Can CO2 be used as an indicator of the probability of cross-infection?

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.

Estimating SARS-CoV-2 infection risk in university dormitories using CO2 pulse injections

Air movement dynamics within three student dormitories were studied with simulated carbon dioxide (CO2) pulse injections to understand SARS-CoV-2 transmission risk. CO2 decay rate, proportion of shared air, and transport time were calculated from dynamic CO2 measurement data within simulated source and adjacent receptor rooms. Applying a Wells-Riley infection risk analysis with these results, the risk of SARS-CoV-2 infection in adjacent rooms ranged from 1% to 58% assuming an average emission rate of 5 quanta per hour and exposure duration of 3.5 days. Door opening status was very influential in resulting risk and vertical transport from source to above rooms was observed in all dormitories. © 2022 17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022. All rights reserved.

Assessment of diffuse ceiling ventilation performance on transmission of airborne infectious diseases

Ventilation systems have been widely used to satisfy the occupants' indoor air quality and thermally comfort conditions. Various air distribution systems have been developed to supply clean air, including mixing, displacement, and diffuse ceiling ventilation systems. Diffuse ceiling systems are recent air distribution systems that supply cold air to the occupant area using perforated diffuse panels. These systems distribute air with a low velocity, minimizing the draft risk and dissatisfaction in highly dense spaces. The transmission risk of airborne infectious diseases like Covid-19 from the infected patient is high in waiting rooms. Thus, there is a demand to assure a secure environment for medical staff and patients in the waiting rooms. This study aims to numerically investigate the impact of the relative distance of the contamination source and exhaust on the transmission of airborne infectious diseases in the waiting room equipped with the diffuse ceiling ventilation system. In this regard, the release of Covid-19 from 4 different patients was investigated separately using the computational fluid dynamics technique. The distribution of the airborne infectious diseases is simulated by releasing SF6 tracer gas. The simulation result revealed that the contaminated patient located adjacent to the room's outlet had no contamination risk for other patients and staff in the waiting room. © 2022 17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022. All rights reserved.

Ventilation Assessment at an Elderly-Care Home in Belgium After a Covid-19 Outbreak

Following a COVID-19 outbreak in an elderly-care home in Belgium by winter/2020, an assessment of the ventilation conditions at said care home was conducted in summer/2021. Four common-rooms were selected as the most-likely involved in the outbreak and assessed via (artificially-injected) CO2-decay test for average air change rates (ACHs) measurement. Two of the rooms were also assessed via passive tracer gas test for long-term ACHs measurement, using decane-D22 as tracer. The average ACHs measured (via both methods) ranged from 1, 8 to 3, 6 h-1 in summertime, being thus probably higher than the ACHs during the outbreak. Nevertheless, none of the ACHs measured comply with the latest recommendations for COVID-19 prevention. Ventilation grilles and decentralized ventilation systems in common areas could enhance the building's ventilation, but thoughtful installation is essential;experience shows that thermal discomfort often leads to closing ventilation grilles even during a pandemic, resulting in significantly diminished fresh-air supply. © 2022 17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022. All rights reserved.

A Novel IoT-Enabled Wireless Sensor Grid for Spatial and Temporal Evaluation of Tracer Gas Dispersion.

Current IoT applications in indoor air focus mainly on general monitoring. This study proposed a novel IoT application to evaluate airflow patterns and ventilation performance using tracer gas. The tracer gas is a surrogate for small-size particles and bioaerosols and is used in dispersion and ventilation studies. Prevalent commercial tracer-gas-measuring instruments, although highly accurate, are relatively expensive, have a long sampling cycle, and are limited in the number of sampling points. To enhance the spatial and temporal understanding of tracer gas dispersion under the influence of ventilation, a novel application of an IoT-enabled, wireless R134a sensing network using commercially available small sensors was proposed. The system has a detection range of 5-100 ppm and a sampling cycle of 10 s. Using Wi-Fi communication, the measurement data are transmitted to and stored in a cloud database for remote, real-time analysis. The novel system provides a quick response, detailed spatial and temporal profiles of the tracer gas level, and a comparable air change rate analysis. With multiple units deployed as a wireless sensing network, the system can be applied as an affordable alternative to traditional tracer gas systems to identify the dispersion pathway of the tracer gas and the general airflow direction.

