Case StudyPurdue Saves $400,000 per Year by Replacing its Central Lab Vacuum System

ByPeterCoffeyVACUUBRAND,INC.

Summary: By investigating the origins of its high water costs, Purdue University discovered an opportunity to save some $400,000 annually in water and energy costs by replacing the central laboratory vacuum system in their Biochemistry building. The technology solution further offered the university the flexibility to tailor vacuum supplied to the needs of individual labs, and the significant advantages in adaptability of the vacuum utility over time as needs change with budget and scientific priorities.

THE PROBLEM: In2012,PurduenoticedthattheirwaterandseweragecostsfortheirBiochemistrybuildingalonewererunningover$350,000ayear.Astheyinvestigatedfurther,theydeterminedthattheywerenotonlyusingnearly60milliongallonsofwaterperyear,butalsothatthereweresubstantialcoststoproducethesteam($73,000)aswellelectricitycosts.Aswitheveryuniversitythatfacespressuresontuitionlevelsandoperatingcosts,Purduesawtheveryhighoperatingcostsasapotentialsourceofsavingsfortheuniversity.

Aninvestigationofthesourceofthehighwatercostspointedthemtothecentralvacuumsystemsupportingthelabsinthisbuilding.Thevacuumwasdeliveredtothelabalongwithotherlabutilities:water,electricityandgases.WhatwasunusualatPurduewasthatthevacuumwasproducedwithasteamejectorsystemsuppliedbythecampussteamplant.It’snotunusualforoldercampusestohavecampusheatprovidedbyasteamplant.WhenPurdue’s1930s-eraBiochemistrybuildingwasupdatedandexpandedinthe1950s–withwater,electricityandseweragecostslow,andthesteamplantavailable– itmadealotofsensetousecampussteamtogeneratevacuum.(Exhibit1)

Thesteamejectorsystemproducesvacuumbycreatinghighpressuresteam–at120psi–andforcingitthroughaVenturinozzle.Theexpansionofthesteamasitpassesthroughthenozzlecreatessuctionthatprovidesthelabvacuumfortheentirebuilding.Thephysicsaresimilartothoseofthewater-jetaspiratorsusedtoproducevacuumatcupsinksinmanyolderlabs. (Exhibit2)Purduehadatwo-stageejectorsystem.SteamentersthefirststageoftheVenturiand,asitexits,iscondensedwithafloodofcooldomesticwatersupply.Moresteamisaddedatthesecondstagetocreatedeepervacuum,usingadditionalwatertocondensethesteam.Then,thecondensedsteam andcoolingwateraredischargedtothemunicipalsewersystem.

Exhibit 1: Purdue University Biochemistry Building

Exhibit 2: A steam ejector system: high pressure steam passing though the venture throat creates vacuum

Special thanks for Doug Bradley of Loftus Engineering and Luci Keazer of Purdue University for data included in this case study.

The appeal of steam ejector vacuum: Thetwo-stagesteamejectorsystemwasabletoproduceadeepervacuumlevelinitscentralvacuumsystemthaninmostcentralvacuumsystems.Testedatthevacuumports,thevacuumwasasgoodas15–30mbar(29.3in.Hg,gauge)insomelocations,and50to120mbar(28.4–25in.Hg,gauge)inotherlocations.Forreference,atmosphericpressureisabout1000mbaratsealevel,andanewcentralvacuumsystemtypicallyprovidesvacuumofabout200mbar(24in.Hg,gauge).

Despitethecostsavingsthatwenotedearlier,inconceptthesteamejectorsystemhadapparentadvantageswhenfirstimplemented:

• First,itreliedonsteamfromthecampussteamplant.Thatseemslikeitmightbefreeenergy,butthatisnotthecaseaswewillseeshortly.

• Second,withnomovingparts,thevacuumgenerationportionofthesystemwasveryreliableandrequiredonlyinfrequentmaintenance.

