What Is CRAH?_
A CRAH (Computer Room Air Handler) is an air-handling unit that cools data center air using chilled water supplied from the facility's chiller plant, then circulates it to equipment. CRAHs differ from CRAC units, which use a built-in refrigerant compressor (direct expansion). In GPU facilities, CRAHs handle the residual air-cooling load not captured by liquid cooling, and they remain essential for cooling network gear, the small air-cooled fraction of liquid-cooled racks, and the room itself.
Technical Details
A CRAH passes return air across a chilled-water coil fed by the facility chiller plant, transferring heat to the water loop, and uses variable-speed fans to circulate supply air — often through a raised floor plenum or overhead ducting into a contained cold aisle. Because the cooling comes from central chillers rather than per-unit compressors, CRAHs scale efficiently in large facilities and pair well with economizer strategies. In a liquid-cooled GPU hall, direct-to-chip cooling removes most rack heat to the facility water loop, but a residual air load remains — switches, the un-plated fraction of each server, and rear-door exhaust — so CRAH (or rear-door heat exchanger) capacity is still sized into the design. Airflow management — containment, blanking panels, sealed penetrations — keeps CRAH supply air from mixing with hot exhaust.
How Leviathan Systems Works with CRAH
Leviathan Systems deploys GPU racks within CRAH-cooled halls, managing the airflow details — blanking panels, cable-penetration sealing, containment integration — that keep air cooling effective alongside liquid cooling.
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