CRAC and CRAH
CRAC and CRAH are the two main types of precision cooling unit in a data center. A CRAC, or Computer Room Air Conditioner, uses its own refrigerant compressor. A CRAH, or Computer Room Air Handler, uses chilled water from a central plant.
CRAC and CRAH units are the workhorses of traditional air-cooled data center design. Both push conditioned air into the room, typically through a raised floor plenum or overhead ducting, and return warm exhaust air for reconditioning.
The difference
A CRAC unit uses a refrigerant circuit with its own compressor, cooling air through direct expansion. A CRAH unit uses chilled water produced by a central plant, passing air across a coil to move heat into the water loop. At scale, centralizing chiller production is usually more efficient, which is why large facilities lean toward CRAH.
Where they are being displaced
As rack densities climb, moving enough air to cool a cabinet becomes physically impractical. High density and AI deployments increasingly rely on rear door heat exchangers, direct-to-chip liquid cooling, or immersion, with air systems handling only the remaining load.
Why it matters for marketing
Cooling is where the sustainability story and the capacity story meet, and it is usually reduced to a single specification line.
For providers selling into AI and high density workloads, cooling strategy is now a primary buying criterion rather than back-of-house detail. A prospect evaluating whether your facility can host their deployment needs to know your cooling approach, your supported density ceiling, and whether liquid is available today or on a roadmap. That belongs on the facility page in plain language, not in a spec sheet PDF.
Common questions
What is the difference between a CRAC and a CRAH unit?
A CRAC unit contains its own refrigerant-based compressor and cools air directly, working much like a large dedicated air conditioner. A CRAH unit has no compressor and instead uses chilled water supplied from a central plant, with a coil and fans moving heat into that water loop. CRAH systems are generally more efficient at scale.
Why do data centers need precision cooling instead of normal air conditioning?
Because data centers require tight control of both temperature and humidity, and comfort cooling is designed for neither. Air that is too dry invites electrostatic discharge, air that is too humid risks condensation, and equipment fails faster under swings in either. Precision units hold much narrower tolerances than building HVAC.