Air distribution in data hall for air-cooled IT racks

This note illustrates two common air distribution methods in data halls housing air-cooled IT racks:

Raised Floor System:
This method uses CRAC (Computer Room Air Conditioner) or CRAH (Computer Room Air Handler) units to cool hot return air and distribute cold air through a raised floor plenum into the IT racks. Hot and cold air streams are separated using aisle containment (hot or cold aisle containment) to prevent thermal mixing and bypass airflow.

Non-Raised Floor System:
This method uses FWUs (Fan Wall Units) or horizontal-discharge CRAH units to supply cold air directly into the room at floor level. Similar to raised floor designs, aisle containment (or ceiling return plenums) is implemented to isolate hot exhaust air from the supply air stream.