Air is drawn from the surrounding building or warehouse environment (ambient air), filtered once through ceiling-mounted HEPA fan filter units (FFUs), supplied into the cleanroom, and then exhausted directly out of the room—never returned to the cleanroom for reuse.

Airflow path:

• Ambient air → plenum above ceiling → HEPA FFUs (filters and pushes air down) → cleanroom (typically unidirectional or turbulent flow) → low-wall exhaust grilles → exhausted into the surrounding facility space.

Key characteristics:

• No dedicated air handling unit (AHU) or recirculation loop for the cleanroom.
• Temperature and humidity are not actively controlled inside the cleanroom (they follow the conditions of the surrounding space).
• The cleanroom essentially “borrows” cooling from the warehouse/building HVAC.

Air is continuously pulled from inside the cleanroom, conditioned, re-filtered, and returned. Most of the air stays in a closed loop, with only a small percentage of fresh makeup air introduced as needed for pressurization and ventilation.

Airflow path:

• Cleanroom air → low-wall returns → plenum or dedicated AHU (where it is cooled/heated, humidified/dehumidified, and pre-filtered) → HEPA filtration (terminal filters or FFUs) → supplied back into the cleanroom via ceiling diffusers or FFUs.

Key characteristics:

• Dedicated HVAC system provides precise temperature and humidity control.
• Air passes through filtration multiple times, which helps achieve lower particle counts.
• Heat loads from lighting, equipment, processes, and personnel are managed internally rather than dumped into the surrounding space.