofthetimeatareducedflowthatisbelowtheirBEP. Peakflow
istypicallyseveraltimesgreaterthanaveragedailyflowandcanbeanorderofmagnitudedifferent
thanminimumflow,especiallyforsmallsystemsorsystemswithsignificantinflowandinfiltration(I&I).
Insomesystems,theseprojectedfutureflowsareneverreachedduringthedesignlifeofthepump.
Forexistingtreatmentplants,utilitiesshouldevaluatetheoperationofexistingpumpsand
identifyopportunitiesforenergyreduction.Agoodstartingpointistodeterminetheefficiencyof
existingpumpingsystems,focusingfirstonpumpsthatoperateforthemosthoursandhavepotential
problemsasidentifiedbythebulletlistinSection3.1(presenceofbypasslines,throttledvalves,etc.).
Plantsshouldcollectperformanceinformationontheflowrate,pressure,anddeliveredpowertothe
pumps.
Field
measurements
may
be
necessary
if
the
plant
does
not
regularly
record
this
information.
Pumpandsystemcurvescanthenbeconstructedtodeterminetheactualoperatingpointsofthe
existingsystem.Operatingpointsmorethan10percentdifferentthantheBEPsignalroomfor
improvement.DetailedguidanceonpumpsystemassessmentisprovidedinthePumpSystemsMatter
publication,PumpSystemBasicAssessmentGuide,availableonlineat
http://www.pumpsystemsmatter.org/content_detail.aspx?id=3334
Toimproveefficiency,utilitiesshouldconsiderreplacingoraugmentinglargecapacitypumps
thatoperateintermittentlywithsmallercapacitypumpsthatwilloperateforlongerperiodsandcloser
totheirBEP. Whenreplacingapumpwithasmallerunit,boththehorsepowerandefficiencychange. A
quickwaytoestimatetheannualenergycostsavingsistoapproximatecostbeforeandafterthe
improvementanddeterminethedifferenceusingthefollowingequation:
AnnualEnergySavings($)=[hp1xL1x0.746xhrxE1xC][hp2xL2x0.746xhrxE2xC] Eq.31
Where:
hp1=horsepoweroutputforthelargercapacitypump
hp2=horsepoweroutputforthesmallercapacitypump
L1=loadfactoroflargercapacitypump(percentageoffullload/100 determinedfrompump
curve)
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L2=loadfactorofsmallercapacitypump(percentageoffullload/100 determinedfrompump
curve)
hr=annualoperatinghours
C=energy(electricpower)rate($/kWh)
E1=efficiencyofthelargercapacitypump
E2=efficiencyofthesmallercapacitypump
SeeExample31forhowtheTownofTrumbullwasabletosavemorethan$1,500peryearbyaddinga
smallpumptooneofitsexistingsewagepumpingstations.Whenappliedcorrectly,replacementof
standarddriveswithVFDscanalsoyieldsignificantimprovements(seeSection3.3foradditional
discussion).
Forgreenfieldplantsand/ornewpumpstations,utilitiesshouldconsiderandplanforstaging
upgradesoftreatmentcapacityaspartofthedesignprocess.Forexample,multiplepumpscanbe
specifiedtomeetafuturedesignflowinsteadofonelargepumpsothatindividualpumpscanbe
installedasneeded,sayatyearzero,yearten,andyeartwenty.TheStateofWisconsinsFocuson
Example31 TownofTrumbull,CT,ImprovesEfficiencyatReservoirAvenuePumpStation
BACKGROUND:WastewaterfromtheTownofTrumbull,insouthwesternCT,iscollectedand
conveyedtoaWWTPinBridgeportviatensewagepumpstations. Oneofthese,theReservoirAvenue
Pumpstation,consistingoftwo40hpdirectdrivepumpsdesignedtohandleanaveragedailyflowof
236gallonsperminute(gpm). Eachpumpwasoperatedatareducedspeedof1320rpmat50.3feet
oftotaldynamichead(TDH)withadutypointofapproximately850gpm. Abubblertypelevelcontrol
systemwasusedtoturnthepumpsoffandon. Onepumpcanhandletheentirepeakinflow(usually
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Energybestpracticesguidebook(FocusonEnergy2006)estimatesthatstagingoftreatmentcapacity
canresultinenergysavingsbetween10and30percentoftotalenergyconsumedbyaunitprocess.
