Predictions and measurements of the stack effect on indoor airborne virus transmission in a high-rise hospital building

Transmission of droplet aerosols in an elevator cabin: Effect of the ventilation mode

The recent outbreak of COVID-19 has threatened public health. Owing to the relatively sealed environment and poor ventilation in elevator cabins, passengers are at risk of respiratory tract infection. However, the distribution and dispersion of droplet aerosols in elevator cabins remain unclear. This study investigated the transmission of droplet aerosols exhaled by a source patient under three ventilation modes. Droplet aerosols produced by nose breathing and mouth coughing were resolved using computational fluid dynamics (CFD) simulations. We adopted the verified renormalization group (RNG) k-ε turbulence model to simulate the flow field and the Lagrangian method to track the droplet aerosols. In addition, the influence of the ventilation mode on droplet transmission was evaluated. The results showed that droplet aerosols gathered in the elevator cabin and were difficult to discharge under the mixed and displacement ventilation modes with specific initial conditions. The inhalation proportion of droplet aerosols for air curtain was 0.016%, which was significantly lower than that for mixed ventilation (0.049%) and displacement ventilation (0.071%). The air curtain confined the transmission of droplet aerosols with the minimum ratios of inhalation, deposition, and suspension and is thus recommended to reduce the exposure risk.

A noncontact modular infectious disease screening clinic aiming to achieve zero cross-contaminations

Screening clinics play a major role in preventing the transmission of infectious diseases. The main problem that should be addressed is the exposure to cross-infection between healthcare workers and individuals intended to be tested. In this study, a noncontact modular screening clinic (NCMSC) was developed that addresses the problems of existing screening clinics and the risks of cross-contamination during the infectious disease sampling process. The space and ventilation system of the NCMSC were designed to effectively remove viral aerosols to avoid cross-contamination. The spatial configurations that enabled noncontact specimen sampling and pressure differential control was achieved. Regarding the measurement method with the use of tracer gas, an experimental field test framework and procedure that can evaluate the cross-contamination between rooms were presented. It is the observation of pollutants (tracer gas) in two different modes (normal breathing and AGP from a patient) in a screening clinic with ventilation, compared to the room next door, where the HCW is located. Additionally, based on onsite experiments using SF₆ tracer gas that mimics the viral aerosol at an actual scale, it was verified that no cross-contamination occurred in the NCMSC; accordingly, it was possible to protect sufficiently the healthcare workers. It will be possible to use the outcomes of this study as basic data for the development of standards for the installation and operation of screening clinics for infectious diseases.

Computational decision-support tools for urban design to improve resilience against COVID-19 and other infectious diseases: A systematic review

The COVID-19 pandemic highlighted the need for decision-support tools to help cities become more resilient to infectious diseases. Through urban design and planning, non-pharmaceutical interventions can be enabled, impelling behaviour change and facilitating the construction of lower risk buildings and public spaces. Computational tools, including computer simulation, statistical models, and artificial intelligence, have been used to support responses to the current pandemic as well as to the spread of previous infectious diseases. Our multidisciplinary research group systematically reviewed state-of-the-art literature to propose a toolkit that employs computational modelling for various interventions and urban design processes. We selected 109 out of 8,737 studies retrieved from databases and analysed them based on the pathogen type, transmission mode and phase, design intervention and process, as well as modelling methodology (method, goal, motivation, focus, and indication to urban design). We also explored the relationship between infectious disease and urban design, as well as computational modelling support, including specific models and parameters. The proposed toolkit will help designers, planners, and computer modellers to select relevant approaches for evaluating design decisions depending on the target disease, geographic context, design stages, and spatial and temporal scales. The findings herein can be regarded as stand-alone tools, particularly for fighting against COVID-19, or be incorporated into broader frameworks to help cities become more resilient to future disasters.

