ABSTRACT
Ventilation performance plays a significant role in distributing contaminants and airborne infections indoors. Thus, poorly ventilated public spaces may be at high risk due to the presence of both infectious and susceptible people. Adapting HVAC ventilation systems to mitigate virus transmission requires considering ventilation rate, airflow patterns, air balancing, occupancy, and feature placement. The study aims to identify poorly ventilated spaces where airborne transmission of pathogens such as SARS-CoV-2 could be critical. This study is focused on evaluating the ventilation performance of the building stock and the safety of using the facilities based on measured indoor CO2. The results revealed the spaces with the potential risk of indoor airborne transmission of COVID-19. The study proposes recommendations for utilising air ventilation systems in different use cases. © 2022 17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022. All rights reserved.
ABSTRACT
In recent work, a Hierarchical Bayesian model was developed to predict occupants' thermal comfort as a function of thermal indoor environmental conditions and indoor CO2 concentrations. The model was trained on two large IEQ field datasets consisting of physical and subjective measurements of IEQ collected from over 900 workstations in 14 buildings across Canada and the US. Posterior results revealed that including measurements of CO2 in thermal comfort modelling credibly increases the prediction accuracy of thermal comfort and in a manner that can support future thermal comfort prediction. In this paper, the predictive model of thermal comfort is integrated into a building energy model (BEM) that simulates an open-concept mechanically-ventilated office space located in Vancouver. The model predicts occupants' thermal satisfaction and heating energy consumption as a function of setpoint thermal conditions and indoor CO2 concentrations such that, for the same thermal comfort level, higher air changes per hour can be achieved by pumping a higher amount of less-conditioned fresh air. The results show that it is possible to reduce the energy demand of increasing fresh air ventilation rates in winter by decreasing indoor air temperature setpoints in a way that does not affect perceived thermal satisfaction. This paper presents a solution for building managers that have been under pressure to increase current ventilation rates during the COVID-19 pandemic. © 2022 17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022. All rights reserved.
ABSTRACT
The validity of using CO2 as an indicator of airborne infection probability was studied. Tracer gas measurements were conducted in a field lab with two breathing thermal manikins resembling "infected” and "susceptible” persons seated at desks. The room was ventilated with a mixing air distribution. Experiments were performed at three ventilation rates. CO2 gas was dosed into the air exhaled by the manikins to simulate the metabolic CO2 generation by people. Simultaneously, nitrous oxide (N2O) tracer gas was dosed into the air exhaled by one of the manikins ("infected person”) to simulate the emission of exhaled infectious particles. CO2 and N2O concentrations were measured at several points. The probability of infection was calculated based on the concentration of CO2 and N2O measured in the air inhaled by the exposed manikin ("susceptible person”). The results did not confirm that CO2 can be used as a proxy to assess the infection probability. © 2022 17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022. All rights reserved.
ABSTRACT
The coronavirus disease may spread by airborne aerosols, especially in a poorly ventilated enclosure. Natural ventilation can reduce the transmission of infection. The WHO suggested the minimum ventilation rate of 10 L/s/person in non-residential settings. The objective was to evaluate risk of airborne infection with different settings in natural ventilated classroom. The risk was evaluated by using the modified Wells-Riley equation associated with the variation of contaminant concentration simulated by a multi-zone airflow model. The results provide the guidance of natural ventilation strategy in the classroom to reduce the transmission of airborne infection disease. © 2022 17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022. All rights reserved.
ABSTRACT
Under the influence of COVID-19, it is recommended to ventilate to reduce the risk of infection in the room. In an air-conditioned room, window open can increased the ventilation rate that caused by indoor and outdoor temperature difference. However, there is a concern that opening window in the air-conditioned room will increase the heating and cooling load due to air leakage. In addition, it is difficult to maintain the appropriate ventilation rate because the outdoor air temperature changes time to time. To solve this problem, we have developed an automatic window opening system to control the natural ventilation rate. In this study, actual measurements were conducted to understand the operating performance of the system, and its effect on the indoor thermal environment. As a result, it was confirmed that the ventilation rate could be controlled by this system. © 2022 17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022. All rights reserved.
