Energy-efficient control strategy for variable spe

ORIGINALARTICLEEnergy-efficientcontrolstrategyforvariablespeed-drivenparallelpumpingsystemsJuhaViholainen&JussiTamminen&TeroAhonen&JeroAhola&EsaVakkilainen&RistoSoukkaReceived:11April2012/Accepted:10December2012#SpringerScience+BusinessMediaDordrecht2012AbstractThearticleaimstofindasolutionfortheenergyefficiencyimprovementsinvariablespeed-controlledparallelpumpingsystemswithlesserinitialdataandwithoutadditionalflowmeteringandstart-upmeasurements.Thispaperintroducesanewcontrolstrategyforvariablespeed-controlledparallelpumpsbasedonflowrateestimationandpumpoperationanalysisutilizingvariablespeeddrives.Theenergy-savingpotentialofthenewcontrolstrategyisstudiedwithsimulationsandlaboratorymeasurements.Theenergyconsumptionoftheparallelpumpsusingthenewcontrolstrategyiscomparedwiththetraditionalrotationalspeedcontrolstrategyofparallelpumps.Thebenefitofthenewcontrolstrategyistheoppor-tunitytooperatevariablespeed-controlledparallelpumpsinaregionwhichsuggestsimprovedenergyefficiencyandlowerriskofmechanicalfailureofthecontrolledpumpscomparedwithtraditionalcontrol.Thearticleconcludesbydiscussingtheimplicationsofthefindingsfordifferentapplicationsandvaryingsystemconditions.KeywordsVariablespeeddrives.Pumps.Energyefficiency.Processcontrol.FluidflowcontrolIntroductionPumpsarewidelyusedinindustrialandservicesectorapplications.Theyconsumeapproximately10–40%oftheelectricityinthesesectors(deAlmeidaetal.2003).Pumpingsystemsarefoundtohaveasignifi-cantpotentialforenergyefficiencyimprovements(Binder2008;Kayaetal.2008;Ferreiraetal.2011;PembertonandBachmann2010;Zhangetal.2012).Thepressureforenergyefficiencyimprovementshasledtoanincreasingnumberofvariablespeeddrives(VSDs)inpumpingapplications,sinceinmanyinstances,variablespeedpumpinghasbeenshowntobeaneffectivewaytoreducethetotalpumpingcosts,especiallyinsystemsthatrequireawiderangeofflow(BernierandBourret1999;Pemberton2003;EuropumpandHydraulicInstitute2004).Pumpingsystemswithawidelyvaryingflowratedemandareoftenimplementedusingparallel-connectedpumps(Hooper1999;Volk2005).Thereareseveralcontrolmethodsavailableforoperatingtheparallel-connectedpumps.Inthesimplestcase,EnergyEfficiencyDOI10.1007/s12053-012-9188-0J.Viholainen(*):R.SoukkaDepartmentofEnvironmentalEngineering,LappeenrantaUniversityofTechnology,53850Lappeenranta,Finlande-mail:[e-mail]:T.Ahonen:J.AholaDepartmentofElectricalEngineering,LappeenrantaUniversityofTechnology,53850Lappeenranta,FinlandE.VakkilainenDepartmentofEnergyTechnology,LappeenrantaUniversityofTechnology,53850Lappeenranta,Finlandparallel-connectedpumpsareoperatedwithanon–offcontrolmethod,whereadditionalparallelpumpsarestartedandstoppedaccordingtothedesiredflowrate.Inthesystemswheremoreaccurateflowregulationisneeded,theadjustmentcanbecarriedoutbyapplyingthrottlingorrotationalspeedcontrolforasinglepump,whileotherpumpsarecontrolledwiththeon–offmeth-od.Thebenefitsusingrotationalspeedcontrolinsteadofthethrottlingcontrolmethodarewidelystudied(RossmannandEllis1998;Carlson2000;EuropumpandHydraulicInstitute2004;Hovstadiusetal.2005)andarethereforeexcludedfromthisstudy.Energyoptimizationofparallel-connected,rota-tionalspeed-controlledpumpshasbeenstudiedtosomeextent(Izquierdoetal.2008;Bortonietal.2008;YangandBorsting2010),andtheresultshaveshownthatthereisamajorenergy-savingpotentialinthesectorofparallelpumping.InBortonietal.(2008),theoptimalrotationalspeedforparallelpumpsispredicted,inordertogainenergysavings,usingamathematicaloptimization-basedtoolsuitableforpro-grammablelogiccontrollers.However,thesuggestedoptimizedcontrolmethodrequiresadequateinforma-tionfromthesystemcurve,includingstart-upfieldmeasurementsusingpressuresensorsandflowmeters.Inmanyparallelpumpingcases,sufficientdataforenergyoptimizationfromcontinuouslychangingsys-temsareavailableonlytolimitedextent(Kinietal.2008;Arantoetal.2009).Analternativeapproachtoobtaintherequiredsysteminformationcanbethemodel-basedflowmonitoringmethodinwhichtheflowrateofeachparallelpumpisestimatedwithoutseparateflowmetersbasedonpressuremeteringortorqueandrotationalspeedestimatesoftheVSD(HammoandViholainen2006;Ahonenetal.2012).Theaimofthisstudyistointroduceanewcontrolstrategyforvariablespeed-controlledparallel-connectedcentrifugalpumps(laterreferredtoaspar-allelpumps)inasystemwherepumpsinindividualpipingpartsfeedacommonoutletpipeline.Thesug-gestedcontrolstrategycanofferajustifiedbasefortheenergyefficiencyimprovementinvariablespeed-controlledparallelpumpingsystems,eveninsuchcaseswheretheinformationonthepumpingsystemislimitedorchanging.Thesuggestedcontrolstrategyisbasedonthesimpleuseofexistingpumpingmon-itoringsolutionsofamodernVSDandaknownrelationbetweenthepreferableoperationareaofacentrifugalpumpandtheenergyefficiencyofthepumping.Byimplementingthesuggestedcontrolstrategyinthecontrolprocedure,theflowrateoftheparallelpumpingsystemcanbeadjustedwithim-provedenergyefficiencycomparedwithtraditionalrotationalspeedcontrol.Thecontrolstrategycanbeappliedforinstancetoparallelpumpslocatedinwaterstations,wastewaterpumpingstation