Airborne transmission of biological agents within the indoor built environment: a multidisciplinary review

The nature and airborne dispersion of the underestimated biological agents, monitoring, analysis and transmission among the human occupants into building environment is a major challenge of today. Those agents play a crucial role in ensuring comfortable, healthy and risk-free conditions into indoor working and leaving spaces. It is known that ventilation systems influence strongly the transmission of indoor air pollutants, with scarce information although to have been reported for biological agents until 2019. The biological agents' source release and the trajectory of airborne transmission are both important in terms of optimising the design of the heating, ventilation and air conditioning systems of the future. In addition, modelling via computational fluid dynamics (CFD) will become a more valuable tool in foreseeing risks and tackle hazards when pollutants and biological agents released into closed spaces. Promising results on the prediction of their dispersion routes and concentration levels, as well as the selection of the appropriate ventilation strategy, provide crucial information on risk minimisation of the airborne transmission among humans. Under this context, the present multidisciplinary review considers four interrelated aspects of the dispersion of biological agents in closed spaces, (a) the nature and airborne transmission route of the examined agents, (b) the biological origin and health effects of the major microbial pathogens on the human respiratory system, (c) the role of heating, ventilation and air-conditioning systems in the airborne transmission and (d) the associated computer modelling approaches. This adopted methodology allows the discussion of the existing findings, on-going research, identification of the main research gaps and future directions from a multidisciplinary point of view which will be helpful for substantial innovations in the field.

Vented Individual Patient (VIP) Hoods for the Control of Infectious Airborne Diseases in Healthcare Facilities

By providing a means of separating the airborne emissions of patients from the air breathed by healthcare workers (HCWs), vented individual patient (VIP) hoods, a form of local exhaust ventilation (LEV), offer a new approach to reduce hospital-acquired infection (HAI). Results from recent studies have demonstrated that, for typical patient-emitted aerosols, VIP hoods provide protection at least equivalent to that of an N95 mask. Unlike a mask, hood performance can be easily monitored and HCWs can be alerted to failure by alarms. The appropriate use of these relatively simple devices could both reduce the reliance on personal protective equipment (PPE) for infection control and provide a low-cost and energy-efficient form of protection for hospitals and clinics. Although the development and deployment of VIP hoods has been accelerated by the coronavirus disease 2019 (COVID-19) pandemic, these devices are currently an immature technology. In this review, we describe the state of the art of VIP hoods and identify aspects in need of further development, both in terms of device design and the protocols associated with their use. The broader concept of individual patient hoods has the potential to be expanded beyond ventilation to the provision of clean conditions for individual patients and personalized control over other environmental factors such as temperature and humidity.

Ventilation strategies and design impacts on indoor airborne transmission: A review

The COVID-19 outbreak has brought the indoor airborne transmission issue to the forefront. Although ventilation systems provide clean air and dilute indoor contaminated air, there is strong evidence that airborne transmission is the main route for contamination spread. This review paper aims to critically investigate ventilation impacts on particle spread and identify efficient ventilation strategies in controlling aerosol distribution in clinical and non-clinical environments. This article also examines influential ventilation design features (i.e., exhaust location) affecting ventilation performance in preventing aerosols spread. This paper shortlisted published documents for a review based on identification (keywords), pre-processing, screening, and eligibility of these articles. The literature review emphasizes the importance of ventilation systems' design and demonstrates all strategies (i.e., mechanical ventilation) could efficiently remove particles if appropriately designed. The study highlights the need for occupant-based ventilation systems, such as personalized ventilation instead of central systems, to reduce cross-infections. The literature underlines critical impacts of design features like ventilation rates and the number and location of exhausts and suggests designing systems considering airborne transmission. This review underpins that a higher ventilation rate should not be regarded as a sole indicator for designing ventilation systems because it cannot guarantee reducing risks. Using filtration and decontamination devices based on building functionalities and particle sizes can also increase ventilation performance. This paper suggests future research on optimizing ventilation systems, particularly in high infection risk spaces such as multi-storey hotel quarantine facilities. This review contributes to adjusting ventilation facilities to control indoor aerosol transmission.