3.3 Motors
Thecostofrunningelectricmotorscanbethelargestfractionofaplantstotaloperatingcosts.
WEFestimatesthatelectricmotorsmakeup90percentoftheelectricenergyconsumptionofatypical
wastewatertreatmentplant(WEF2009). Inefficientmotors,operationoutsideofoptimalloading
conditions,andmechanicalorelectricalproblemswiththemotoritselfcanleadtowastedenergyatthe
plantandareopportunitiesforsavings.
Thepercentenergysavingsresultingfromreplacingoldermotorswithpremiummotorsis
modest,typicallybetween4and8percent(NEMAStandardMG1.2006).Savingscanbehigherwhen
energyauditsrevealthatexistingmotorsachieveverylowefficiencies,orwhenexistingmotorsare
oversizedand/orunderloaded.Manyplantshavecoupledmotorreplacementswithupgradesfrom
fixedspeedtovariablespeeddrivesforsignificantlyhigherenergysavings.
Ingeneral,upgradingmotorsisaconventionalECMthathasbeenpracticedatwastewater
treatmentplantsforsometime.Becausethemainfocusofthisreportisinnovativeratherthan
conventionaltechnologies,thissectioncontainsonlyabriefoverviewofmaterial,anddirectsthereader
tootherpublicallyavailablewebsitesandreferencesfordetailedinformation.Specifically,Section3.3.1
describesmotorefficiencyandsummarizescurrentmotorefficiencystandards,andSection3.3.2
provideslinkstomotormanagementtoolsandsoftware.Theexceptiontoconventionalpracticesisthe
emergenceofnew,ultraefficiencymotors,whicharedescribedinSection3.3.3.
Inadditiontotoolsandreferencesidentifiedinsubsequentsections,thereaderisreferredto
thefollowingwebsitesfortechnicalinformationonmotors:
TheU.S.DOEprovidesextensiveinformationaspartoftheirMotorChallengesProgram.Publicationsincludedownloadablebooks,tipsheets,andfactsheetsontechnicalandeconomic
topicsrelatedtomotors.See
http://www1.eere.energy.gov/industry/bestpractices/techpubs_motors.html foralistof
publishedmaterialandrelevantweblinks.
TheConsortiumforEnergyEfficiency(CEE)providestechnicalmaterial,links,andfactsheets
underitsMotorsandMotorSystemsIndustrialProgram(http://www.cee1.org/ind/mot
sys/mtrmsmain.php3).
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3.3.1 MotorEfficiencyandEfficiencyStandards
Motorefficiencyisameasureofmechanicalpoweroutputcomparedtoelectricalpowerinput,
expressedasapercentage.
Motorefficiency=Pm/Pe Eq.32
Where:
Pm=mechanicalpoweroutputofthemotorinWatts
Pe=electricalpowerinputtothemotorinWatts(WEF2009)
Nomotoris100percentefficientallmotorsexperiencesomepowerlossduetofriction,electrical
resistancelosses,magneticcorelosses,andstrayloadlosses.Smallermotorsgenerallyexperience
higherlossescomparedtolargermotors.
TheUnitedStatesCongress,intheEnergyPolicyAct(EPACT)of1992,setminimumefficiency
standardsforvarioustypesofelectricmotorsmanufacturedinorimportedtotheUnitedStates.
Minimumnominal,fullloadefficienciestypicallyrangefrom80to95percentdependingonsize(i.e.,
horsepower)andothercharacteristics.Motorsmanufacturedsince1997wererequiredtocomplywith
EPACTstandardsandtobelabeledwithacertifiedefficiencyvalue.
