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WirthResearchBuildingSimulationandAirborneInfection

05/05/21

ProfDarrenWoolfCIBSEBuildingSimulationGroupChair&HeadofBuildingPhysics,WirthResearch


• Whatarethekeyairborneinfectionsimulationandanalysistoolscharacteristicsandconsiderations?• Whatnewtoolsandapplicationsareonthehorizon?• Whatcouldmovingforwardusingthesetoolsandapplicationslooklike?

Keyquestions

2


Toolscharacteristicsandconsiderations


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!


Findingthebalancebetweenenvironmentalqualityandenvironmentefficiency

5

Asventilationrateé,concentrationêandenergydemandéAGuidetoEnergyEfficientVentilation,Liddament1996

/safety

CIBSEEvent‘Indoorair

quality,airdistributionand

ventilation:Strikingabalance

betweenqualityand

efficiency’,January2012


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)?


Definingacceptabletolerances

7

•  Fillingunknownepidemiologicalrangeswith‘sensibleassumptions’(low,mediumorhigh)ormoresimplifiedcalculations

untilmoreaccurateinformationandmethodsbecomeavailable

•  Recognizingsensitivityofproposedventilationstrategieswiththeirassociatedsizingthroughsensitivitytesting

•  Isitpossibletodefineanacceptabletoleranceinrealworldscenarios(outsidetestchambers)notingspatial,temporalandbuildingscience

disparities?

•  Doesthisreallymatterwhenobjectiveistospecifypractical,viable

designsolutionswithsufficientoperationalflexibility?


Designofscenarios

8

•  Batchingofsourcesfordesignpurposes,e.g.doesahighlyinfectiousscenariowithamaskequatetoalessinfectiousonewithoutone?

•  Tabulatingdifferentactivity/facecoveringscenariosfordifferenttoolsandmodels,e.g.recognizingdifferentinputformats

•  Positioningofreceptors,e.g.manikinsversusmixed-zoneorbreathingzonefora

childinpushchair•  Occupancydensitywithsingleormultipleactivities

•  Whatboundariesarerecommendedforperformance-leddesign?

•  Howmuchstandardizationisneededinsupportofdesignconsistency?


Newtoolsandmethods


DTMwithadvancedcontrols

10

StandardCO2control:•  Ventsopenat1000ppm

•  LowCO2

IAQcontrolstrategywithhighCO2setpoint

Highlights:•  Highairchangerate•  HighPM2.5(peak

above40µg/m³)

•  Energyuse(heating)145Wh/m²/day


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


CFDwithbiophysicsHighlights

•  Evaporation+Langrangianparticletracking+aerosoldropletnuclei(dispersion)models-two-phaseflow

•  Evaporationratedependentuponmoisturecontentandairtemperature

•  Stickyornon-stickysurfacesforparticledeposition•  Gridofsources1.5mabovefloorlevelappliedtofixedvectorfield

•  Nearfieldlargerdropletsandaerosolscontinuumsizechangeandtransport(horizontallyandvertically)

12

Dropletdiameterdecayovertime

Effectofevaporationandairspeedondropletsize

Userdefinedfunctionsbaseduponexperimentaldata


CFDwithbiophysics

13

PollutantRemovalEffectiveness(basicderivedoutput)

PRE

OpenAirservice@WirthResearch

HighPREgood?

Contaminantvulnerabilityorrevisedsocialdistancing(baseduponuserdefinedrelationships)

1mdistance(minimum)

2mdistancerequired

3mdistancerequired

>5mdistancerequired5mdistancerequired

4mdistancerequired

Notinareaswherehorizontalairmovementdominate


Movingforward


Newprojectscopes?(I)

15

•  Over-occupancyriskassessment•  UpgradingthermalcompliancemodelstothermalperformancemodelswithIAQ

proxiesforairborneinfection(0.5-1.0dayswork?)

