Campos, LC

Canales, ME

Carpentieri, M

Ciric, L

Nasir, ZA

UCL Discovery

Efficacy of ultraviolet germicidal irradiation based portable air cleaningdevices in built environments: Impact of environmental conditionsZ.A.Nasir1*, M. Carpentieri1, L.Campos1, L.Ciric1 and M. Canales11Healthy Infrastructure Research Centre, Department of Civil, Environmental and GeomaticEngineering, University College London, WC1E 6BT, UK*Corresponding email: z.nasar@ucl.ac.ukKeywords: PAC, UVGI, Environmental conditions1 IntroductionPortable air cleaning (PAC) devices are populardue to their low noise emission, highergonomics and user friendly interface.Currently, a wide variety of PAC technologiesexists (e.g. filtration, ionization, oxidation,electrostatic precipitation, ultraviolet germicidalirradiation (UVGI)). PAC devices based onUVGI have an impact on air hygiene and reducethe risk of aerosol disease transmission indifferent built environments.Few studies have been carried out on theireffectiveness under different environmentalconditions. These studies, which employedmodels or were conducted within test chamberswith controlled aerosol generation, have shownthat variables such as particle size, air cleanertechnology and position of the air cleaner in aroom can affect air cleaner performance(Novoselac and Siegel, 2009; Zuraimi et al.2011). However, real life built environments arenot well mixed and often have considerablespatio-temporal variation in pollutantconcentration and complex air flow patternsbetween different spaces or even within thesame enclosed space.This paper provides the preliminary results of astudy that aims to use a UVGI-based PACdevice as an example to demonstrate the impactof environmental conditions on the efficacy ofdisinfecting airborne bacteria in anenvironmentally controlled chamber using bothexperimental and mathematical (ComputationalFluid Dynamics - CFD) models.2 Materials and MethodsInitial experimental measurements were carriedout in a secondary chamber (1m3) constructedinside a stainless steel environmental chamber(43.2 m3) and connected to a level II biosafetycabinet in an ante-chamber. A microbial solution(Serratia marcescens) was aerosolized into thechamber using a 6-jet nebulizer to test theefficacy of the UVGI-based PAC device. Afteraerosolization, an Andersen 6-stage viableimpactor containing Tryptone Soy Agar plateswas used to collect sequential air samples atpredetermined time intervals (3 minutes each) tocalculate the microbial decay rate over time. Thecolonies were enumerated and the total numbersof culturable colony forming units per cubicmeter (CFU/m3) were calculated for each stageof the Anderson impactor. Total counts for allthe stages were also calculated. Experimentswere carried out with the PAC device on and offunder poor air mixing and well air mixingconditions. Total and size resolved clean airdelivery rates (CADR) were computed by:CADR (m3/h) = V (KPAC − Kn)Where CADR is the clean air delivery rate(m3/h), V is the volume of the chamber (m3),KPAC is the first order decay constant with PACdevice turned on and Kn is the first order decayconstant with PAC device turned off. CFDsimulations carried out using ANSYS Fluent14.5. 3D meshes with various degrees ofrefinement were used to model the smallchamber with second order discretisation and arealizable k- turbulence model.3 Results and discussionThe performance of the PAC device variedunder different air mixing conditions and higherair cleaning efficacy was observed under wellmixed air condition. Overall, the CADR for poorand well mixed air conditions were 16 m3h-1 and23 m3h-1, respectively. Figure 1 and 2 show thebacterial decay rates under poor and well mixedair conditions.Figure 1. Bacterial decay rates with the PAC device turnedon and with the PAC device turned off under poor mixedair conditions.Figure 2. Bacterial decay rates with the PAC device turnedon and with the PAC device turned off under well mixedair conditions.With reference to size resolved efficacy, a trendof higher performance was observed in fine sizefractions (in the size range of 1.1-2.1 µm and0.65-1.1µm ).Figure 3. Initial computational mesh for the CFDsimulations of the PAC within the secondary chamber.Some preliminary runs of the CFD model wereperformed to assess its capabilities and extendthe scope of the experiments. The simulationshelped visualise the air pathlines, highlightingthe complex flow established even within thissmall secondary chamber. Further analyses andmore simulations are in progress which shouldhighlight the difference in residence time of theparticles.Figure 4. Air pathlines calculated by the CFD model,coloured by velocity magnitude.4 ConclusionsInitial experimental results have shown aconsiderable variation in CADR under differentair mixing conditions. The CFD simulationshave highlighted the complex behaviour of airwithin the small chamber and will be used toinvestigate different environmental conditionsand room sizes. The experimental measurementsare currently being extended to main chamberunder different air mixing conditions.AcknowledgementsThis study is funded by the Engineering andPhysical Science Research Council, UnitedKingdom, grant reference EP/G029881/1. M.Carpentieri is funded by FP7/2007- 2013 –242497.5 ReferencesNovoselac A, and Siegel J A. 2009. Impact ofplacement of portable air cleaning device inmultizone residential environments. Buildingand Environment, 44(12), 2348-2356.Zuraimi M S, Nilsson G J, Magee R J. 2011.Removing indoor particles using portable aircleaners: Implications for residential infectiontransmission. Building and Environment,46(12), 2512-2519.View publication stats

Efficacy of ultraviolet germicidal irradiation based portable air cleaning devices in built environments: Impact of environmental conditions

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Efficacy of ultraviolet germicidal irradiation based portable air cleaning devices in built environments: Impact of environmental conditions

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