Search

The spreading of a disease largely occurs in buildings or in collective transport. The microenvironment flow processes around people contribute to the cross-infection risk, for example when two persons are standing close to each other. The cross-infection risk is also dependent on the macro-environment e.g. distribution of velocity and turbulence in the room, particularly when the background airflow is strong. The surrounding temperature and the presence of a vertical temperature gradient can also modify airflows in the microenvironment and subsequently influence the cross-infection risk. This work is based on a fully mixed flow in a room without a vertical temperature gradient, considering different room temperatures.Exhalation flow and aerosol distribution are studied by smoke experiments and the cross-infection risk is expressed as concentration in the susceptible breathing zone normalized by the concentration in the room.

Gennem tiderne har vi haft forskellige pandemier. Men med coronapandemien er det blevet tydeligt, at det er virus transporteret i dråber, i luften og ved nærkontakt, der er problemet. Det betyder, at vi skal revidere kravene til indeluft og tage højde for infektionsrisiko. Vi er nødt til at revolutionere måden, hvorpå vi ventilerer, filtrerer og renser luften i vores bygninger og offentlige opholdsrum, for at vi kan være langt bedre rustet, end vi er i dag, når næste pandemi rammer. Det kalder på et paradigmeskifte. Sammen med 40 internationale forskere fra 14 lande har vi skrevet en artikel, som er blevet publiceret i tidsskriftet Science med titlen ”A paradigm shift to combat indoor respiratory infection” (Morawska et al. 2021). Vores hovedbudskab er, at fokus i bygningsreglementer, standarder og guidelines vedrørende indeluftkvalitet bør opprioriteres og ændres fra komfort til helbred. Det betyder, at kvaliteten af luft i bygninger, hvor der færdes mennesker, skal prioriteres i en helt anden grad, end den bliver i dag. Når der i dag tales om god luftkvalitet, er der i de fleste tilfælde kun fokus på komfort, altså temperatur, og behagelig luft (EN 16798, 2020). Det bør ændres, så der fremover bliver taget højde for helbred og infektionsrisiko gennem indeluften, ligesom man i dag tager højde for helbredet gennem krav til håndtering af vand og fødevarer. I dag bliver luftens kvalitet prioriteret med hensyn til helbred hovedsagelig på sygehusene eller i andre specielle miljøer. Men det vil kræve et paradigmeskifte inden for bygningers tekniske installationer, hvis det samme skal gælde i alle bygninger.

Det Nationale Forskningscenter for Arbejdsmiljø (NFA) har i det forløbne år været vært for et velbesøgt møde om støv i udeluften, indeklimaet og i arbejdsmiljøet. Abstracts herfra ses i dette nummer af "Sundhed og Miljø".

Povl Ole Fanger har haft – og har stadig – en kæmpe indflydelse på, hvordan vi i dag tænker indeklima og ventilation i vores bygninger.Hans banebrydende arbejde og vejen til hans resultater er nu blevet samlet i en helt unik bog, hvor flere af hans nationale og internationale kolleger har bidraget til historien om personen Professor P.O. Fanger.Bogen er blevet til ved et kæmpe arbejde udført af frivillige kræfter i Danvak samt økonomiske bidrag fra fonde og virksomheder. Bogen sælges i Danvaks boghandel, se link herunder.

To indeklimaeksperter fra BUILD, professor Peter V. Nielsen og lektor Chen Zhang på Aalborg Universitet skriver om luftbåren smittespredning.Artiklen diskuterer ”smittespredning, både i nærfeltet og i fjernfeltet mellem personer” og viser eksempler på ” betydningen af personers orientering, afstand imellem personer samt indflydelsen af ventilationssystemet”. Artiklen er rigt illustreret med tegninger, der f.eks. viser overførsel af virus mellem to personer, der står over for hinanden i forskellig afstand.

Har du endnu ikke haft corona og vil gerne undgå det? Så kan det være en god idé ikke at pakke mundbindene helt væk endnu, skriver de to forskere.

