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WirthResearchBuildingSimulationandAirborneInfection
05/05/21
ProfDarrenWoolfCIBSEBuildingSimulationGroupChair&HeadofBuildingPhysics,WirthResearch
©2020WirthResearchLtd.Allrightsreserved.PrivateandConfidential.
• Whatarethekeyairborneinfectionsimulationandanalysistoolscharacteristicsandconsiderations?• Whatnewtoolsandapplicationsareonthehorizon?• Whatcouldmovingforwardusingthesetoolsandapplicationslooklike?
Keyquestions
2
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Toolscharacteristicsandconsiderations
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Somespatial,temporalandbuildingsciencedisparities
4
Experimental/fieldwork• Limitedmeasurementssometimessingle
pointbyzone
• Sometimeshighfrequencysampling(not
ifidentificationneeded)
• Sampleresiliencefromcapturetotesting• Proxiesversuslimitedbiology&
epidemiologyatmicroscale
Dynamicthermalmodelling(DTM)• Multi-mixed-zoneDTM(oftencoarsezones)
• Typicallyonehourtimesteps–limitedto6min
intervals?
• Detailedsystemsmodelsandcontrolspossible
• Goodcaptureofsurfacetemperaturesimportantforbuoyancy-drivenflows
Analytical/simple(?)tools• Singlepoint/mixed-zoneoutputs
• Steadystateortransientdefinedbycalculationtype
• Simpleorcomplexphysics
Computationalfluiddynamics(CFD)modelling• Detailedairmovement– advancedaerosol
turbulence/mixing/transportcapture
• Mainlysteady-statebutcouldbeminutes(not
practicallyhours)
• Somedetailedsourceorreceptormodelspossible
Limitedbiology&epidemiologyintools/modelsbutstillusefulfordesignpurposes!
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Findingthebalancebetweenenvironmentalqualityandenvironmentefficiency
5
Asventilationrateé,concentrationêandenergydemandéAGuidetoEnergyEfficientVentilation,Liddament1996
/safety
CIBSEEvent‘Indoorair
quality,airdistributionand
ventilation:Strikingabalance
betweenqualityand
efficiency’,January2012
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Treatmentofsourcesandreceptors
DrAbigailHathway‘CFDModellingofPathogenTransportduetoHumanActivity’,UniversityofLeedsPhD,2008(nowUniversityofSheffield&AIRBODS)
6
Simplermulti-zonemodelsarecomparedtoCFDandfoundtoperformwellatsimulatingthebioaerosoldecaywithinlarge
spacesthatcanbeassumedtobewellmixed,howevertheyare
notrefinedenoughtosimulatethedetailrequiredtostudythe
transferofinfectionbetweenindividualpatients.
Manyquestionstotranslateintoacceptedsimulationandanalysisinputs,
forexample:
• Onsourceside,isadifferentapproachneededformasksand
impactofairmovementoverbody?• Onreceptorside,whatcanwelearn
frompreviousinhalereffectiveness
researchtoguideourventilationrisk
models(smallerdropletsdeposit
deeperintorespiratorytract)?
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Definingacceptabletolerances
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• Fillingunknownepidemiologicalrangeswith‘sensibleassumptions’(low,mediumorhigh)ormoresimplifiedcalculations
untilmoreaccurateinformationandmethodsbecomeavailable
• Recognizingsensitivityofproposedventilationstrategieswiththeirassociatedsizingthroughsensitivitytesting
• Isitpossibletodefineanacceptabletoleranceinrealworldscenarios(outsidetestchambers)notingspatial,temporalandbuildingscience
disparities?
• Doesthisreallymatterwhenobjectiveistospecifypractical,viable
designsolutionswithsufficientoperationalflexibility?
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Designofscenarios
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• Batchingofsourcesfordesignpurposes,e.g.doesahighlyinfectiousscenariowithamaskequatetoalessinfectiousonewithoutone?
• Tabulatingdifferentactivity/facecoveringscenariosfordifferenttoolsandmodels,e.g.recognizingdifferentinputformats
• Positioningofreceptors,e.g.manikinsversusmixed-zoneorbreathingzonefora
childinpushchair• Occupancydensitywithsingleormultipleactivities
• Whatboundariesarerecommendedforperformance-leddesign?
• Howmuchstandardizationisneededinsupportofdesignconsistency?