TheNationalElectricalManufacturersAssociation(NEMA)premiumefficiencystandardhas
existedsince2001(NEMA2006)asavoluntaryindustrystandardandhasbeenwidelyadopteddueto
itspower(andthuscost)savingsoverEPACT1992compliancestandards.The2007EnergyActraised
efficiencystandardsofmotorstoNEMApremiumefficiencylevelsandsetnewstandardsformotorsnot
coveredbypreviouslegislation.The2007act,whichcomesintoforceinDecember2010,issummarized
onlineathttp://www.motorsmatter.org/resources/gen_legislation.html.
Submersible
motors
are
commonly
used
in
wastewater
treatment
plants.
They
serve
specialized
applicationsinenvironmentsthatarenotsuitedforNEMAmotors. Thereiscurrentlynoefficiency
standardforsubmersiblemotorsandtheirefficiencyislessthanNEMAmotors. Additionally,their
powerfactorisusuallylower. Theirselectionisusuallydrivenbytheapplication,thoughsome
applicationshavealternativesthatuseNEMAmotors. Efficiencyshouldbeconsideredintheevaluation
ofalternativesintheseapplicationsasitaffectsthelifecyclecostusedintheselectionprocess.
Operatingefficiencyinthefieldisusuallylessthanthenominal,fullloadefficiencyidentifiedby
themotormanufacturer.Onereasonforthisistheoperatingload.Asaruleofthumb,mostmotorsare
designedtooperateatbetween50and100percentoftheirratedload,withmaximumefficiency
occurringatabout75percentofmaximumload.Forexample,amotorratedfor20horsepower(hp)
shouldoperatebetween10and20hpandwouldhaveitsbestefficiencyaround15hp.Largermotors
canoperatewithreasonableefficiencyatloadsdowntothe25percentrange(USDOE1996).Motors
operatedoutsideoftheoptimalloadingloseefficiency.Otherfactorsthatreduceefficiencyinthefield
includepowerquality(I.e.,propervoltage,amps,andfrequency)andtemperature.Motorsthathave
beenrewoundtypicallyarelessefficientcomparedtotheoriginalmotor.
Accuratelydeterminingtheefficiencyofmotorsinserviceataplantischallengingbecausethere
isnoreliablefieldinstrumentformeasuringmechanicaloutputpower.Severalmethodsareavailable,
however,toapproximatemotorefficiency.Forasummary,seetheU.S.DepartmentofEnergyfactsheet
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onthesubject(USDOE2005),availableonlineat
http://www1.eere.energy.gov/industry/bestpractices/pdfs/estimate_motor_efficiency_motor_systemts
2.pdf.OnemethodistousefieldmeasurementsandtechnicaldataintheMotorMaster+softwaretool
toestimateefficiency.Section3.3.2providesadditionalinformationonthistool.
3.3.2 MotorManagementPrograms
Wastewaterutilitiesshouldconsiderpurchasingnewenergyefficientpremiummotorsinstead
ofrewindingolderunitswhenreplacingequipmentandwhenmakingmajorimprovementsattheplant
(seethetextboxinthissectionforadditionalrecommendations). Motorreplacementisbestdoneas
partofaplantwidemotormanagementprogram.Afirststepinprogramdevelopmentistocreatean
inventoryofallmotorsattheplant.Theinventoryshouldcontainasmuchinformationaspossible
includingmanufacturersspecifications,nameplateinformation,andfieldmeasurementssuchas
voltage,amperage,powerfactor,andoperatingspeedundertypicaloperatingconditions.Followingthe
datagatheringphase,plantmanagersshouldconductamotorreplacementanalysistodeterminewhich
motorstoreplacenowandwhicharereasonablyefficientandcanbereplacedinthefutureorattimeof
failure.
Akeyinputtoanymotorreplacementanalysisiseconomics.Asimpleapproachistocalculate
theannualenergysavingsofthenewmotorcomparedtotheoldunitanddeterminethepaybackperiod
inyears(inotherwords,whenwillthecumulativeenergysavingsexceedtheinitialcosts).Thefollowing
simpleequationcanbeusedtodetermineannualenergysavings:
AnnualEnergySavings($)=hpxLx0.746xhrxCx(Ep Ee) Eq.33
Where:
hp=horsepoweroutputofmotor
L=loadfactor(percentageoffullload/100)
0.746=conversionfromhorsepowertokWunits
hr=annualoperatinghours
C=energy(electricpower)rate($/kWh)
Ee=existingmotorefficiencyasapercentage
Ep=premiummotorefficiencyasapercentage
WhenShouldPlantsConsiderBuyingNewEnergyEfficientMotors?
