Seasonal variations of indoor air quality and thermal conditions and their correlations in 220 classrooms in the Midwestern United States

In this 2-year, seasonally-repeated study, the research team surveyed the baseline conditions of indoor air quality (IAQ) and thermal conditions (TC) of 220 classrooms in the Midwestern region (Nebraska and Iowa) of the United States of America. Seasonal variations of each IAQ and TC variable and correlations between variables were also examined. CO2 concentrations were acquired from each of the classrooms while simultaneously monitoring outdoor CO2 concentration, particle counts, formaldehyde concentration, air temperature, globe temperature, and relative humidity. Ventilation rate and absolute humidity level were also estimated. The results showed the mean CO2 concentration of 220 classrooms during the occupied hours throughout the measured seasons was 1171 ppm. The average ventilation rate was 5.6 L/s-person, below the suggested value by ASHRAE Std 62.1. Other IAQ and TC variables were found to be well-maintained when compared to the NIOSH or EPA standards. Large seasonal variations were found in humidity level, ventilation rate, particle counts, and formaldehyde concentration. It is therefore suggested that the monitoring of classroom IAQ and TC should be done periodically across the whole school year to comprehensively describe the conditions. There were significant correlations between IAQ and TC variables, which suggest relationships between these variables. This study revealed the baseline conditions and examined the seasonal variations of the classroom IAQ and TC of the region for the first time. Further benefits, such as improvement of classroom IAQ and TC, may result from this study.