Responsiveness and Adaptability of Healthcare Facilities in Emergency Scenarios: COVID-19 Experience

The COVID-19 pandemic revealed many vulnerabilities of the contemporary built environment along with limited preparedness and low efficiency in mitigating unexpected and unprecedented challenges. This article discusses the efficiency and responsiveness of basic hospital spatial layouts in three different scenarios: normal operation; the segregation of a large number of patients and still providing them with access to emergency healthcare, typical for a pandemic; and a sudden, extremely high number of admissions typical for compound disasters and terrorist attacks. A set of parameters and a method for general adaptability assessment (GAAT) that can be used as a tool in decision-making processes as well as evaluation of both existing facilities and the new models for resilient hospitals resulting from the experience of the pandemic are proposed. The paper emphasizes why factors among which adaptability, convertibility, and scalability should be at the very core of hospital development and management strategies. It also discusses new models of adaptable healthcare facilities that enable day-to-day operations to continue alongside a pandemic, and other emergency scenarios.

Evaluation of airborne particle exposure for riding elevators

Social distancing is a key factor for health during the COVID-19 pandemic. In many indoor spaces, such as elevators, it is difficult to maintain social distancing. This investigation used computational-fluid-dynamics (CFD) to study airborne particle exposure in riding an elevator in a typical building with 35 floors. The elevator traveled from the ground floor to the 35th floor with two stops on floor 10 and floor 20, comprising 114 s. The CFD simulated the dispersion of the aerosolized particles exhaled by an index person while breathing in both lobby and elevator areas. The study calculated the accumulated dose of susceptible riders riding in elevators with the index person under different conditions including different ventilation rates, air supply methods, and elevator cab geometries. This investigation also studied a case with a single cough from the index person as the person entered the elevator. The results show that, due to the short duration of the average elevator ride, the number of particles inhaled by a susceptible rider was low. For the reference case with a 72 ACH (air changes per hour) ventilation rate, the highest accumulated particle dose by a susceptible passenger close to the index person was only 1.59. The cough would cause other riders to inhale approximately 8 orders of magnitude higher particle mass than from continuous breathing by the index person for the whole duration of the ride.

Reducing indoor virus transmission using air purifiers

Air purifiers are limited to small polluting airborne particles and poor air circulation (fan) for bringing airborne particles inside the device. Thus, the optimal utility of domestic air purifiers (DAPs) for eliminating airborne viruses is still ambiguous. This paper addresses the above limitations using computational fluid dynamics modeling and simulations to investigate the optimal local design of a DAP in an indoor space. We also investigate the integrated fan system and the local transport of airborne viruses. Three different scenarios of using standard DAP equipment ( 144     m 3 / h ) are explored in an indoor space comprising a furnished living room 6 × 6 × 2.5     m 3 . We show that the local positioning of a purifier indoors and the fan system embedded inside it can significantly alter the indoor airborne virus transmission risk. Finally, we propose a new indoor air circulation system that better ensures indoor airborne viruses' local orientation more efficiently than a fan embedded in a standard DAP.

Anthropogenic chemicals and their impacts on microbes living in buildings

Humans spend the vast majority of their time indoors where complex interactions occur among indoor anthropogenic chemicals, indoor microbiomes and human occupants. This paper summarizes previous work addressing interactions between anthropogenic chemicals associated with indoor household products and building materials, and microorganisms found within the built environment. Water availability seems to determine the extent to which microbes are impacted by anthropogenic chemicals, since desiccation remains one of the primary stressors regulating microbial viability indoors. Several lines of evidence suggest that both fungi and bacteria are capable of transforming biodegradable ingredients originating from various products used indoors when water is present. Previous research also establishes positive and significant correlations between anthropogenic chemicals that are antimicrobial and antibiotic resistance gene abundance. As researchers move towards understanding complex indoor environments as well as the role of anthropogenic chemicals in shaping microbiomes, in situ activities associated with the viable indoor microbial population merit more attention.