How should we design our homes, offices and buildings in the future so that they become more robust in relation to COVID-19 and future pandemics? It has medics from i.a. The Statens Seruminstitut, ventilation technicians and architects set out to investigate.

A CFD workshop on a geometry that can be typical for deep buildings and tunnels took place in 2015 at the ISHVAC-COBEE 2015 conference. The fluid problem investigated in the workshop is known as the backward facing step flow. Members of the workshop made Computational Fluid dynamics (CFD) predictions of the air distribution without having measurements for comparison. Their results show a significant diversity, among other things due to the chosen turbulence models.A benchmark for the backward-facing step flow is introduced to validate the numerical predictions as well as to assess the influence of different turbulence models, wall functions and other important elements of the software.

A novel ventilation system is presented in this study, named diffuse wall ventilation. The system is suitable for renovation projects, where the low ceiling and visible inlet and ducts are not accepted due to space limitation and design preference. The ventilation performance is evaluated by the numerical method under different operating conditions and inlet configurations. The CFD results indicate that diffuse wall ventilation creates a stratified flow pattern that is comparable to displacement ventilation. Due to the large inlet area, the air velocity in the occupied zone is much lower than displacement ventilation. The half-wall inlet provides the best performance in preventing cross-infection between occupants. The personal exposure index εexp for the target person is up to 11.8, the values with the full-wall inlet and lamella inlet are 2.16 and 5.04, respectively. This study indicates that diffuse wall ventilation is a promising ventilation principle for office buildings with low ceiling height.

Hvordan bør fremtidens boliger, kontorer og bygninger indrettes, så større robusthed opnås ift. COVID-19 og kommende pandemier? Dette har bl.a. medicinere fra Statens Seruminstitut, ventilationsteknikere og arkitekter undersøgt.Håbet er at dette projekt fremadrettet vil danne grundlag for videre forskning og indsatser for at vores bygninger og fremtidige byggerier bliver sundere, bedre og med væsentlig reduceret smitte risiko imellem mennesker.

The Covid-19 pandemic has caused untold disruption and enhanced mortality rates around the world. Understanding the mechanisms for transmission of SARS-CoV-2 is key to preventing further spread but there is confusion over the meaning of “airborne” whenever transmission is discussed. Scientific ambivalence originates from evidence published many years ago, which has generated mythological beliefs that obscure current thinking. This article gathers together and explores some of the most commonly held dogmas on airborne transmission in order to stimulate revision of the science in the light of current evidence. Six ‘myths’ are presented, explained, and ultimately refuted on the basis of recently published papers and expert opinion from previous work related to similar viruses. There is little doubt that SARS-CoV-2 is transmitted via a range of airborne particle sizes subject to all the usual ventilation parameters and human behaviour. Experts from specialties encompassing aerosol studies, ventilation, engineering, physics, virology and clinical medicine have joined together to present this review, in order to consolidate the evidence for airborne transmission mechanisms and offer justification for modern strategies for prevention and control of Covid-19 in healthcare and community.

Hvordan bør fremtidens boliger, kontorer og bygninger indrettes, så større robusthed opnås ift. COVID-19 og kommende pandemier? Dette har bl.a. medicinere fra Statens Seruminstitut, ventilationsteknikere og arkitekter undersøgt. Håbet er at dette projekt fremadrettet vil danne grundlag for videre forskning og indsatser for at vores bygninger og fremtidige byggerier bliver sundere, bedre og med væsentlig reduceret smitte risiko imellem mennesker. Denne rapport er kommet til, ved et stærkt samarbejde mellem ildsjæle indenfor medicin, ventilation og arkitektur. Inden projektet fik den fornødne økonomiske støtte og blev igangsat, er der udført et stort forarbejde. Dette forarbejde blev opstartet umiddelbart efter vores Statsminister lukkede Danmark ned den 11. marts 2020. Hen over foråret og sommeren 2020 blev projektopgaven defineret og sent efterår 2020 kunne projektarbejdet opstartes, da den nødvendige finansiering blev tilvejebragt. Rapporten er opdelt i 5 tekniske dele, som alle kan læses individuelt. De omhandler medicinske-, arkitekt-, ventilations- og drift og vedligeholdsperspektiverne for begrænsning af smittespredning i bygninger samt en rapport del der omhandler målemetoder.Rapporten er til sidst samlet et mere populistisk skrevet Resumé, som tager udgangspunkt i de vigtigste punkter fra de tekniske dele af rapporten. Sluttelig er der udarbejdet en konklusion. Resumé og konklusion findes i Del 6 og 7.Inden rapporten blev færdigskrevet, blev der afholdt en konsensuskonference med udvalgte deltagere, rapporten fra denne konference findes i Del 8 – bilag 1.