The limitations of steam ejector vacuum:DespitethereliabilityoftheVenturisteamproductionsystem,thecentralvacuumsystemoverallhadanumberofissues:

1. Whilethevacuumgeneratoritselfwasquitereliable,thevacuumlineshadlongsincegottencloggedwithinternalcorrosionanddepositionofcondensedchemicals.Moreimportantly,thelimescalebuildupatthevacuumgeneratorrequiredperiodicacidtreatmentstokeepthepipesfromsealingoffcompletely.(Exhibit3)

2. Theproblemswiththepipingsystemledtoregularmaintenancecallsfromlabpersonneltoun-clogpipeswhenalabwasgettingnovacuum.Thelimedepositswouldsometimesclogthepipesenoughthatthecondensingwatercouldnotdischargefastenough.Whenthathappened,thewaterwouldbackupintothevacuumlinesandliterallyspitoutthevacuumvalves.

3. Alotofenergywasneededtoproducethesteam.Eventhoughthecampusheatswithsteam,agreatdealofextrasteamwasneededtosupportthevacuumsystem,soitwasnotreallyusingavailablesteam.Itwasincremental andsignificant.

4. Theamountofwaterneededforsteammake-upandcondensationwastremendous–4.9milliongallonsamonth,almost60milliongpy–andtheseweragecostsforsuchhugevolumesofwaterexplainthehighwateruseandcost.Tovisualizethismuchwater,imagine300railtankcarsofwaterpermonthsupplyingthewaterforthesteamejectorsystem.

Partofthereasonforthevolumeofthewaterusedisthatbecausetherehadtobevacuumwheneveranyoneneedsit–imaginearesearcherworkingeveningsorweekends–sothevacuumsystemhastooperate24/7.WhilethewatersupplywasrelativelyinexpensiveforPurduecomparedtomustcampuses–asitcamefromwellsonuniversityproperty-dischargewasintothetownseweragelines,whichwerechargedatstandardrates.Watersupplyforthebuildingcost“only”$17,000ayear,butthewastewaterfeeswerefully20timesthewatersupplycharges.

Besidestheoperationalandeconomicdisadvantagesofthesteamsystem,therewereclearscientificdisadvantages:

1. Whilethecentralvacuumsystemproducedvacuumaslowas15mbarinsomelocations,whichisquitegood,inotherlocationsitmightbe120mbarandhighlyvariablemomenttomoment.Vacuumat120mbarisampleforfiltrationandaspirationapplications,butthedeepervacuumisneededfortheevaporativeworkcommoninchemistrylabs.

2. Anyoneneedingdeeperorpredictablevacuumneededadditionalpumps.Atypicalapplicationthatoftenrequiresdeepervacuum–say,aslowas2mbar–isarotaryevaporator.ThatmeansthatPurduewaspayingtwiceforvacuum:forcentralsupplyandagainatpointofuseforpumpstoproducevacuumthatwasusefulfordemandingapplications.

Exhibit 3: Mineral deposits from the steam injector system blocked this pipe to the point that it needed to be cut out and replaced in 2004

Exhibit 4: Purdue's water usage for the Biochemistry building was the equivalent of 300 rail tank cars full per month.

3. Becauseofthecloggedpipes,vacuumwasnotalwaysevenavailablewhenneeded.

4. Vacuumlevelscouldalsobeaffectedbythenumberofusersonthesystematanyonetime.

5. Pressuredifferentialsinsideanybuilding-widesystemcanleadtocrosscontaminationbetweenlabs;anopenvalveinonelabcreatesahighpressurepointrelativetothevacuumalreadyestablishedinanotherlab.Vaporflowmovestothedeepervacuumlocationwithinthepipingsystem.

Theinstability,unpredictability,andriskofcrosscontaminationarecommontoallbuilding-widevacuumsystems,butwereaggravatedbythecloggedpipesatPurdue.

OPTIONS: OncePurduediagnosedthecauseoftheBiochemistrybuilding’shigh

watercosts,theschooldecideditneededtoreplaceitssteamejectorvacuumsystem.Itisimportanttorecognizethatthesavingsopportunityaroseonlybecausestaffwaslookingcarefullyatutilitycosts,andinturntracingthosehighcoststosomethingasinnocuousasthelabvacuumsystem.