Mitigation of breathing contaminants: Exhaust location optimization for indoor space with impinging jet ventilation supply

Densely occupied spaces (e.g., classrooms) are generally over-crowded and pose a high risk of cross-infection during the pandemic of COVID-19. Among various ventilation systems, impinging jet ventilation (IJV) system might be promising for such spaces. However, the exhaust location of the IJV system used for densely occupied classrooms is unclear. This study aims to investigate the effects of exhaust location on the removal of exhaled contaminants in a classroom (15 × 7 × 5 m3) occupied by 50 students. Exhaled contaminants are modeled by a tracer gas released at the top of each manikin. The reference case has three exhausts evenly distributed in the ceiling. The results indicate that: a) a recirculation airflow entraining exhaled contaminants exists above the occupied zone;b) this recirculation air flow entrains contaminants and accumulates them at the upper part of the room near the diffuser;c) locating merely one exhaust on the same side of the supply diffuser leads to the best indoor air quality, i.e., it reduces the mean age of air from 278 s to 243 s, the mass fraction of CO2 from 753 ppm to 726 ppm, and the concentration of tracer gas from 305 ppm to 266 ppm;d) this layout still performs the best when the supply velocity drops to 0.5 m/s. It is worth noting that the proposed layout has fewer exhausts than the reference case but performs better. These results conclude that the exhaust for large spaces is not evenly distributed but depends on the indoor airflow pattern: the key is locating the exhaust near the region with high contaminant concentration. Factors determining the recirculation airflow are suggested to be further studied. © 2023 Elsevier Ltd

Evaluating methods for estimating whole house air infiltration rates in summer: implications for overheating and indoor air quality

PurposeAccurate values for infiltration rate are important to reliably estimate heat losses from buildings. Infiltration rate is rarely measured directly, and instead is usually estimated using algorithms or data from fan pressurisation tests. However, there is growing evidence that the commonly used methods for estimating infiltration rate are inaccurate in UK dwellings. Furthermore, most prior research was conducted during the winter season or relies on single measurements in each dwelling. Infiltration rates also affect the likelihood and severity of summertime overheating. The purpose of this work is to measure infiltration rates in summer, to compare this to different infiltration estimation methods, and to quantify the differences.Design/methodology/approachFifteen whole house tracer gas tests were undertaken in the same test house during spring and summer to measure the whole building infiltration rate. Eleven infiltration estimation methods were used to predict infiltration rate, and these were compared to the measured values. Most, but not all, infiltration estimation methods relied on data from fan pressurisation (blower door) tests. A further four tracer gas tests were also done with trickle vents open to allow for comment on indoor air quality, but not compared to infiltration estimation methods.FindingsThe eleven estimation methods predicted infiltration rates between 64 and 208% higher than measured. The ASHRAE Enhanced derived infiltration rate (0.41 ach) was closest to the measured value of 0.25 ach, but still significantly different. The infiltration rate predicted by the "divide-by-20” rule of thumb, which is commonly used in the UK, was second furthest from the measured value at 0.73 ach. Indoor air quality is likely to be unsatisfactory in summer when windows are closed, even if trickle vents are open.Practical implicationsThe findings have implications for those using dynamic thermal modelling to predict summertime overheating who, in the absence of a directly measured value for infiltration rate (i.e. by tracer gas), currently commonly use infiltration estimation methods such as the "divide-by-20” rule. Therefore, infiltration may be overestimated resulting in overheating risk and indoor air quality being incorrectly predicted.Originality/valueDirect measurement of air infiltration rate is rare, especially multiple tests in a single home. Past measurements have invariably focused on the winter heating season. This work is original in that the tracer gas technique used to measure infiltration rate many times in a single dwelling during the summer. This work is also original in that it quantifies both the infiltration rate and its variability, and compares these to values produced by eleven infiltration estimation methods.

