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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 Personal Micro Environment (PME) depends directly on the heat transfer in the surrounding environment. For the displacement ventilation systems the convective transport mechanism, which is found in the thermal plume around a person, influences the human exposure to pollutants. The aim of this research is to increase the knowledge of how the thermal plume generated by a person affects the PME and therefore the concentration of contaminants in the inhalation area. An experimental study in a displacement ventilation room was carried out. Experiments were developed in a full scale test chamber 4.10 m (length), 3.2 m (width), 2.7 m (height). The incoming air is distributed through a wall-mounted displacement diffuser. A breathing thermal manikin exhaling through the mouth and inhaling through the nose was used. A tracer gas, N2O, was used to simulate the gaseous substances, which might be considered as biological contaminants, exhaled by the manikin. The manikin was operated in three different heat fluxes with a value of: 0W, 94 W and 120 W. During the experiments six concentration probes were situated in the room. Three concentration tubes were fixed on the surface of the manikin at three different heights: hips, chest and nose (inhalation). The three other tubes were situated in a vertical line at 0.50 m from the manikin and at the same three heights. The results show the highest concentration of contaminants around the manikin when the manikin heat load is fixed to 0W. However, the concentration is significantly reduced in the case with 120 W, especially in the breathing area.

En gruppe indeklimaforskere, samlet under den nordiske VVS-tekniske forening Scanvac, opfordrer i dette fælles dokument til en anerkendelse af, at der forekommer luftbåren smittespredning af covid-19 i bygninger og andre indeklimaer, og at der skal forskes og investeres i løsninger til at forhindre det.Som opsummering foreslås:* Det skal anerkendes, at luftbåren smittespredning er en reel transmissionsrute i opholdssteder i bygninger og i transportsektoren.* Rehvas covid-19 vejledning skal anvendes for at reducere smittespredninger i den nuværende pandemi.* Forskningsagenturer og industrien skal investere i praktiske tekniske løsninger, som beskytter imod luftbåren smittespredning i indemiljøet, bygninger og transportfaciliteter.* Bygningsreglementet, standarder og vejledninger skal revideres og opdateres, så byggebranchen er forberedt til kommende epidemier.* De foreslåede aktiviteter vil reducere risikoen for luftbåren smittespredning og de vil også give en generel forbedret folkesundhed i tiden mellem epidemier.

Diffuse ceiling ventilation is an air distribution system where the air is supplied from the entire ceiling surface, giving a low supply velocity. The flow pattern in the room is controlled by the heat sources. The system generates high mixing and the air velocities in the room are not influenced by the flow rate to the room, but dependent on the heat load and heat load distribution. Experiments showed that the selected ceiling surface material had only a small influence on the performance of the system and that the room height and heat load distribution can have a strong influence on the performance.

This study investigates the characteristics of human exhalation during breathing and coughing. Experiments employing one breathing thermal manikin are conducted in a full-scale test room with a mixing ventilation system. Two artificial lungs are used to generate discontinuous airflows with specific flow rates and temperatures for breathing and coughing, respectively. Smoke visualizations are conducted to show the formation, movement and vanishing of the exhalation jets from nose and mouth separately. The transient velocity distribution generated by breathing and coughing in different places are analyzed. This study investigates the characteristics of human exhalation during breathing and coughing. Experiments employing one breathing thermal manikin are conducted in a full-scale test room with a mixing ventilation system. Two artificial lungs are used to generate discontinuous airflows with specific flow rates and temperatures for breathing and coughing, respectively. Smoke visualizations are conducted to show the formation, movement and vanishing of the exhalation jets from nose and mouth separately. The transient velocity distribution generated by breathing and coughing in different places are analyzed.

