How Is Airflow Properly Designed in an Enclosed Parking Garage?

I start from the code-required minimum exhaust rate applied to the gross floor area of each enclosed level, then check the real operating condition: how many cars are moving at peak, how long they idle, and how the garage is used. The minimum rate handles the code; the demand-control sequence handles the reality that a busy garage needs more than the minimum during surge periods and much less at 3 a.m. Fan capacity is sized for the worst level at full demand, with staging or variable-frequency drives for the turndown. Makeup air is sized to match so the garage does not pull doors off their latches or drag cold air through every gap in the building envelope.

The garage is the dirty zone and everything connected to it is the clean zone. I pressurize stair towers, elevator lobbies, vestibules, and attached office or retail space slightly positive relative to the garage, so that whenever a door opens, clean air flows toward the garage instead of exhaust flowing into the building. Vestibules with self-closing doors at the garage-to-building transition give the pressure cascade a place to work. Commissioning includes pressure mapping with doors in normal operation, because a pressurization strategy that only holds when every door is closed will fail on the first busy day.

An enclosed parking garage airflow design is ready when it clears this checklist. Garages fail on air quality and energy cost — these items address both. • Exhaust sized to the code minimum with 100 percent outside air, no recirculation • Low exhaust inlets at the driving surface and high supply on the opposite side • Jet fans or induction coverage for long floors, verified with a smoke test • CO and NO2 sensors in the breathing zone driving demand-controlled fan operation • Connected spaces held positive to the garage with vestibules at transitions