Purduethenlookedattwooptionsforreplacingthesteamejectorsystem:

1. Aconventionalcentralvacuumsystemrelyingonduplexsystempumpsandallnewtubingthroughoutthebuilding;or,

2. Amodularapproachinwhichpumpswereplacedinthelabsthatneedvacuum,andplumbedonlywithineachlab.

Option 1involvedduplex,oil-lubricatedrotaryvanepumps.(Exhibit5)

• Sincethebuildingneedsvacuumevenifoneofthepumpsisdownforservice,bothpumpsaresizedfor100%ofcapacity,andwereeachratedat11,000Watts.

• A200gallonreceiverhelpsstabilizethevacuumbyservingasabufferwhenusersopenandclosevacuumvalves,andalsocollectscondensedsolventvaporsfromthepipingsystem.

• Maintenanceforthesepumpsinvolvesfrequentoilchecks,periodicfilterchangesandregularcleaningorreplacementofoilfilters,inletfiltersandexhaustmistfilters.

• Sincetheentirepipingsystemwascloggedandcorroded,theentirebuilding-widepipingsystemneededreplacement.Thatwouldrequirenew4”mainsleavingthepump,reducingtobranchpipingthatwouldalsohavetobereplacedintheolderlabs,withnewvacuumfittingsinstalledthroughout.

Option 2wastodecommissiontheentirecentralvacuumsystem,andinstalllocalvacuumnetworksineachlab.Thelocalpumpswouldbesizedtotheneedsofeachlab,andthevacuumwouldbedistributedtothebenchesandfumehoodswithsmalldiameterchemicalresistanttubing.Nobuilding-widepipingwasneeded,norwasthereaneedforareceivertanktobalancetheflow.AsinOption1,newvacuumfittingswouldbeusedthroughoutthelabs.

Thepumpsusedforthelocalvacuumnetworksaredry(thatis,oil-andwater-free)diaphragmpumps.(Exhibit6)

• AllsurfacesexposedtovaporsarefluoropolymerslikeDuPontTeflon®,andsoareextremelycorrosionresistant.

• Thepumpshavevariablespeedmotorsthatcanrespondtodemandwith100%turndowncapability;vacuumisalwaysavailable,butthepumpsoperateonlyasmuchasneededtomeetdemand.Thelargestpumpsareratedat530Watts,buttypicallydrawone-thirdofthatorlessbecauseofthevariablespeedmotors.Whenonstand-by,thepumpsdrawonly2wattstomonitorneed.

Exhibit 5: Duplex, oil-lubricated central vacuum pumps, with 200 gallon

receiver tank. Foot print is 8 feet wide. Receiver over 7 feet high.

Exhibit 6: Local vacuum network pumps with variable speed motors and a compact footprint (approx.

24”x15”) produce vacuum on demand for an entire lab

• Thepumpscanproducevacuumof1.5mbar(29.86in.Hg,gauge),butvacuumlevelsareuserselectable,dependingontheneedsofthelab.

• Vacuumpumpsarequietenoughthatnocabinetsareneededfornoisereduction.

• Thepumpshavetheoptionofcollectingmostwastesolventvaporsatthesourceinthelabratherthandischargethroughthefumehoods.(Thatoptionwasnotspecifiedforthisproject.)

• Thecatchpotsonthepumpscapturevaporsthatcondenseinthevacuumlines;thecatchpotscanbemonitoredvisuallyandemptiedasneeded.Theinletcatchpotprotectsthepumpfromparticulatesandliquids;theexitcatchpotcollectvaporsthatcondensewhenthevacuumisreleasedandvaporsreturntoatmosphericpressure.

• Thelabvacuumnetworksareconnectedinthelabalone,withnotubingorpipingelsewhere.TubingrunsareofsmalldiameterPTFE(chemicalresistant)tubing,installedwithcompressionconnectors,makinginstallationquickandeasy. (Exhibit7)

• Specializedvacuumfixturesareused.Eachvalvehasanintegralcheckvalvethatmanagestheflowinthenetwork.Thatpermitsthesmall,localpumptoservemultipleusersatonce.Thespecializedfittingseliminatetheneedforlargepumpsandreceiversneededinacentralsystem,whilestillprovidingdeeper,morestablevacuum.

THE ANALYSISPurdueevaluatedthetwooptionsbothqualitativelyandquantitatively.

