healthcare ventilation research collaborative: displacement ventilation … · 2013-12-05 · 6...
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H E A L T H C A R E R E S E A R C H C O L L A B O R A T I V E
Healthcare Ventilation Research Collaborative:Displacement Ventilation ResearchPhase II Summary ReportD E C E M B E R 2 0 0 9
A U T H O R S :
Arash Guity, PE, Mazzetti Nash Lipsey BurchBob Gulick, PE, Mazzetti Nash Lipsey BurchPaul Marmion, PEng, Stantec
Health Care Without Harm
has initiated a research
collaborative coordinated
by faculty of the University
of Illinois at Chicago School
of Public Health, with
support from the Pioneer
Portfolio of the Robert Wood
Johnson Foundation, aimed
at stimulating collaborative
research around health and
safety improvements in
health care. The Research
Collaborative is designed to
increase the evidence base
concerning the impacts
of sustainable design,
construction, organization,
operations, materials and
chemicals in the health care
sector on patient, worker and
environmental safety.
This paper is the sixth in a
series of papers in which
the Collaborative provides
research and analysis of factors
influencing patient, worker
and environmental safety and
sustainability in the healthcare
sector. The editors of this series
are Peter Orris, MD, MPH and
Susan Kaplan, JD.
TA B L E O F C O N T E N T S
Acknowledgements.........................................................................................................................................4
1. Executive.Summary..................................................................................................................................5
2. Background..............................................................................................................................................7
2.1 History..............................................................................................................................................................7
2.1.1 Context...................................................................................................................................................7
2.1.2 PhaseIandtheHealthcareVentilationResearchCollaborative..........................................................7
2.2 SystemComparison:DisplacementVentilationvs.OverheadVentilation....................................................8
2.3 CodeConsiderations........................................................................................................................................8
3. Hypothesis...............................................................................................................................................9
4. Approach.................................................................................................................................................9
4.1 EmpiricalAnalysis............................................................................................................................................9
4.1.1 Objective................................................................................................................................................9
4.1.2 ExperimentalSetup................................................................................................................................9
4.1.3 TestingandValidation.........................................................................................................................11
4.2 InitialNumericalModelingandValidation..................................................................................................12
4.2.1 Objectives.............................................................................................................................................12
4.2.2 ModelingSetup....................................................................................................................................12
4.2.3 TestingandValidation.........................................................................................................................17
4.2.4 StatisticalComparison.........................................................................................................................17
4.3 ParametricNumericalTesting........................................................................................................................17
4.3.1 Objectives.............................................................................................................................................17
4.3.2 Metrics..................................................................................................................................................17
4.3.3 Testing..................................................................................................................................................18
5. Key.Findings..........................................................................................................................................20
5.1 EmpiricalTestingResults...............................................................................................................................20
5.2 ParametricTestingResults.............................................................................................................................20
5.2.1 ImpactofHotSummerConditionsandSupplementalCooling.........................................................22
5.2.2 ImpactofColdWinterConditionsandSupplementalHeatingModes..............................................22
5.2.3 ImpactofAirDiffuserandGrilleLocations........................................................................................23
5.2.4 ImpactofCeilingHeight.....................................................................................................................23
5.2.5 ImpactofMovementonDisplacementVentilation............................................................................24
5.2.6 ImpactofCoughingonDisplacementVentilation..............................................................................24
6. Recommendations..................................................................................................................................25
6.1 GeneralRecommendations............................................................................................................................25
6.2 DesignStrategies............................................................................................................................................25
7. APPENDICES.......................................................................................................................................26
7.1 TerminologyandAbbreviations.....................................................................................................................26
7.2 HVRCAdvisoryCommittee.........................................................................................................................26
ThefollowingAppendicesareavailableintheonlineversion,availableat:http://www.noharm.org/lib/downloads/doc_index.php
7.3 EmpiricalTesting
7.4 NumericalTesting
7.5 StatisticalAnalysis
7.6 MovementStudy
L I S T O F TA B L E STable.1:.Empirical.Cases.for.Validation.........................................................................................................11
Table.2:.Parametric.Numerical.Cases............................................................................................................19
Table.3:.Summary.of.Parametric.Study.Results.............................................................................................21
L I S T O F F I G U R E SFigure.1:.Initial.configuration.of.the.patient.room..........................................................................................10
Figure.2:.Dimensions.of.the.patient.room......................................................................................................10
Figure.3:.Photo.of.patient,.bed,.and.caretaker................................................................................................10
Figure.4:.Measurement.locations:.Poles.1-8.for.air.velocity.and.temperature..and.TGs.1-5.for.tracer.gas.or.particles...........................................................................................................10
Figure.5:.Initial.numerical.model.setup..........................................................................................................12
Figure.6:.Summer.Base.Case.Normalized.Contaminant.Concentration:.Whole.Room.....................................13
Figure.7:.Summer.Base.Case.Normalized.Contaminant.Concentration:.At.Caregiver.Height..........................13
Figure.8:.Summer.Base.Case:.3ppm.Iso-Surface.for.DV.at.4.ACH................................................................13