CFD is one of the most important approaches for predicting and evaluating the airflow in the indoor environment. Although there has been a continuous improvement of computer performance and CFD technology in the past few decades, the uncertainty in CFD prediction remains high due to the user dependency on building meshes, selecting turbulence models, defining boundary conditions, and choosing numerical schemes. Benchmark tests are therefore an important approach to validate the CFD models and guide the selection of proper turbulence models under different flow regimes. This study aims to perform a benchmark test for the isothermal backward-facing step flow under different flow regimes. The benchmark test is conducted in a small-scale model and LDA is employed to identify airflow patterns. The benchmark results indicate that the SST k-ω model could be a good option to predict low turbulent flow while the Realizable k-ε and RSM models can be used for fully developed turbulent flow. CFD is one of the most important approaches for predicting and evaluating the airflow in the indoor environment. Although there has been a continuous improvement of computer performance and CFD technology in the past few decades, the uncertainty in CFD prediction remains high due to the user dependency on building meshes, selecting turbulence models, defining boundary conditions, and choosing numerical schemes. Benchmark tests are therefore an important approach to validate the CFD models and guide the selection of proper turbulence models under different flow regimes. This study aims to perform a benchmark test for the isothermal backward-facing step flow under different flow regimes. The benchmark test is conducted in a small-scale model and LDA is employed to identify airflow patterns. The benchmark results indicate that the SST k-ω model could be a good option to predict low turbulent flow while the Realizable k-ε and RSM models can be used for fully developed turbulent flow.

Hvordan konverterer vi med kort varsel rum i skoler og andre bygninger til midlertidige isolationsrum for at aflaste sundhedsvæsenet ved fremtidige spidsbelastninger?

The report express some thoughts about the influence of the air distribution on droplet infection and airborne cross infection. The text is based on full-scale experiments with tracer gas and numerical simulation.First: what is the difference between droplet infection and airborne infection?