ABSTRACT
To quantitatively evaluate the effect of increasing ventilation using the immediately practicable method on infection risk, the ventilation rate in a classroom was measured by the concentration decay method using CO2. The measured value was then substituted into the Wells-Riley model to evaluate aerosol infection risk in steady and non-steady states. In the classroom, the air change rate per hour (ACH) ranged from 3.1 to 10.2, and the local mean age of air tended to be larger near the outlet. It was also shown that opening the windows increased the ventilation rate the most, resulting in a more evenly distributed local mean age of air. We also showed that the aerosol infection risk in the classroom could be significantly reduced by increasing ventilation, suppressing vocalization, and wearing a mask, compared to some outbreaks of COVID-19. © 2022 17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022. All rights reserved.
ABSTRACT
Site visits were made to ten (non-healthcare) workplace COVID-19 outbreaks to assess ventilation. Measurements of carbon dioxide (CO2), temperature and humidity were made. Room activity and occupancy was observed, and ventilation management assessed. CO2 readings were used to identify areas of poor air quality, and where possible, airflow measurements were made at ventilation openings and CO2 decay rates were used to estimate ventilation rates. Poorly ventilated, regularly occupied spaces were frequently identified by this work. Measures to reduce transmission risk and improve ventilation included opening windows and reducing room capacities. Attempts at reconfiguration of mechanical ventilation systems were not common. Thermal comfort and heating costs were factors cited that influenced decision making. Overall understanding of ventilation was low and identified a need for simple tools to allow stakeholders to assess their workspaces. © 2022 17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022. All rights reserved.
ABSTRACT
This study investigates the effectiveness of an upper-room UVGI system in a small classroom. Mixing ventilation can increase virus removal when combined with a UVGI system more effectively than displacement ventilation combined with a UVGI system, especially in cases where the ventilation rate is low. © 2022 17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022. All rights reserved.
ABSTRACT
Air temperature and CO2 concentration were measured in classrooms with ventilation system from April 2018 through March 2022. It is assumed that, under the COVID-19 circumstances, windows of the classrooms, where ventilation system was working, were basically kept open throughout a year. The average air temperature at foot level was 11℃ during winter period because of cold outdoor air infiltration. The estimated ventilation rate tended to decrease during winter period. However, the estimated ventilation rate per person more than 30 m3/h was obtained in case of half number of pupils in the classroom with Hybrid-Flexible lesson for the whole day. © 2023 Architectural Institute of Japan. All rights reserved.
ABSTRACT
School classrooms are often reported as having insufficient ventilation with elevated indoor CO2 concentrations. This paper reports on pre-pandemic field measurements of CO2 concentration levels conducted for an academic year in 10 classrooms from four primary and a secondary school in Victoria, Australia. Measured CO2 concentrations across the 10 classrooms which were operated with a mix of intermittent natural ventilation and air-conditioning for cooling or heating, on average ranged between 657 ppm and 2235 ppm during school hours with median over 1000 ppm in 70% of classrooms. All 10 classrooms in the study exceeded the Australian recommended limit of 850 ppm. Using average peak CO2 concentrations from year-long measurements, estimated ventilation rate (VR) of 4.08 Ls-1 per person show under-performing classrooms where 60% had VRs 35–40% lower than the 10-12 Ls−1 per person Australian recommendation. Estimated VR range of 1.24–2.07 Ls-1 per person using peak maximum CO2 levels were 19–30% lower than ASHRAE recommendation of 6.7 Ls-1 per person. These VRs translate to a range of air change rates on average between 0.52 and 0.88 h−1 ± 0.26–0.59, well below the 6.0 h−1 recommendation for good indoor ventilation by the World Health Organisation in the context of COVID-19 pandemic. Characterisation of ventilation and indoor air quality in current Australian classroom stock is critical for the improvement of classroom design, induction on room operating practices, understanding of the school community on the relevance of building ventilation on school performance and health, and development of appropriate ventilation and indoor air quality guidelines for schools. © 2023 The Authors
