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

Abstract

Literature on CO₂ levels in classrooms routinely focus on CO₂ 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 CO₂, 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 CO₂ levels varied greatly between buildings built after 1981 and before 1955, from 126 ppm over 24 hours to 179 ppm over the 9 am to 5 pm timeframe. There were lesser differences between buildings built between 1956 and 1980 and before 1955, showing CO₂ levels from 23 ppm over 24 hours to 30 ppm over the 9 am to 5 pm timeframe. The parts per million differences were statistically significant over the 24-hour period and the 9 am to 5 pm period. Class occupancy greatly affected CO₂ levels in tested classrooms, with statistically significant differences from 187 ppm 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 5 ppm difference for buildings build before 1955 and between 1956 and 1980 and were not statistically significant. The rate of CO₂ decrease was slower in buildings built after 1981 with a decrease of 65.4 ppm per hour compared to a decrease of 77.9 ppm 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 79–113 ppm higher average CO₂ than total HVAC systems installed before 2000 during a 24-hour timeframe and a 9am-5pm timeframe. While none of the classrooms had CO₂ levels that exceeded federal limits for CO₂ exposure, there is a scarcity of data and guidelines of CO₂ levels within a collegiate setting. The data provides information on changes in CO₂ levels related to classroom occupancy and differences in CO₂ levels based on building age.