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Indoor airflow patterns and the spreading of respiratory air were studied using the large-eddy simulation (LES) computational fluid dynamics (CFD) approach. A large model room with mixing ventilation was investigated. The model setup was motivated by super-spreading of the SARS-CoV-2 virus with a particular focus on a known choir practice setup where one singer infected all the other choir members. The room was heated with radiators at two opposite walls in the cold winter time. The singers produced further heat generating buoyancy in the room. The Reynolds number of the inflow air jets was set to R e = 2750 , corresponding to an air-changes-per-hour (ACH) value of approximately 3.5. The CFD solver was first validated after which a thorough grid convergence study was performed for the full numerical model room with heat sources. The simulations were then executed over a time of t = 20 min to account for slightly more than one air change timescale for three model cases: (1) full setup with heat sources (radiators+singers) in the winter scenario, (2) setup without radiators in a summer scenario, and (3) theoretical setup without buoyancy (uniform temperature). The main findings of the paper are as follows. First, the buoyant flow structures were noted to be significant. This was observed by comparing cases 1/2 with case 3. Second, the dispersion of the respiratory aerosol concentration, modeled as a passive scalar, was noted to be significantly affected by the buoyant flow structures in cases 1–2. In particular, the aerosol cloud was noted to either span the whole room (cases 1–2) or accumulate in the vicinity of the infected singer (case 3). Turbulence was clearly promoted by the interaction of the upward/downward moving warmer/cooler air currents which significantly affected the dispersion of the respiratory aerosols in the room. The study highlights the benefits of high-resolution, unsteady airflow modeling (e.g. LES) for interior design which may consequently also impact predictions on exposure to potentially infectious respiratory aerosols. • Airflow and virus super-spreading during a choir practice is investigated numerically. • Large-Eddy Simulation (LES) is used to capture the physics in high spatial resolution. • Flow structures and aerosol dispersion are compared between three model set-ups. • Respiratory aerosol dispersion is noted to be significantly affected by buoyancy. • Flow physics strongly impact the numerically predicted aerosol exposure. [ABSTRACT FROM AUTHOR]

The ongoing Covid-19 pandemic, and its associated public health and socioeconomic burden, has reaffirmed the necessity for a comprehensive understanding of flow-mediated infection transmission in occupied indoor spaces. This is an inherently multiscale problem, and suitable investigation approaches that can enable evidence-based decision-making for infection control strategies, interventions, and policies; will need to account for flow physics, and occupant behavior. Here, we present a mesoscale infection transmission model for human occupied indoor spaces, by integrating an agent-based human interaction model with a flow physics model for respiratory droplet dynamics and transport. We outline the mathematical and algorithmic details of the modeling framework, and demonstrate its validity using two simple simulation scenarios that verify each of the major sub-models. We then present a detailed case-study of infection transmission in a model indoor space with 60 human occupants; using a systematic set of simulations representing various flow scenarios. Data from the simulations illustrate the utility and efficacy of the devised mesoscale model in resolving flow-mediated infection transmission; and elucidate key trends in infection transmission dynamics amongst the human occupants. [ABSTRACT FROM AUTHOR]

The ventilation system of an operating theatre (OT) in a hospital needs to provide a comfortable and healthy surgical environment, particularly to minimise the risk of airborne infection. Engineering standards are available to outline specialised ventilation design and installation requirements based on knowledge accumulated from quality research and day-to-day practices. In this paper, the integrated effect of a reduction in supply air velocity and changed medical lamp positions on the ultra-clean ventilation performance of a standard OT environment is reported. The dispersion of infectious particles from both the surgical team and the patient were examined through computational fluid dynamic analysis. It was observed that variations in supply velocity and medical lamp configuration will only slightly affect the thermal comfort environment. However, they could have a serious effect on the movement of infectious particles and hence increase the cross infection risk. [ABSTRACT FROM AUTHOR]

• We evaluate effects of ventilation and social distancing on aerosol exposure. • We study transport dynamics of exhaled aerosols in human breathing zone. • Ventilation strategy notably affects the airborne infection risk. • Buoyancy-driven airflow can cause elevated human exposure to viral aerosols. • A 2 m social distance may not effectively reduce the risk of infectious aerosols. Airborne transmission of virus via respiratory aerosols plays an important role in the spread of infectious diseases in indoor environments. Ventilation and social distancing are two major control strategies to reduce the indoor airborne infection risk. However, there is a present lack of science-based information on how the human exposure to viral aerosols vary with ventilation condition and social distance. The objective of this study is to explore the transport patterns of respiratory aerosols in occupied spaces and assess the occupant exposure risk under different ventilation strategies, social distances and aerosol emission modes. The study results show that buoyancy-driven flow regime (can be found in many residential settings) can lead to a longer transmission distance and elevated exposure to viral aerosols than the mixing airflow, thereby causing higher cross-infection risk in indoor environments. The results also suggest that a 2 m (6 ft) social distance alone may not ensure control of indoor airborne infections. [ABSTRACT FROM AUTHOR]

The world is having an unprecedented time due to the pandemic. Currently, more than 93 million people have been infected, and over 2 million people have passed away since 2020. SARS-CoV-2 has forced people to change their lifestyles and patterns. Under the pandemic, buildings are no longer safe shelters. The infected transmit infectious viruses to other occupants by direct contact or indirect contact (i.e., indoor airflow). In addition, the airflow from electric heat pump systems can propel indirect contact in indoor spaces. However, the impact of airflow is still not sufficiently identified to develop virus control strategies in buildings. Therefore, this study selected a restaurant in Seoul, Korea, to experiment with airborne virus transmission of direct airflow in winter using virus-similar particles. The results of this study verified the potential exposure of droplets or aerosols to occupants that can be delivered by air current from heating systems in winter. The effect of kitchen hoods was also confirmed as additional ventilation equipment without additional budget investment in restaurants. The recommendations of this study are expected to improve the guidelines for restaurants to ensure occupant's safety during the COVID-19 period. [Display omitted] • This study investigated the impact of heating systems on the indoor behavior of airborne virus transmission in a restaurant during wintertime. • The spread and concentration of virus-similar particles were tracked and analyzed by Optical Particle Counters (OPC) and Particle Image Velocimetry (PIV) equipment. • The risk of direct airflow and the effect of ventilation (e.g., kitchen hoods and windows) were identified to suggest recommendations for securing the safety in restaurants. • The experiment revealed potential exposure of airborne contaminants by indoor airflow from heating systems and provided control methods to mitigate occupants' risk from the virus (i.e., SARS-CoV-2) in winter. [ABSTRACT FROM AUTHOR]