The following scientists reviewed the document: Jonathan Abbatt, John Adgate, Alireza Afshari, KangHo Ahn, Francis Allard, Joseph Allen, Celia Alves, Meinrat O. Andreae, Isabella Annesi-Maesano, Ahmet Arısoy, Andrew P. Ault, Gwi-Nam Bae, Gabriel Bekö, Scott C. Bell, Allan Bertram, Mahmood Bhutta, Seweryn Bialasiewicz, Merete Bilde, Tami Bond, Joseph Brain, Marianna Brodach, David M. Broday, Guangyu Cao, Christopher D. Cappa, Annmarie Carlton, Paul K. S. Chan, Christopher Chao, Kuan-Fu Chen, Qi Chen, Qingyan Chen, David Cheong, Per Axcel Clausen, Ross Crawford, Derek Clements-Croome, Geo Clausen, Ian Clifton, Richard L. Corsi, Benjamin J. Cowling, Francesca Romana d'Ambrosio, Ghassan Dbaibo, Richard de Dear, Gianluigi de Gennaro, Peter DeCarlo, Philip Demokritou, Hugo Destaillats, Joanna Domagala-Kulawik, Neil M. Donahue, Caroline Duchaine, Marzenna R. Dudzinska, Dominic E. Dwyer, Greg Evans, Delphine K. Farmer, Kevin P. Fennelly, Richard Flagan, Janine Fröhlich-Nowoisky, Manuel Gameiro da Silva, Christian George, Marianne Glasius, Allen H. Goldstein, João Gomes, Michael Gormley, Rafal Górny, David Grimsrud, Keith Grimwood, Charles N. Haas, Fariborz Haghighat, Michael Hannigan, Roy Harrison, Ulla HaverinenShaughnessy, Philippa Howden-Chapman, Per Heiselberg, Daven K. Henze, Jean-Michel Heraud, Hartmut Herrmann, Philip K. Hopke, Ray Horstman, Wei Huang, Alex Huffman, David S. Hui, Tareq Hussein, Gabriel Isaacman-VanWertz, Jouni J.K. Jaakkola, Matti Jantunen, Lance Jennings, Dennis Johansson, Jan Kaczmarczyk, George Kallos, David Katoshevski, Frank Kelly, Søren Kjærgaard, Luke D. Knibbs, Henrik N. Knudsen, GwangPyo Ko, Evelyn S.C. Koay, Jen Kok, Nino Kuenzli, Markku Kulmala, Kazukiyo Kumagai, Prashant Kumar, Kazumichi Kuroda, Kiyoung Lee, Nelson Lee, Barry Lefer, Vincent Lemort, Xianting Li, Dusan Licina, Chao-Hsin Lin, Junjie Liu, Kam Lun E. Hon, John C. Little, Li Liu, Janet M. Macher, Ebba Malmqvist, Corinne Mandin, Ivo Martinac, Dainius Martuzevičius, Mark J. Mendell, David Miller, Claudia Mohr, Luisa T. Molina, Glenn Morrison, Roya Mortazavi, Edward Nardell, Athanasios Nenes, Mark Nicas, Zhi Ning, Jianlei Niu, Hidekazu Nishimura, Colin O'Dowd, Bjarne W. Olesen, Paula J. Olsiewski, Spyros Pandis, Daniel Peckham, Tuukka Petäjä, Zbigniew Popiolek, Ulrich Pöschl, Wayne R. Ott, Kimberly Prather, Andre S. H. Prevot, Hua Qian, Shanna Ratnesar-Shumate, James L. Repace, Tiina Reponen, Ilona Riipinen, Susan Roaf, Allen L. Robinson, Yinon Rudich, Manuel Ruiz de Adana, Masayuki Saijo, Reiko Saito, Paulo Saldiva, Tunga Salthammer, Joshua L. Santarpia, John H. Seinfeld, Gary S. Settles, Siegfried Schobesberger, Paul T. J. Scheepers, Max H. Sherman, Alan Shihadeh, Manabu Shiraiwa, Jeffrey Siegel, Torben Sigsgaard, Brett C. Singer, James N. Smith, Armin Sorooshian, Jerzy Sowa, Brent Stephens, Huey-Jen Jenny Su, Jordi Sunyer, Jason D. Surratt, Kazuo Takahashi, Nobuyuki Takegawa, Jørn Toftum, Margaret A. Tolbert, Euan Tovey, Barbara J. Turpin, Annele Virtanen, John Volckens, Claire Wainwright, Lance A. Wallace, Boguang Wang, Chia C. Wang, Michael Waring, John Wenger, Charles J. Weschler, Brent Williams, Mary E. Wilson, Armin Wisthaler, Kazimierz Wojtas, Douglas R. Worsnop, Ying Xu, Naomichi Yamamoto, Xudong Yang, Hui-Ling Yen, Hiroshi Yoshino, Hassan Zaraket, Zhiqiang (John) Zhai, Junfeng (Jim) Zhang, Qi Zhang, Jensen Zhang, Yinping Zhang, Bin Zhao, Tong Zhu., Understanding the transmission of respiratory infections indoors requires expertise in many distinctly different areas of science and engineering, including virology, aerosol physics, flow dynamics, exposure and epidemiology, medicine, and building engineering, to name the most significant. No one person has expertise in all these areas. However, collectively, the community of the signatories to the Comment understands the characteristics and mechanisms behind the generation of respiratory microdroplets, survival of viruses in the microdroplets, transport of the microdroplets and human exposure to them, and the airflow patterns that carry microdroplets in buildings. We have dedicated our careers working in this multidisciplinary field, and our statement stems from our collective expertise spanning the entire field.