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Newtoolsandmethods
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DTMwithadvancedcontrols
10
StandardCO2control:• Ventsopenat1000ppm
• LowCO2
IAQcontrolstrategywithhighCO2setpoint
Highlights:• Highairchangerate• HighPM2.5(peak
above40µg/m³)
• Energyuse(heating)145Wh/m²/day
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DTMwithadvancedcontrols
11
Revisedcontrolstrategy:• RelaxCO2setpoint(1500ppm)
• CloseventsifoutdoorPM2.5above
threshold
HolisticIAQcontrolstrategyrequiringextracoding
Highlights:• OutdoorPM2.5aboveindoorPM2.5(peak
below40µg/m³)
• Energyuse(heating)105Wh/m²/day
(28%lessduetorelaxationofCO2limit)
Whatwouldanairborneinfectioncontrolstrategylooklike?UseofIAQproxiesforairborneinfection?CalculatingUV&filtrationsystemvalue?
CIBSEBSGEvent‘HackingSimulation’,March2018https://www.cibse.org/networks/groups/building-simulation/bsg-past-presentations
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CFDwithbiophysicsHighlights
• Evaporation+Langrangianparticletracking+aerosoldropletnuclei(dispersion)models-two-phaseflow
• Evaporationratedependentuponmoisturecontentandairtemperature
• Stickyornon-stickysurfacesforparticledeposition• Gridofsources1.5mabovefloorlevelappliedtofixedvectorfield
• Nearfieldlargerdropletsandaerosolscontinuumsizechangeandtransport(horizontallyandvertically)
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Dropletdiameterdecayovertime
Effectofevaporationandairspeedondropletsize
Userdefinedfunctionsbaseduponexperimentaldata
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CFDwithbiophysics
13
PollutantRemovalEffectiveness(basicderivedoutput)
PRE
OpenAirservice@WirthResearch
HighPREgood?
Contaminantvulnerabilityorrevisedsocialdistancing(baseduponuserdefinedrelationships)
1mdistance(minimum)
2mdistancerequired
3mdistancerequired
>5mdistancerequired5mdistancerequired
4mdistancerequired
Notinareaswherehorizontalairmovementdominate
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Movingforward
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Newprojectscopes?(I)
15
• Over-occupancyriskassessment• UpgradingthermalcompliancemodelstothermalperformancemodelswithIAQ
proxiesforairborneinfection(0.5-1.0dayswork?)
• Testforallowableupperoccupancydensityindifferentspacetypes• Breathingzoneventilationefficiencytests• Includebreathingzoneairchangeratesinadditiontoroomairchangeratesfor
minimumfreshairguidance
• Definingairborneinfectionventilationcontrolmodes• Forahybridsystemoperatingincoolnaturalventilationmode,atwhatpoint
doesthespacebecometoocoldandtoopoorlyventilatedforsafeairborne
infectionlimits?• Whatcombinationofenvironmentalwithbiophysicsmeasuresareappropriate
todrivetheswitchtomechanicalheatingmode?’
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Newprojectscopes?(II)
16
• Roomcornersafetychecks• Cooler-than-ambientsurfacetemperaturesdrawpolluted
airdownwards.What’stherisktothecornerbreathingzone
whereairmovementisreduced?
• Designingforsecureventilation• Windowventilationflowraterestrictedbyblindorcurtain
usageandmayclosewindowduetosecurityfears
• Howcanwedesignmoresecureventilationsystemsto
improvepurgeventilation,e.g.naturallytemperedsupplyairentryawayfromthebuildingperimeter? Moreairbricksplushit&miss
floorventsair-connectedto
thechimneystacks?
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Understandingairborneinfectiondynamics
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• Coachloadofpeopleovershortperiod• Personsmovingandturning–impactonemissionsourcesand
turbulentmixing
• Buildupanddecayindifferentdesignscenarios• Defininganairborneinfectioncontrolmodeinconsiderationofthe
dynamics–purgeventilation?• Doorsopening,closingandrevolving• Lifts• Reanimationofparticlesoffsurfaces,e.g.throughbedmaking
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Increasedairborneinfectionresiliencethroughincreased
climatechangeresilience?
Timeofchangedthinking?
