Healthcare Ventilation Research Collaborative: Displacement Ventilation … · 2013-12-05 · 6 Healthcare Ventilation Research Collaborative: Displacement Ventilation Research –

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


3. DVshouldnotbeusedforspaceheating,i.e.:

a. Providingsupplyairfromthelowsidewalldis-placementdiffuseratahighertemperaturethantheroom’stemperaturewillresultindecreasedperformanceoftheDVsystem.

b. Whenusingasupplementalheatingmethodsuchasradiantorconvectivebaseboardheat-ing,theperformanceoftheDVcanbemain-tained,ifnotimproved.

4. Theplacementofthesupplyairdiffuserisnotcritical,butshouldbecoordinatedwiththeroomdesign.Thediffusershouldbelocatedatlowlevelinalocationthatwillnotbeblockedwithsolidfurnituresuchasastoragecabinet.

5. Thetoilettransfergrilleshouldbelocatedathighlevel.TheempiricalexperimentsshowedthattheDVeffect/pluming/highlevelremovalofairborneparticlescanbeseriouslyaffectedifthesupplyairisallowedtoshortcircuitatlowlevel,directlyintothetoiletroom.


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


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.


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


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.


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


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


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


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


Figure 17: 3ppm Iso-Surface for DV at 4 ACH with

High Supply Air Temperature

Figure 16: DV with Warmer Temperature Supply


Baseboard Heating


Radiant Heating Panels


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)


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).


• 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.


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


Winter Chicago -10F

Reduced 4 67.1 Radiant Heating

4 DV with Baseboard Heater


Winter Chicago -10F

Patient, Caregiver only

4 67.1 Baseboard Heater

5 Overhead 4ACH

Overhead Close to Window

Summer LA 105F


No

6 Overhead 4ACH


Winter Chicago -10F


4 Adjustable, up to 105F

No

7 DV at 4 ACH - w Radiant Cooling Panel


Summer LA 105F

Standard 4 67.1 Radiant Cooling

8 Overhead 6 ACH in Summer


Summer LA 105F


No

9 DV 4 ACH w Solar Loading


Summer Reduced Temp 97F

Standard 4 60 No

10 DV 4 ACH w High Supply Temperature


WinterChicago -10F


4 87F No

11 DV 4 ACH w 12’ Ceiling Height

Displacement Side wall above Patient

Summer LA 105F

Standard 4 60F No


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


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


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


8.258.5

1.231.06

1.451.38

1.311.19

1.39 1.62 0.830.80


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.


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).


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.


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.


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


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


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

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