Figure.9:.Summer.Base.Case:.3ppm.Iso-Surface.for.OHV.at.6.ACH.............................................................13
Figure.10:.Temperature.profile.for.DV.at.4.ACH..........................................................................................14
Figure.11:.Velocity.profile.for.DV.at.4.ACH................................................................................................14
Figure.12:.Temperature.profile.for.OHV.at.6.ACH.......................................................................................14
Figure.13:.Velocity.profile.for.OHV.at.6.ACH.............................................................................................14
Figure.14:.3ppm.Iso-Surface.for.DV.at.4.ACH.............................................................................................14
Figure.15:.3ppm.Iso-Surface.for.OHV.at.6.ACH..........................................................................................14
Figure.16:.DV.with.Warmer.Temperature.Supply..........................................................................................15
Figure.17:.3ppm.Iso-Surface.for.DV.at.4.ACH.with.High.Supply.Air.Temperature.......................................15
Figure.18:.3ppm.Iso-Surface.for.DV.at.4.ACH.with.Radiant.Heating.Panels.................................................15
Figure.19:.3ppm.Iso-Surface.for.DV.at.4.ACH.with.Baseboard.Heating........................................................15
Figure.20:.Normalized.tracer.gas.concentration.profiles.(comparison.of.low..and.high.level.auxiliary.exhaust.with.4.ACH.and.6.ACH.respectively)..........................................................16
Figure.21:.3ppm.Iso-Surface.for.OHV.at.6.ACH..........................................................................................16
Figure.22:.3ppm.Iso-Surface.for.DV.at.4.ACH.............................................................................................16
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report4
Theauthorsgratefullyacknowledgethesupportandcontributionsofthefollowingindividualsandorganizations:
Healthcare.Ventilation.Research.CollaborativeBobGulick,PE,LEED®AP,Principal,MazzettiNashLipseyBurch1
WalterVernon,PE,LEED®AP,Principal,MazzettiNashLipseyBurchJohnPappas,PE,LEED®AP,Principal,MazzettiNashLipseyBurchArashGuity,PE,LEED®AP,HVRCProjectManager,MazzettiNashLipseyBurch1
ChristyLove,EIT,LEED®AP,MechanicalDesigner,MazzettiNashLipseyBurchPaulMarmion,PEng,LEED®AP,ManagingPrincipal;BuildingEngineering,Stantec1
RayPradinuk,MAIBC,LEED®AP,HealthcareResearchandInnovationLeader,StantecWeiranXu,PhD,MentorGraphics2
AndyManning,PhD,MentorGraphics2
Qingyan(Yan)Chen,PhD,SchoolofMechanicalEngineering,PurdueUniversity2
YonggaoYin,PhD,SchoolofEnergyandEnvironment,SoutheastUniversity,Nanjing,ChinaandSchoolofMechanicalEngineering,PurdueUniversity2
JitendraK.Gupta,SchoolofMechanicalEngineering,PurdueUniversity2
SagnikMazumdar,PhD,UniversityofMedicineandDentistryofNewJersey2
EnidK.Eck,RN,MPH,RegionalDirector,InfectionPreventionandControl,KaiserPermanenteAlfDyck,PEng,VicePresidentofEngineering,E.H.PriceBradTully,ResearchandDevelopmentManager,E.H.PriceJulianRimmer,E.H.PriceJohnMesservy,DirectorofCapitalandFacilitiesPlanning,PartnersHealthcareSystemInc.TeerachaiSrisirikul,DirectorofUtilities&Engineering,PartnersHealthcareSystemInc.PaulaWright,RN,BSN,CIC,DirectorofInfectionControlUnit,PartnersHealthcareSystemInc.AndrewStreifel,MPH,HospitalEnvironmentSpecialist,UniversityofMinnesotaMikeBuck,SafetyandHealthComplianceSpecialist,UniversityofMinnesotaJudeneBartley,MS,MPH,CIC,VicePresident,EpidemiologyConsultingServicesInc.SeanBrice,PE,LEED®AP,DirectorofEngineering,ThompsonConsultantsInc.RalphGifford,ThompsonConsultantsInc.MaryMcNaughton,RN,BSN,MSA,CIC,InfectionControlPractitioner,ProvidenceHealthcareBillRavanesi,MA,MPH,HealthcareWithoutHarmLindaDickey,RN,MPH,CIC,UniversityofCaliforniaIrvineMedicalCenterRussOlmsted,MPH,CIC,Epidemiologist,InfectionControlServices,TrinityHealthSystem
HVRC.Advisory.CommitteeDr.PaulJensen,PhD,PE,CIH,Captain,EngineerDirector,CentersforDiseaseControlandPreventionDr.FarhadMemarzadeh,PhD,PE,NationalInstitutesofHealthDr.MicheleR.Evans,DrPH,NationalInstitutesofHealthDr.BernardT.Baxter,PhD,MD,UniversityofNebraskaMedicalCenterDr.AnjaliJoseph,PhD,DirectorofResearch,CenterforHealthDesignChrisRousseau,PE,Newcomb&BoydJeffreyHardin,DeputyDirectorofMedicalFacilitiesCenterofExpertise,USArmyCorpsofEngineers
Supporting.OrganizationsKaiserPermanentePartnersHealthcare
A C K N O W L E D G E M E N T S
1 HVRCSteeringGroup2 HVRCResearcher
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report 5
Lowsidewalldisplacementventilation(DV)inhospitalpatientroomsappearedpromisinginhealth-careapplicationsasanHVACapplicationtoreduceoperatingcostandfirstcostwhileprovidingimprovedenvironmentalcomfort,ventilationeffectiveness,andinfectioncontrol.Testingin2006and2007invendorlaboratoriesandinthefieldsupportedthehypothesisthatlowsidewallventilationattwothirdstheairflowoftraditionalmixingoverheadventilation(OHV)hadequalorbetterperformanceinallareas.Aswithanychange,practicalquestionsarosefromhospitaldesign,operationsandcodeenforcementagenciesregardingDV.Thequestionsprecipitatedamoreformalresearcheffortin2008tomorerigorouslytestthefindingsfrom2006and2007,andtocreateandvalidateaComputa-tionalFluidDynamics(CFD)designtooltorespondtothequestionsthathadbeenraised.
Aformalresearchprocesswasundertaken,includingindependent,highlyqualified,empiricalandnumericalresearchersandanindependentadvisorycommittee.Dr.YanChenofPurdueUniversitywasselectedforempiricaltesting,andDr.WeiranXuandDr.AndyManningofMentorGraphics(formerlyFlomerics)wereselectedfornumericalCFDmodeling.Thepur-poseoftheresearchwastocomparetheperformanceofDV–attwothirdsairflow–toacode-compliantOHVconfiguration,consideringenvironmentalcomfort,ventilationeffectiveness,andparticledisper-sioncontrol(asurrogateforairbornepathogens).Theempiricaltestingwasusedtovalidatethenumericalmodel,sothatthenumericalmodelcouldthenbeusedtoevaluateperformanceunderavarietyofdynamicconditionsthatwouldbedifficulttosimulateinanempiricalmodel.
Inordertobeacknowledgedbyregulatingandstan-dardsbodiesasanacceptablemethodofventilation,thealreadyacceptedminimumoverheadairflowrateofsixairchangesperhour(ACH)wasusedastheyard-stickagainstwhichtomeasuretheperformanceofDV.
Thisresearcheffortfocusedonlow-risk,singlepatienthospitalrooms.TheroomconfigurationwasmodeledaccordingtoKaiserPermanente’sstandardsingle-bedpatientroomwithabathroomontheexteriorwall.TheresearchconcludedthatDVat4ACHperformedequallyorbetterthanOHVat6ACHforthermalcomfort,ventilationeffectivenessandcontaminantconcentration,andthattheperformanceofDVisdependentonseveralintegratedelementsoftheairdeliveryandroomexhaustairsystemdesign.Thestudyidentifiedthefollowingdesignissuesthatneedtobecarefullyconsidered:
1. ThecoolingcapacityofaDVsystemislimitedbytheminimumallowablesupplyairtemperaturerequiredtomaintainthermalcomfort.
2. RoomthermalgainsandlossesmustbecontrollediftheperformanceoftheDVsystemistobemain-tained,i.e.:
a. Facadesshouldbedesignedtominimizethethermalgainsandlossestopreventwarmandcoldsurfaces,especiallywithrespecttoglazing.ThewarmsurfacescouldaffecttheDVairflow.
b. Manualorautomaticsolarshadingdevicesshouldbeinstalledtominimize/eliminatedirectsolargains.Thefieldtestsshowedthatfloorsurfaceswarmedupbydirectsolargainscanactasathermalhotspot,creatinglocal-izedthermalchimneys,andcausingmostofthedisplacementsupplyairtoshortcircuitthebreathinglevel.
c. Lightingandmedicalequipmentloadsshouldbeminimized.
1.E X E C U T I V E S U M M A R Y
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report6
3. DVshouldnotbeusedforspaceheating,i.e.:
a. Providingsupplyairfromthelowsidewalldis-placementdiffuseratahighertemperaturethantheroom’stemperaturewillresultindecreasedperformanceoftheDVsystem.
b. Whenusingasupplementalheatingmethodsuchasradiantorconvectivebaseboardheat-ing,theperformanceoftheDVcanbemain-tained,ifnotimproved.
4. Theplacementofthesupplyairdiffuserisnotcritical,butshouldbecoordinatedwiththeroomdesign.Thediffusershouldbelocatedatlowlevelinalocationthatwillnotbeblockedwithsolidfurnituresuchasastoragecabinet.
5. Thetoilettransfergrilleshouldbelocatedathighlevel.TheempiricalexperimentsshowedthattheDVeffect/pluming/highlevelremovalofairborneparticlescanbeseriouslyaffectedifthesupplyairisallowedtoshortcircuitatlowlevel,directlyintothetoiletroom.
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report 7
2.1 History
2.1.1 ContextHealthcarefacilitiesareoneofthemostdifficulttypesofbuildingsto“green”.Giventheirpurposeinserviceofvulnerablepopulations,theyareregulatedmoreheavilythananyotherbuildingtype.Theymustfunctionfirstandforemostinacapacitythatensuresqualityofpatientcareandoccupant(caregiv-ers,visitors,andpatients)safety,andassuch,infec-tioncontrolcannotbecompromisedbytheneedorthemeanstoreduceenergy.
