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With a growing emphasis on indoor air quality (IAQ) in educational environments, CO 2 monitoring in classrooms has become commonplace. CO 2 data can be used to estimate outdoor air change rate (ACH) based on the mass balance principle, which can be further linked to human health, performance, and building energy consumption. This study used a novel machine learning method to automatically segment CO 2 concentration time series data into build-up, equilibrium, and decay periods, and then estimated classroom ACH using the corresponding CO 2 mass balance equations. This method, applied to 40 classrooms in two mechanically ventilated K-6 schools, generated up to ten ACH estimates per day per classroom. A comparison with ACH calculated using the mechanical ventilation rates with 100% outdoor air reported by the building automation system during the study period reveals a slight underestimation by the decay and build-up methods, while the equilibrium method produced closer estimates. These differences may be attributed to uncertainties in occupancy, activity, CO 2 emission rates, and air mixing. This research underscores the potential of leveraging CO 2 data for more comprehensive IAQ assessments and highlights the challenges associated with accurately estimating ACH in real-world settings.

Background: An October, 2021 review of Public Health Ontario's COVID-19 guidance for congregate settings such as shelters and long-term care homes demonstrated that this guidance did not include references to ventilation or filtration. In April 2022, an interdisciplinary team with expertise in indoor air quality (IAQ), engineering, epidemiology, community programming and knowledge translation launched a virtual ventilation and filtration consultation program for community spaces in Toronto, Ontario. The program gives people working in community spaces direct access to IAQ experts through 25-min online appointments. The program aims to help reduce the risk of COVID-19 transmission in community spaces, and was designed to help compensate for gaps in public health guidance and action., Methods: Representatives from participating organizations (n. 27) received a link to an online survey via email in April 2023. Survey questions explored the impacts of the program on topics such as: purchase and use of portable air filters; maintenance and use of bathroom fans; and, maintenance and modification of HVAC systems. Survey participation was anonymous, and no demographic information was collected from participants., Results: Representatives from 11 organizations completed the survey (40%). Of those who responded, nine (82%) made changes as a result of the program, with eight (73%) making two or more changes such as purchasing portable air filters and increasing routine maintenance of HVAC systems., Conclusions: When presented with brief access to expert support and tailored plain language guidance, people working in community spaces increased their use of ventilation and filtration strategies for COVID-19 infection prevention and control., (© 2024. The Author(s).)

High-efficiency filtration in residential forced-air heating, ventilation, and air conditioning (HVAC) systems protects equipment and can reduce exposure to particulate matter. Laboratory tests provide a measure of the nominal efficiency, but they may not accurately reflect the in situ efficiency of the filters because of variations in system conditions and changes in filter performance over time. The primary focus of this paper is to evaluate the effective filtration efficiency, which is inclusive of any loading and system impacts, in 21 occupied residential homes through in-duct concentration measurements. We considered the role of filter media by testing both electret and non-electret media, as well as the role of loading by considering new and used filters. The results show that filters with higher nominal efficiency generally had higher effective filtration efficiency in the same home. In terms of performance change, there is no significant difference in efficiency between initial and 3-month non-electret filters, but the efficiency of electret filters generally decreased over time. However, both nominal efficiency and performance change were vastly overshadowed by the wide variety in loading and system conditions across homes, making it hard to predict filter efficiency in a given home without in situ measurements., (© 2019 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Public Health Ontario (PHO) is mandated by legislation to share scientific advice during infectious disease outbreaks and help reduce health inequities in Ontario, Canada. PHO was founded in part to address the failures of Ontario's public health system during the 2003 outbreak of SARS-CoV-1, which included the failure to address airborne transmission. By January 2021, public health authorities had access to a body of literature suggesting SARS-CoV-2 was airborne, and had received urgent warnings from scientists. We set out to document how PHO responded to the likelihood – and, eventually, the certainty – of airborne transmission in the context of its guidance for congregate settings such as long-term care and shelters. In October 2021, we reviewed PHO's public, written COVID-19 guidance for these settings, with a focus on indoor air quality (IAQ) measures that mitigate airborne transmission, such as ventilation. We identified 11 PHO documents for congregate settings. They contained no references to IAQ measures. We did, however, find references to IAQ measures in parallel documents for schools, summer camps, and clinical offices. Our findings demonstrate PHO omitted key infection prevention measures from its COVID-19 guidance for congregate settings, putting workers and residents at greater risk of exposure, illness and death, and exacerbating health inequities. [ABSTRACT FROM AUTHOR]

Abstract Ventilation using outdoor air can have both favorable and unfavorable impacts on indoor air pollution. It also can be an important contributor to energy use in buildings. Outdoor ventilation air change rate (ACR), the rate at which outdoor air enters a building divided by its volume, is a temporally dynamic metric that can be used to characterize ventilation performance of buildings. Conventional measurement techniques for ACR have either complex or invasive experimental procedures, or present a temporal snapshot of ACR. In this study, we further developed and explored a novel signal processing approach to measure yearlong time-resolved ACR in a residence using the variations in indoor and outdoor CO 2 concentrations. Results showed that ACR varied considerably over the year [geometric mean (GM) = 0.47/h, geometric standard deviation (GSD) = 3.44] and that the air change rates calculated from the signal processing approach were in good agreement (on average, within 13%) with those measured simultaneously from 15 hour-long decay periods. In addition, estimates of ACR were largely insensitive to the occupancy status of the building. This behavior may be because the indoor CO 2 concentration variations introduced by changes in occupancy status were not large enough to impact long-term ACR values, but they may be sufficient to impact short-term ACR values. Moreover, we anticipate that cut-off frequency and filter order, two parameters needed for the signal processing approach, may be building-specific and can influence calculations of air change rates in a given building. The results suggest that this approach has promise for assessing time-varying ACR in buildings with time-resolved indoor and outdoor concentration measurements. Highlights • Ventilation measured with a signal processing approaches reveals temporal dynamics in air exchange rate (AER). • The approach requires measurement of indoor and outdoor CO 2 concentrations but no release of a tracer gas. • Over a year the geometric mean (geometric standard deviation) AER in a residence was 0.47/h (3.44). • The application of the signal processing approach is sensitive to the selection of the concentration filtering parameters. • The results suggest a valuable way to assess time-resolved ventilation rates in buildings [ABSTRACT FROM AUTHOR]