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The role of carbon dioxide and particulate matter for assessing ventilation and respiratory disease transmission in buildings

DESCRIPTION OF THE SESSION

Historically, various contaminant concentration measurements, including carbon dioxide (CO2) and particulate matter (PM), have been used by industry and researchers to assess ventilation, filtration, and/or indoor air quality (IAQ) in buildings. However, throughout the COVID-19 pandemic, there has been increased application of CO2 and PM concentration measurements. Researchers have attempted to connect indoor CO2 concentrations with the airborne transmission risk of COVID-19 [1], use indoor PM number counts as a surrogate for assessing the airborne transmission risk of COVID-19 [2], develop CO2-based demand-controlled ventilation (DCV) strategies specifically for reducing the spread of COVID-19 [3], and connect outdoor PM concentrations with COVID-19 mortality rates [4]. Moreover, governments across various countries and regions have invested in a significant number of IAQ sensors, including both CO2 and PM, in public and commercial buildings, such as schools, offices, and hospitals. For example, in Québec, Canada, the Ministry of Education has funded the installation of ~90,000 CO2 monitors in schools across the province [5] and in Norway, Nordre Follo municipality has funded the installation of ~1,000 CO2 and PM monitors in all of its schools [6].

While the application of CO2 measurements to indicate ventilation performance, IAQ, and respiratory infection risk has increased, current standards and guidance sometimes provide inconsistent guidance and recommendations on the interpretation of CO2 data. It is noted that many recommended CO2 limits are provided without sufficient rationales [7]. For example, many practitioners and researchers use 1,000 ppm as a CO2 concentration limit for acceptable IAQ and refer to ASHRAE Standard 62.1 [8]; however, no current ASHRAE standard provides a CO2 limit [9]. To address the inconsistent recommendations and use of CO2 measurements, researchers have indicated several questions that need to be answered to guide the use of CO2 data in buildings [7], [10]. For example, what CO2 concentration can be used to reflect the occupancy level and ventilation demand in the space, what is the variation of CO2 generation rates from different occupants, how should CO2 sensors be selected based on both their performance and cost-effectiveness, how should CO2 sensor locations be selected in spaces with various ventilation systems, how can CO2 data be used to control ventilation systems, and what interventions should be taken at different CO2 concentrations?

While the application of PM measurements to indicate ventilation and filtration performance, IAQ, and respiratory disease transmission has increased, there is still limited guidance on how to monitor indoor PM and use the data to understand and optimize building ventilation. Part of the reason for this may be the lack of accurate PM sensors that can be widely deployed [11]. Despite the fact that many countries and institutions have established IAQ standards that include a limit for PM [12], the links between PM concentration, viral concentration and the risk of infection remains unclear [13]. Since particle transport can be affected by not only the PM concentration but also the type of confined spaces and ventilation systems [14], [15], a guideline for using PM data for ventilation control is needed [16]. There are several questions that remain to ensure PM measurements are applied correctly. For example, how should PM sensors be selected based on both their performance and cost-effectiveness, how can PM data be used to assess the performance of ventilation and filtration systems, how can PM data be used to control ventilation and filtration systems, how can PM concentrations be related to viral load and concentration, how does relative humidity affect the behaviour of particles, and what particle sizes and composition should be used to experimentally assess ventilation and filtration system performance?

OBJECTIVES OF THE SESSION

The objective of this topical session is to discuss some of the potential applications and limitations of CO2 and PM concentration measurements for assessing ventilation and filtration performance, IAQ, and respiratory disease transmission in buildings. Researchers with a breadth of expertise and publications in this area will present their research. The session programme outlined below includes the individuals selected to present, the expected presentation titles, and the corresponding presentation objective.

SESSION PROGRAMME

  1. Uncertainty analysis of CO2 concentrations as a metric of ventilation. Dr. Oluwatobi Oke, PhD | Postdoctoral Engineering Research Associate, NIST, United States & Dr. Andrew Persily, PhD | Fellow, National Institute of Standards and Technology (NIST), United States
  2. Evaluation of Uncertainties of Using CO2 for Studying Ventilation Performance and Indoor Airborne Contaminant Transmissions. Dr. Liangzhu (Leon) Wang, PhD PEng | Full Professor, Concordia University, Canada
  3. Effects of ventilation on airborne transmission: particle measurements and performance evaluation. Dr. Huijuan Chen, PhD | Researcher, Research Institute of Sweden (RISE), Sweden
  4. Impact and benefits of the air cleaning measures implemented in two schools. Dr. Liang (Grace) Zhou, PhD | Senior Research Officer, National Research Council Canada (NRC), Canada

SESSION CHAIRS

  1. Justin Berquist, PhD(c) PEng, | Research Officer, National Research Council Canada (NRC), Canada | ASHRAE Epidemic Task Force member (past)
  2. Svein Ruud, Tekn. Lic. | Senior Expert, Research Institute of Sweden (RISE), Sweden | Nordic Ventilation Group member (current          

SESSION DURATION

-90 minutes

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