Characterizing ventilation and air movement in residential and school environments : assessing potential for improvements and exposure reduction

Date

2022-08-04

Authors

Kumar, Sangeetha

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Abstract

Air quality is an increasingly pertinent concern within indoor environments where humans spend most of their time. Poor indoor air quality, typically as a result of improvements in energy efficiency or mismanagement of buildings, can lead to adverse health outcomes. Various control strategies can be implemented to optimize indoor air quality indoors. Of particularly interest in this study is the use of air mixing and mechanical ventilation systems. Through a combination of field studies, controlled experiments, and modeling exercises this research addressed three main objectives. This research aims to: (a) investigate air movement, pollutant dispersion, and source control by the means of improving kitchen range hoods standards, (b) characterize typical CO₂ concentrations, ventilation rates, and building systems in classroom environments, and (c) assess the impact of improved ventilation and air movement on exposure. Specifically, this research study focuses on highly-occupied—in terms of quantity of occupants and duration of occupancy—indoor environments: residential and classroom environments. First, to understand how air movement influences air velocities and turbulence, this research conducts controlled experiments to analyze mechanical mixing and buoyancy driven flows. Results demonstrate that the momentum generated from forced air significantly increases as supply flow rate increases, and typically near surface velocities are higher. Buoyancy driven flow, mimicked through heat sources, creates localized increases in velocities but temperature differences between rooms and between outdoor rooms drives mixing between rooms. A follow-up study analyzed gas-phase and particulate pollutant dispersion due to mechanical mixing and buoyancy driven flows. A set of experiments analyzed the effect of mechanical mixing and source duration (mimicking cooking) on assumptions for ‘well-mixed’ indoor environments in multi-zone homes. Analyzed results exhibit that the time to perfect mixing, low variance across all rooms of the house, is lower for mechanical mixing versus buoyancy driven flow. Contaminant removal effectiveness, how well a space removes pollutants, is higher for no mechanical mixing indicating that with regards to exposure, there’s more differences between rooms. Lastly, a series of Monte Carlo simulation using assumptions validated by the previous study and aggregated input data from relevant literature ascertained the minimum capture efficiency required by range hoods to reduce exposure to PM₂.₅ and NO₂ indoors. This standard is driven by smaller homes that use gas stoves. Further reductions in exposure to cooking-related contaminants can be found through increased back-burner usage or auto range hood (always using your range hood). Expanding on existing literature of classroom environments, this dissertation explores CO₂ concentrations, ventilation rates, and building systems in high school classrooms in Central Texas. Results from this study demonstrate wide-spread underventilation of classrooms in comparison to code and standards as well as differences in maintenance and operation between portable and permanent classrooms. Increases in ventilation rates in the second sampling year reduced potential to exposure of human-generated contaminants in the space. As a follow-up investigation, this study also explored ventilation and building systems in university classroom environments, pre-COVID and post-COVID. Due to the complexity of systems and the dynamic occupancy, most university classrooms are well-ventilated, if not over-ventilated. Monitoring ventilation during the COVID-era of the pandemic found increased ventilation rates and reduced occupancy led to lower CO₂ concentrations and potential risk for exposure.

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