Conversely,healthcarefacilitiesofferauniqueopportu-nityforincorporatingsustainablestrategiesthatsimul-taneouslyimprovethehealingenvironmentandreducetheenvironmentalimpact.Healthcarefacilitiesrankasthesecondhighestbuildingtypeforenergy-density,sothecorrespondingpotentialtoreduceenergyuseissignificant.Alternateventilationmethodssuchasdis-placementventilation(DV)haveproveninothertypesoffacilities(suchasschools,officebuildings,andareasofassembly)toimproveindoorenvironmentalqualityandthermalcomfortwithreducedenergyconsumptioncomparedtotraditionalmixingoverheadventilation(OHV)systems.
Thethermalandventilationeffectivenessperfor-manceofDVhasbeenwelldocumented.Theissuethatdifferentiateshealthcareventilationfromotherbuildingtypesisairborneinfectioncontrol.WhiletherearestudiesthathaveconsideredairborneparticlemovementwithDV,none(tothebestoftheauthors’knowledge)hasdoneasidebysidecomparisonofDVtoOHVconsideringenvironmentalcomfort,ventila-tioneffectiveness,andparticlecontrolalltogether.
2.1.2 Phase I and the Healthcare Ventilation Research CollaborativeTheHealthcareVentilationResearchCollaborative(HVRC)wasformedin2006bytwohealthcareengineer-ingdesigncompanies(StantecandMazzettiNashLipseyBurch)toconsolidatetheeffortsofseveralorganizationstowardthecommongoalofpromotingimprovedpatientandstaffsafetyandsustainabledesigninhealthcarefacili-tiesthroughtheimplementationofinnovativeengineer-ingconceptsthathavebeenthoroughlyandscientificallydocumented.TheHVRCrepresentsagroupofindustryprofessionalsincludinghealthcareproviders,infectioncontrolexperts,architects,engineers,equipmentmanu-facturers,andaffiliatedprofessionals.ThecurrentrosteroftheHVRCislistedintheAcknowledgements.
InPhaseI,researchwasconductedtoassessbothnatu-ralventilationandDVinexamrooms,patientroomsandemergencywaitingrooms.Researchmethodsincludedlaboratorymockups(attheE.H.Pricelabora-toryinWinnipeg,Canada),fieldtesting,andcomputa-tionalfluiddynamics(CFD)analysis.TestingfocusedonenvironmentalcomfortperASHRAEStandard55,ventilationeffectivenessperASHRAEStandard62,andparticledispersionperatestdesignedbyAndrewStreifel,MPH,HospitalEnvironmentSpecialistattheUniversityofMinnesota.
PhaseIresultsindicatedthatDVat4ACHinapatientroomprovidesbetterparticledispersal,ventila-tioneffectiveness,andenvironmentalcomfortthanOHVat6ACH.However,morestringenttestproce-dureswereneededtodemonstrateconclusiveresults.
Dr.FarhadMemarzadeh,oftheNationalInstitutesofHealth,recommendedadetailedfollow-upeffortbeper-formed,undertheguidanceofanindependentadvisorycommittee,withadoubleblindcomparisonbetweenanempiricalandnumericaltest.Akeypurposeoftheempiricaltestingwouldbetovalidateanumericalmodelandfacilitateitsuseforevaluatingmultipleroomandsystemdesignconfigurationsinamorepracticalandfea-siblemannerthancontinuedphysicaltesting.ContainedhereinaretheresultsofthisfollowupPhaseIIresearch.
2.B A C K G R O U N D
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report8
2.2 System Comparison: Displacement Ventilation vs. Overhead VentilationConventionalOHVsystemsgenerallysupplyairinamannersuchthattheairintheentireroomisfullymixed.Incoolingmode,thecoolsupplyair,typicallyaround55°Fatdesignconditions,exitstheoutletathighveloc-ityandinducesroomairtomixandequalizetempera-ture.Becausetheentireroomisessentiallyfullymixed,temperaturevariationsaresmallwhilethecontaminantconcentrationisfairlyuniformthroughouttheroom.
DVsystems,ontheotherhand,introduceairatlowvelocitiesandatlowleveltospecificallyavoidinduc-tionandmixing.Suchsystemsutilizenaturalbuoyancyandconvectiveforces(createdbyheatsourcessuchaspeople,lighting,equipment,etc.)tomovecontami-nantsandheatfromtheoccupiedzonetothereturnorexhaustgrillesabove.
Coolair(coolerthantheroomair)issuppliedatlowvelocityintothelowerzoneandpoolsacrossthefloorbecauseitismore‘dense’orlessbuoyantthantheroomair.Convectionfromheatsourcesthendrawstheairverticallyintotheupperzonewherehighlevelreturnopeningsextracttheair.Inmostcases,theseconvectionheatsourcesarealsothecontaminationsources(people,equipment,etc.),therebybringingthecontaminantsdirectlytotheupperportionoftheroom,awayfromtheoccupants.Indoingso,theairqualityintheoccupiedzoneisgenerallyconsideredsuperiortothatachievedwithmixingroomairdistribution,andthethermalloadsintheoccupiedzonearelessthantheentireroomvolume.ASHRAE’sSystemPerformanceEvaluationandDesignGuidelinesforDisplacementVentilation3describeshowthermalloadscanbediscountedwhenusingDV.
Sincetheconditionedairissupplieddirectlyintotheoccupiedspace,thesupplyairtemperaturesmustbehigherthanmixingsystemstoavoidoverlycooltem-peraturesatthefloor.ByintroducingtheairathighersupplyairtemperaturesandloweroutletvelocitiesthanOHVsystems,ahighlevelofthermalcomfortcanbeachievedwithDV.
TheenergybenefitsforDVcomefromthefactthatairissuppliedatahighertemperaturethanwithOHVsys-tems,andmuchofthethermalcoolingloadinthespacedoesnotcomeintotheoccupiedzonebutisdrawn
throughnaturalbuoyancyandconvectiondirectlytotheupperunoccupiedzonewithoutmixing.Thisresultsinhigherreturnairtemperaturesandlowerairflowrates,whichcontributetoareducedmechanicalcoolingandventilationplantsizeandenergyconsumption.
Becauseitreliesonmorepassiveforcesforitseffective-ness,DVcanbealessrobustsystemthanOHV.Assuch,anintegrateddesignapproachisgenerallyrecommendedtooptimizeitsperformance.Thekeyparametersaffect-ingDVperformanceareinvestigatedinthisstudy.
2.3 Code ConsiderationsIntheUnitedStates,healthcarefacilitydesignrequire-ments,includingtheirHVACsystems,aregovernedonastate-by-statebasis.MoststatesutilizetheGuidelinesforDesignandConstructionofHealthCareFacilitiespublishedbytheFacilitiesGuidelinesInstitute(FGI)asthebasisoftheirregulations.VentilationrequirementsforhospitalsandoutpatientfacilitiesarecoveredinTable2.1-2oftheGuidelines(2006Edition),prescrib-ingspace-pressurerelationships,minimumairexchangerates(forbothtotalandOSA),exhaustrequirements,andtemperatureandhumiditycontrols.
ExtensivefootnotestoTable2.1-2provideclarifica-tionsandexceptionstotheserequirements.Forexam-ple,theTablerequiresminimumsof6airchangestotaland2outsideair(OSA)changesforpatientrooms,andminimumsof12airchangestotaland2OSAchangesforemergencywaitingrooms,butFootnote10allowstheminimumtotalairchangesinapatientroomtodropto4ifusingsupplementalheatingand/orcool-ing.So,technically,theGuidelinesallowDVaslowas4ACHinapatientroomwithsupplementalheatingand/orcooling.However,whilemoststateregulationsincludeaversionofTable2.1-2,theextenttowhichthefootnotesareadoptedvarieswidely.
TheHealthGuidelinesRevisionCommittee(HGRC),inconjunctionwiththeFacilityGuidelinesInstitute,updatestheGuidelineseverythreeyears.