This study investigates the characteristics of human exhalation through the mouth with three different ventilation strategies: displacement ventilation, mixing ventilation and without ventilation. Experiments were conducted with one breathing thermal manikin in a full scale test room where the exhalation airflow was analyzed. In order to simulate the gaseous exhaled substances in human breathing, N2O was used as a tracer gas. The concentration of N2O and the velocity of the exhaled flow were measured in the center line of the exhalation flow. The velocity decay of the exhalation flow versus distance was analyzed for the three ventilation strategies. The relationship between gas concentration values and distance from the manikin was also examined. The measurements show distribution system. Two equations could be applied to describe the relationship between distance from the manikin and, respectively, peak velocity values and maximum mean gas-concentration values. This study investigates the characteristics of human exhalation through the mouth with three different ventilation strategies: displacement ventilation, mixing ventilation and without ventilation. Experiments were conducted with one breathing thermal manikin in a full scale test room where the exhalation airflow was analyzed. In order to simulate the gaseous exhaled substances in human breathing, N2O was used as a tracer gas. The concentration of N2O and the velocity of the exhaled flow were measured in the center line of the exhalation flow. The velocity decay of the exhalation flow versus distance was analyzed for the three ventilation strategies. The relationship between gas concentration values and distance from the manikin was also examined. The measurements show distribution system. Two equations could be applied to describe the relationship between distance from the manikin and, respectively, peak velocity values and maximum mean gas-concentration values.

An investigation on the scenarios of the spill plume and its equation was presented in this paper. The study includes two aspects, i.e., the small-scale experiment and the numerical simulation. Two balcony spill plume models are assessed by comparing with the FDS (Fire Dynamic Simulation) and small scale model experiment results. Besides validating the spill model by experiments, the effect of different fire location on balcony plume is also discussed.The results show that the balcony equation in NFPA would give good predictions on the mass flow rate. And the balcony plume entrainment coefficient is independent of the fire location. The Investigations in this paper are useful for the fire engineers in designing smoke control systems. An investigation on the scenarios of the spill plume and its equation was presented in this paper. The study includes two aspects, i.e., the small-scale experiment and the numerical simulation. Two balcony spill plume models are assessed by comparing with the FDS (Fire Dynamic Simulation) and small scale model experiment results. Besides validating the spill model by experiments, the effect of different fire location on balcony plume is also discussed.The results show that the balcony equation in NFPA would give good predictions on the mass flow rate. And the balcony plume entrainment coefficient is independent of the fire location. The Investigations in this paper are useful for the fire engineers in designing smoke control systems.

This paper focuses on measuring the inlet velocity from a HESCO diffuser used in the IEA Annex 20 work as a function of the volume flow it provides. The aim of the present work is to establish a relation between the inlet velocity, the effective area and the airflow. This is important because the inlet velocity is a very important boundary condition both in CFD calculation and general flow measurements. If only the volume flow and the geometrical area are used, a relatively large error in the inlet velocity may result. From the detailed measurements it was possible to establish an expression between the inlet velocity and the effective area. This paper focuses on measuring the inlet velocity from a HESCO diffuser used in the IEA Annex 20 work as a function of the volume flow it provides. The aim of the present work is to establish a relation between the inlet velocity, the effective area and the airflow. This is important because the inlet velocity is a very important boundary condition both in CFD calculation and general flow measurements. If only the volume flow and the geometrical area are used, a relatively large error in the inlet velocity may result. From the detailed measurements it was possible to establish an expression between the inlet velocity and the effective area.

Accuracy in estimation of airflow through windows is the key parameter for modelling and designing of naturally ventilated buildings. The flow through windows is usually described by the orifice flow plate equation. This equation involves the discharge coefficient. In practice, often a constant value of discharge coefficient is used. The constant value of discharge coefficient leads to deceptive airflow estimation in the cases of centre-pivot roof windows. The object of this paper is to study and evaluate the discharge coefficient of the centre pivot roof window. Focus is given on unidirectional flows i.e. inflow and outflow. CFD techniques are used to predict the airflow through the modelled window. Analytical orifice flow equation is used to calculate the discharge coefficient. Results are compared with experimental results. It is concluded that the single value of the discharge coefficient leads to ambiguous estimation of airflow rates. The discharge coefficient decreases with increase in flap opening area. The discharge coefficient also depends upon the flow direction.

