Heat Pump For Heating And Cooling Water For Aquacultural Production

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Title:
Heat Pump For Heating And Cooling Water For Aquacultural Production
Physical Description:
Fact sheet
Creator:
Baird, C.D.
Publisher:
University of Florida Cooperative Extension Service, Institute of Food and Agriculture Sciences, EDIS
Place of Publication:
Gainesville, Fla.
Publication Date:

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Acquisition:
Collected for University of Florida's Institutional Repository by the UFIR Self-Submittal tool. Submitted by Melanie Mercer.
Publication Status:
Published
General Note:
"May 1993"
General Note:
"Circular 1096"

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Source Institution:
University of Florida Institutional Repository
Holding Location:
University of Florida
Rights Management:
All rights reserved by the submitter.
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IR00004484:00001


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Circular1096 TheInstituteofFoodandAgriculturalSciencesisanequalopportunity/affirmativeactionemployerauthorizedtoprovideresearch,educational informationandotherservicesonlytoindividualsandinstitutionsthatfunctionwithoutregardtorace,color,sex,age,handicap,ornational origin.Forinformationonobtainingotherextensionpublications,contactyourcountyCooperativeExtensionServiceoffice. FloridaCooperativeExtensionService/InstituteofFoodandAgriculturalSciences/UniversityofFlorida/JohnT.Woeste,Dean May1993HeatPumpforHeatingandCoolingWater forAquaculturalProduction1 C.D.Baird,R.A.Bucklin,C.A.WatsonandF.A.Chapman2Aquaculture,asignificantindustryinFlorida, includestheproductionofornamentalfish,catfish, alligators,oysters,andotheraquaticspecies.The largestportionofaquaculturesalescomesfrom ornamentalfishproducedprimarilyinopenponds. Fisharealsoheldandproducedinbuildingsand greenhouses,whichoftenemployflow-throughwater systems.Thesesystemsrequirelargequantitiesof wateranddonotprovideoptimumgrowing conditions;theenergyrequiredtoheatthesebuildings duringthewinterrepresentsamajorproductioncost. Someproducersareconsideringindoor recirculatingsystems,wheretheonlywaterpumped fromthewellaftertheinitialfillingismakeupwater toreplacewaterlostduringevaporationandwater usedtobackflushfilters.Eventhesesystemsrequire substantialheatingduringthewinterandheatingof themake-upwellwateratothertimes,sinceoptimum growthtemperaturesexceedthenormaltemperature ofwellwater.Coolingisalsorequiredduringthe summerduetoheatbuildupinsidethestructure.HEATPUMPSFORHEATING ANDCOOLINGWATERAheatpumpisidealforthisapplication,sincethe samemechanicalrefrigerationsystemprovidesboth heatingandcooling.Theheatpumpsystemdescribed hereissimilartothoseusedforresidentialair conditioningsystems,exceptthatitisusedtoheatand coolwaterinsteadofair. Aheatpumpisamechanicalrefrigerationsystem thatpumpsheatfromtheoutsidetotheinsideduring thewinterandfromtheinsidetotheoutsideinthe summer.Aheatpumpoperateslikeanair conditionerworkinginreverse.Anairconditioner removesheatfromtheairinsideahousethroughan evaporator(coldcoil)anddischargesitoutside throughacondenser(hotcoil)duringwarmweather. Duringcoldweather,theheatpumputilizesreversible valvestointerchangetheevaporatorandthe condenser.Thus,thehotcoilinsideandthecoldcoil outsideallowthesystemtoremoveheatfromthe outsideanddischargeitinside.ATYPICALHEATPUMPSYSTEM FORHEATINGANDCOOLINGThesystemdescribedhereusesatypical2-ton (24,000Btuh)residentialheatpumpmodifiedtoheat andcoolwaterinthetemperaturerangeneededfor aquaculturalproduction(Figure1).Insteadofcooling airwithanevaporatorcoil,whichisusuallylocated insidetheductsysteminaresidentialapplication,this systemusesacoppercoilmadefromcoppertubing andlocatedinthewatertank.Sincecopperistoxic tofish,thecoppertubingispaintedwithblackepoxy enamel.Thiscoilutilizestwo50-footcircuitsof3/8inchcoppertubing,whichcoolsthewaterinwarm 1.ThisdocumentwaspublishedMay1993asCircular1096,aseriesoftheFloridaEnergyExtensionService,FloridaCooperativeExtension Service,InstituteofFoodandAgriculturalSciences,UniversityofFlorida. 2.C.D.Baird,Professor,andR.A.Bucklin,AssociateProfessor,AgriculturalEngineering;C.A.Watson,AquacultureExtensionAgentII, HillsboroughCounty,Seffner;andF.A.Chapman,AssistantProfessorofFisheriesandAquaculture,CooperativeExtensionService,Institute ofFoodandAgriculturalSciences,UniversityofFlorida,GainesvilleFL32611.