Which factors influence the extent of indoor transmission of SARS-CoV-2? A rapid evidence review

Background

This rapid evidence review identifies and integrates evidence from epidemiology, microbiology and fluid dynamics on the transmission of SARS-CoV-2 in indoor environments.

Methods

Searches were conducted in May 2020 in PubMed, medRxiv, arXiv, Scopus, WHO COVID-19 database, Compendex & Inspec. We included studies reporting data on any indoor setting except schools, any indoor activities and any potential means of transmission. Articles were screened by a single reviewer, with rejections assessed by a second reviewer. We used Joanna Briggs Institute and Critical Appraisal Skills Programme tools for evaluating epidemiological studies and developed bespoke tools for the evaluation of study types not covered by these instruments. Data extraction and quality assessment were conducted by a single reviewer. We conducted a meta-analysis of secondary attack rates in household transmission. Otherwise, data were synthesised narratively.

Results

We identified 1573 unique articles. After screening and quality assessment, fifty-eight articles were retained for analysis. Experimental evidence from fluid mechanics and microbiological studies demonstrates that aerosolised transmission is theoretically possible; however, we found no conclusive epidemiological evidence of this occurring. The evidence suggests that ventilation systems have the potential to decrease virus transmission near the source through dilution but to increase transmission further away from the source through dispersal. We found no evidence for faecal-oral transmission. Laboratory studies suggest that the virus survives for longer on smooth surfaces and at lower temperatures. Environmental sampling studies have recovered small amounts of viral RNA from a wide range of frequently touched objects and surfaces; however, epidemiological studies are inconclusive on the extent of fomite transmission. We found many examples of transmission in settings characterised by close and prolonged indoor contact. We estimate a pooled secondary attack rate within households of 11% (95% confidence interval (CI) = 9, 13). There were insufficient data to evaluate the transmission risks associated with specific activities. Workplace challenges related to poverty warrant further investigation as potential risk factors for workplace transmission. Fluid mechanics evidence on the physical properties of droplets generated by coughing, speaking and breathing reinforce the importance of maintaining 2 m social distance to reduce droplet transmission.

Conclusions

This review provides a snap-shot of evidence on the transmission of SARS-CoV-2 in indoor environments from the early months of the pandemic. The overall quality of the evidence was low. As the quality and quantity of available evidence grows, it will be possible to reach firmer conclusions on the risk factors for and mechanisms of indoor transmission.

Gaseous pollutant transport from an underground parking garage in a Mediterranean multi-story building-Effect of temporal resolution under varying weather conditions

Indoor air dynamics and quality in high density residential buildings can be complex as it is affected by both building parameters, pollution sources, and outdoor meteorological conditions. The present study used CONTAM simulations to investigate the intra-building transport and concentration of an inert pollutant continuously emitted from an underground garage of a 15-floor building under moderate Mediterranean weather. The effects of outdoor meteorological conditions (air temperature, wind speed and direction) on indoor distribution of the emitted pollutant was tested under constant conditions. The importance of using actual transient meteorological data and the impact of their temporal resolution on calculated concentrations and exposure levels were also investigated. Vertical profiles of air exchange rate (AER) and CO concentration were shown to be sensitive to indoor-outdoor temperature difference, which controls the extent of the stack effect and its importance relative to wind effect. Even under constant conditions, transient mode simulations revealed that the time needed for pollutant distribution to reach steady state can be quite long (>24h in some cases). The temporal resolution (1h vs. 8h) of the meteorological data input was also found to impact calculated exposure levels, in an extent that varied with time, meteorological conditions and apartment position.