Qualitativeassessment

Purduewantedtoassesstheseconsiderations:

1. Howinvasivewouldthevacuumsystemrenovationbe?Thisisaworkinglabbuildingandonlythevacuumsystemwasbeingreplaced.

2. Wouldtheresultingvacuumbeconsistentlyavailableinthelabs,andatthedesignpressures?Forhowlongwouldallvacuuminthebuildingbelostwhilethereplacementsystemisinstalled?

3. Howchemicalresistantwouldthepumpsandtubingbe?Sincecorrosivevaporsaredrawnintoavacuumsystem–especiallyinachemistrybuilding–thiswasamajorconcern.

4. Whatriskwasthereofcrosscontaminationbetweenlabsthrough vacuumtubing?

5. Whatwouldbethemaintenancedemands?Comparetheservicedemandsoftwolargecentralizedpumpswiththoseofadistributedapproachtovacuumsupply,with25pumps.

Lookingatthecentralvacuumsystem:

1. Pipingrunswouldbeneededthroughouttheentirebuilding,makingtheprocessquiteinvasiveinaworkingbuilding.

2. Vacuumwouldbeavailable,butpressurevariabilitywouldoccurlabtolabandtimetotime.

3. Whilecopperpipingcouldbeexpectedtolastalongtime,itisstillsubjecttocorrosionandpinholeleaksthatleadtolossofvacuumandpumpingcapacityovertime.

4. Pressuredifferentialsbetweenlabswouldalmostcertainlyleadtosomecross-contamination.

5. Themaintenancescheduleinvolvedregularoilchangesandfilterchangesat1000–2000hourintervals.Sincemostcentralpumpsneedtorun24/7sothatvacuumisavailableifneededanywhereinthebuilding,thismeansoilchangesevery6to12weeks.

Exhibit 7: Local vacuum networks are plumbed with small diameter PTFE tubing that resists corrosive lab vapors much better than copper.

Lookingatthemodularvacuumsystems

1. Allconstructioniswithinthelabs.Thisnotonlyavoidsdisruptioninthehallsforinstallationoftrunk-linepiping,butalsomeansthatonlyonelabatatimeneededtobedisrupted.

2. Thecheckvalvesineachfittingensureminimalpressurespikes.Importantly,iftherewereaproblemwithoneofthepumps–say,astudentsucksliquidreagentsintoapump–itwouldonlyaffectonelab.Inaddition,vacuumfromthesteamejectorcentralsystemwouldcontinuetobeavailabletoeachlabuntilimmediatelybeforeitsvacuumsystemwasrenovated.

3. ThePTFEtubingofthenetworkandfluoropolymerwettedpathofthepumpsimpartsexceptionalcorrosionresistance–significantlybetterthanthecopperalternative.

4. Withnointerconnectionbetweenlabs,theriskofinter-labcross-contaminationthroughvacuumlinesiseliminated.

5. Withnooiltochange,pumpingonlyondemand(lessthan40hoursaweekinnearlyallcases),and15,000hourserviceintervals,thepumpsareexpectedtogoyearswithoutservice.

Purdueconcludedthatthemodularvacuumapproachhadtheadvantageineverycategory–invasiveness,vacuumstability,corrosionresistance,crosscontaminationriskandmaintenance.Inaddition,themodularapproachprovideddeepervacuumtothescientistsinthelab,andtheabilitytoadjustvacuumlevelsasneedschanged.(Exhibit8)

Quantitative assessment involved the following calculations:

1. Whatwouldbethecostsofgypsumboardceilingdemolitionandreinstallation?

2. Whatcostswouldbeincurredforequipment,pipingandinstallationcosts,additionalrequirements,andwhatsoftcostswouldbeincurred?

3. Operationally,howdotheelectricity,steam,waterandmaintenancecostsofbothreplacementalternativescomparewiththecurrentsystem,andwithoneanother?

Itturnedoutthatthecapitalcostsofthetworeplacementoptionswereprettycomparable.Theequipmentcostsofthemodularapproachwereabithigher,buttheywereoffsetbythelowerdemo/reinstallationcosts.Avoidingbuilding-widepipingprovidedsignificantmaterialandlaborsavings.Thecentralsystemalsoincurredstagingcosts,whereasthemodularsystemcouldbeinstalledalabatatime,onlydecommissioningthesteamejectorsystemwhentheentireprojectwascompleted.(Exhibit9)

Qualitative System ComparisonOption 1: Central system Option 2: Modular

Invasiveness More invasive Less invasive

Vacuum stability Lessreliable Morereliable

Corrosion resistance Lessresistant Moreresistant

Cross-contamination risk Morerisk Lessrisk

Maintenance Moremaintenance Lessmaintenance

Researcher: “I couldn’t believe how strong the vacuum is.”