The present report describes the main findings of the research project “Increased potential for energy savings through increasing the cooling capacity further in diffuse ceiling ventilation”(Øget energibesparelsespotentiale ved yderligere forøgelse af kølekapaciteten ved diffus loftsindblæsning).The project has been carried out at Danish Building Research Institute (SBi) in collaboration with one industrial partner, Troldtekt company, Denmark and Department of Civil Engineering, Aalborg University. The project has been financially supported by ELFORSK, a research and development program administrated by the Danish Energy Association under sagsnr. 876175 and projekt nr. 349-065.The project was launched in April 2017and completed in March2019.

This paper concerns the use of Computational Fluid Dynamics (CFD) for the prediction of room air movement and provide a guide on selecting of the proper turbulence model. The benchmark which developed here for the first time is a backward-facing step flow problem. The measurements is performed in a small-scale model and the velocity filed is measured by Particle Image Velocimetry (PIV). The measurements focus on transitional flow and fully developed turbulent flow at isothermal condition. The PIV measurements and different CFD predictions are compared. The CFD predictions are generally slightly diverse, and this is, among other things, the result of using different turbulence models as well as using different software codes, grid distribution and boundary values etc. The k-ϵ family of turbulence models is an option for fully developed flow, and the k-ω family does work for transitional low turbulent flow in this backward-facing step flow.

Flow elements combined with a building energy simulation tool can be used to indicate areas and periods when there is a risk of draught in a room. The study tests this concept by making a tool for post-processing of data from building energy simulations. The objective is to show indications of draught risk during a whole year, giving building designers a tool for the design stage of a building.The tool uses simple one-at-a-time calculations of flow elements and assesses the uncertainty of the result by counting the number of overlapping flow elements. The calculation time is low, making it usable in the early design stage to optimise the building layout. The tool provides an overview of the general draught pattern over a period, e.g. a whole year, and of how often there is a draught risk.

The concept of air stability is derived from atmospheric stability, which represents the extent of stability of room air. Experiments on thermal manikin were performed to investigate the effect of air stability on the dispersion of exhaled flow. Seven cases with the combination of three ventilation patterns (no ventilation, mixing ventilation and displacement ventilation) and two breathing modes (continuous and periodic) were applied. The trajectory of exhaled flow was visualized and measured by smoke visualization and velocity measurement, respectively. The results show that both the continuous and periodic exhalation are significantly affected by the air stability with respect to the trajectory and velocity decay. Meanwhile, the turbulence highly develops in the periodic flow, making the contaminant mix well with the ambient air and the flow flatter in comparison with continuous jet. As the stable condition restrains the upward movement of the flow, it becomes flatter under stable condition compared with neutral condition even though they have similar Ar and body plume. In addition, the velocity decay is smaller for stable condition because it entrains less ambient air.

The characteristics of centre pivot roof windows for wind driven single-sided ventilation has not been studied before. These types of windows are dominating roof windows in Europe. Knowledge of flow characteristics of this kind of window is essential for accurate designing of natural ventilation systems. In this study, numerical methods were used to characterise a centre-pivot roof window for wind-driven single-sided ventilation. A 1:20 scale model house of the Energy Flex House (Denmark) was used in this study. The roof slope was 36o. It was found that the single-sided ventilation through the centre-pivot roof window can be characterised by a factor called the flow factor. The flow factor was a function of the sash opening-angle and wind direction. The flow factor increased with increase in opening-angle and decreased with increase in wind direction.