Fornewinstallations
Whenpurchasingnewequipmentpackages
Whenmakingmajormodificationstotheplant
Insteadofrewindingolder,standardefficiencyunits
Toreplaceoversizedand/orunderloadedmotors
Aspartofapreventivemaintenanceorenergyconservationprogram
Source: MotorChallengeFactSheet:BuyinganEnergyEfficiencyElectricMotor. Availableonline
athttp://www1.eere.energy.gov/industry/bestpractices/pdfs/mc0382.pdf
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Simplepaybackinyearscanthenbecalculatedasthenewmotorcost(capitalplusinstallation)
dividedbytheannualenergysavings.Whencomparingbuyingapremiummotorinsteadofrewinding
anexistingone,thecostofrewindingtheexistingmotorshouldbesubtractedfromthemotorcost.Any
cashrebatefromyourlocalelectricutilityorstateenergyagencyshouldalsobesubtractedfromthe
costofthenewmotor. Whenreplacingpumps,motors,orcontrolsystems,upgradingtheelectrical
service,wiring,transformers,andothercomponentsoftheelectricalsystemshouldbeconsideredin
calculatingenergysavingsandlifecyclecosts. Utilitiesshouldalsoconsidertheimportanceofreliability
andenvironmentalfactorswhenmakingmotorreplacementdecisions.Morerobusteconomicanalyses
suchasnetpresentvaluelifecyclecostanalysisshouldbeconsidered,especiallyforlargeexpenditures.
TheENERGYSTARCashFlowOpportunity(CFO)calculatorisaneasytousespreadsheettool
thatcanhelpplantmanagerscalculatesimplepaybackaswellascostofdelay,whichisthelost
opportunitycostiftheprojectisdelayedtwelvemonthsormore.Thelastsheetoftheworkbook
providesasummarythatcanbegiventoseniormanagersanddecisionmakerstohelpconvincethemof
thefinancialsoundnessofenergyefficiencyupgrades.TheCFOcalculatorandotherfinancialtoolsare
availableforfreedownloadathttp://www.energystar.gov/index.cfm?c=assess_value.financial_tools.
Thetaskofmotorinventorymanagementandreplacementanalysisismadesignificantlyeasier
bypublicallyavailablesoftwaretools.DevelopedbytheDOEIndustrialTechnologiesProgram,
MotorMaster+isamotorselectionandmanagementtool,availablefreeonlineat
http://www.motorsmatter.org/.Itincludesinventorymanagementfeatures,maintenancelogging,
efficiencyanalysis,savingsevaluation,andenergyaccounting.Itincludesacatalogof17,000motors
from14manufacturers,includingNEMAPremiumefficiencymotors,andmotorpurchasing
information.InadditiontoMotorMaster+software,thesponsorsoftheMotorDecisionsMatter
campaigndevelopedaspreadsheettooltoassistplantmanagerswithmotorreplacement/repair
decisionmaking.Thetoolistitledthe1*2*3ApproachtoMotorManagementandisavailableforfree
downloadathttp://www.motorsmatter.org/tools/123approach.html.
3.3.3
Innovative
and
Emerging
Technologies
SiemensEnergyandAutomationincooperationwiththeCopperDevelopmentAssociationhas
developedultraefficientcopperrotorsquirrelcagetypeinductionACmotors.Thesemotorsexceed
NEMApremiumfullloadefficiencystandardsbyupto1.4percent;however,theyareonlycurrently
availableinoutputsupto20hp.Inadditiontousinghighconductivitycopperrotorsinplaceof
aluminum,thenewmotorshavethefollowingefficiencyimprovements:
Optimizedrotorandstatordesign
Lowfrictionbearings
Improvedcoolingsystem
Polyureabasedgrease
Dynamicallybalancedrotors
Precisionmachinedmatingsurfacesforreducedvibration
ThemotorsinsulationisdesignedtobecompatiblewithVFDs(USDOE2008).