ASHRAEhadalsorecentlydevelopedStandard 170: Ventilation of Healthcare Facilities,whichdefinesventilationsystemrequirementsforhealthcarefacili-ties.Ratherthanhaveparallelguidelinesforventila-tionrequirementsforhealthcarefacilities,theHGRCelectedtoadoptStandard170toreplaceTable2.1-2intheGuidelines forthe2010Edition.
3 Chen,QingyanandLeonGlicksman.SystemPerformanceEvaluationandDesignGuidelinesforDisplacementVentilation.ASHRAE:2003.
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report 9
3.H Y P O T H E S I S
TheHVRCinitiatedtheformationofanAdvisoryCommitteein2007toserveasanindependentpartytoguidetheresearchandevaluatetheresults.TheAdvi-soryCommitteerosterisincludedasAppendix7.2.
Theresearchconsistedoftwoindependentblindcomponents:empiricalanalysisandnumericalanalysis.ResearchersforeachcomponentwereselectedwiththeguidanceoftheAdvisoryCommitteebasedontheirgeneralexperience,qualifications,andcapabilitytomeettherequirementsofadetailedtestprotocol.
Theempiricalresearchanalyzedenvironmentalcom-fortandparticledispersionforasingle-bedhospitalpatientroom(withabathroom),comparinganOHVsystemat6ACH(currentacceptedminimum)tolowsidewallDVat4ACH.
Inaddition,theempiricalOHVandDVtestswerecomparedtoanumericalcomputationalfluiddynamic(CFD)simulationforthepurposesofvalidation.Theblind,independenttestresultsweresubmittedtotheHVRCforastatisticalcorrelationevaluation.
Followingvalidation,thenumericalmodelwasusedtotestanumberofkeyparameters,includingoutdoorconditions,supplyairtemperatures,grilleanddiffuserlayouts,andsupplementalheatingandcooling.
Additionalempiricalandnumericaltestingwasperformedtoevaluatetheeffectsofcoughingandmovement.
4.1 Empirical AnalysisDr.Qingyan(Yan)ChenofPurdueUniversitycon-ductedtheempiricalanalysis.Anenvironmentalchamberwascreatedtosimulateaone-personpatientroom,inwhichthepatientcouldbreatheorcoughoutcontaminants.ThecompleteresultsoftheempiricalstudyareincludedinAppendix7.3.Anoverviewoftheresearchfollowsbelow.
4.1.1 ObjectiveTheobjectivesoftheempiricalanalysiswereto:
• Developatestingconfigurationtocomparetheper-formanceofaconventionalOHVsystemwithalowsidewallDVsystematlowerairflowrates;
• Collectmeasurementstobeusedforestablishingboundaryconditionsforthenumericalmodel;and
• Providehighqualityoutputresultstofacilitatevali-dationofthenumericalmodel.
Asecondaryobjectivewastodetermineatanearlystageoftheexperimentalprocesswhetheratracergas(SF6)couldbeusedtosimulatecontaminantsbreathedorcoughedoutbyapatient,sincetracergasesaremuchsimplertomodelthanactualparticles.
4.1.2 Experimental SetupTheempiricalvalidationtestsweredoneatroomenvelopeconditionsasclosetoadiabaticaspracticallypossible,withboundaryconditionscarefullymeasuredandsuppliedtothenumericalanalysisteamsothatthesamesurfacetemperatures,roomloads,andairflowratescouldbeusedforbothmodels.Comparisonmea-surementsincludedtemperature,velocity,andtracergas(SF6)concentrations.
TheHVRCinitiatedthisresearchtodetermineiflowsidewallDVcanmaintainorimproveairbornepathogenremovalfrompatientroomsatequalorlowerairchangeratesthanthosecurrentlyrequiredusingconventionalOHV,whilemaintainingorimprovingpatientandstaffcomfort,andreducingenergyuseandenvironmentaldegradation.Ifthehypothesisisproven,theresultswillpromptrevisionstocodesandstandardsforhealthcaredesignandconstruction.
4.A P P R O A C H
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report10
Figure 1: Initial configuration of the patient room
Figure 2: Dimensions of the patient room
Figure 3: Photo of patient, bed,
and caretaker
Figure 4: Measurement locations: Poles 1-8 for air velocity and temperature and TGs 1-5 for
tracer gas or particles
ThepatientroomsetupwasbasedonaKaiserTemplateHospitalsingle-bedpatientroom.Figures1through4showtheinitialconfigurationandmeasurementlocations.
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report 11
Thepatientroomincludedthefollowingelements:
a. Patient(thermalmanikin)lyingonbed –breath-ingzoneat1.1maboveflooristhecontaminantsource;patientassumedtobecontaminantsource
b. Caretaker(thermalmanikin)standingatbedside –breathingzoneat1.7mabovefloor;oneofthecriti-calpointsformeasuringcontaminantconcentration
c. FortheOHVconfiguration:overheadceilingdif-fusercenteredabovebed
d. FortheDVconfiguration:lowsidewallsupplydif-fuseragainstwalloppositefootofbed
e. ForbothDVandOHV:mainroomexhausthighonheadwall –nearinteriorwall
f. ForbothDVandOHV:transfergrilletobath-room –initiallylowintoiletdoor,thenmovedtohighwallabovebathroomdoor
g. Interiorloads:Equipmentoninteriorwall,TVonwalloppositebed,lightsonceiling
h. Temperatureandvelocitymeasurements:eightpolelocationsatsevenelevationseach,foratotalof56points
i. Tracergas/Particleconcentrationmeasurements:fivepolelocations,fouraroundbedandonenearexteriorwindow,representinglocationsofpeopleinroom,atsevenelevations,foratotalof30points
TheempiricaltestingconsistedofeightcasesdesignedtotestOHVvs.DVsystems.ThecasesaresummarizedinTable1below.
4.1.3 Testing and ValidationMultipletestcaseswereruninthelab.CaseslookedatanOHVsystemat6ACH,andlowsidewallDVatboth4and6ACH.Testswereperformedforbothtracergas(SF6)and1micronand3micronparticlestoevaluatetheacceptabilityofusingoftracergasasasurrogateforparticles.Initialtestingdemon-stratedpoorperformanceoftheDVsystemwhenthetransfergrillebetweenthepatientroomandthetoiletwaslocatedatlowlevel.FurthertestswererunwithahightransfergrillewhichshowedasignificantimprovementoftheDVsystem.Subsequenttestswereperformedwiththehightransfergrillelocation.Two(2)basecaseswereestablished(cases1and2inTable1)tobeusedforvalidationofthenumericalmodel.Evenwithsignificanteffortstocreateadiabaticroomenvelopeconditions,heattransfercannotbetotallyeliminatedinthephysicalworld.Assuch,itwascriti-caltomeasureairflowcharacteristicsandtherateofheattransferonallsurfacesoftheroomtoestablishboundaryconditionsforthenumericaltestingteam.Eachcasewasrunthreetimestoverifytherepeatabil-ityofthedata.
Table 1: Empirical Cases for Validation
Cases
ROOM CONDITIONS
Contaminant sourceVentilation Bathroom exhaust grille Flow rate (ACH)
1 OverheadSupply Lowlevel 6 SF6
2 SidewallDisplacement Lowlevel 4 SF6
3 OverheadSupply Highlevel 6 SF6
4 SidewallDisplacement Highlevel 4 SF6
5 SidewallDisplacement Lowlevel 6 SF6
6 SidewallDisplacement Highlevel 6 SF6
7 SidewallDisplacement Highlevel 4 1μmparticles
8 SidewallDisplacement Highlevel 4 3μmparticles
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report12
Empiricaltestingproducedtwoprimaryoutputs:mea-suredtestoutputdatafortemperature,velocity,andtracergasconcentration,aswellasboundarycondi-tionsfordefiningthenumericalbasecaseanalysis.Boundaryconditionsincludedthefollowing:
a. Roomdimensions
b. Grillelocations
c. Airflows
d. Datameasuringpointdimensions
e. Interiorloadsandlocations,includingthermalmanikins
f. Wallheattransferdata
g. Supplydiffuservelocityprofiles
Theempiricaltestoutputdatawerekeptblindtothenumericalmodelers.