Exhibit 8: Qualitative System

comparison

Exhibit 9: Comparative construction costs

Theoperatingcostsofthetwonewoptionsbothofferedverysubstantialadvantagescomparedwiththesteamsystem.EitherwouldhavemadeahugedifferenceinPurdue’soperatingcostsbyavoidingthecostofwatersupplyandseweragecharges.

Oncethesteamsystemoperatingcostswereremovedfromtheequation,however,thesignificantoperatingcostadvantagesofthemodularsystemwereevident.Theabilitytomatchpumpingtomomentaryneedsanywhereinthebuildingallowsthemodularpumpstosaveelectricity,andthelongerserviceintervalsofthedrypumpsreducemaintenancecosts.(Exhibit10)

THE DECISION & INSTALLATIONThedecisionwasclear:themodularapproachhadcomparablecapitalcoststothecentralsystem,butloweroperatingcosts,andalsohadtheedgeinallofthequalitativeconsiderations.Purduechosetoinstallthelocalvacuumnetworks.

Oncethedecisionwasmade,theprojectwasfast-tracked.TheorderwasplacedinearlyOctober2012,withdeliveryinmid-November.Everythingwasstagedandreadytobegindemolitionandconstructionatthestartoftheuniversity’swinterbreak.A90dayconstructionschedulewasplannedtooutfitthe25labs.Asitturnedout,theinstallationtooklesstimethananticipated,andprojectconstructionwascompletedin60days–30daysaheadofschedule.Workwascompletedinanaverageofabouttwodaysperlabincludingdemo,installationandrebuild.

Theprojectmanagerschosetomountthepumpshighonthewallsinthelabs,runtubingatceilinglevel,anddroplinesdowntobenchesandfumehoods(Exhibit11).Thisapproachallowedthemtoaddthepumpstothelabswithoutusingpreciousbench,floororcabinetspace.Nosound-isolationwasneededbecausethepumpsrunsoquietly;theyaresilentwhenonstand-by,andhumatavolumequieterthanthefumehoodswhenoperating.Vacuumportswereinstalledonbenchtopsinsomelocations,andonfumehoodselsewhere.

Exhibit 11: Purdue saved bench space and took advantage of the network pumps' quiet operation by mounting them on wall brackets.

Exhibit 10: Comparative Operating Costs chart)

OUTCOMEThepre-projectanalysisprovedaccurate.Theuniversityissaving$30,000amonthinwatersupplyandseweragecostsalone,loweringannualoperatingcostsforlabvacuumfromabout$400,000toabout$5000.Energysavingsfromtheavoidedcostsofcreatingsteamhavenotbeencalculated,butaddsignificantlytothesavingsfromtheproject.Thepumpsrequiresomeenergy,ofcourse,buteachpumpdrawsonly530Wattswhenoperatingatfullspeed.Experienceindicatesthatthevariablespeedpumpstypicallyoperateatafractionoffullspeed,drawingonlyaboutone-thirdofratedpowerwheninoperation,orabout175Watts,forsomethinglessthan20hoursperweek.Thiscompareswith11,000Wattscontinuously(168hoursperweek)withthecentralsystempumps.Energysavingsareestimatedtobegreaterthan90percentcomparedwiththecentralvacuumsystemapproach,andevenmorewhencomparedwiththesteamsystem.

Beyondthedirectcostsavings,thevacuumsupplyisdeeper,morereliable,andadjustable.Maintenancedemandsarereducedbecausethedrypumpsrequirelittleserviceandtheconstantcallsonmaintenanceforthepriorsystemhavebeeneliminated.Andtheprojectwascompletedwithminimaldisruptiontoexistinglabs.

