CRAH

CRAH is an acronym most commonly used in data center and information technology facility engineering, standing for Computer Room Air Handler. It refers to a type of air handling unit that conditions and circulates air within a data center or server room. A CRAH typically uses a central chilled-water system to remove heat from the air via cooling coils, with fans moving air across the coils and back into the room.

In operation, room air is drawn into the CRAH, passes over a chilled-water coil, and is discharged back into the space. The unit is designed to handle high airflow and is often deployed in raised-floor or overhead ducted configurations. CRAHs are frequently used in hot aisle/cold aisle containment setups and can include filtration, humidity sensors, and controls to maintain environmental conditions within ASHRAE-recommended ranges. Many CRAHs employ variable-speed fans and are connected to a central chiller plant, which can improve energy efficiency, especially at scale. They may also be paired with air-side economizers to take advantage of favorable outside conditions.

CRAH units are typically contrasted with CRAC units (Computer Room Air Conditioners), which are self-contained cooling systems that use refrigerant-based cooling rather than chilled water. In practice, data centers may use a mix of CRAH and CRAC equipment depending on design goals, redundancy requirements, and energy strategy. While the acronym CRAH is most common in data center HVAC, it is not widely used to denote other concepts outside this field.