On airborne virus transmission in elevators and confined spaces

The impact of air ventilation systems on airborne virus transmission (AVT), and aerosols in general, in confined spaces is not yet understood. The recent pandemic has made it crucial to understand the limitations of ventilation systems regarding AVT. We consider an elevator as a prototypical example of a confined space and show how ventilation designs alone, regardless of cooling or heating, contribute to AVT. Air circulation effects are investigated through multiphase computational fluid dynamics, and the performance of an air purifier in an elevator for reducing AVT is assessed. We have investigated three different flow scenarios regarding the position and operation of inlets and outlets in the elevator and a fourth scenario that includes the operation of the air purifier. The position of the inlets and outlets significantly influences the flow circulation and droplet dispersion. An air purifier does not eliminate airborne transmission. The droplet dispersion is reduced when a pair of an inlet and an outlet is implemented. The overall practical conclusion is that the placement and design of the air purifier and ventilation systems significantly affect the droplet dispersion and AVT. Thus, engineering designs of such systems must take into account the flow dynamics in the confined space the systems will be installed.

Study on the transmission route of virus aerosol particles and control technology of air conditioning in the enclosed space

The patient's breathing and air conditioning system in the enclosed space are the main factors that cause indoor cross-infection. However, the research on the influence and the control mechanism of different air conditioning systems on the transmission path of virus aerosol particles exhaled by patients is still limited. To evaluate the effects of different air conditioning systems on the spread of human exhaled pollutants, computational fluid dynamics (CFD) was used to study the movement and diffusion of exhaled air from two rows of 12 sitting adults in a hospital's closed transfusion room. In this paper, three different air conditioning systems are considered: Ceil-supply and Down-return (Ceil-to-Down), Up-supply and Down-return (Up-to-Down), Down-supply and Up-return (Down-to-Up). The distribution of exhaled air velocity, temperature, and virus particle concentration were studied, and it is found that the horizontal diffusion distance of exhaled pollutants is about 0.75 -1.1 m. When up to down systems are used, the air conditioning system shall be closed in time in case of respiratory infectious diseases, so as to avoid cross-infection in the enclosed space. A relatively clean air area with a height of about 1.1 m will be formed, which can inhibit the transmission of the virus to a certain extent when using the down-to-up system. But for those who are exposed to the enclosed space for a long time, the down-to-up system is not the most suitable air conditioning system.

A Bibliometric Analysis of Corona Pandemic in Social Sciences: A Review of Influential Aspects and Conceptual Structure

Corona pandemic has affected the whole world, and it is a highly researched area in biological sciences. As the current pandemic has affected countries socially and economically, the purpose of this bibliometric analysis is to provide a holistic review of the corona pandemic in the field of social sciences. This study aims to highlight significant, influential aspects, research streams, and themes. We have reviewed 395 journal articles related to coronavirus in the field of social sciences from 2003 to 2020. We have deployed 'biblioshiny' a web-interface of the 'bibliometrix 3.0' package of R-studio to conduct bibliometric analysis and visualization. In the field of social sciences, we have reported influential aspects of coronavirus literature. We have found that the 'Morbidity and Mortality Weekly Report' is the top journal. The core article of coronavirus literature is 'Guidelines for preventing health-care-associated pneumonia'. The most commonly used word, in titles, abstracts, author's keywords, and keywords plus, is 'SARS'. Top affiliation is 'The University of Hong Kong'. Hong Kong is a leading country based on citations, and the USA is on top based on total publications. We have used a conceptual framework to identify potential research streams and themes in coronavirus literature. Four research streams are found by deploying a co-occurrence network. These research streams are 'Social and economic effects of epidemic disease', 'Infectious disease calamities and control', 'Outbreak of COVID 19,' and 'Infectious diseases and the role of international organizations'. Finally, a thematic map is used to provide a holistic understanding by dividing significant themes into basic or transversal, emerging or declining, motor, highly developed, but isolated themes. These themes and subthemes have proposed future directions and critical areas of research.

Numerical investigation of gaseous pollutant cross-transmission for single-sided natural ventilation driven by buoyancy and wind

Single-sided natural ventilation was numerically investigated to determine the impact of buoyancy and wind on the cross-transmission of pollution by considering six window types commonly found in multistory buildings. The goal of this study was to predict the gaseous pollutant transmission using computational fluid dynamics based on the Reynolds-averaged Navier-Stokes equations and baseline k-ω turbulence equations. The results indicated that ventilation rates generally increased with increasing wind speeds if the effects of buoyancy and wind were not suppressed; however, the re-entry ratio representing the proportion of expelled air re-entering other floors and the corresponding risk of infection decreased. If the source of the virus was on a central floor, the risk of infection was the highest on the floors closest to the source. Different window types were also considered for determining their effectiveness in controlling cross-transmission and infection risk, depending on the source location and driving force (e.g., buoyancy and wind).