TheU.S.DepartmentofEnergy(USDOE),incooperationwithBaldorElectricCompanyandother
privatepartners,isdevelopinganewgradeofUltraEfficientandPowerDenseElectricMotors,withthe
goalofa15percentreductioninmotorenergylossoverNEMApremiummotors.Forexample,ifa
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NEMApremiummotorwithparticularcharacteristicsandoutputhorsepowerwas92percentefficient
andthushad8percentloss,thisnewgradeofmotorwouldreducelossby0.15*8%=1.2percent,fora
newoverallefficiencyof93.2percent.Thenewgradeofmotorwillalsobe30percentsmallerinvolume
and30percentlowerinweight,leadingtodecreasedmotorcostduetolowermaterialscosts(USDOE
2009).Formoreinformation,seeDOEswebsiteat
http://www1.eere.energy.gov/industry/intensiveprocesses/pdfs/electric_motors.pdf.
3.4 PowerFactor
Powerfactorisimportantbecausecustomerswhoseloadshavelowpowerfactorrequire
greatergenerationcapacitythanwhatisactuallymetered. Thisimposesacostontheelectricutility
thatisnototherwiserecoveredbytheenergyanddemandcharges. Therearetwotypesofpowerthat
makeupthetotalorapparentpowersuppliedbytheelectricutility. Theirrelationshipisshownin
Figure31. Thefirstistheactivepower. MeasuredinkW,itisthepowerusedbytheequipmentto
producework. Thesecondisthereactivepower. Thisisthepowerusedtocreatethemagneticfield
necessaryforinductiondevicestooperate. ItismeasuredinkVARs.
Figure31. VectorRelationshipofACPower
Powerfactoristheratiooftheactivepowertotheapparentpower. Thepowerfactoroffully
loadedinductionmotorsrangesfrom80to90percentdependingonthetypeofmotorandthemotors
speed. Powerfactordeterioratesastheloadonthemotordecreases. Otherelectricaldevicessuchasspaceheatersandolderfluorescentorhighdischargelampsalsohavepoorpowerfactor. Treatment
plantshaveseveralmotors,numerouslamps,andoftenelectricheaters,which,combined,lowersthe
facilitysoverallpowerfactor.
Powerfactormaybeleadingorlagging. Voltageandcurrentwaveformsareinphaseina
resistiveACcircuit. However,reactiveloads,suchasinductionmotors,storeenergyintheirmagnetic
fields. Whenthisenergygetsreleasedbacktothecircuititpushesthecurrentandvoltagewaveforms
outofphase. Thecurrentwaveformthenlagsbehindthevoltagewaveform. Whentheloadis
capacitive,theoppositeoccurs,andthecurrentwaveformleadsthevoltagewaveform.
Improvingpowerfactorisbeneficialasitimprovesvoltage,decreasessystemlosses,frees
capacitytothesystem,anddecreasespowercostswherefeesforpoorpowerfactorarebilled. Power
factorcanbeimprovedbyreducingthereactivepowercomponentofthecircuit. Addingcapacitorsto
aninductionmotorisperhapsthemostcosteffectivemeanstocorrectpowerfactorastheyprovide
reactivepower. Synchronousmotorsareanalternativetocapacitorsforpowerfactorcorrection.
Synchronousmotorscanberunatlagging,unity,orleadingpowerfactorbycontrollingtheirfield
excitation. Whenthefieldexcitationvoltageisdecreased,themotorrunsinlaggingpowerfactor. This
conditioniscalledunderexcitation. Whenthefieldexcitationvoltageismadeequaltotherated
voltage,themotorrunsatunitypowerfactor. Themotorrunsatleadingpowerfactorwhenthefield
Active Power,kW
ReactivePower,kVAR
ApparentPower,kVAR
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excitationvoltageisincreasedabovetheratedvoltage. Thisconditioniscalledoverexcitation. When
overexcited,theycanprovidesystempowerfactorcorrection. Synchronousmotorsabove300hpand
below1200rpmareoftenlessexpensivethanacomparableinductionmotor(ThumannandDunning,
2008).