Using the big data analysis and basic information from lecture Halls to predict air change rate

School lecture halls are often designed as confined spaces. During the period of COVID-19, indoor ventilation has played an even more important role. Considering the economic reasons and the immediacy of the effect, the natural ventilation mechanism becomes the primary issue to be evaluated. However, the commonly used CO2 tracer gas concentration decay method consumes a lot of time and cost. To evaluate the ventilation rate fast and effectively, we use the common methods of big data analysis - Principal Component Analysis (PCA), K-means and linear regression to analyze the basic information of the lecture hall to explore the relation between variables and air change rate. The analysis results show that the target 37 lecture halls are divided into two clusters, and the measured 11 lecture halls contributed 64.65%. When analyzing the two clusters separately, there is a linear relation between the opening area and air change rate (ACH), and the model error is between 6% and 12%, which proves the feasibility of the basic information of the lecture hall by calculating the air change rate. © 2023 Elsevier Ltd

Non-contact Screening Center of Infectious Diseases for Cross Infection Prevention-Focusing on the Viral Aerosol Removal Efficiency by a Ventilation System

In this study, to fundamentally solve the risk of cross-infection in screening centers responding to infectious diseases, a new non-contact screening center was developed that supplemented the problems of existing screening centers. Numerical analysis was performed on the effectiveness of a ventilation system to remove viral aerosols and prevent cross-infection. Moreover, full-scale field measurements and SF6 tracer gas simulating viral aerosol was used under the same conditions as it was for the numerical analysis, comparison, and verification when CFD simulations were performed. Currently, COVID-19 screening centers operating in Korea can be divided into five types;the risk of cross-infection is very high due to its structure where the movement of medical staff and suspected patients cannot be separated. As a result of the CFD simulation on the ventilation system of a non-contact screening center, among the 3,000 particles generated from a patient, not a single particle was transmitted from the specimen collection booth to the adjacent examination room. More than 99% of the particles were removed by the ventilation system after 559 seconds. As a result of the in-situ measurement, the concentration of SF6 gas generated in the specimen collection booth was effectively reduced by the ventilation system. Additionally, the SF6 gas was not detected in the examination room due to the maintenance of an appropriate differential pressure. © 2022, Architectural Institute of Korea. All rights reserved.

Ventilation Efficiency According to Tilt Angle to Reduce the Transmission of Infectious Disease in Classroom

Understanding of the droplet transmission of respiratory diseases is necessary to control the outbreak of COVID-19. HVAC systems considering droplet transmission are commonly used to prevent numerous respiratory diseases by reducing indoor virus concentrations. The transmission of the virus was directly related to indoor flow patterns generated by HVAC systems. Thus, a study on operating conditions such as direction or the tilt angle was required. In this study, the effective ventilation rate and probability of droplet transmission according to the tilt angle of supply air and the number of people were studied. A CO2 tracer gas method was used to validate the results of simulations. The breathing plane and personal respiratory zone were introduced for the probability of droplet transmission. The result showed that ventilation performance showed 17% of the maximum difference among tilt angles. Various turbulent kinetic energies were obtained according to the seated positions, resulting in non-uniform CO2 concentration. Numerous conditions were examined with locational analysis of individuals. As a result, the flow rates for ventilation were recommended to be higher than 250 m(3)/h and 350 m(3)/h with a tilt angle of 60 degrees for an occupancy of 8 and 16 people, respectively.

Numerical Simulations of the Effects of the Radiant Floor Combined with the Displacement Ventilation of the Spread of Exhaled Contaminants in the Confined Space

The COVID-19 pandemic has seen the importance of confined space ventilation to reduce the risks of cross infection. To evaluate and compare the relative impacts of different mitigation strategies is important in order to reduce the risk of infection in a given situation. Using CFD methods, this study aimed to modulate the spread of exhaled contaminants in a floor-heated and ventilated space. Three different inlet velocities and four floor temperatures were used to assess the effect of the radiant floor combined with the displacement ventilation (RFDV) on room airflow and pollutant spread. Results show that RFDV reduced exposure to infection from 87% to 50% compared to the reference case. The inlet velocity is required to increase when the floor temperature is higher to decrease the contaminant exposure risk to in the room. This research provides a timely and necessary study of the ventilation and heating systems. These findings are expected to be useful for designing future of RFDV. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