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HeatPumpforAquaculturalProduction Page2weatherandheatsitincoolweather. Figure1. Heatpumpsystemusedforheatingandcoolinginaquaculture.Sincethetemperaturerangerequired foraquacultureproductionisdifferent fromthatrequiredforresidentialair conditioning,the2-toncompressorin theheatpumpmustbereplacedwith a1-toncompressor.Thisallowsthe capacityofthecompressortomatch thatoftheoutsidecoil,acondition necessarytocreatetheoperating temperaturesusedinaquacultural production.Temperaturesaremost criticalinthecoolingmode.Ifthe sizeofthecompressorwerenot reduced,theoutsidecoil(condenser) wouldoverheatinthecoolingmode. Reducingthesizeofthecompressor iseasierthanincreasingthesizeof thecondenserandhastheadditional advantageofenhancingsystem efficiency.Thesystemalsomustbe equippedwithanautomaticswitchoverthermostatwithseparatetemperaturesettingsfor heatingandcooling.Thedifferencebetweenthehighandlow-temperaturesettings,whichconstitutesthe neutralzone,mustbedeterminedbytheproduction requirementsofeachfishspecies. Theheatpumpsysteminthisexampleisinstalled ina20x30-footinflateddouble-polygreenhousethat hasbeensprayedontheoutsidewithaheavycoatof whitepaint.Blackpolyethylenefilmhasbeenplaced ontheinsideroofofthegreenhousetofurtherreduce thesolarload.Anotheroptionwouldbetousewhitepaintedblackpolyethyleneontheoutside;however, thewhitepainthasatendencytopeelunlesstheblack polyethyleneistreatedpriortopainting.Anexhaust fan,settooperatewhentheinsidetemperature exceeds80F,providesventilationforthestructure.PERFORMANCEANDENERGYEFFICIENCYIntheheatingmode,thesystemproduces approximately18,000Btuhwhenthewater temperatureis80Fandtheoutsidetemperatureis 50F.Thepowerrequiredtooperatethesystem undertheseconditionsis1.1kW.Thiscorresponds toanenergyefficiencyratio(EER)of16Btuh/kW, whichrepresentsnearlyfivetimestheefficiencyof electricalresistanceheating.Sinceitismoredifficult toextractheatfromairasthetemperatureislowered, however,theoutputoftheairsourceheatpump variesconsiderablywithambienttemperature.Figure 2showstheperformanceofthissystemasafunction ofambienttemperature;italsodemonstrateshowthe performanceofthesameunitwouldchangeiftheair sourceoutdoorcoilwerereplacedwithawatersource coilusingwellwater(orwaterfromanothersource) at72F.Thesedataarebasedonafishtank temperatureof80F.Theadvantagesofthewater sourceheatpumpcanbeseenclearlyinFigure2. Notonlydoesthepump'scapacityremainalmost constantforvaryingambientconditions,itresultsin asignificantincreaseinunitefficiency.Intheair sourceheatpump,reducedcapacityforlowerambient temperaturesiscompoundedbytheneedformore heatincoldweather.Formostairsourceheatpump applications,additionalheatneededincoldweather issuppliedbyelectricresistanceheaters,whichare veryinefficient.Althoughitisdifficulttoobtainwater sourceheatpumpswithverysmallcapacitiesandoften impossibleorimpracticaltoobtainwaterforthisuse, watersourceheatpumpsshouldalwaysbeconsidered.HEATINGWATERAsindicatedearlierinthisdocument,aheat pump'slowtemperatures(inthe80Frange)makeit averygoodchoiceforaquaculturalproduction.The highertherequiredtemperature,thelessefficienta heatpumpbecomes.Thisisnottrueforothertypes ofheatingsystems,suchasthosethatuseelectric resistance,gas,oroil. Gasandoilareusuallyconsideredtobetheleast expensivemethodsofheatingwater.Forlow