4.2 Initial Numerical Modeling and ValidationDr.AndyManningandhisassociate,Dr.WeiranXu,withMentorGraphics(previouslyFlomerix),conductedthenumericalmodelingresearch.CompleteresultsofthenumericalresearchareincludedinAppendix7.4.Anoverviewoftheresearchfollowsbelow.
4.2.1 ObjectivesTheobjectiveoftheinitialnumericalanalysiswastovalidatethenumericalmodelfromtheempiricalresults.Oncevalidated,thenumericalmodelcouldbeusedtoevaluatearangeofvariablesappliedtoDVandOHV.
4.2.2 Modeling SetupThenumericalmodelwassetuptomatchtheempiri-calmodel,basedonboundarydataprovided.Figure5showsthemodelsetup.
Figure 5: Initial numerical model setup
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report 13
Figure 7: Summer Base Case Normalized Contaminant Concentration:
At Caregiver Height
Figure 6: Summer Base Case Normalized Contaminant Concentration:
Whole Room
Figure 8: Summer Base Case: 3ppm Iso-Surface
for DV at 4 ACH
Figure 9: Summer Base Case: 3ppm Iso-Surface
for OHV at 6 ACH
C O L O R F I G U R E S
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report14
Figure 10: Temperature profile for DV at 4 ACH
Figure 13: Velocity profile for OHV at 6 ACH
Figure 12: Temperature profile for OHV at 6 ACH
Figure 11: Velocity profile for DV at 4 ACH
Figure 14: 3ppm Iso-Surface for DV at 4 ACH
Figure 15: 3ppm Iso-Surface for OHV at 6 ACH
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report 15
Figure 17: 3ppm Iso-Surface for DV at 4 ACH with
High Supply Air Temperature
Figure 16: DV with Warmer Temperature Supply
Figure 19: 3ppm Iso-Surface for DV at 4 ACH with
Baseboard Heating
Figure 18: 3ppm Iso-Surface for DV at 4 ACH with
Radiant Heating Panels
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report16
Figure 21: 3ppm Iso-Surface for OHV at 6 ACH
Figure 22: 3ppm Iso-Surface for DV at 4 ACH
Figure 20: Normalized tracer gas concentration profiles (comparison of low and
high level auxiliary exhaust with 4 ACH and 6 ACH respectively)
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report 17
4.2.3 Testing and ValidationNumericalvalidationtestingwasconductedtocreatedataforcomparisontotheempiricalstudy,usingtheboundaryconditions(walltemperatures,roomgeom-etry,roomloads,andairflowvalues)fromtheempiricalanalysis.Twobasecaseswereusedforvalidationofthenumericalmodel:oneforanOHVsystemat6ACHandoneforaDVsystemat4ACH.
Anearlysubsetoftheresearchwastoconstructapatientbreathingmodelthatsimulatedtheeffectofrealbreathingandwasconsistentwithempiri-caltesting.Thepurposeofthisanalysiswastoevaluatewhetherthenumericalsimulationsshouldbeperformedassumingaconstantrateofexhalation(constantbreathing)oractualbreathing(inhalationandexhalation).Theresultoftheanalysiswasthat“constantbreathing”wouldaccuratelyrepresenttherateofparticlereleaseofactualbreathing.Appendix7.4includesasummaryofthetestingandverificationofa“constantbreathing”numericalmodelthatassistedinsubsequentmodeling.
Thevalidationperiodwasextendedduetomanyiterativerunstofinetunetheboundaryconditions,ofwhichheattransferthroughtheenvelopeandvelocityprofilesfromthesupplydiffusersprovedmostchalleng-ing.Theboundaryconditionswererefinedtothepointofgoodcorrelationofnumericaltoempiricaldata.
Figures6-9onpage13(andFigures12-16inAppendix7.4availableintheonlineversion)showthecomparison.
4.2.4 Statistical ComparisonAnindependentstatisticalcomparisonoftheempiri-calandnumericaldatawasconductedbyDr.FarhadMemarzadeh,todeterminethelevelofagreementbetweentheempiricalandnumericalmodelsandcon-firmthatthenumericalmodelcouldserveasanappro-priaterepresentationoftheempiricaltest.Appendix7.5includesthecompletestatisticalcomparison.
Theresultsbetweenthetwomodelsdemonstratedacceptableagreement,particularlyintermsoftrend-ingoftheoutputsinthebreathingzone,allowingforextendeduseofthedevelopednumericalmodelformorecomplextestingandcomparisonofDVandOHV.
4.3 Parametric Numerical TestingAfterthenumericalmodelwasvalidated,Dr.ManningandDr.Xusetupnumerical(CFD)modelsthatvariedanumberofkeyparameterstotesttheresearchinitia-tive’scentralhypothesis.
4.3.1 Objectives Theoverallobjectiveofthisresearchproject–andofthisportionoftheproject-wastostudyandcomparetheperformanceofOHVandDVsystemsinasingle-bedhospitalpatientroom.Thedistinctemphasisofapatientroomventilationsystemistheabilitytoremovecontaminantswhilemaintainingacceptablethermalcomfort,andtheparametricnumericaltestingwasdesignedtoevaluatetheseparallelgoals.
4.3.2 MetricsTwomainsetsofmetricswereestablishedtocompareperformance,asfollows:
a. ThermalComfort
Therearethreestandardmeasuresfordetermi-nationofthesuitabilityofanenvironmentforhumanoccupation:
• Fanger’scomfortequationsforPercentageMeanVote(PMV)andPredictedPercentageDissatisfied(PPD).PMVandPPDwereempiri-callyderivedfromhumanresponsestotestconditions,inwhichindividualsreportedtheirlevelofcomfortfromverycoldtoveryhot.Theindiceswerethendevelopedtodescribeasetofroomconditionsintermsofthepercent-ageofoccupantswhoarelikelytobedissatis-fiedwiththoseconditions.Theseindicesdonotaccountforthediscomfortexperiencedwhenmovingfromoneregiontoanotherwithdifferentconditions(theAirDistributionPerformanceIndexdescribedbelowaddressesmovementeffects).
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report18
• Comfort(Resultant)Temperature.Thether-malcomfortofaroomdepends,toasignificantdegree,ontheradiativeexchangebetweentheoccupantsandtheirsurroundings.Theconceptofmeanradianttemperatureisusedtodescribethisradiativeexchange,andisdependentuponthesurfacetemperatureofthesurround-ings.Theresultanttemperature,byextension,describesthecombinedeffectofmeanradianttemperature,airtemperature,andvelocity.
• AirDiffusionPerformanceIndex(ADPI).ADPIisaparameterthatmeasurestheuni-formityofthespaceintermsofthepropor-tionofthevolumewithavelocitylowerthan0.35ms-1(70ftmin-1)anddrafttemperaturebetween-1.7°Cand+1.1°Cfromthemeantemperature.Uniformityisnormallyconsid-eredgoodintheoccupiedregionofamixedflowdesigniftheADPIforthatregionexceeds80%.Althoughthismeasurewasdesignedforestablishingwhethercoolingjetsfrommixedflowventilationsystemsarewelldissipated,thismeasurecanbecautiouslyappliedtodeterminethegeneraluniformityofotherenvironments.