ABSTRACT
Most people spend 80-90% of their lives indoors. This makes controlling the airborne transmission of respiratory viruses such as influenza, rhinovirus, SARS, and COVID-19 in indoor environments important for healthy building outcomes. Though direct transmission from droplets and surfaces is usually a more effective means of infection transfer, buildings need to operate assuming aerosol transmission can be a serious risk. This study used simulations to assess the impacts of occupant density and ventilation rates as control measures to reduce the risk of aerosol transmission of COVID-19 in large and small offices. The simulation outputs were selected to correspond with in situ CO2 sensors and control points. The results of the simulation can be used to set targets for CO2 and other parameters that can be measured by low-cost sensors to manage risk of infection due to aerosol transmission. © International Building Performance Simulation Association, 2022
ABSTRACT
Since the beginning of the COVID19 pandemic, there has been a lack of data to quantify the role played by breathing-out of pathogens in the spread of SARS-Cov-2 despite sufficient indication of its culpability. This work aims to establish the role of aerosol dispersion of SARS-Cov-2 virus and similar airborne pathogens on the spread of the disease in enclosed spaces. A steady-state fluid solver is used to simulate the air flow field, which is then used to compute the dispersion of SARS-Cov-2 and spatial probability distribution of infection inside two representative classrooms. In particular, the dependence of the turbulent diffusivity of the passive scalar on the air changes per hour and the number of inlet ducts has been given due consideration. By mimicking the presence of several humans in an enclosed space with a time-periodic inhalation-exhalation cycle, this study firmly establishes breathing as a major contributor in the spread of the pathogen, especially by superspreaders. Second, a spatial gradient of pathogen concentration is established inside the domain, which strongly refutes the well-mixed theory. Furthermore, higher ventilation rates and proximity of the infected person to the inlet and exhaust vents play an important role in determining the spread of the pathogen. In the case of classrooms, a ventilation rate equivalent to 9 air changes or more is recommended. The simulations show that the "one-meter distance rule"between the occupants can significantly reduce the risk of spreading infection by a high-emitter. © 2023 Author(s).
ABSTRACT
TB, COVID-19, MERS, and SARS are all serious infectious diseases that are transmitted by the air or aerosol via coughing, spitting, sneezing, speaking, or wounds. When restaurants and bars reopen and continue operations in some parts of the United States, the Centers for Disease Control and Prevention (CDC) gives the following suggestions for how operators can reduce risk for employees, customers, and communities while also restricting the spread of COVID-19. The more and longer a person interacts with others, the greater the risk of COVID-19 spreading. Therefore, we need to be informed of its management and treatment. As a result, for the control and reduction of potentially polluted air, such as CO2 levels, good air quality management is required. They investigated the protective effectiveness of face masks against airborne transmission of infectious SARS-CoV-2 droplets and aerosols in response to the World Health Organization's recommendation to wear face masks to prevent the spread of COVID-19. Using nine different forms of mask efficiency, this research provides a mathematical model for calculating the chance of airborne transmission in a classroom. The fourth-order Runge-Kutta approach is used to approximate the model solution. The proposed strategy strikes a balance between the number of students allowed to stay in the classroom and the effectiveness of nine different masks. We can see how utilizing nine different masks and a well-ventilated system in the classroom can help to reduce the risk of airborne infection. © 2023, IAENG International Journal of Applied Mathematics. All Rights Reserved.