Thefeasibilityofaddingcapacitorsdependsonwhethertheelectricutilitychargesforlow
powerfactor. Correctivemeasuresareinfrequentlyinstalledsincemanyelectricutilitiesdonotcharge
smallcustomersforpoorpowerfactorbutratherpriceitintotheelectricalratesasacostofbusiness.A
costevaluationisneededtodeterminethetypeofcorrectionequipmenttouse. Theevaluationshould
includemotortype,motorstarter,exciter(forsynchronousmotors),capacitorsandswitchingdevicesif
needed,efficiency,andpowerfactorfees(IEEE1990). Manufacturersshouldbeconsultedbefore
installingcapacitorstoreducedvoltagesolidstatestartersandVFDsastherecanbeproblemsifthey
arenotproperlylocatedandapplied.
3.5 VariableFrequencyDrives(VFDs)
VFDsareusedtovarythespeedofapumptomatchtheflowconditions. Theycontrolthe
speedofamotorbyvaryingthefrequencyofthepowerdeliveredtothemotor. Theresultisaclose
matchoftheelectricalpowerinputtothepumpwiththehydraulicpowerneededtopumpthewater.
AsillustratedbytheredareasinFigure32,othermethodsusedtocontrolflowexpendmoreelectrical
powerthanthehydraulicpowerneeded. Throttlingvalvesdecreaseflowbymovingtheoperatingpoint
onthepumpscurvetotheleft.Thisisachievedbyartificiallyincreasingtheheadagainstwhichthe
pumpworks. Bypasscontrolreturnsaportionofthewaterpumpedbacktothesuctionsideofthe
pump,whichwastesaportionoftheenergyusedtorecirculatethewaterwithnousefulwork.
Stop/startcontrolisindicativeofanoversizedpumpthatpulsestomatchflow. Whilethisachieves
thesameamountofworkasasmallerpumpoperatingcontinuously,itdoessoatahigherpower(kW)
demand. VFDsareaproventechnologythatismoreefficientthanthesecontrolmethodsandare
ideallysuitedinsituationswheretheflowrateishighlyvariable.
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Figure32.WastedEnergyinAlternativeControlSchemesComparedtoVariableFrequencyDrives
Source:providedcourtesyofPumpSystemsMatterandtheHydraulicInstitute,Parsippany,NJ
www.PumpSystemsMatter.org
3.5.1 EnergySavings
VFDshavebeenusedbymanywastewaterutilitiestoconserveenergyandreducecosts.A
literaturereviewfoundnumeroussuccessstorieswithenergysavingsrangingfrom70,000kWh/yrfor
smallerWWTPs(i.e.averagedailyflowof710mgd)to2,800,000kWh/yrforlargerWWTPs(i.e.average
dailyflowof80mgd)(EPRI1998;EfficiencyPartnership2009;USDOE2005c).VFDsarenowmore
availableandaffordable,andpaybacksforVFDsrangefromsixmonthstofiveyearsdependingonthe
existinglevelofcontrolandannualhoursofoperation(FocusonEnergy,2006).
Toapproximatethepotentialenergysavings,utilitiesshoulddevelopacurveofactualflowin
hourlyincrementsduringaday.Usingthecurve,energyconsumedbyaconstantspeedmotorand
throttlingvalvecanbeestimatedandcomparedtoenergyconsumedbyaVFDsystemthatmatchthe
hourlyflowratetopowerused.
3.5.2 Applications
VFDscanbeinstalledatremotecollectionsystempumpingstations,atliftstations,onblowers,
andonoxidationditchaerationrotordrives.AcommonapplicationofVFDsisforpumpsthatexperience
alargevariationindiurnalflow,suchasatwastewaterpumpingstations. However,ifVFDsarenot
selectedandappliedcorrectly,theycanwasteenergy. Operatingbelow75%forfullload,VFDscanhave
verylowefficiencies. InselectingaVFD,informationshouldbeobtainedfromtheVFDmanufacture
showingtheefficiencyatdifferentturndownrates.