Numerical investigation of gaseous pollutant cross-transmission for single-sided natural ventilation driven by buoyancy and wind

Single-sided natural ventilation was numerically investigated to determine the impact of buoyancy and wind on the cross-transmission of pollution by considering six window types commonly found in multistory buildings. The goal of this study was to predict the gaseous pollutant transmission using computational fluid dynamics based on the Reynolds-averaged Navier-Stokes equations and baseline k-ω turbulence equations. The results indicated that ventilation rates generally increased with increasing wind speeds if the effects of buoyancy and wind were not suppressed; however, the re-entry ratio representing the proportion of expelled air re-entering other floors and the corresponding risk of infection decreased. If the source of the virus was on a central floor, the risk of infection was the highest on the floors closest to the source. Different window types were also considered for determining their effectiveness in controlling cross-transmission and infection risk, depending on the source location and driving force (e.g., buoyancy and wind).

Investigation on the contaminant distribution with improved ventilation system in hospital isolation rooms: Effect of supply and exhaust air diffuser configurations

This study, that is practice-based learning in a real hospital construction project, has evaluated the ventilation performance of three strategies in the protection of health care workers and HVAC control for airborne infectious diseases induced by contaminated exhaled air from patients in a negative pressure isolation room. This paper examines air flow path and airborne pollutant distribution by computational fluid dynamics modeling and field measurement. In hospitals, the risk of virus diffusion mainly depends on air flow behavior and changes in direction caused by supply air and exhaust air locations. An improved isolation room ventilation strategy has been suggested, and is found to be the most efficient in removing contaminants based on the observations and simulation results from three ventilation systems. The results show that ventilation systems utilizing the "low-level extraction" technique are very effective at removing pollutants in the human breathing zone. A new clean isolation room ventilation strategy has been developed that employs two exhaust air grilles on the wall behind the bed at low floor level, coupled with a fan filter unit, and is found to have the highest pollutant removal efficiency.

Experimental Study on the Aerodynamic Sealing of Air Curtains

Controlling the air quality is of the utmost importance in today’s buildings. Vertical air curtains are often used to separate two different climatic zones with a view to reduce heat transfer. In fact, this research work proposes an air curtain aimed to ensure a proper separation between two zones, a clean one and a contaminated one. The methodology of this research includes: (i) small-scale tests on water models to ensure that the contamination does not pass through the air curtain, and (ii) an analytical development integrating the main physical characteristics of plane jets. In the solution developed, the airflow is extracted from the contaminated compartment to reduce the curtain airflow rejected to the exterior of the compartment. In this research work, it was possible to determine the minimum exhaust flow necessary to ensure the aerodynamic sealing of the air curtain. This article addresses the methodology used to perform the small-scale water tests and the corresponding results.

Residential inter-zonal ventilation rates for exposure modeling

Residential inter-zonal (e.g., between rooms) ventilation is comprised of fresh air infiltration in and exfiltration out of the whole house plus the "fresh" air that is entering (and exiting) the room of interest from other rooms or areas within the house. Clearly, the inter-zone ventilation rate in any room of interest will be greater than the infiltration/exfiltration ventilation rate of outdoor air for the whole house. The purpose of this study is to determine how much greater the inter-zonal ventilation rate is in typical U.S. residences compared to the whole house ventilation rate from outdoor air. The data for this statistical analysis came from HouseDB, a 1995 EPA database of residential ventilation rates. Analytical results indicate that a lognormal distribution provides the best fit to the data. Lognormal probability distribution functions (PDFs) are provided for various inter-zonal ventilation rates for comparison to the PDF for the whole house ventilation rates. All ventilation rates are expressed as air change rates per hour (ACH). These PDFs can be used as inputs to exposure models. This analysis suggests that if one were performing a deterministic analysis for unknown housing stocks in the U.S., a default mean and median ACH values of 0.4/hr and 0.3/hr, respectively, for whole house ventilation would be appropriate; and 0.7/hr and 0.6/hr, respectively, for inter-zonal ventilation.