Analysis of aerosol spreading in a German Inter City Express (ICE) train carriage

This paper focuses on the propagation of aerosols in a rolling stock passenger compartment. Extensive measurements were carried out in our stationary test vehicle DIRK, an ICE 2 rail car, operated in a climate chamber. It is shown that the propagation of aerosols only occurs for a distance of a few seat rows. Furthermore, the maximum percentage of particles exhaled by a passenger and inhaled by another passenger is less than 0.35%. A mouth-nose-protection (surgical mask) at the aerosol source reduces this value to a maximum of 0.25%. Moreover, the use of a mouth-nose-cover reduced the propagation lengths. Here, only the effect of the mask at the source was considered, a further reduction of inhaled aerosols will be achieved when the receivers also wear masks. It is concluded that, for this type of passenger coach, the indirect propagation of aerosols, i.e., via the HVAC system, is nearly irrelevant compared to the direct propagation from one passenger to another. However, there is a non-zero aerosol transport via the HVAC system, resulting in local inhaled particles far away from the source of around 0.015–0.026%, which is more than one order of magnitude lower than on the most highly contaminated seats.

Tempo-spatial infection risk assessment of airborne virus via CO2 concentration field monitoring in built environment.

The aerosol transmission was academically recognized as a possible transmission route of Coronavirus disease 2019 (COVID-19). We established an approach to assess the indoor tempo-spatial airborne-disease infection risks through aerosol transmission via real-time CO2 field measurement and occupancy monitoring. Compared to former studies, the proposed method can evaluate real-time airborne disease infection risks through aerosol transmission routes. The approach was utilized in a university office. The accumulated infection risk was calculated for three occupants with practical working schedules (from occupancy recording) and one hypothesis occupant with a typical working schedule. COVID-19 was used as an example. Results demonstrated that the individual infection risks diversified with different dwell times and working places in the office. For the three occupants with a practical working schedule, their 3-day accumulated infection risks were respectively 0.050%, 0.035%, 0.027% and 0.041% due to 11.6, 9.0 and 13.8 h exposure with an initial infector percentage of 1%. The results demonstrate that location and dwell time are both important factors influencing the infection risk of certain occupant in built environment, whereas existing literature seldom took these two points into consideration simultaneously. On the contrary, our proposed approach treated the infection risks as place-by-place, time-by-time and person-by-person diversified in the built environment. The risk assessment results can provide early warning for building occupants and contribute to the transmission control of air-borne disease.

Investigating dilution ventilation control strategies in a modern U.S. school bus in the context of the COVID-19 pandemic.

Fresh air ventilation has been identified as a widely accepted engineering control effective at diluting air contaminants in enclosed environments. The goal of this study was to evaluate the effects of selected ventilation measures on air change rates in school buses. Air changes per hour (ACH) of outside air were measured using a well-established carbon dioxide (CO2) tracer gas decay method. Ventilation was assessed while stationary and while traversing standardized route during late autumn/winter months in Colorado. Seven CO2 sensors located at the driver's seat and at passenger seats in the front, middle, and rear of the bus yielded similar and consistent measurements. Buses exhibited little air exchange in the absence of ventilation (ACH = 0.13 when stationary; ACH = 1.85 when mobile). Operating the windshield defroster to introduce fresh outside air increased ACH by approximately 0.5-1 ACH during mobile and stationary phases. During the mobile phase (average speed of 23 miles per hour (mph)), the combination of the defroster and two open ceiling hatches (with a powered fan on the rear hatch) yielded an ACH of approximately 9.3 ACH. A mobile phase ACH of 12.4 was achieved by the combination of the defroster, ceiling hatches, and six passenger windows open 2 inches in the middle area of the bus. A maximum mobile phase ACH of 22.1 was observed by using the defroster, open ceiling hatches, driver window open 4 inches, and every other passenger window open 2 inches. For reference, ACHs recommended in patient care settings where patients are being treated for airborne infectious diseases range from 6 to ≥12 ACHs. The results indicate that practical ventilation protocols on school buses can achieve air change rates thought to be capable of reducing airborne viral transmission to the bus driver and student passengers during the COVID-19 pandemic.

