Building age is a determining factor of indoor CO2 levels in a University setting

Literature on CO 2 levels in classrooms routinely focus on CO 2 exposure in primary education settings, but comparatively little attention has been given to higher education settings such as colleges. Due to concerns about the relationship between COVID-19 and CO 2 , the University of South Carolina’s (USC) Environmental Health and Safety Department (EHS) monitored indoor air quality for 26 buildings and 198 classrooms from the Fall of 2021 to the Spring of 2022 in general purpose university classrooms. 30 Onset HOBO data loggers were used to monitor these classrooms. Average CO 2 levels varied greatly between buildings built after 1981 and before 1955, from 126ppm over 24 hours to 179ppm over the 9am to 5 pm timeframe. There were lesser differences between buildings built between 1956-1980 and before 1955, showing CO 2 levels from 23ppm over 24 hours to 30ppm over the 9am to 5 pm timeframe. The parts per million differences were statistically significant over the 24-hour period and the 9am to 5 pm period. Class occupancy greatly affected CO 2 levels in tested classrooms, with statistically significant differences from 187ppm to 192 ppm in buildings built after 1981 and those built before 1955 and between 1956 and 1980 when the classroom was at least 50% occupied. However, these levels dropped to only a 5ppm difference for buildings build before 1955 and between 1956 and 1980 and were not statistically significant. The rate of CO 2 decrease was slower in buildings built after 1981 with a decrease of 65.4ppm per hour compared to a decrease of 77.9ppm per hour in buildings built before 1955. The results were comparable based on the age of the HVAC systems in the buildings, showing total HVAC systems installed after 2000 were 79ppm to 113ppm higher average CO 2 than total HVAC systems installed before 2000 during a 24-hour timeframe and a 9am-5pm timeframe. While none of the classrooms had CO 2 levels that exceeded federal limits for CO 2 exposure, there is a scarcity of data and guidelines of CO 2 levels within a collegiate setting. The data provides information on changes in CO 2 levels related to classroom occupancy and differences in CO 2 levels based on building age. • For a 24-hour period, CO 2 levels were 104ppm to 126ppm higher in buildings built after 1981 compared to buildings built between 1956 and 1980 and buildings built before 1955 • In classrooms with at least 50% occupancy, CO 2 levels were 187ppm to 192ppm higher in buildings built after 1981 compared to buildings built before 1955 and buildings built between 1956 and 1980 • In occupied buildings, total HVAC systems installed after 2000 were 79ppm to 113ppm higher average CO 2 than total HVAC systems installed before 2000 for a 24-hour timeframe and a 9am-5pm timeframe, respectively • CO 2 levels in university classroom buildings have not been extensively tested in previous years