Air Quality: Ventilation, Filtration, and Pollutant Management
What the exam tests
Air questions focus on the hierarchy of indoor air quality: eliminate or isolate sources, ventilate with outdoor air, then filter and monitor. You should be able to interpret CO2, PM2.5, and TVOC readings and choose the control that addresses the cause.
Core rules
- Source control comes first: smoke-free policies, low-emission materials, entryway systems, separate chemical storage, and construction pollution management.
- Ventilation must meet the referenced ASHRAE 62.1 procedure for outdoor air and exhaust. Increased ventilation is not automatically better if outdoor air is polluted.
- Filtration is a supplement, not a substitute. WELL air filtration features call for adequately rated filters, commonly MERV 13 or better, with proper installation, sealing, and replacement.
- Monitoring uses indicators: CO2 for ventilation adequacy, PM2.5 for particulates, and TVOC or targeted compounds for sources. Monitors must be calibrated and placed in occupied zones.
Worked example
A conference room reports CO2 of 1,300 ppm by mid-morning while the air handler is running. The likely cause is insufficient outdoor air per occupant, not a need for a portable HEPA unit. Check the outdoor-air damper, economizer, occupancy schedule, and CO2 sensor calibration. If the room is over-occupied, adjust design occupancy or add demand-controlled ventilation. Filtration would not fix a CO2 problem because CO2 is a ventilation indicator.
Traps
Treating CO2 as a toxic pollutant rather than a ventilation indicator. Assuming a high-MERV filter compensates for closed outdoor-air dampers. Ignoring outdoor air quality when increasing ventilation. Testing only in unoccupied conditions.