PPDwaschosenastheonlythermalcomfortindexforthisstudysinceitistheonemostwidelyusedandunderstood.
b. VentilationEffectiveness/ContaminantRemoval
Therearetwomaincategoriesofindicestomea-surethecontaminantcontrolcapabilityofventila-tionsystems:
• VentilationEffectiveness,ortheabilityofaventilationsystemtoremoveinternallygeneratedpollutantsfromabuilding,zone,orspace.VentilationEffectiveness(asdefinedbyASHRAE62.1)iscalculatedforthecaregiver,visitor,andwholeroom.AfurtherrefinementofVentilationEffectivenessisthePersonalExposureIndex,whichreflectsthecontami-nantconcentrationattheexactbreathinglocationofthecaregiver,versussimplythecontaminantconcentrationatthegeneralbreathingzone.
• AirChangeEffectiveness,ortheabilityofaventilationsystemtodistributeventilationairtoabuilding,zone,orspace.AirChangeEffectivenessisdefinedbyASHRAEStan-dard129-1997.ArefinementofAirChangeEffectivenessis“AirDistributionEffective-ness”,whichspecificallyaddressesdisplace-mentcoolingsystemsandiscurrentlyunderconsiderationbyASHRAE.
Fourindiceswerethususedtoevaluatetheresultsfromacontaminantremovalperspective:
• VentilationEffectiveness
• PersonalExposureIndex
• AirChangeEffectiveness
• AirDistributionEffectiveness
4.3.3 TestingInordertosystematicallyinvestigatethecharacteristicsofDVandOHVsystems,aseriesofcasesweredevelopedtotest(usingCFDmodeling)thefollowingparameters:
• Impactofhotsummerconditions(includingsolargain)
• Impactofsupplementalcooling
• Impactofvaryingsupplyairtemperatures
• Impactofcoldwinterconditions
• Impactofsupplementalheating
• Impactofairdiffuserandgrillelocations
• Impactofceilingheight
• ImpactofmovementonDV
• ImpactofcoughingonDV
Table2summarizesthecases.
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report 19
Table 2: Parametric Numerical Cases
#Description/
PurposeVentilation
TypeMain
Return Weather Load ACHSupply
Temp (degF)
Additional Cooling/Heating
1 DV Limit with Solar Load
Displacement Above Patient
Summer LA 105F
Standard 4 Adjustable, 60F low limit
No
2 Overhead Overhead Close to Window
Winter Chicago -10F
Reduced 6 Adjustable, up to 105F
No
3 DV with Radiant Heating Panel
Displacement Above Patient
Winter Chicago -10F
Reduced 4 67.1 Radiant Heating
4 DV with Baseboard Heater
Displacement Above Patient
Winter Chicago -10F
Patient, Caregiver only
4 67.1 Baseboard Heater
5 Overhead 4ACH
Overhead Close to Window
Summer LA 105F
Standard 4 Adjustable, 55F low limit
No
6 Overhead 4ACH
Overhead Close to Window
Winter Chicago -10F
Patient, Caregiver only
4 Adjustable, up to 105F
No
7 DV at 4 ACH - w Radiant Cooling Panel
Displacement Above Patient
Summer LA 105F
Standard 4 67.1 Radiant Cooling
8 Overhead 6 ACH in Summer
Overhead Close to Window
Summer LA 105F
Standard 6 Adjustable, 55F low limit
No
9 DV 4 ACH w Solar Loading
Displacement Above Patient
Summer Reduced Temp 97F
Standard 4 60 No
10 DV 4 ACH w High Supply Temperature
Displacement Above Patient
WinterChicago -10F
Patient, Caregiver only
4 87F No
11 DV 4 ACH w 12’ Ceiling Height
Displacement Side wall above Patient
Summer LA 105F
Standard 4 60F No
12 DV 4 ACH w 12’ Ceiling Height
Displacement Above Patient on the ceiling
Summer LA 105F
Standard 4 60F No
Standard Load = Load from Patient, Caregiver, TV, Equipment. Reduced Load: Patient, Caregiver only
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report20
ThekeyfindingsofthePhaseIIresearcharesumma-rizedinthissection.Completeresultsaredetailedinindividualresearchpapers,referredtothroughoutthisdocumentandincludedasAppendices.
5.1 Empirical Testing ResultsInthecourseofestablishingarobustsetofboundaryconditionsforthenumericalmodel,theempiricaltest-ingyieldedinterimresultsthatinformedthefinalsetupofthepatientroomthatwasthenusedforcomplexnumericaltesting.
Thethreekeyresultsoftheempiricaltestingwereasfollows:
a. DVdidnotperformwellwhenthetransfergrilletothetoiletroomwaslocatedatlowlevel.Withmorethanhalfofthesupplyairtransferredviathetoiletroom,supplyairwasshortcircuitedreduc-ingtheDVeffectivenessintheroom.Whenthetransfergrillewaslocatedathighlevel,DVperfor-mancesignificantlyimproved,evenatareducedairchangerate.
b. SF6tracergaswasavalidsurrogatefor1and3micronairborneparticles.
c. Withthehightoilettransfergrille,DVat4ACHperformedequallyorbetterthanOHVat6ACHforenvironmentalcomfort,ventilationeffective-ness,andtracergasconcentration.
5.2 Parametric Testing ResultsThenumericaltestingresultsforthebasecasesshowedthatDVat4ACHperformedequallyorbetterthanOHVat6ACHforthermalcomfort,ventilationeffec-tiveness,andcontaminantconcentration.
Thebasecaseresultsareillustratedinthefigures10-13(seepage14).
Themodelersdevelopedavisualconcepttodisplayareasofconstantcontaminantconcentrationwithinthepatientroom.Figures14and15(seepage14)showthroughtheuseofaniso-surface,theextenttowhichcontaminantsspreadintheDVandOHVscenarios.Astheiso-surfacedemonstrates,theDVairflowpatternresultsinamorecontainedcontaminantconcentrationathighlevel.
Thenumericalmodelingwasalsousedtotestmorecomplexparametersbeyondthescopeofthebasecasesusedforvalidation.Theresultsforthesetestsaresum-marizedinTable3.
5.K E Y F I N D I N G S
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report 21
Table 3: Summary of Parametric Study Results
#Description
/Purpose
PPDPatient AreaVisitor Area
VE for caregiver
at 1.1m1.7m
VE for visitor
at 1.1m1.7m
VEWhole room
at 1.1m1.7m PEI ADE ACE
# Description /Purpose
PPDPatient AreaVisitor Area
VE for caregiver at1.1m1.7m
VE for visitorat1.1m1.7m
VEWhole roomat1.1m1.7m
PEI ADE ACE
1 DV Limit with Solar Load
8.618.91
1.221.05
1.451.38
1.311.18
1.36 1.62 0.950.91
2 Overhead 7.0621.1
0.990.87
1.121.09
1.041.00
1.07 N/A 0.840.82
3 DV with Radiant Heating Panel
5.899.84
1.671.48
1.391.37
1.711.63
1.89 N/A 1.601.18
4 DV with Baseboard Heater
7.058.37
3.242.58
2.532.37
3.072.61
3.26 N/A 0.850.71
5 Overhead 4 ACH 5.96.64
0.970.80
1.191.19
1.010.90
0.99 N/A 0.920.91
6 Overhead 4 ACH 5.7514.99
1.030.94
1.091.08
1.061.03
1.10 N/A 0.750.74
7 DV at 4 ACH - w Radiant Cooling Panel
12.5311.57
1.651.35
1.911.60
1.771.53
1.94 1.81 1.081.28
8 Overhead 6 ACH in Summer
8.178.74
0.800.76
0.940.94
0.810.79
0.84 N/A 0.790.80
9 DV 4 ACH w Solar Loading
9.313.18
1.251.06
1.571.51
1.351.20
1.45 1.62 0.870.84
10 DV 4 ACH w High Supply Temperature
5.812.33
0.900.90
0.940.98
0.940.98
0.97 N/A 0.750.85
11 DV 4 ACH w 12’ Ceiling Height
8.258.5
1.231.06
1.451.38
1.311.19
1.39 1.62 0.830.80
12 DV 4 ACH w 12’ Ceiling Height
7.197.86
1.140.99
1.261.16
1.191.08
1.30 1.84 0.970.93
See section Summary of Metrics for definition of PPD, VE, PEI, and ACE.
