1/ Plots from our Healthy High School PRIDE (Partnership in Research on Indoor Environments) project, a 4-yr USEPA funded study and intense analysis of 46 high school classrooms in Central Texas. 
2/ Plot A shows air exchange rate in permanent and portable classrooms in the unoccupied setting (end of school day to start of next school day). The x is mean value and central line on bars is median. Variation shown via percentiles and min/max.
3/ The mechanical systems were off in plot A. All ventilation was via infiltration. Note much lower values and spread for permanent classrooms. Portable classrooms are connected directly to outdoors, leakier, and prone to greater ventilation by infiltration.
4/ Plot B shows air exchange rates for classrooms during the occupied school day. The red line shows approximate ventilation rate based on ASHRAE 62.1-2019 for a majority of classrooms.
5/ Note severely under-ventilated permanent classrooms (primarily for energy savings) in both seasons. Portable classrooms had a central tendency of much higher ventilation, but with significantly greater variation than permanent classrooms.
6/ Portable classrooms, highly criticized for poor environmental conditions in past research, do provide greater opportunities for natural ventilation via open windows, open doors to outside, etc., as well as filtration. Problem = greater students/ft2 (in our study).
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