Fuzzy-Control-of-The-Compressor-Speed-in-a-Refrige

FuzzycontrolofthecompressorspeedinarefrigerationplantC.Apreaa,R.Mastrullob,C.Rennoa,*aDepartmentofMechanicalEngineering,UniversityofSalerno,ViaPonteDonMelillo1,84084Fisciano(Salerno),ItalybDETEC,UniversityofNaplesFedericoII,P.leTecchio80,80125Naples,ItalyReceived8August2002;receivedinrevisedform18December2003;accepted18February2004AbstractInthispaper,referringtoavaporcompressionrefrigerationplantsubjectedtoacommerciallyavailablecoldstore,acontrolalgorithm,basedonthefuzzylogicandabletoselectthemostsuitablecompressorspeedinfunctionofthecoldstoreairtemperature,ispresented.Themainaimistoevaluatetheenergysavingobtainablewhenthefuzzyalgorithm,whichcontinuouslyregulatesthecompressorspeedbyaninverter,isemployedtocontrolthecompressorrefrigerationcapacityinsteadoftheclassicalthermostaticcontrol,whichimposeson/offcyclesonthecompressorthatworksatthenominalfrequencyof50Hz.Thevariationofthereciprocatingcompressorspeedisobtainedbycontrollingthecompressorelectricmotorsupplycurrentfrequencyintherange30–50Hz,asitisnotpossibletoconsidervaluessmallerthan30Hzbecauseofthelubricationtroublesduetothesplashsystem.Inthisrange,twoamongthemostsuitableworkingfluidsproposedfortheR22substitution,suchastheR407C(R32/R125/R134a23/25/52%inmass)andtheR507(R125/R143A50/50%inmass)aretested.Comparingthecompressorspeedfuzzycontrolwiththeclassicalthermostaticcontrol,frequentlyusedinthecoldstoresandinotherrefrigerationsystems,theexperimentalresultsshowameaningfulenergysavingequaleventoabout13%whentheR407Cisusedasaworkingfluid.Inparticular,toexplainfromtheenergysavingpointofviewthebestperformancesoftherefrigerationplantwhenthecompressorspeedvaries,anexergeticanalysisisrealized.Besides,withregardtotheinvertercost,thepay-backperioddeterminedismorethanacceptablefortheplantsizeexamined.q2004ElsevierLtdandIIR.Allrightsreserved.Keywords:Compressionsystem;Coldroom;Pistoncompressor;Variablespeed;Regulation;Fuzzylogic;R407C;R507Re´gulationa`logiqueflouedelavitessed’uncompresseurd’uneinstallationfrigorifiqueMots-cle´s:Syste`mea`compression;Chambrefroide;Compresseura`piston;Vitessevariable;Re´gulation;Logiquefloue;R407C;R5071.IntroductionThevaporcompressionrefrigerationplants,thoughdesignedtosatisfythemaximumload,workatpart-loadformuchoftheirlifegenerallyregulatedbyon/offcyclesofthecompressor,workingatthenominalfrequencyof50Hz,imposedbyathermostaticcontrolwhichdeterminesahighenergyconsumption.Moreover,theinefficientuseofelectricitytosupplytherefrigerationandair-conditioningcompressorsisconsideredasanindirectcontributiontothegreenhousegasesemittedintheatmosphere;theseemis-sionscanbereducedbyimprovingtheenergyconversionefficiencyoftheabovementionedsystems.Atheoreticalcomparisonofvariousrefrigerationcapacitycontrolmethodsinfullandpart-loadconditionsshowsthatthecompressorspeedvariationisthemostefficienttechnique0140-7007/$-seefrontmatterq2004ElsevierLtdandIIR.Allrightsreserved.doi:10.1016/j.ijrefrig.2004.02.004InternationalJournalofRefrigeration27(2004)639–648*Correspondingauthor.Tel.:þ39-089-964327;fax:þ39-089-964037.E-mailaddress:[e-mail](C.Renno).[1,2].Thismethodofrefrigerationcapacitycontrol,whichconsistsinvaryingthecompressorspeedtocontinuouslymatchthecompressorrefrigerationcapacitytotheload,hasbeenanalyzedduringthelastyears[3–10].Aninvertercanbeusedtoregulatethecompressorspeed.Therearedifferenttypesofelectronicvariable-speeddrives,butthepulse-widthmodulatedsourceinverter(PWM)isthemostsuitableforitslowcostandhighefficiency.Theapplicationofthistypeofcontroloftherefrigerationcapacitytoacommercialcompressor,thoughpresentssomeadvantagesintermsofenergysaving,determinessomedisadvantagessuchastheinvertercostandsometroubleslinkedtothecompressorlubricationandreliability[11,12]andtothecorrectworkingoftheexpansiondevices.Thislastproblemisnegligiblewhenthesecondaryfluidsattheheatexchangersareingas-phase,asintheplantexamined,butitseemstoberemarkablewhenthesecondaryfluidsareintheliquid-phase[13].So,theprimaryaimofthispaperistosetupacontrollercapableofregulatingcontinuouslythespeedofareciprocatingcompressorfrequentlyusedincoldstoresandinothersmallsizerefrigerationsystemswhosethistypeofcompressorgenerallyhasnooilpump.Thiskindofcontrolallowsustomatchthecompressorrefrigerationcapacitytothecoolingloadatanytime,sothatthecompressorcanalsoworkatotherfrequenciessmallerthan50Hz.Itistobeconsideredthatwiththeclassicalthermostaticcontrolfrequentlyusedinthecoldstoresandinothersmallsizerefrigerationsystems,thecompressorworksonlyat50Hz.Inparticular,referringtoavaporcompressionrefrigerationplantsubjectedtoacommerciallyavailablecoldstore,acontrolalgorithmbasedonthefuzzylogic,andabletoselectthemostsuitablecompressorspeedinfunctionofthecoldstoreairtemperature,ispresentedinthispaper.Apartfromthefuzzylogic,thecompressorspeedcontrolmightalsobeobtainedbymeansofothertechniquessuchasthetraditionalproportional-integralandderivativecontrol(PID)[14–18].Inparticular,thefuzzycontrollogic,comparedwithPID,allowsbothtousebettertheexperimentalknowledgerelatedtothetrendofthevariab