An important element in the natural ventilation design procedure is the flow-pressure characteristics of a window with a -given opening area. The flow in the room is another important element that is often ignored in the design phase due to lack of relevant information on the air movement. This paper shows the outcome of experiments with the room air distribution. The results show that the velocity distribution in the occupied zone can be described by a semiempirical model.

Today there is an increasing focus on the importance of a proper ventilation system to obtain good working conditions in the term of air and thermal quality to ensure high productivity. Different ventilation principles are used, e.g., mixing ventilation and displacement ventilation. In order to ensure that the ventilation system meets the demands it is important to know which parameters that influence the performance of the system. In this work the mixing ventilation principle was investigated. When the mixing ventilation principle is used for the design of a ventilation system it is assumed that the air is fully mixed. The objective of this work is to determine the influence of the location of a pollutant, temperature differences and whether the room is furnished or not. It is also investigated if it is sufficient to determine the mean concentration in the room to determine the personal exposure. Full scale experiments along with a breathing thermal manikin (BTM) have been used. The results show that the location of the sources is of great importance, just as well as temperature differences. Furthermore, the concentration in the breathing zone showed large differences throughout the room.

This paper presents a numerical model that by means of computational fluid dynamics (CFD) is capable of dealing with both pollutant transport across the boundary layer and internal diffusion in the source without prior knowledge of which is the limiting process. The model provides the concentration distribution in the room air as well as in the source.

The application of Computational Fluid Dynamics (CFD) for ventilation research and design of ventilation systems has increased during the recent years. This paper provides an investigation of direct description of boundary conditions for a complex inlet diffuser and a heated surface. A series of full-scale experiments in a room ventilated by the mixing principle have been performed for validation of the models. The experimental results include measurements of temperature as well as measurements of velocity and turbulence by Laser Doppler Anemometry (LDA). A simple model of the complex inlet diffuser showed good agreement with the experimentally obtained results although differences were observed in the flow far from the inlet. None of the investigated models of the heated surface did provide satisfactory results.

Transmission of the exhaled substances from one person to another in indoor environment is influenced by many individual factors.

Normally we protect ourselves from cross infection by supplying fresh air to a room by a diffuser, and this air is distributed in the room according to different principles such as: mixing ventilation, displacement ventilation, vertical ventilation, etc. Often this air distribution has the consequence that it is necessary to supply a very large amount of air to the whole room to obtain a sufficient dilution of the airborne infections. When people are seated, a way to supply air direct to the breathing zone is to use "Personalized Ventilation". Personalized ventilation has shown to be very efficient in the protection of people from cross infection. A personalized ventilation device has been developed in the form of a neck support pillow. The air is supplied to the free convection boundary layer of the person, and the layer then transports the air to the breathing zone. The velocities in this process are very small and draught may be able to disturb the process. Therefore, this research work deals with the effectiveness of the system with different levels and directions of draught. The measurements are made with a full-scale manikin in a wind tunnel. The results show that the boundary layer and the process in the breathing zone are rather independent of draught at velocities up to 0.2 m/s. Normally we protect ourselves from cross infection by supplying fresh air to a room by a diffuser, and this air is distributed in the room according to different principles such as: mixing ventilation, displacement ventilation, vertical ventilation, etc. Often this air distribution has the consequence that it is necessary to supply a very large amount of air to the whole room to obtain a sufficient dilution of the airborne infections. When people are seated, a way to supply air direct to the breathing zone is to use "Personalized Ventilation". Personalized ventilation has shown to be very efficient in the protection of people from cross infection. A personalized ventilation device has been developed in the form of a neck support pillow. The air is supplied to the free convection boundary layer of the person, and the layer then transports the air to the breathing zone. The velocities in this process are very small and draught may be able to disturb the process. Therefore, this research work deals with the effectiveness of the system with different levels and directions of draught. The measurements are made with a full-scale manikin in a wind tunnel. The results show that the boundary layer and the process in the breathing zone are rather independent of draught at velocities up to 0.2 m/s.