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report22
5.2.1 Impact of Hot Summer Conditions and Supplemental CoolingThemetricPPD(PercentageofPeopleDissatisfied),describedinsection4.3.2above,determinesthether-malcomfortofaspacebasedontemperatureanddraftcomponents.PPDindicatesthepercentageofpeoplethatwouldbeuncomfortablegiventheairtemperatureandvelocityconditions.ASHRAEStandard55indi-catesthatvaluesof20orlessareacceptable,meaningthattheairtemperatureandvelocitywouldbeaccept-ableformorethan80%ofoccupants.
Thestandardfurtherstatesthatfornon-mixingsys-tems,suchasDV,airtemperaturestratificationshouldnotexceed3.6°Fforseatedoccupantsand5.4°Fforstandingoccupantstoensurethermalcomfort.
ThesummerbasecaseresultsaresummarizedinTable3,Cases1and8.Thebaselinesupplyairtemperaturewassetat67°Fwithanassumedmaximumtemperatureat44inchesabovethefloorof73°F.TheresultsforincreasingsolargainsarereflectedinCases1and9.
Theroomairtemperatureandthermalcomfortweresignificantlyaffectedbytheincreaseindirectsolargainswithafixedsupplyairtemperature,whilethecoolingcapacityofDVwaslimitedbytheacceptablesupplyairtemperature.
TheDVsystem’sventilationeffectivenesswasreducedbydirectsolargain.However,thermalcomfortprovedtobethelimitingfactor,meaningthat,aslongasther-malcomfortismaintained,ventilationeffectivenessrequirementswillbemet.Thus,theroom’sdirectsolarheatgainsshouldnotexceedlevelsthatcompromisethermalcomfort.
AlthoughthethermalcomfortwasmaintainedinCases1and9,the5.4°Fairtemperaturestratificationrequirementwasnotsatisfiedduetotherequiredlowsupplyairtemperatureof60°Ftoachievethatlevelofthermalcomfort.Thus,asupplementalcoolingstrategy,suchasisusedinCase7(withradiantcooling),mayberequiredtosimultaneouslysatisfybothrequirementsoftheStandardforcertainclimates.
Theresultsofthesupplyairtemperaturesensitiv-ityanalysiswereusedasthebasisfordeterminingtheeffectivenessofceilingmounted,radiantcoolingpanelstoprovidesupplementarycooling(Case7).Forthisanalysis,theDVsystemsupplyairtemperaturewasfixedat67°Fandtheroomthermalgainswereincreased.Theanalysisshowsthatradiantcoolingpan-elseffectivelymaintainedoccupantthermalcomfortwithincreasingthermalgains.
5.2.2 Impact of Cold Winter Conditions and Supplemental Heating ModesCase10(Table3)studiedtheimpactofincreasingsup-plyairtemperature.
DuetothesamebuoyancyprinciplesthatallowtheDVsystemtoworkincoolingmode,supplyingairintotheroomthatiswarmerthantheroomair’stemperatureresultsintheairimmediatelyrisingasitentersthespace.Thewarmersupplyaircannotdroptowardthefloortoformstratifiedlayers.Figure16(seepage15)illustratestheairflowpatternoftheDVsystemusingahighersupplyairtemperaturethanthatoftheroom’s.
ThelowerventilationeffectivenessandlongermeanageofairintheoccupiedregionindicateareductioninperformanceoftheDVsystemintermsofindoorairquality.
BecauseoftheineffectivenessofheatingviathesupplyairinaDVsystem,twodifferentstrategiesforsupple-mentalheatingweretested:baseboardconvectorsandceilingmountedradiantheatingpanels. RefertoCases3and4inTable3.
Figures17through19(seepage15)showtheiso-sur-facecomparisonbetweenthehighsupplyairtem-peraturecase(Case10)andthesupplementalheatingstrategies(Cases3and4).
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report 23
5.2.3 Impact of Air Diffuser and Grille Locationsa. RoomtoToiletTransferGrille
Initialempiricaltestingusedatransfergrillelowinthetoiletroomdoorasthemeanstomakeupairtooffsetexhaust.Thisarrangementwasintendedtorepresentairtransferredviaagrille,adoorundercutorboth.Afterearlyresultsdem-onstratedpoordisplacementperformance,itwasdeterminedthatahighpercentageofthesupplyairwasshortcircuitingviathetoiletroom,limitingthedisplacementmechanismintheroom.At4ACH,thetotalsupplyairtothepatientroomwas114CFM.With78CFMexhaustedviathetoilet,68%ofthesupplyairwasbeingshortcircuited.Thetransfergrillewasrelocatedhighonthetoiletroomwall,abovetheoccupiedzone,andtheper-formanceoftheDVsystemimproveddramatically.
Figure20(seepage16)showsthattheperformanceoftheDVsystemat4ACH,withalow-leveltransfergrilletothetoilet,islessdesirableascom-paredwithanOHVsystemat6ACH.Whenthetransfergrilleislocatedathighlevel,however,theperformanceisbetterthanthatoftheOHVsystem.
Thisresearchdidnotevaluatethecomfortorventilationeffectivenessinthetoiletroom.Thisresearchalsodidnotevaluatetheeffectsofanopentoiletroomdoorforeitherdisplacementoroverheadsupply.Itisanticipatedtheperformancewouldbesimilartoalargerroomwithtwoexhaustgrillelocations.
b. MainRoomExhaustGrille
Themainroomexhaust(orreturn)grillewaslocatedintheceilingabovetheheadofthepatientbedforallnumericalcases.Thisloca-tionwasselectedbasedontheassumptionthatparticledispersionwouldbecontrolledtosomeextentbythelocationofthegrille.Numericalmodelingdemonstratedtheeffectivenessoftheexhaustgrillelocation.
Figures21and22(seepage16)compareparticleconcentrationsofthestandardoverheadarrange-mentat6ACHvs.displacementat4ACH,andshowthattheselectedexhaustlocationeffectivelylimitsthedispersionofparticlesintheoccupiedzoneandabove.
5.2.4 Impact of Ceiling HeightTwonumericalcaseswereconductedtotesttheimpactofroomceilingheightonthermalcomfortandventila-tioneffectiveness.RefertoCases11and12onTable3.
Itwasfoundthatincreasingtheceilingheightfrom9to12feetinthebasecaseonlyslightlyreducedtheventilationeffectiveness;however,thermalcomfortwasimproved.
Theadditionalvolumeintheupperleveloftheroomallowscontaminantsmorespaceabovetheoccupiedzoneinwhichtocollectbeforebeingventedout,whilecreatingalargervolumefortheairtofilloverall(whenevaluatingairchangeeffectivenessforthewholespace).Placingtheroomexhaustgrilleasclosetothepatientaspossible(i.e.,directlyabovethepatientbed),regardlessofceilingheight,willresultinthemostdirectpathforcontaminantremoval.
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report24
5.2.5 Impact of Movement on Displacement VentilationAdiscretestudywascompletedtotesttheimpactofmovingobjectsoncontaminantconcentrationdistribu-tioninasingle-bedpatientroomwithDVat4ACH.TheinvestigationalsoevaluatedacaseofOHVwith6ACHforcomparison.ThefulltestdetailsandresultsareincludedinAppendix7.6.
