Applications of ultraviolet-C light in improving indoor air quality with engineering and photometric approaches
Date
2023-05
Authors
Li, Peiyang
Major Professor
Advisor
Koziel, Jacek A.
Ramirez, Brett C.
Gates, Richard S.
Jenks, William S.
Zimmerman, Jeffrey J.
Committee Member
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Abstract
Infectious diseases such as seasonal influenza and more recently COVID-19 can be transmitted via aerosols and spread from one person to another. Improving indoor air quality (IAQ) has become vital for the public to combat disease transmission in indoor air through mitigating inhalable aerosols. Air cleaning devices with filtration and targeted treatment capabilities can help improve IAQ. An air cleaning prototype was evaluated and upgraded by adding UV-C (germicidal) light and tested on its removal efficiency on viable airborne bacteria and particulate matter (PM). The combination of filtration and UV-C treatment provided ‘double-barrier’ assurance for air purification and lowered the risk of spreading infectious micro-organisms. Between the inlet and treated air, the upgraded prototype inactivated nearly 100% of viable airborne bacteria and removed up to 97% of TSP, 91% of PM10, 87% of PM4, 87% of PM2.5, and 88% of PM1. The performance in the low flow rate mode was generally better than in the high flow rate mode. In addition, a 25-day experiment was conducted to treat indoor air with intermittent ON and OFF days in which PM and viable airborne bacteria were measured to quantify the treatment effect. The results showed an average of 55% reduction of total suspended particulate (TSP) concentration between OFF days and ON days. An average of 47% reduction of total airborne viable bacteria concentrations was achieved between OFF days (~3,200 CFU/m3) and ON days (~2,000 CFU/m3). A cross-validation (CV) model was established to predict PM concentrations with five input variables, including the status of the air cleaner, time, ambient temperature, indoor relative humidity, and day of the week. The model can approximately predict the trend of PM concentrations, and future improvements may be made to improve its accuracy.
Practical estimation of UV irradiance is essential in determining the UV fluence (dose) and facilitating design of tubular UV lamp configurations for indoor air treatment. It is generally understood that the inverse square law applies well to point light sources (light irradiance or illuminance is inversely proportional to the square of distance from the light source). However, there has been a recognition in the industry that the inverse square correlation does not work well for tubular light sources in the commonly defined near-field (d < 5L) applications, such as portable air cleaners (with built-in UV light bulbs), heating, ventilation, and air-conditioning (HVAC) ducts. An investigation on UV-C light irradiance from tubular (L = 0.9 m) light bulbs (and similarly sized visible fluorescence bulbs used as a reference) at near- and far-field in three power output (1-, 4-, and 8-bulb) scenarios and modeled them with a line- and a point-source models. Our experimental results indicate that line source estimation generally fits better (i.e., evaluated by R-squared values, standard errors, root mean squared errors) than the point source estimation in both inverse square and inverse relationships. Alternatively defined near-field distance (d < 2L) irradiation has an acceptable inverse relationship over distance, while alternatively defined far-field distance (d ≥ 2L) irradiation approximately follows an inverse square relationship. The findings are beneficial for UV irradiance estimation for indoor air quality improvement and airborne disease mitigation efforts. Computer software modeling on UV irradiance based on illuminating engineering society (IES) files were also explored. The modeling results indicated high variability and difference compared with measured light intensity, which signifies the importance of further investigation to find out sources of error and improve the accuracy of modeling.
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dissertation