Room HVAC Influences on the Removal of Airborne Particulate Matter: Implications for School Reopening during the COVID-19 Pandemic

Holistic understanding of ventilation rate in occupational health risk control

Throughout the history of occupational health risk control, ventilation has been implemented widely as a tried-and-true method to reduce exposure intensity to airborne contaminants. Proper determination of the ventilation rate merits careful consideration when addressing concerns directed toward occupational health and indoor air quality in commercial buildings, albeit this does not translate well among the current engineering and scientific community. This article aims to facilitate a better understanding and proper determination of ventilation rates as a countermeasure for occupational health risk control. To that end, guidance is provided to select the appropriate ventilation rate for nonpandemic versus pandemic scenarios in terms of pertinent regulatory/professional codes and mathematical modeling tools. Limitations and assumptions of the models are summarized to facilitate proper application. Furthermore, the emerging DNA-based aerosol tracing technology, which helps to verify ventilation efficacy, is discussed.

Implemented indoor airborne transmission mitigation strategies during COVID-19: a systematic review

The COVID-19 pandemic has inflicted major economic and health burdens across the world. On the other hand, the potential airborne transmission of SARS-COV-2 via air can deeply undermine the effectiveness of countermeasures against spreading the disease. Therefore, there is an intense focus to look for ways to mitigate the COVID-19 spread within various indoor settings. This work systematically reviewed articles regarding airborne transmission of SARS-COV2 in various indoor settings since the onset of the pandemic. The systematic search was performed in Scopus, Web of Science, and PubMed databases and has returned 19 original articles carefully screened with regard to inclusion and exclusion criteria. The results showed that the facilities, such as dormitories and classrooms, received the most attention followed by office buildings, healthcare facilities, residential buildings, and other potential enclosed spaces such as a metro wagon. Besides, the majority of the studies were conducted experimentally while other studies were done using computer simulations. United States (n = 5), Spain (n = 4) and China (n = 3) were the top three countries based on the number of performed research. Ventilation rate was the most influential parameter in controlling the infection spread. CO₂ was the primary reference for viral spread in the buildings. The use of natural ventilation or a combination of mechanical and natural ventilations was found to be highly effective in the studies. The current work helps in furthering research on effective interventions to improve indoor air quality and control the spread of COVID-19 and other respiratory diseases.

Supplementary information

The online version contains supplementary material available at 10.1007/s40201-023-00847-0.

Reducing Virus Transmission from Heating, Ventilation, and Air Conditioning Systems of Urban Subways

Aerosols carrying the virus inside enclosed spaces is an important mode of transmission for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), as supported by growing evidence. Urban subways are one of the most frequented enclosed spaces. The subway is a utilitarian and low-cost transit system in modern society. However, studies are yet to demonstrate patterns of viral transmission in subway heating, ventilation, and air conditioning (HVAC) systems. To fill this gap, we performed a computational investigation of the airflow (and associated aerosol transmission) in an urban subway cabin equipped with an HVAC system. We employed a transport equation for aerosol concentration, which was added to the basic buoyant solver to resolve the aerosol transmission inside the subway cabin. This was achieved by considering the thermal, turbulent, and induced ventilation flow effects. Using the probability of encountering aerosols on sampling surfaces crossing the passenger breathing zones, we detected the highest infection risk zones inside the urban subway under different settings. We proposed a novel HVAC system that can impede aerosol spread, both vertically and horizontally, inside the cabin. In the conventional model, the maximum probability of encountering aerosols from the breathing of infected individuals near the fresh-air ducts was equal to 51.2%. This decreased to 3.5% in the proposed HVAC model. Overall, using the proposed HVAC system for urban subways led to a decrease in the mean value of the probability of encountering the aerosol by approximately 84% compared with that of the conventional system.

Challenges and Actions of IAQ under COVID-19: A Survey of Taiwanese People's Perception of Epidemic Prevention and Indoor Places Certification

COVID-19 is still spreading around the world, and the pandemic has awakened the public's attention to environmental cleanliness. This article used an online survey for people living in Taiwan, and a total of 1206 valid questionnaires were collected in October 2021. According to the survey results of Taiwanese people's awareness of and needs for epidemic prevention and IAQ, 94.4% of the respondents agreed that maintaining IAQ during the COVID-19 pandemic is very important for prevention. In addition, 95.4% of them also pointed out that the "Clean and Safe" mark certification should be promoted in public places. Finally, this article also uses hierarchical regression to analyze public perceptions of seven indoor places, including elevators, restaurants, dwellings, offices, gyms, kindergartens, and long-term care centers. The results found that: (1) from the perspective of epidemic prevention, improving IAQ through ventilation strategies could prevent the spread of the COVID-19 pandemic, and (2) from the perspective of promotion certification, the elevators, restaurants and offices could establish strengthened IAQ, dwellings, gyms and long-term care centers should emphasize the display of IAQ information in entrances and exits, and kindergartens should focus on increasing safety and reducing infection.

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.