ABSTRACT
The COVID-19 pandemic has urged the need to reconsider how our built environments influence our health conditions. The new guidelines have highlighted the importance of environmental settings in the virus transmission process. Given that external air ventilation is a major element of a building's energy performance, it is necessary to investigate the influence of the new settings on the building's energy consumption. This study aims to determine the energy performance and infection risk of underfloor air distribution UFAD and overhead systems OH when exposed to varying levels of external air ventilation. The findings indicate that raising the rate of outside ventilation increases a building's energy usage in all climates. It is also shown that the UFAD system shows its energy-saving potential the most in cold climates and higher ventilation rates. These findings suggest that it is critical to consider distinct ventilation techniques to prevent rising energy consumption rates while lowering the risk of viral transmission. © 2022 Society for Modeling & Simulation International (SCS)
ABSTRACT
Houses are the places where people spend most of their time. That is why indoor air quality at home is essential for public health. Sufficient ventilation is the factor to avoid accumulation of pollutants in indoor air, which include microorganisms, such as SARS-CoV-2. Therefore, adequate ventilation is needed to provide good indoor air quality for human health and reduce infection risk at home. There are no reports of residential ventilation rates in Turkey. In this study, CO2 concentrations were measured in two residences in Izmir, Turkey. Three experiments were conducted to determine background concentrations and the rate of natural ventilation with infiltration and opening windows. Results show that air exchange provided by infiltration is low for both case rooms, while adequate ventilation could be achieved with natural ventilation under the studied conditions. Infiltration provided air exchange and ventilation rates of 0.18 h-1 and 5.9 m3/h for Case 1 and 0.29 h-1 and 8.23 m3/h for Case 2, respectively. Air exchange and ventilation rates were increased to 2.36 h-1 and 76.9 m3/h for Case 1 and 1.2 h-1 and 34 m3/h for Case 2, respectively, by opening the windows. Although ventilation can be provided by opening the windows, the other factors that determine its rate, e.g., meteorological variables, cannot be controlled by the occupants. Consequently, people cannot ensure the good indoor air quality in bedrooms and sufficient reduction in transmission of pathogenic microorganisms;therefore, risk of spreading diseases such as COVID-19 at home. © 2022 by the Author(s).
ABSTRACT
Suspected and confirmed cases of infectious diseases such as COVID-19 are diagnosed and treated in specific hospital isolation wards, posing a challenge to preventing cross-infection between patients and healthcare workers. In this study, the Euler-Lagrange method was used to simulate the evaporation and dispersion of droplets with full-size distribution produced by fluctuating coughing and breathing activities in an isolation ward. The effects of supply air temperature and relative humidity, ventilation rates and patient postures on droplet distribution were investigated. The numerical models were validated by an aerosol experiment with an artificial saliva solution containing E. coli bacteria conducted in a typical isolation ward. The results showed that the small size group of droplets (initial size ≤87.5 µm) exhibited airborne transmission in the isolation ward, while the large size group (initial size ≥112.5 µm) were rapidly deposited by gravitational effects. The ventilation rate had a greater effect on the diffusion of droplet nuclei than the supply air temperature and relative humidity. As the air changes per hour (ACH) increased from 8 to 16, the number fraction of suspended droplet nuclei reduced by 14.2% and 6.4% in the lying and sitting cases, respectively, while the number fraction of escaped droplet nuclei increased by 16.2% and 14.6%. Regardless of whether the patient was lying or sitting, the amount of droplet nuclei deposited on the ceiling was highest at lower ventilation rates. These results may provide some guidance for routine disinfection and ventilation strategies in hospital isolation wards.
ABSTRACT
The COVID-19 pandemic has urged the need to reconsider how our built environments influence our health conditions. The new guidelines have highlighted the importance of environmental settings in the virus transmission process. Given that external air ventilation is a major element of a building's energy performance, it is necessary to investigate the influence of the new settings on the building's energy consumption. This study aims to determine the energy performance and infection risk of underfloor air distribution UFAD and overhead systems OH when exposed to varying levels of external air ventilation. The findings indicate that raising the rate of outside ventilation increases a building's energy usage in all climates. It is also shown that the UFAD system shows its energy-saving potential the most in cold climates and higher ventilation rates. These findings suggest that it is critical to consider distinct ventilation techniques to prevent rising energy consumption rates while lowering the risk of viral transmission. © 2022 SCS.