18https://www.cibsejournal.com/general/florence-nightingale-nurse-and-building-engineer/
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/753688/Prevention_is_better_than_cure_5-11.pdf
https://news.sky.com/story/ella-kissi-debrah-death-legally-binding-targets-for-particulate-matter-pollution-should-be-set-coroner-warns-12282251
https://www.hsph.harvard.edu/news/hsph-in-the-news/air-pollution-linked-with-higher-covid-19-death-rates/
https://www.weforum.org/agenda/2020/04/link-between-air-pollution-covid-19-deaths-coronavirus-pandemic/
Importanceofventilationinensuringtheswiftrecovery
ofpatientsandreducing
cross-infection
https://www.ukcleanair.org&http://breathingcity.org
https://www.ukcolumn.org/article/grenfell-tower-and-search-truth
BuildingSafety&Competence–‘Engineersneedtostudydisasters’
Façadefocusinitiallymovingto
overheatingandthenpollutionrisk?
https://earthobservatory.nasa.gov/world-of-change/global-temperatures
Holisticcoupledindoor-outdoorflows
‘Scientificadvancesthatcouldseelife-
threateningviraloutbreaksstoppedbefore
theystart’
https://www.kcl.ac.uk/news/air-pollution-restricting-childrens-lung-development
Long-termexposuretoairpollutionmaybe“oneofthemostimportant
contributorstofatalitiescausedbythe
COVID-19virus”aroundtheworld.
Stuntedchildlunggrowth!!!
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Acircleofresilienceandvirtuosity?Cooler&
cleanercitiesthrough
urbanbluegreening(?)
Morenaturallyventilatedbuildings
andexercisinglocally
Healthypopulation(physicaland
mental)
Increasedproductivityandassetvalue.Highergeared
funding.
Increasedairborne
infection&climatechange
resilience
POSITIVE
Hotter&dirtiercities
Moremechanicallyventilatedbuildingsandfilters/energyusage/exhausted
heat
Unhealthypopulation(physicaland
mental)
Reducedproductivityandassetvalue
Reducedairborne
infection&climatechange
resilience
NEGATIVE
Weneedtogetalotbetteratjoiningthedots!EarthwatchEuropewebinaronNature-BasedSolutions,‘Generatingurbancoolislandsusingbluegreensolutions’,DarrenWoolf
https://us02web.zoom.us/rec/share/Sy-IqOk_R4o6m9wt1AdzXn-GuFF9geNJ-AnlHMu8YVgcZrmePm_BmRVX791DufoX.1t6Tlsm-gLnYABhz
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Keyconsiderationsandchallengesmovingforward(I)
20
Improvingairborneinfectionresiliencethroughbetteruseofsimulationandanalysis:
• Betterunderstandingoftooluncertainties&toleranceswithassociatedspatial,temporaland
buildingsciencedisparities
• Betterdesignofscenariosfordifferentapproachesrecognizinglimitationsofeachapproachat
differentdesignstages• Integratingairborneinfectionthinkingintodigitaltwinswithbettercontrolstrategies• Replacingcurrentassumptionsorsimplifiedmethodswithbetterepidemiologicalevidence
whenitbecomesavailable–developmentofbiophysicsmodelsinbuiltenvironmentcontext
• Indirectlyimprovingairborneresiliencethroughdevelopingbetter-linkedbuildingsimulation
andanalysistoolstoguideapositive‘circleofresilienceandvirtuosity’• Improvedunderstandingofbreathingzonesandefficientdeliveryofdilutingairfordeveloping
betterairborneinfectionoperationalcontrolmodes
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Keyconsiderationsandchallengesmovingforward(II)
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Improvingairborneinfectionresiliencethroughbetterdesignpracticesandimprovedpolicies:
• Designingintelligentspacesforoptimumenergy/ventilationbalance
• DevelopingbetterunderstandingofoverlapbetweenIAQproxiesandairborneinfectioncontrolstrategiessupportingopportunitiesforincreasedhealthandproductivity
• Incorporatinglessonslearntfromhospital-acquiredinfections,currentairborneinfectionresearchandexpertbioaerosolscientistmetrics&practices(e.g.useofquanta,Wells-Riley&
doseresponsemethods)intomainstreambuildingdesignpractices
• Generallylookatdiseaseandventilationcontrolwithneweyes• Breakingsilosthroughadoptingmultidisciplinaryholisticdesignprocesses–betterprocurementofstudiesandservices!
• Betterregulationsandpoliciesinsupportofincreasedresilience,e.g.NewCleanAirActorEnvironmentalProtectionActtoincorporateairborneinfection?
• Weneedtopromotesaferenvironments,upskillandbebettercommunicators!
©2020WirthResearchLtd.Allrightsreserved.PrivateandConfidential.
www.wirthresearch.com
WirthResearchBuildingSimulationandAirborneInfection
05/05/21
ProfDarrenWoolfCIBSEBuildingSimulationGroupChair&HeadofBuildingPhysics,WirthResearch