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VFDsarenotapplicableinallsituations.VFDsmaynotbeeffectivewhenalargestatichead
mustbeovercomeorwherethereislittlevariationintheflowrate(WEF2009).Additionally,some
motorsarenotsuitedforusewithVFDs.Whenthedrivereducesthefrequencytothemotorthevoltage
decreases.However,theamperageincreaseswhichcangenerateheat.Morecommonly,voltagespikes
thatdevelopfromthenonsinusoidalwaveformproducedbyVFDscandamagemotorinsulationifnot
properlyfiltered.Conductorswithinthemotorshouldbeproperlyinsulatedandthemotorsshouldbe
capableofdissipatingtheheat.
3.5.3 VFDStrategiesforWastewaterPumpingStations
VFDscanbecostlytoinstallinanexistingpumpstationandrequirespaceintheelectricalroom.
Therangeofflow,numberofpumps,andhoursofoperationalsoneedtobeconsideredwhen
evaluatingtheimplementationofVFDcontrol.AlthoughequippingallpumpswithVFDsprovides
maximumoperationalflexibility,thiscanbecostlyand,inretrofitprojects,notalwaysfeasible.Often
therewardsofhavingVFDscanbeachievedatlesscostwithhalforasfewasonepumpbeing
equipped.
OneVFDcanbefeasibleinsmallstationswheretwopumpsareruninduty/standbymode
becausethedutypumprunsthemajorityofthetime,reapingthesavingswiththeVFD.Insituations
wherebothpumpsareruninthelead/lagmodetocovertherangeofflowencountereditisusually
beneficialtohavebothpumpsequippedwithVFDs.Thisallowsthepumpstoalternatetheleadposition,
whichbalancestheirhours,anditsimplifiesthecontrolsasbothpumpscanbeoperatedinthesame
manner.
Inthecaseoflargerstationswiththreeormorepumpsofthesamesizeoperatedinlead/lag
mode,thenumberofVFDsneededdependsontherangeofflowandthespaceavailable.Ifonepump
runsthemajorityofthetimewithinfrequentassistancefromtheothers,thenoneVFDwouldlikely
suffice.However,ifthesecondpumpoperatesfrequently,thenatleasttwoVFDsarerecommended.In
thetwoVFDscenario,whenaninfrequentpeakflowisneeded,thethirdconstantspeedpumpcan
providethebaseloadwhilebothVFDdrivenpumpsadjusttomeetthedemand.Dependingonthesize
ofthepumps,itcouldbemorebeneficialtoinstallasmallerpumpinsteadandrunitwithaVFD.This
maximizestheefficiencyofthesystembecausewhenthelargepumpsarerun,theyareneartheirBEP
withouttheheatlossesgeneratedbyVFDs.
Largestationswithmultiplepumpsofdifferentsizesneedtobeevaluatedonacasebycase
basis.Typically,VFDsareplacedonthesmallerpumpssothattheycanbeusedtofillinthepeaks
beforeanotherlargepumpisturnedon.Thecontrolsaresimpleandsequencingiseasytomaintain
whenapumpisdownforservice.Additionally,thecostislowerassmallVFDsarelessexpensivethan
largeones.
Itisimportanttoruneachpumpperiodically. Bearingsinpumpsthatsittoolongcanbe
damagedfrombrinnellingandstuffingboxescandryoutandleak. ItisbeneficialfromanO&M
standpointtoexerciseequippedatintervalsrecommendedbytheequipmentmanufacturertoensure
theirreliabilitywhencalledupon. Energywise,itisbesttodothisduringoffpeakelectrichourssuchas
morningoronweekends.