Diffusion characteristics and risk assessment of respiratory pollutants in high-speed train carriages

Due to the density of people in the cabins of high-speed trains, and the development of the transportation network, respiratory diseases are easily transmitted and spread to various cities. In the context of the epidemic, studying the diffusion characteristics of respiratory pollutants in the cabin and the distribution of passengers is of great significance to the protection of the health of passengers. Based on the theory of computational fluid dynamics (CFD), a high-speed train cabin model with a complete air supply duct is established. For both summer and winter conditions, the characteristics of the flow field and temperature field in the cabin, under full load capacity, and the diffusion characteristics of respiratory pollutants under half load capacity are studied. Taking COVID-19 as an example, the probability of passengers being infected was evaluated. Furthermore, research on the layout of this type of cabin was carried out. The results show that it is not favorable to exhaust air at both ends, as this is likely to cause large-area diffusion of pollutants. The air barrier formed in the aisle can assist the ventilation system, which can prevent pollutants from spreading from one side to the other. Along the length of the train, the respiratory pollutants of passengers almost always spread only forward or backward. Moreover, when the distance between passengers and the infector exceeds one row, the probability of being infected does not decrease significantly. In order to reduce the probability of cross infection, and take into account the passenger efficiency of the railway, passengers in the same row should be separated from each other, and it is best to ride on both sides of the aisle. In the same column, passengers only need to be separated by one row, and it is not recommended to use the middle of the carriage. The number of passengers in the front and back half of the cabin should also be roughly the same.

Assessing the use of portable air cleaners for reducing exposure to airborne diseases in a conference room with thermal stratification.

The COVID-19 pandemic has highlighted the need for strategies that mitigate the risk of aerosol disease transmission in indoor environments with different ventilation strategies. It is necessary for building operators to be able to estimate and compare the relative impacts of different mitigation strategies to determine suitable strategies for a particular situation. Using a validated CFD model, this study simulates the dispersion of exhaled contaminants in a thermally stratified conference room with overhead heating. The impacts of portable air-cleaners (PACs) on the room airflow and contaminant distribution were evaluated for different PAC locations and flow rates, as well as for different room setups (socially distanced or fully occupied). To obtain a holistic view of a strategy's impacts under different release scenarios, we simultaneously model the steady-state distribution of aerosolized virus contaminants from eight distinct sources in 18 cases for a total of 144 release scenarios. The simulations show that the location of the source, the PAC settings, and the room set-up can impact the average exposure and PAC effectiveness. For this studied case, the PACs reduced the room average exposure by 31%-66% relative to the baseline case. Some occupant locations were shown to have a higher-than-average exposure, particularly those seated near the airflow outlet, and occupants closest to sources tended to see the highest exposure from said source. We found that these PACs were effective at reducing the stratification caused by overhead heating, and also identified at least one sub-optimal location for placing a PAC in this space.

A new method for air exchange efficiency assessment including natural and mixed mode ventilation.

The COVID-19 health crisis highlighted the correlation between air exchange efficiency and virus airborne transmission. Air exchange efficiency is a performance index able to characterize ventilation effectiveness in buildings. Some standards, such as ASHRAE 129, clearly define assessment procedures of air exchange efficiency for mechanical ventilation, adopting tracer gas techniques. However, standardized procedures are based on measurements at the exhaust and cannot be adopted for natural and mixed mode ventilation strategies. In the '80s, Sandberg suggested that tracer gas decay technique enables to measure simultaneously the nominal time constant (through air change rate measurements) and the mean age of air in several points of the ventilated zone. This paper aims to present practical issues and uncertainty analysis related to the implementation of this approach, in a new commissioning protocol. For this purpose, we compare the new procedure, based on Sandberg's observation, with the ASHRAE 129 protocol for mechanical ventilation. Results coming from field campaigns show that the difference between air exchange efficiency values obtained using ASHRAE 129 protocol (51.8%) and the new procedure (47.4%) are usually negligible in low airflow rate, considering an average uncertainty of ± 7.0%. Results show that the procedure is robust and that it is technically possible to implement it to natural and mixed-mode ventilation.