Traditionally, air is supplied to the aircraft cabin either by individual nozzles or by supply slots. The air is expected to be fully mixed in the cabin, and the system is considered to be a mixing ventilation system. This paper will describe different air distribution systems known from other applications namely: the traditional mixing ventilation, displacement ventilation, downward ventilation and finally a personalized ventilation system as well, which is used in addition to the other systems.The experiments are made in a full-scale left side section of a single-aisle (Boeing 737) cabin with four seats. The four persons are simulated by thermal manikins. Velocity, temperature and cross-infection risk are measured by hot spheres, thermocouples and tracer gas.

Downward flow ventilation systems are one of the most recommended ventilation strategies when contaminants in rooms must be removed and people must be protected from the risk of airborne cross-infection. This study is based on experimental tests carried out in a room with downward flow ventilation. Two breathing thermal manikins are placed in a room face to face. One manikin’s breathing is considered to be the contaminated source to simulate a risky situation with airborne cross-infection. The position of the manikins in relation to the diffuser and the location of diffuser in the room as well as the distance between the manikins are being changed to observe the influence of these factors on the personal exposure of the target manikin. The results show that the DWF in different situations often is unable to penetrate the microenvironment generated by the manikins. The downward ventilation system can give an unexpected high level of contaminant exposure of the target manikin, when the distance between the manikins is reduced.

At present mixing ventilation is mostly used in practice. Although it has been applied for many years the conditions for its optimal performance in practice are not widely understood. A new REHVA design guide book is giving an overview of the nature of mixing ventilation, design methods and its evaluation under laboratory conditions and in practice.

In this guidebook most of the known and used in practice methods for achieving mixing air distribution are discussed. Mixing ventilation has been applied to many different spaces providing fresh air and thermal comfort to the occupants. Today, a design engineer can choose from large selection of air diffusers and exhaust openings.

The report contain a list of project ideas proposed by the scientific staff at the Department of Civil Engineering, Aalborg University, and some companies.

Experiments are conducted in a full-scale chamber equipped with whole floor and whole ceiling supply or exhaust to form approximately zero and larger temperature gradients corresponding to unstable and stable air conditions. It can be observed that the air with smoke exhaled from a life-sized thermal manikin is locked and stratified at certain heights at stable condition while it mixes well with the ambient air and is diluted quickly through upper openings when the air is relatively unstable. The concentration of contaminant simulated by tracer gas (N2O) is measured both around and 0.35m from the manikin, indicating that the person who exhales the contaminant may not be polluted by himself as the protective effect of the thermal boundary layer around the body, especially in stable condition with two concentration zones and clean air drawn from the inlets. However, other persons facing the respiration some distance away may suffer higher contaminant exposure if the air in room is quite stable and contaminant from the mouth can penetrate a longer horizontal distance. In addition, the air stability slightly changes the velocity profiles, giving higher velocity decay and more turbulent mixing with surrounding air at unstable air condition.

Ventilation is one of the ways that humans can keep the indoor air quality at the proper level. Portable air cleaners have been developed to improve indoor air quality while reducing the energy consumption of the ventilation system. The aim of this study is to find the correct turbulence model and particle phase model for simulating an air cleaner in a room. In addition, the aim is to study the impact of location of an air cleaner in a room. The dynamics of the particle inside a room was simulated by computational fluid dynamics software. Furthermore, the air change rate was measured by both tracer gas and particles with different sizes.The proper turbulence model was selected after comparing the results with the behaviour of the gass in the test room. The simulations showed the effect that the location of an air cleaner had on the particle level. The results showed that the location of the air cleaner in relation to inlet, outlet and particle source had a significant effect on the effectiveness of the air cleaner.