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USDOE.1999.MotorChallengeProjectFactSheet.CityofMilfordPumpOptimizationProjectYields
$96,000NetPresentValue.U.S.DepartmentofEnergy,OfficeofIndustrialTechnologiesEnergy
EfficiencyandRenewableEnergy.
http://www1.eere.energy.gov/industry/bestpractices/pdfs/milford.pdf
USDOE.BuyinganEnergyEfficientElectricMotor.OfficeofIndustrialTechnologies,EnergyEfficiency
andRenewableEnergy.DOE/GO10096314
http://www1.eere.energy.gov/industry/bestpractices/pdfs/mc0382.pdf
USDOE.2000.PerformanceImprovementsatWastewaterTreatmentPlants.OfficeofIndustrial
Technologies,EnergyEfficiencyandRenewableEnergy.
http://www1.eere.energy.gov/industry/bestpractices/pdfs/fairf.pdf
USDEO2005a.MotorSystemsTipSheet#2:EstimatingMotorEfficiencyintheField.Industrial
TechnologiesProgram,EnergyEfficiencyandRenewableEnergy.DOE/GO1020052021.
http://www1.eere.energy.gov/industry/bestpractices/pdfs/estimate_motor_efficiency_motor_systemts
2.pdf
USDOE.2005b.CaseStudyTheChallenge:ImprovingSewagePumpSystemPerformance,Townof
Trumbull.U.S.DepartmentofEnergy,EnergyEfficiencyandRenewableEnergy.
http://www1.eere.energy.gov/industry/bestpractices/case_study_sewage_pump.html
USDOE.2005c.OnondagaCountyDepartmentofWaterEnvironmentProtection:ProcessOptimization
SavesEnergyatMetropolitanSyracuseWastewaterTreatmentPlant.U.S.DepartmentOfEnergy,Energy
EfficiencyandRenewableEnergy.
http://www1.eere.energy.gov/industry/bestpractices/pdfs/onondaga_county.pdf
USDOE.2008.NewMotorTechnologiesBoostSystemEfficiency.UnitedStatesDepartmentofEnergy
IndustrialTechnologiesProgram.PublishedintheSummer2008issueofEnergyMatters
http://www1.eere.energy.gov/industry/bestpractices/energymatters/archives/summer2008.html#a284
USDOE.2009.UltraEfficientandPowerDenseElectricMotors.UnitedStatesDepartmentofEnergy,
EnergyEfficiencyandRenewableEnergyDivision.
http://www1.eere.energy.gov/industry/intensiveprocesses/pdfs/electric_motors.pdf
WashingtonStateUniversity(WSU)CooperativeExtensionEnergyProgram.2003.MotorMaster+
Version4.0UserGuide. DevelopedfortheU.S.DepartmentofEnergy.Availableonlineat
http://www1.eere.energy.gov/industry/bestpractices/pdfs/motormaster_user_manual.pdf
WaterEnvironmentFederation(WEF),2009.ManualofPractice(MOP)No.32:EnergyConservationin
WaterandWastewaterFacilities.PreparedbytheEnergyConservationinWaterandWastewater
TreatmentFacilitiesTaskForceoftheWaterEnvironmentFederation.McGrawHill,NewYork.
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4. DesignandControlofAerationSystems
4.1 IntroductionTheaerationprocesscanaccountforthelargestenergydemandofanyoperationatthefacility.
Althoughthedemandissitespecificandcanvarywidelyfromplanttoplant,thefractionofenergyused
foraerationrangesfrom25toasmuchas60percentoftotalplantenergyuse(WEF2009). Becauseof
thehighenergyuseassociatedwithaeration,energysavingscanbegainedbydesigningandoperating
aerationsystemstomatch,ascloselyaspossible,theactualoxygendemandsoftheprocess. Through
improvedunderstandingoftheoxygendemandsofaparticularwastewaterandhowthosedemands
fluctuatewithtimeofdayandseason,wastewatertreatmentplants(WWTPs)canbuildflexibilityinto
theiraerationsystemssothatoperationcanaddressrealtimedemandsefficiently.
Section4.2inthischapterdescribesenergyconservationmeasures(ECMs)foraerationsystems.
Section4.3followswithadiscussionofaerationcontrol,includingconventionalcontrolbasedon
dissolvedoxygen(DO)measurementsandinnovativecontrolstrategies. Innovativeandemerging
technologiesforcontrolofbiologicalnitrogenremovalarediscussedinSection4.4. SeeChapter5for
innovativeECMsrelatedtonewcommerciallyavailablebloweranddiffuserequipment.
4.2 ECMsforAerationSystemsWastewaterisaeratedbyeitherbub