Gaseous pollutant transmission through windows between vertical floors in a multistory building with natural ventilation

Natural ventilation is an effective strategy to control thermal comfort in buildings, and can be enhanced depending on the window style. The combination of natural ventilation and window can also facilitate the removal or dilution of gaseous pollutants from indoor sources in newly decorated buildings. However, the windows on the same facade may cause gaseous pollutant cross-transmission during single-sided natural ventilation between households on different floors close to the source. Although some research has focused on the pollutant cross-transmission in buildings, the simplification of windows into rectangular openings often affects accurate knowledge of pollutant transmission characteristics. Therefore, this investigation explored gaseous pollutant cross-transmission through real windows during single-sided, buoyancy-driven ventilation in a multistory building. Six types of windows were modeled for the indoor pollutant of gaseous formaldehyde (HCHO). Computational fluid dynamics (CFD) was utilized to solve characteristics of pollutant transmission inside and outside the multistory building. The results indicated that the ventilation rates, thermal profiles and pollutant transmission inside and outside the building varied for each window type, although the open window areas were identical. The re-entry ratio of exhausted air entering upper floors and the infection risk of epidemic viruses caused by airborne cross-transmission was sensitive to ventilation rates and window configurations, while the sensitivities for window configurations varied case by case. The comparisons also revealed that the specification of ambient temperature and pollutant release rate ultimately did not affect the evaluation of pollutant cross-transmission using CFD.

Multi-zone simulation of outdoor particle penetration and transport in a multi-story building

In areas with poor ambient air quality, indoor particle concentrations can be significantly affected by particulate matter originating outdoors. The indoor environments of multi-zone and multi-story buildings are affected differently by outdoor particles compared with single-family houses, because of the buildings' more complicated airflow characteristics. The objective of this study is to analyze outdoor particle penetration and transport, and their impact on indoor air, in a multi-zone and multi-story building using a CONTAMW simulation. For the airflow and particle transport analysis, the building leakage, penetration coefficients, and deposition rates were determined by on-site experiments. The results of airflow simulations for cold winters show that outdoor air infiltrates through the lower part of building and exfiltrates from the upper part. The results of the particle simulation also indicated that the airflow characteristics, combined with deposition rates, cause the lower floors of a multi-story building to be exposed to higher fine particle concentrations compared with the upper floors of the building. The study demonstrated that the CONTAMW simulation can be useful in analyzing the impact of outdoor particles on indoor environments through the identification of key particle transport parameters and validated airflow simulations.

The airborne transmission of infection between flats in high-rise residential buildings: A review

The inter-flat airborne cross-transmission driven by single-sided natural ventilation has been identified recently in high-rise residential buildings, where most people live now in densely populated areas, and is one of the most complex and least understood transport routes. Given potential risks of infection during the outbreak of severe infectious diseases, the need for a full understanding of its mechanism and protective measures within the field of epidemiology and engineering becomes pressing. This review paper considers progress achieved in existing studies of the concerned issue regarding different research priorities. Considerable progress in observing and modeling the inter-flat transmission and dispersion under either buoyancy- or wind-dominated conditions has been made, while fully understanding the combined buoyancy and wind effects is not yet possible. Many methods, including on-site measurements, wind tunnel tests and numerical simulations, have contributed to the research development, despite some deficiencies of each method. Although the inter-flat transmission and dispersion characteristics can be demonstrated and quantified in a time-averaged sense to some extent, there are still unanswered questions at a fundamental level about transient dispersion process and thermal boundary conditions, calling for further studies with more advanced models for simulations and more sound experiments for validations.