ABSTRACT
Featured Application: Periodic ventilation can be a useful strategy for reducing the risk of any airborne transmitted disease. It is particularly well-suited for naturally ventilated environments in cold weathers, as it allows for a compromise between IAQ and thermal comfort, and does not require any modification to existing buildings. The importance of Indoor Air Quality (IAQ) has been highlighted by the COVID-19 pandemic, particularly due to the possibility of long-distance airborne transmission. Consequently, assessment of ventilation rates and estimation of infection risk has become a matter of the utmost importance. In this paper, a naturally ventilated elementary school classroom is studied, where carbon dioxide ((Formula presented.)) concentrations were measured during five months. Ventilation rates are calculated via a fully-mixed box model and the airborne risk of infection for SARS-CoV-2 is assessed. Risk results are found to steadily decline from winter to spring. Furthermore, analytical simulations for different scenarios are conducted. It is shown that periodic ventilation significantly reduces the transmission risk, even if it occurs only during very reduced time spans. The results show that periodic ventilation is a useful strategy for reducing the risk of any airborne transmitted disease. It is particularly well-suited for naturally ventilated environments in cold weathers, as it allows for a compromise between IAQ and thermal comfort, and does not require any modification to existing buildings. © 2022 by the authors.
ABSTRACT
Leading health authorities have suggested short-range airborne transmission as a major route of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). However, there is no simple method to assess the short-range airborne infection risk or identify its governing parameters. We proposed a short-range airborne infection risk assessment model based on the continuum model and two-stage jet model. The effects of ventilation, physical distance and activity intensity on the short-range airborne exposure were studied systematically. The results suggested that increasing physical distance and ventilation reduced short-range airborne exposure and infection risk. However, a diminishing return phenomenon was observed when the ventilation rate or physical distance was beyond a certain threshold. When the infectious quantum concentration was less than 1 quantum/L at the mouth, our newly defined threshold distance and threshold ventilation rate were independent of quantum concentration. We estimated threshold distances of 0.59, 1.1, 1.7 and 2.6 m for sedentary/passive, light, moderate and intense activities, respectively. At these distances, the threshold ventilation was estimated to be 8, 20, 43, and 83 L/s per person, respectively. The findings show that both physical distancing and adequate ventilation are essential for minimising infection risk, especially in high-intensity activity or densely populated spaces.
ABSTRACT
After the outbreak of COVID-19, it is worrisome that how to cope with the spread of the pandemic. Ventilation is the most important engineering control measure, ASHRAE, REHVA, SHASE and authoritative institutions in China have issued many documents on how to apply HVAC system to prevent and control the spread of COVID-19, and thus this paper summarizes the contents related to the ventilation rate and air distribution. Besides, traditional total volume ventilation has the disadvantages of insufficient ventilation rate, less efficiency for short-term exposure events at short range and high energy consumption during the pandemic. Source control based on advanced air distribution has the advantages of high control efficiency, personalized adjustable, fast response and high energy saving potential, which can make up the disadvantages of the total volume ventilation scheme. Therefore, this paper systematically summarizes the technical types of source control based on advanced air distribution in coping the spread of respiratory infectious diseases. Considering that the design of ventilation system in the post-pandemic era is facing the development of "combination of normal time and pandemic period", the advantages of applying source control in the post-pandemic era and the application schemes of source control in high-risk scenarios are discussed, and the directions that need to be further explored in order to implement the design concept of"combination of normal time and pandemic period" are also discussed. This paper aims to provide a reference for the compilation of subsequent guidelines, and to bring some new ideas and enlightenments to the ventilation design for future pandemic prevention. © 2022, Editorial Department of Journal of Hunan University. All right reserved.