The transmission of exhaled small particles from one person to another in an indoor environment can take place both directly (in the microenvironment around the persons) and via the room air distribution. The impact of these transmission routes for two persons is investigated in detail by evaluating the exposure to gaseous substances (simulating particles

Airborne cross infection is based on transmission of microorganisms attached to exhaled droplets or particles. Traditionally two transmission routes are considered, namely via droplet nuclei (< 5-10 μm) and via droplets (> 5-10 μm), and they correspond to two infection routes: droplet infection and airborne infection. A transition may take place from droplet-borne infection to airborne infection, because the exhaled droplets may evaporate in the air and droplets become droplet nuclei.Full-scale experiments on the movement of droplet nuclei (airborne infection) have been performed in a number of experiments using breathing thermal manikins and tracer gas for the simulation of microorganism-laden particles movement in indoor and outdoor environment. Full-scale experiments are conducted with droplet movement (droplet infection) using one or two thermal manikins.First the paper will discuss earlier measurements on the flow in the microenvironment around persons with respect to droplet nuclei (< 5- 10 μm). Measurement of settled particles (droplets > 5-10 μm) on the floor around a manikin (person) will then be shown for different heat releases from the manikin. These results are in good agreement with the expectation of a settlement within a “short” distance of 1.5 m, Lidwell and Williams (1961). Experiments with the exhalation of particles from a source manikin close to the other manikin are also performed. The results show that in this case the change in the microenvironment will influence the particle distribution in the proximity surrounding of the manikins.

We protect ourselves from airborne cross-infection in our indoor environment by supplying fresh air to the room by natural or mechanical ventilation. The air is distributed in the room according to different principles as e.g. mixing ventilation, downward ventilation, displacement ventilation, etc. A large amount of air is supplied to the room to ensure dilution of airborne infection.The paper discusses both the macroenvironment and the microenvironment. The macroenvironment is the conditions created by the air distribution system, and the microenvironment is the conditions created by the local flow around persons in combination with the surrounding conditions.Analyses of the flow in the room (macroenvironment) show a number of parameters that play an important role in minimising of airborne cross-infection. The air flow rate to the room must be high, and the air distribution pattern can be designed to have high ventilation effectiveness. Furthermore, personalized ventilation may reduce the risk of cross-infection. Personalized ventilation can be used especially in hospital wards, aircraft cabins and, in general, where people are located at defined positions.Analyses of the flow in the microenvironment show that a number of variables are important, as e.g. distance between people, people’s posture, surrounding temperature gradients and surrounding temperature, activity level, etc.Experiments with tracer gas simulating droplet nuclei and experiments with large particles, simulating droplets are used for the study of airborne cross-infection risk and for the study of dropletborne transmission of a disease. CFD predictions are used to support these experiments.

The level of exposure to human exhaled contaminants in a room depends not only on the air distribution system but also on people’s different positions, the distance between them, people’s activity level and height, direction of exhalation, and the surrounding temperature and temperature gradient. Human exhalation is studied in detail for different distribution systems: displacement and mixing ventilation as well as a system without mechanical ventilation. Two thermal manikins breathing through the mouth are used to simulate the exposure to human exhaled contaminants. The position and distance between the manikins are changed to study the influence on the level of exposure. The results show that the air exhaled by a manikin flows a longer distance with a higher concentration in case of displacement ventilation than in the other two cases, indicating a significant exposure to the contaminants for one person positioned in front of another. However, in all three cases, the exhalation flow of the source penetrates the thermal plume, causing an increase in the concentration of contaminants in front of the target person. The results are significantly dependent on the distance and position between the two manikins in all three cases.

The purpose of this investigation is to compare the different flow patterns obtained for the 2D isothermal test case defined in Annex 20 (1990) using different turbulence models. The different results are compared with the existing experimental data. Similar study has already been performed by Rong et al. (2008) using Ansys CFX 11.0. In this report, the software Star-CCM+ has been used.