En los últimos años ha surgido un especial interés en entender los mecanismos de transmisión de infecciones cruzadas entre personas. El Síndrome Respiratorio Agudo Severo (SARS, por sus siglas en ingles) que tuvo lugar en Asia en el año 2003 reabrió el estudio de la transmisión de diferentes enfermedades vía aérea como una de las rutas de transmisión más activas.Las infecciones cruzadas entre personas son causadas por la transmisión de patógenos, como virus o bacterias, entre personas en ambientes interiores. Cuando una persona respira, habla, estornuda o tose, pequeñas partículas, denominadas “droplet nuclei”, que pueden contener contaminantes biológicos, son dispersadas en el aire. Estas pequeñas partículas pueden seguir las corrientes de flujos de aire dentro de una habitación y provocar altas concentraciones de contaminantes en diferentes áreas dentro de un recinto interior. Este hecho puede provocar una alta exposición a contaminantes exhalados y un riesgo de infección cruzada a personas susceptibles de ser contagiadas situadas en la misma habitación.Existen numerosas evidencias de que los sistemas de ventilación y distribución de aire juegan un papel crucial en la dispersión de los contaminantes exhalados por personas en recintos interiores. Sin embargo, existen muchos parámetros que influencian el riesgo de infección cruzada entre personas en una habitación climatizada, como son: la posición relativa entre las personas, la distancia de separación entre ellas, su diferencia de alturas, su nivel de actividad, las funciones respiratorias de las personas (si exhalan el aire por la nariz o por la boca, si se produce un estornudo, etc.) o la velocidad y nivel de turbulencia del aire en el micro-ambiente alrededor de las personas.El objetivo principal de esta tesis es analizar la relación de alguno de los parámetros detallados anteriormente con el riesgo de infección cruzada que se puede generar entre personas dentro de una habitación. La influencia de diferentes estrategias de climatización sobre el micro-ambiente de las personas, sobre la dirección de la exhalación y sobre la dispersión de contaminantes exhalados en el aire ha sido también estudiada.Se han realizado numerosos estudios experimentales considerando dos personas dentro de una misma habitación climatizada mediante diferentes sistemas. La simulación de la personas se ha llevado a cabo mediante maniquíes térmicos que incluían funciones respiratorias. La exhalación de uno de ellos era considerada la fuente biológica de contaminantes mientras que el otro era la persona susceptible de ser contagiada a través del aire. Los estudios experimentales incluyen diferentes posiciones relativas entre personas y distintas distancias de separación.Los resultados muestran una significativa influencia de la distancia de separación y la posición relativa entre las personas en la transmisión de patógenos por el aire y el riesgo de infección cruzada entre personas. Algunos de los sistemas de ventilación de aire considerados hasta ahora como adecuados en la prevención de este tipo de contagios a través del aire, como es el sistema de ventilación vertical a baja velocidad, no han mostrado especial protección contra las infecciones cruzadas en los ensayos experimentales. La exposición frente a contaminantes exhalados varía significativamente entre los distintos casos y los resultados han sido analizados minuciosamente a lo largo de esta tesis. Los resultados obtenidos dejan patente la influencia de las condiciones interiores de aire generada por los distintos sistemas de climatización en la transmisión de patógenos a través del aire en recintos interiores, en la calidad de aire que proporcionan a las personas y por lo tanto en el riesgo de infecciones cruzadas que se puede generar., In recent years, an interest in understanding the mechanisms of cross-infection between people in the same room has increased significantly. The SARS (Severe Acute Respiratory Syndrome) outbreak occurred in Asia in 2003 reopened the study of the airborne disease transmission as one of the most prevalent transmission routes.Airborne cross-infection of diseases is caused by the transmission of pathogens, such as viruses or bacteria, between people and across