PurdueUniversityfacesthesamefundingpressuresconfrontinguniversitiesacrossthecountry,astheuniversityastheystruggletomanagecoststominimizetuitionincreases.BasedontheexperiencewiththeBiochemistryBuildingrenovation,Purduehassinceinstalledorcontractedformodularvacuumnetworksin5otherlocations–insomecasesforindividuallabs,andformoreextensiveinstallationsinothercases.

GENERAL APPLICATIONWhilethePurdueUniversitysteamejectorvacuumsystemofferedanexceptionalopportunityforcostsavings,suchsystemsarenotcommon.Aresimilarsavingsavailableinotherinstitutions?

Afewexamplespointtotheopportunities:

• Acentralvacuumsystemsupportedbyawaterringpumpwilltypicallyconsumeamilliongallonsofwaterormoreayear.Thatwaterisalsobeingcontaminatedwithsolventvaporsfromlabapplications.Ifthebuilding’spipingsystemissound,replacingtheliquidringpumpwithothertechnologiescouldsavethousandsofdollarsayearinwaterandtreatmentcostsandsupportthecollege’ssustainabilityobjectives.

• Inlabbuildingswithoutcentralvacuumsystems,water-jetaspiratorsarestillusedinalotoflabstocreatevacuum.Operating10hoursaweek–say,threelabperiods–thesedevicescaneachuse50,000gallonsofwateroverthecourseofaschoolyear.20ofthemwoulduse1milliongallonsperyear.Attypicalwaterandseweragechargesof$5.00to$10.00per1000gallons.Thatamountsto$5000-$10,000ofwaterperyear.Twentysmalloil-freepumpscouldprovidecomparablevacuumat$15,000to$40,000(dependingonthevacuumrequirements),forapaybackperiodof2to8years.Itmakeseconomicsensetolookatin-labvacuumalternatives–evenapartfromthewasteofwaterassociatedwithusingwateraspiratorsforvacuum.

• Anotherapproachmaybetoinvestigatehowmanylabsareusingthecentralvacuumsystem.Insomeresearchfacilities,onlyveryfewpeoplemaybeusingthecentralvacuumsystem,eitherbecausedrylabsrepresentalargefractionofthescientificprogram,orbecausethescientistsneedmorereliableordeepervacuumthancentralvacuumcansupply.Insuchacase,itmaybepossibletoshutdownyourcentralsystemaltogether,andsaveenoughonoperatingcoststoprovidepoint-of-usevacuum–eitherindividualpumpsorthenetworkswedescribedhere–insteadofcentralvacuum,withtheassociatedenergyandmaintenancesavings.

Project manager: “I was surprised that the system was so effective and so simple at the same time.”

CONCLUSIONS1. Therecanbesomeverysignificantopportunitiesforoperatingsavingsbytakingaclose

lookatthecostoflabutilities.It’sworththeanalysis.

2. Bytakingamodular,lab-by-labapproach,a“minimallyinvasive”constructionprojectcanberolledoutwithonlylimiteddisruptiontoon-goingoperations.

3. Suchmodulartechnologiescancontributetotheadaptabilityofasciencebuildingovertime,preservingthevalueofcapitalfacilities.

4. Upgradeofvacuumutilitiescanbeaccomplishedalabatatime,avoidinglargeconstructionexpenditureswhilecontinuouslyupgradingfacilitiesasanadjuncttoscheduledmaintenance.

5. Multi-userlocalvacuumnetworkscansavevaluablebenchandfloorspaceinalabcomparedwithreplacingcentralsupplywithindividualpumpsforeachapplication.

6. Thequalityofthevacuum–bothdepthofvacuumandstability–caneliminatetheneedformanyindividualpumpsthatwouldotherwisebeneededtocompensateforthelimitationsofcentralvacuumperformance.Thiscansaveonlabequipmentcostsaswellasspace.

7. Projectsundertakentoachieveoperatingsavingsmayalsoprovidetechnicaladvantagestolaboperations,enhancingscientificpracticewhilereducingcosts.

Campus facilities engineer: "The demand response makes these energy efficient, and the modularity makes this a sustainable option; we can update vacuum a lab at a time over the years. We immediately saw the projected water savings."

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Special thanks for Doug Bradley of Loftus Engineering and Luci Keazer of Purdue University for data included in this case study.