TECHNICAL FEATURE FIGURE 1 Photo showing the classroom space used as a testbed for the current study (in a pre-COVID-19 layout). FIGURE 2 Plan view of the classroom space used as a testbed for the current study in its reduced occupancy configuration. 1 8 9 16 17 24 2 7 10 15 18 23 3 6 11 14 19 5 12 13 20 22 21 4 Normally, this room is equipped to accommodate 48 students and one instructor, resulting in an occupant density of 2.6 m2/person (28 ft2/person); however, the room layout was modified in response to COVID-19 for a nominal 2.1 m (7 ft) separation between students and a 3 m (10 ft) buffer separation between the instructor and seated students. The reconfiguration of the room reduced the occupant capacity from 49 to 17 (16 students and 1 instructor), which decreased the occupant density to 7.4 m2/person (80 ft2/person). Figure 2 shows a plan view of the reduced occupant density classroom along with relative layout of the room's four HVAC supply diffusers and single overhead return grille. The minimum and maximum supply airflow rates for this classroom space are 391 m3/h (230 cfm) and 1700 m3/h (1,000 cfm), respectively, corresponding to air change rates that range from 1 ach to 4.7 ach. To simulate occupants within the room, CPR manikins (torso and head only) were deployed and positioned at each of the 16 student locations, with one positioned at Student Desk Vacant Desk Supply Diffuser Instructor Podium Return Grille Single Source Location the front of the room to simulate an instructor (Figure 3). The manikins were modified to enable a generated NaCl aerosol to be discharged through their mouths into the room and/or to draw room air samples through their mouths for particle analysis. This ability to use the manikins for " exhaling " or " inhaling " aerosol enabled assessment of both discharged and drawn-in particle concentrations when the manikins were fitted with face masks. Each student location included an incandescent (75 W) light bulb to simulate sensible heat load from occupants. Evaluating the Well-Mixed Assumption Aerosol testing was conducted in the classroom to assess validity of the well-mixed assumption in the FIGURE 3 Classroom space set with CPR manikins (a) from the front looking back and (b) from the back looking forward. A. B. M AY 2021 ashrae.org ASHRAE JOURNAL 13http://www.ashrae.org