•  Testforallowableupperoccupancydensityindifferentspacetypes•  Breathingzoneventilationefficiencytests•  Includebreathingzoneairchangeratesinadditiontoroomairchangeratesfor

minimumfreshairguidance

•  Definingairborneinfectionventilationcontrolmodes•  Forahybridsystemoperatingincoolnaturalventilationmode,atwhatpoint

doesthespacebecometoocoldandtoopoorlyventilatedforsafeairborne

infectionlimits?•  Whatcombinationofenvironmentalwithbiophysicsmeasuresareappropriate

todrivetheswitchtomechanicalheatingmode?’


Newprojectscopes?(II)

16

•  Roomcornersafetychecks•  Cooler-than-ambientsurfacetemperaturesdrawpolluted

airdownwards.What’stherisktothecornerbreathingzone

whereairmovementisreduced?

•  Designingforsecureventilation•  Windowventilationflowraterestrictedbyblindorcurtain

usageandmayclosewindowduetosecurityfears

•  Howcanwedesignmoresecureventilationsystemsto

improvepurgeventilation,e.g.naturallytemperedsupplyairentryawayfromthebuildingperimeter? Moreairbricksplushit&miss

floorventsair-connectedto

thechimneystacks?


Understandingairborneinfectiondynamics

17

•  Coachloadofpeopleovershortperiod•  Personsmovingandturning–impactonemissionsourcesand

turbulentmixing

•  Buildupanddecayindifferentdesignscenarios•  Defininganairborneinfectioncontrolmodeinconsiderationofthe

dynamics–purgeventilation?•  Doorsopening,closingandrevolving•  Lifts•  Reanimationofparticlesoffsurfaces,e.g.throughbedmaking


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!!!


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


Keyconsiderationsandchallengesmovingforward(I)

20

Improvingairborneinfectionresiliencethroughbetteruseofsimulationandanalysis:

•  Betterunderstandingoftooluncertainties&toleranceswithassociatedspatial,temporaland

buildingsciencedisparities

•  Betterdesignofscenariosfordifferentapproachesrecognizinglimitationsofeachapproachat

differentdesignstages•  Integratingairborneinfectionthinkingintodigitaltwinswithbettercontrolstrategies•  Replacingcurrentassumptionsorsimplifiedmethodswithbetterepidemiologicalevidence

whenitbecomesavailable–developmentofbiophysicsmodelsinbuiltenvironmentcontext

•  Indirectlyimprovingairborneresiliencethroughdevelopingbetter-linkedbuildingsimulation

andanalysistoolstoguideapositive‘circleofresilienceandvirtuosity’•  Improvedunderstandingofbreathingzonesandefficientdeliveryofdilutingairfordeveloping

betterairborneinfectionoperationalcontrolmodes


Keyconsiderationsandchallengesmovingforward(II)

21

Improvingairborneinfectionresiliencethroughbetterdesignpracticesandimprovedpolicies:

•  Designingintelligentspacesforoptimumenergy/ventilationbalance

•  DevelopingbetterunderstandingofoverlapbetweenIAQproxiesandairborneinfectioncontrolstrategiessupportingopportunitiesforincreasedhealthandproductivity

•  Incorporatinglessonslearntfromhospital-acquiredinfections,currentairborneinfectionresearchandexpertbioaerosolscientistmetrics&practices(e.g.useofquanta,Wells-Riley&

doseresponsemethods)intomainstreambuildingdesignpractices

•  Generallylookatdiseaseandventilationcontrolwithneweyes•  Breakingsilosthroughadoptingmultidisciplinaryholisticdesignprocesses–betterprocurementofstudiesandservices!

•  Betterregulationsandpoliciesinsupportofincreasedresilience,e.g.NewCleanAirActorEnvironmentalProtectionActtoincorporateairborneinfection?

•  Weneedtopromotesaferenvironments,upskillandbebettercommunicators!


www.wirthresearch.com

WirthResearchBuildingSimulationandAirborneInfection

05/05/21

ProfDarrenWoolfCIBSEBuildingSimulationGroupChair&HeadofBuildingPhysics,WirthResearch

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