Multizone Modelling of SARS-CoV-2 Airborne Transmission in Mechanically Ventilated Buildings

This study contributes to a better understanding of the airborne transmission risks in multizone, mechanically ventilated buildings and how to reduce infection risk. A novel modeling approach combining the Wells-Riley and the US National Institute of Standards and Technology (NIST) CONTAM models was applied to a multizone whole building to simulate exposure and assess the effectiveness of different mitigation measures. A case study for the US Department of Energy large office prototype building was conducted to illustrate the approach. © 2022 17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022. All rights reserved.

Using CONTAM to Design Ventilation Strategy of Negative Pressure Isolation Ward considering Different Height of Door Gaps

Infectious disease departments in hospitals require pressure gradient to create unidirectional airflow to prevent the spread of contaminants, typically by creating active air infiltration through the difference between supply and exhaust air volumes. The door gap is the channel of air flow between rooms, so its height has an important influence on the pressure difference and infiltration air volume of the room. There is still a lack of research on setting reasonable ventilation strategies according to the different height of door gaps at different positions in the building. In this study, model of a set of isolation ward was established and analyzed using the multi-zone simulation software CONTAM, and the ventilation strategies with different height of door gaps were applied to the actual infection diseases department. The results show that in a building with ventilation system divided by functional area, the difference in the height of the door gaps requires different active infiltration air volumes. Pressure fluctuations in the medical and patient corridors are greater than in other rooms. The significance of this study is to understand the active infiltration of air to guide the design and operation of ventilation systems in infectious disease hospitals or building remodeled to isolate close contacts of Covid-19 patients. It is also instructive for the design of pressure gradients in clean workshops, biological laboratories, and other similar buildings.

Evaluating SARS-CoV-2 airborne quanta transmission and exposure risk in a mechanically ventilated multizone office building.

The world has faced tremendous challenges during the COVID-19 pandemic since 2020, and effective clean air strategies that mitigate infectious risks indoors have become more essential. In this study, a novel approach based on the Wells-Riley model applied to a multizone building was proposed to simulate exposure to infectious doses in terms of "quanta". This modeling approach quantifies the relative benefits of different risk mitigation strategies so that their effectiveness could be compared. A case study for the US Department of Energy large office prototype building was conducted to illustrate the approach. The infectious risk propagation from the infection source throughout the building was evaluated. Different mitigation strategies were implemented, including increasing outdoor air ventilation rates and adding air-cleaning devices such as Minimum Efficiency Reporting Value (MERV) filters and portable air cleaners (PACs) with HEPA filters in-room/in-duct germicidal ultraviolet (GUV) lights, layering with wearing masks. Results showed that to keep the risk of the infection propagating low the best strategy without universal masking was the operation of in-room GUV or a large industrial-sized PAC; whereas with masking all strategies were acceptable. This study contributes to a better understanding of the airborne transmission risks in multizone, mechanically ventilated buildings and how to reduce infection risk from a public health perspective of different mitigation strategies.

ENHANCING BATHYMETRIC MAPPING CAPABILITY USING MULTI-ZONE ENSEMBLE FITTING: FACILITATING EMERGING POST COVID-19 DEMANDS

Determination of hydrospatial information across the marine environment has conventionally appeased by vessel-based acoustic surveys. For the first time in history, the unpredictability COVID-19 health crisis has shut down the entire social and economic sectors across the globe. The continuous nationwide lockdown has made it very difficult to mobilize vessels and survey crews for bathymetric mapping. With the emerging remote sensing technology, hydrospatial specialists today have too accustomed to live and work in the new normality. Apparently, hydrography is clearly undergoing dramatic change which an expanded role to serve an increasing number of stakeholders in the blue economy. In order to seek the maximum benefits from the adoption of forth industrial revolution (IR4.0) paradigms, utilization of high-technology sensors and various unmanned autonomous crafts for bathymetric data acquisition to generate actionable data and information to serve the hydrographic communities. In response to the COVID-19 outbreak, hydrographic communities have been forced to accelerate the adoption of emerging technologies to mitigate its impact. Indeed, satellite derived bathymetry (SDB) has become a recognized tool for acquisition to generate actionable hydrospatial data that can alleviate future economic upheavals. Stakeholders are able to extract the bathymetric depth information from the remotely sensed imagery in a split second without physical mobilization and on-site survey. In this paper a new proposed methodology using multi-zone ensemble fitting is introduced for bathymetric determination across the coastal region from high resolution satellite images. By segmentizing the training sets to fit into several designated depth zones, this sequential ensemble fitting approach demonstrates better performance if compares to the traditional single regression algorithm. Derived conclusion points out that newly proposed method can enhance the current bathymetric mapping capability and deliver precise and accurate actionable hydrospatial information in facilitating the emerging demands, in the post COVID-19 era. © ACRS 2021.All right reserved.

A multi-zone spatial flow impact factor model for evaluating and layout optimization of infection risk in a Fangcang shelter hospital

Respiratory infectious diseases have caused several pandemics and scarcity of medical resources. As a temporary hospital for infectious disease patients, the Fangcang shelter hospital requires effective air distribution. We developed the multi-zone SFIF (SFIFM) model by combing a natural ventilation multi-zone model (MIX: Multi-zone Infiltration and eXfiltration) and spatial flow impact factor (SFIF) model, which can calculate the contribution of other zones to the risk of infection in the target zone. Compared with the experimental data in the reference, the model can be used to characterize the influence between zones. A three-zone large building was used for the analysis of the relationship between ventilation rate and SFIFM. An existed Fangcang shelter hospital was evaluated and the layout was optimized with this model. The results showed that both mechanical and natural ventilation would influence SFIFM. By optimizing the layout, the weighted SFIFM on health care worker zone could be reduced by 0.022, and the infection risk could be reduced by 14.42%. This model could more clearly show the relationship between zones, ventilation rate, concentration, and infection risk. It could be applied to evaluate and optimize the location of infectious sources, susceptibles, mechanical ventilation, and purifiers under variable conditions. This model may be helpful in reducing the risk of infection in large space buildings and providing guidance for ensuring public health safety.

Investigation of potential aerosol transmission and infectivity of SARS-CoV-2 through central ventilation systems.

The COVID-19 pandemic has raised concern of viral spread within buildings. Although near-field transmission and infectious spread within individual rooms are well studied, the impact of aerosolized spread of SARS-CoV-2 via air handling systems within multiroom buildings remains unexplored. This study evaluates the concentrations and probabilities of infection for both building interior and exterior exposure sources using a well-mixed model in a multiroom building served by a central air handling system (without packaged terminal air conditioning). In particular, we compare the influence of filtration, air change rates, and the fraction of outdoor air. When the air supplied to the rooms comprises both outdoor air and recirculated air, we find filtration lowers the concentration and probability of infection the most in connected rooms. We find that increasing the air change rate removes virus from the source room faster but also increases the rate of exposure in connected rooms. Therefore, slower air change rates reduce infectivity in connected rooms at shorter durations. We further find that increasing the fraction of virus-free outdoor air is helpful, unless outdoor air is infective in which case pathogen exposure inside persists for hours after a short-term release. Increasing the outdoor air to 33% or the filter to MERV-13 decreases the infectivity in the connected rooms by 19% or 93% respectively, relative to a MERV-8 filter with 9% outdoor air based on 100 quanta/h of 5 µm droplets, a breathing rate of 0.48 m3/h, and the building dimensions and air handling system considered.