We protect ourselves from airborne cross-infection in our indoor environment by supplying fresh air to the room by natural or mechanical ventilation. The air is distributed in the room according to different principles as e.g. mixing ventilation, downward ventilation, displacement ventilation, etc. A large amount of air is supplied to the room to ensure dilution of airborne infection.The paper discusses both the macroenvironment and the microenvironment. The macroenvironment is the conditions created by the air distribution system, and the microenvironment is the conditions created by the local flow around persons in combination with the surrounding conditions.Analyses of the flow in the room (macroenvironment) show a number of parameters that play an important role in minimising of airborne cross-infection. The air flow rate to the room must be high, and the air distribution pattern can be designed to have high ventilation effectiveness. Furthermore, personalized ventilation may reduce the risk of cross-infection. Personalized ventilation can be used especially in hospital wards, aircraft cabins and, in general, where people are located at defined positions.Analyses of the flow in the microenvironment show that a number of variables are important, as e.g. distance between people, people’s posture, surrounding temperature gradients and surrounding temperature, activity level, etc.Experiments with tracer gas simulating droplet nuclei and experiments with large particles, simulating droplets are used for the study of airborne cross-infection risk and for the study of dropletborne transmission of a disease. CFD predictions are used to support these experiments.

Discharge coefficient and wind-pressure coefficient are the key input parameters for estimating the airflow rates in naturally ventilated building designs. This paper focuses on the study of the discharge coefficient (CD) in case of a moveable (bottom-hinged) window flap. Computational fluid dynamics (CFD) techniques are used for estimating the airflow through the window. Focus is given to the window on the windward side of the building. The first objective of this study is to validate the k-ε turbulent model for the estimation of airflow rates through the window. It is done by comparing the numerical results with existing results of full-scale measurements under a laboratory conditions. The second objective is to find an accurate method to estimate the airflow rate (using orifice plate equation) in the case of a window with a moveable flap. It is done by using CFD predictions together with the validated turbulent model. A single value of CD (usually 0.6 to 0.65) is not appropriate for the operable window with moveable flap. The results of the simulation validates that the k-ε turbulent model can predict the airflow rates within an acceptable range, when the pressure difference (across the opening) is higher than 0.5 Pa. This study also confirms that the single value of the CD is not sufficient for a window with moveable flap. At the end, a more accurate method is presented for estimating the airflow through a window with moveable flap.

The use of CFD in ventilation research has arrived to a high level, but there are some conditions in the general CFD procedure which do not apply to all situations in the ventilation research. An example of this isthe turbulence models in Reynolds-averaged Navier-Stokes equations, i.e. (RANS) equations.

Transmission of exhaled small particles from one person to another in an indoor environment can take place, both in a direct way (in the microenvironment around the persons) and via the room air distribution. The impacts of these transmission routes for two persons are investigated in details by evaluating the exposure to gaseous substances (simulating particles < 5 μm) in a room ventilated by displacement ventilation. Experiments employing two breathing thermal manikins are conducted in a full-scale test room. One manikin is the source, and the other manikin is the target. The distance between the two manikins varies from 1.1 m (43 in) to 0.35 m (14 in) in the experiments. A tracer gas N2O is used to represent the gaseous substances exhaled by the source manikin. The concentration of N2O is measured to study the impact of the following parameters on the exposure: distance between manikins, positions as face to face, face to the side of the target manikin, face to the back of the target manikin, and a seated source manikin. The exposure increases with decreasing distance between the manikins, and the highest values are obtained in the face to face position. Face to the side is also giving some exposure of the target manikin, while face towards the target manikin’s back does not give any direct exposure through the microenvironment. The thermal stratification in the room supports a significant exposure of the target manikin when the source manikin is seated breathing towards the chest of a standing manikin.

The correct description of air diffusers plays a crucial role in the CFD predictions of the airflow pattern into a room. The numerical simulation of air distribution in an indoor space is challenging because of the complicated airflow pattern generated. An experimental study has been carried out in a full scale test room, 4.10 m (length), 3.20 m (width), and 2.70 m (height), in order to take velocity measurements of the airflow pattern generated by three different air diffusers: displacement, mixing and a low impulse diffuser. Smoke visualization has been developed to determine the direction of the flow and observe the developed region of the jets. During the experiments the cold air is supplied at a temperature of 16ºC. The air exchange rate is set to 5.6 h-1.