Fourdifferentmovingobjectsintheroomwerecon-sidered,foruptofoursecondsofmovements:avisitorwalkingnearthebedend;acaretakerwalkingalongthebedside;asheetbeingchangedoverthepatientbed,andaswingingdoor.
Thestudyfoundthat:
1. Themovingobjectscancarrythecontaminantintheirwakes.Themovementscancauseswingsinthecontaminantconcentrationinthebreathinglevelofsittingandstandingpositionsfor10to90seconds.Thevariationoftheaveragedcontami-nantconcentrationduetothemovingobjectswaswithin25%forallthecasesstudied.Thevaria-tionatthebreathinglevelwaslowerinthesittingpositionthaninthestandingposition.Sincethevariationlastedforlessthan90s,itwouldnotlikelychangetherisklevelinthepatientroom.
2. Atmosttimes,theDVsystemwith4ACHprovidedbetterairqualitythantheOHVsystemwith6ACH.Thewalkingvisitorandcaretakercouldexperiencealargeswingincontaminantlevelsduetobodymovementsintheward.How-ever,theswingwasgenerallyshort(about30s)soitwasnotlikelytochangetherisklevelforthevisitorandcaretaker.
3. Aroundthebedregionorclosetothecontami-nantsource,theDVsystemhadahighercon-taminantconcentrationthantheOHVsystem.However,inmostpartsoftheroom,theconcen-trationwaslower.
5.2.6 Impact of Coughing on Displacement VentilationAstudywascompletedtotesttheimpactofcoughingonairflowinasingle-bedpatientroom.ThefulltestdetailsandresultsareincludedinAppendix7.4.
Thesimulationresultsshowedthatalthoughthecoughingonlylastedaveryshortperiodoftime(about0.73s),amuchlongertimeperiod(upto5min)neededtobesimulatedinordertocapturetheeffectofthecoughingactivity.
Aroundthebed,whereacaregiverismostlikelytostand,theDVcaseshowedahighercontaminantconcentrationforashortperiodoftime,whileattheendofthesimulated5minutes,theconcentrationwaslowerthanthatwiththeOHVsystem.ThiscanbeexplainedbythefactthatDV‘confines’or‘contains’theconcentrationaroundthepatient,whileOHV-givenitsmixingnatureandhigherACH-isabletodilutethecontaminantbetteraroundthebed.Con-sistentwiththeabovediscussion,DVdeliversabetterconcentrationinthevisitorarea,asitisfurtherawayfromthepatient.
Whenlookingattheroomasawhole,theresultsachievedbythetwoventilationsystemintermsofresponsetocoughingwerecomparable.
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report 25
6.1 General RecommendationsThisresearchefforthasledtothefollowinggeneralrecommendationsfora4ACHDVsysteminasingle-bedpatientroom:
1. Insummertimewarmclimateconditions,accept-ableventilationeffectivenessandcontaminantcontrolcanbeachieved,providedthatthermalcomfortismaintained.
2. WhentheinternalthermalgainsexceedthecoolingcapacityoftheDVsystem,supplementarycooling,suchasradiantcooling,willhavetobeaddedtomaintaintherequiredroomairtempera-tureandcorrespondingthermalcomfort.
3. Supplementalheatingisrecommendedwhenheat-ingisrequired.
4. Thetransferairtothetoiletroomneedstobehigh,abovetheoccupiedzone.
5. Whilemultiplealternativemainexhaustgrillelocationswerenottestedfordisplacementventilation,thelocationabovetheheadofthepatientbedisrecommendedunlessanalternatelocationcanbeshowntobeanimprovementvianumericalmodeling.
6.2 Design StrategiesTheresultsofthenumericalandempiricalanaly-sisshowedthattheparticleremovalefficiencyandthermalcomfortofDVisdependentonanintegrateddesignapproachtoaddressbothwholesystemoptimi-zationandthermalcomfort.Thestudyidentifiedthefollowingroomlayoutandsystemdesignissuesthatneedtobecarefullyconsidered:
1. ThecoolingcapacityofaDVsystemislimitedbytheminimumallowablesupplyairtemperaturerequiredtomaintainthermalcomfort.
2. RoomthermalgainsandlossesmustbecontrollediftheperformanceoftheDVsystemistobemain-tained,i.e.:
a. Facadesshouldbedesignedtominimizethethermalgainsandlossestopreventwarmandcoldsurfaces,especiallywithrespecttoglazing.ThewarmsurfacescouldaffecttheDVairflow.
b. Manualorautomaticsolarshadingdevicesshouldbeinstalledtominimize/eliminatedirectsolargains.Thefieldtestsshowedthatfloorsurfaceswarmedupbydirectsolargainscanactasathermalhotspot,creatinglocal-izedthermalchimneys,andcausingmostofthedisplacementsupplyairtoshortcircuitthebreathinglevel.
c. Lightingandmedicalequipmentloadsshouldbeminimized.
3. DVshouldnotbeusedforspaceheating,i.e.:
a. Providingsupplyairfromthelowsidewalldis-placementdiffuseratahighertemperaturethantheroom’stemperaturewillresultindecreasedperformanceoftheDVsystem.
b. Whenusingasupplementalheatingmethodsuchasradiantorconvectivebaseboardheat-ing,theperformanceoftheDVcanbemain-tained,ifnotimproved.
4. TheplacementoftheDVsupplyairdiffuserisnotcritical,butshouldbecoordinatedwiththeroomdesign.Thediffusershouldbelocatedatlowlevelinalocationthatwillnotbeblockedwithsolidfurnituresuchasastoragecabinet.
5. Thetoilettransfergrilleshouldbelocatedathighlevel.TheempiricalexperimentsshowedthattheDVeffect/pluming/highlevelremovalofairborneparticlescanbeseriouslyaffectedifthesupplyairisallowedtoshortcircuitatlowlevel,directlyintothetoiletroom.
6.R E C O M M E N D AT I O N S
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report26
7.1 Terminology and Abbreviations
Terminology and AbbreviationsTerm Definition
ACH Air Changes Per Hour
AHJ Authority Having Jurisdiction
CFD Computational Fluid Dynamics
CFM Cubic Feet Per Minute
DV Displacement Ventilation
FGI Facilities Guideline Institute
FPM Feet Per Minute
HVRC Healthcare Ventilation Research Collaborative
OHV Overhead Ventilation
PPD Percentage of People Dissatisfied
PPM Parts Per Million
7.2 HVRC Advisory Committee
HVRC.ADVISORY.COMMITTEE
1. Dr.PaulJensen,PhD,PE,CIH,Captain,EngineerDirector,CentersforDiseaseControlandPrevention
2. Dr.FarhadMemarzadeh,Ph.D.,P.E.fromNIH
3. Dr.MicheleR.Evans,DrPHfromNIH
4. Dr.BernardT.Baxter,PhD,MD,UniversityofNebraskaMedicalCenter
5. Dr.AnjaliJoseph,PhD,DirectorofResearch,CenterforHealthDesign
6. ChrisRousseau,P.E.,Newcomb&Boyd
7. JeffereyHardin,DeputyDirectorofMedicalFacilitiesCenterofExpertise,USArmyCorpsofEngineers
7.A P P E N D I C E S
Healthcare Ventilation Research Collaborative: Displacement Ventilation Research – Phase II Summary Report 27
Appendices7.3-7.6areavailableintheonlineversion.Toviewtheseappendices,gotohttp://www.noharm.org/lib/downloads/doc_index.php
•7.3EmpiricalTesting
•7.4NumericalTesting
•7.5StatisticalAnalysis
•7.6MovementStudy
Health Care Without Harm12355 Sunrise Valley Drive, Suite 680 Reston, VA 20191 USAwww.noharm.org
Environmental and Occupational Health SciencesUniversity of Illinois at Chicago School of Public Health835 S. Wolcott, Suite E-144, MC 684Chicago, Illinois 60612