The use of UV-C for improved indoor air quality: Experiments and modeling application for homeland security issues
Disinfection experiments were performed using a custom built 0.46 × 0.46 m (cross-section) by 4.3 m long wind tunnel fitted with a commercially available UV-C lamp unit operated under conditions usually found in HVAC systems (air velocities of 2000-9500 m/h = 130-550 feet/min). Four test organisms were selected. One bacteria, a wild type Escherichia coli (wild type W3110), and three fungi spores: Penicillium aragonense ATCC #42228, Rhodotorula glutinis ATCC #32765, and Cladosporium sp. ATCC #32720, the latter three being common air biocontaminants. Disinfection of E. coli proved to be extremely effective, with more than 98% of the input E. coli killed under various conditions. As expected, disinfection was greater with two UV lights on and at low airflow rates. High relative humidity reduced the efficacy of the disinfection process (95% killed at 97% RH vs 99+% at RH lower than75%). Disinfection of the fungal spores was much more difficult and exhibited more data scattering. A simple model was developed to correlate the experimental data with simple exponential decay based on UV power consumption (i.e., irradiation), exposure time in the wind tunnel, and the specific test organisms. Next, a second model served to predict the expected reduction in indoor bioaerosol concentration for a given building/house etc. depending on the various operating parameters such as the number of UV lights, airflow, source contamination, etc. In particular relevant to Homeland Security was the modeling of the protection of commercial buildings against crop dusting of bioterrorism agents such as anthrax spores using duct mounted UV-C lamps. The model helped in understanding what parameters were most important in developing a strategy to protect buildings from attacks, and maximizing the benefits of UV, while minimizing the energy and equipment costs. The different scenarios showed that germicidal UV can be an effective tool in meeting safe building levels.