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HeatPumpforAquaculturalProduction Page3temperatureapplications,however,a Figure2. Performanceofairsourceandwatersourceheatpumps.heatpump,particularlyawatersource heatpump,islessexpensive.In Table1,thecostsofraisingthe temperatureof10,000gallonsof water10Farecomparedforseveral water-heatingmethods. Inthedemonstrationunit describedhere,thefishtankscontain 500gallonsofwater,asdothesump andothercomponents.The estimatedannualheatingrequirement forsuchasysteminGainesville,FLis approximately22millionBtu,using 1,300kWhofelectricalenergy.At8 centsperkWh,theannualheating costwouldbeapproximately$100. Thisrepresentsasavingsof approximately5,000kWhovertheuse ofelectricalresistanceheating,or approximately$400inoperatingcosts. Thisairsourceheatpumpsystemmaintainswater inthefishtankattemperaturesrangingfrom80Fto anambienttemperatureofapproximately40F. Therefore,somesupplementalheat,suchasthat providedbyelectricalresistanceheaters,isalso necessary.Ifawatersourceheatpumpwereused, supplementalheatwouldnotbeneeded. Nevertheless,electricalresistanceheatersorother sourcesofemergencyheatshouldbeavailableforuse duringperiodsofextremelycoldweatheror mechanicalfailure.Loweringthewatertemperature toalevelbelow80Fisanoptionsomeproducersmay wishtoconsider.Insulatingthegreenhousestructure orusingawell-insulatedconventionalstructurewould alsosignificantlyreducetheheatingrequirementfor suchaheatpumpsystem.COOLINGWATERAspreviouslystated,aheatpumpcanalsobe usedtocoolwater.Toenableittoperformthis function,thesystemisautomaticallyswitchedfrom heatingtocoolingbythethermostatandreversible valves,asshowninFigure1.Insomeapplications, bothheatingandcoolingareneededonthesameday. Howfrequentlythisoccurswilldependonthe temperaturerangerepresentedbythedistance betweenthehighandlowsettingsonthethermostat. Obviously,thedifferencebetweenthesesettings(i.e., theneutralzone)shouldbeaslargeasthefishcan toleratewithoutundesirabletemperaturestress.Ifthe thermostathasaverysmallneutralzone,somemeans ofstoringheatshouldbeconsideredforthesystem, suchasincreasingthewatercapacity,incorporating moremassinthestructure,etc. Inthecoolingmode,aheatpumpoperatesmore efficientlyforaquaculturalproductionthanfor conventionalairconditioningbecausetankwateris normallymaintainedatahighertemperaturethanair inairconditionedbuildings.Thecoolingcapacityof thesystemisapproximately18,000Btuhwithafish tanktemperatureof82F,whichrequires approximately1.4kWatanambienttemperatureof 90F.Theheatpump'scapacityislessvariablewith ambienttemperaturethanintheheatingmode,since theevaporatorcoil(coldcoil)inthefishtanksump ismaintainedatarelativelyconstanttemperature.A changeinevaporatortemperaturecausesachangein thedensityofrefrigerantvaporwhich,inturn, producesachangeintheflowrateofrefrigerant throughthesystem.Lowertemperaturesinthe evaporatorresultinalowercoolingcapacity,andthe effectofambienttemperatureisasignificantchange inthepowerrequirementsforcompressoroperation. Thus,awatersourceheatpumpisalsomuchmore efficientthananairsourceheatpumpforcooling, sincewellwaterat72Fismuchcoolerthanthe averageambienttemperatureduringcooling.Awater sourceheatpumpisusuallyabout20%moreefficient thananairsourceheatpumpinthecoolingmode.

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HeatPumpforAquaculturalProduction Page4Table1. Comparedcostsforheating10,000gallonsofwater10 F. WaterSource HeatPump AirSource HeatPump Natural Gas #2Fuel Oil Propane Gas Electric Resistance $3.18 $4.06 $6.10 $9.20 $15.06 $19.42 Electricity$.08perkWh;naturalgas$.60pertherm;#2fueloil$1.10pergallon;propane$1.25pergallon.SUMMARYIfthesystemsusedinornamentalfishproduction areconvertedfromflow-throughtorecirculating systems,sometypeofheatingandcoolingwillbe necessary.Aheatpumpsystemcanprovideboth heatingandcoolingand,fortemperaturesrequiredin aquaculturalproductionsystems,representstheleast expensivemethodofheating.Itisalsothemost energyefficient,withapproximatelysixtimesthe efficiencyofelectricalresistanceheatingwhenawater sourceheatpumpisused.Whiletheinitialcostofthe systemissignificantlyhigherthanthatofotherheating options,thiscostcanbejustifiedonthebasisthat mechanicalrefrigerationisalsoneededforcooling. Whenselectingaheatpumpforaquacultural applications,producersshouldcarefullymatchthe capacitiesofthecompressor,condenser,and evaporatortoensurethatthecompressorisnot overloadedandthathighefficiencies(EER)canbe obtained.Providinganadequatelyinsulated productionstructureandincreasingthermalmassby incorporatingadditionalwaterstoragecapacityor structuralmasswillalsoincreasetheoverallefficiency ofheatpumpsystems.