environments. When a person is breathing, talking, sneezing or coughing, small particles, which may carry biological contaminants, are spread in the air. These tiny particles or droplet nuclei can follow the air flow pattern in the room and produce high contaminant concentration in different areas of the indoor environment. This fact can provoke a high exposure to exhaled contaminants and a risk of cross-infection to a susceptible person situated in the same room.Abundant evidence shows that the air flow distribution systems play a crucial role in the dispersion of these human exhaled contaminants. However, there are many parameters that influence the cross-infection risk between people situated close to each other in a ventilated room, such as: relative position and separation distance between people, difference in height between them, level of activity, breathing function or process (breathing frequency, exhalation through the mouth or through the nose, coughing, sneezing) or air velocity and turbulence level in the micro-environment around the persons.This thesis analyzes some of these parameters in the influence of cross-infection risk between two people in a room, which are simulated by two breathing thermal manikins. One of the manikins is considered the source of contaminants, which is exhaling contaminated air through the mouth. The influence of different ventilation strategies in the personal micro-environment, the direction of the human exhalation flow and the dispersion of exhaled contaminants has also been studied.Several experimental tests in a full-scale test room have been carried out in order to study the cross-infection risk between two people in a room. Different ventilation strategies and different separation distances, and relative positions, between the manikins produce different levels of contaminant exposure to the susceptible person (target manikin). These results have been discussed and carefully analyzed within this thesis., Der har i de seneste år været en stigende interesse for at undersøge og forstå mekanismerne i krydsinfektion imellem folk, som opholder sig i det samme lokale. SARS-hændelsen (Severe Acute Respiratory Syndrome) som fandt sted i Asien i 2003 betød, at studier af luftbårne transmissionsruter for sygdomme blev et meget aktivt forskningsområde. Luftbåren krydsinfektion of sygdomme foregår ved transmission af patogene som virus eller bakterier imellem personer i indemiljøet. Når en person ånder, taler, nyser eller hoster, vil små biologisk forurenede partikler spredes i luften. Disse små partikler (droplet nuclei) følger luftstrømningsmønsteret i lokalet, og de kan danne høje koncentrationer i forskellige områder af indemiljøet. Dette kan betyde, at der kan opstå en høj eksponering for udåndet forurening og derfor en risiko for krydsinfektion af en påvirkelig person, som befinder sig i samme rum.Mange hændelser viser, at luftfordelingssystemerne spiller en væsentlig rolle i fordelingen af disse udåndede humane forureninger. Der er imidlertid mange parametre, som har indflydelse på risikoen for krydsinfektion imellem folk, som befinder sig tæt ved hinanden i et ventileret lokale, som for eksempel relativ position og afstand, forskel i højde, aktivitetsniveau, åndingsproces (åndingsfrekvens, udånding gennem mund eller gennem næse, hosten eller nysen) samt lufthastighed og turbulensniveau i mikromiljøet rundt om personer.Afhandlingen analyserer nogle af disse parametres indflydelse på risikoen for krydsinfektion imellem to personer i et lokale, idet man betragter en af personerne som en kilde til smitte. Den syge person udånder forurenet luft igennem munden. De forskellige luftfordelingsstrategiers indflydelse på det personlige mikromiljø, retningen af en persons udånding og fordelingen af den udåndede forurening er undersøgt.Der er udført adskillige forsøg for at undersøge risikoen for krydsinfektion i et fuldskala forsøgslokale, hvor to personer er simuleret ved hjælp af to termiske manikiner med åndingsfunktion. Forskellige ventilationsstrategier og forskellige afstande imellem manikinerne samt forskellige relative positioner giver en person (Target manikin) forskellig forureningspåvirkning. Resultaterne er diskuteret og analyseret i denne afhandling.