CRAH vs CRAC: Data Center Cooling Units Compared
Both sit in the data hall and push cold air at the IT equipment. The difference is where the cooling comes from: a compressor inside the unit, or a chilled-water plant outside it.
The difference
| CRAC | CRAH | |
|---|---|---|
| Cooling source | Own compressor and refrigerant circuit | Chilled water from a central plant |
| Main electrical load in the unit | Compressor and fan | Fan only (plant and pumps are elsewhere) |
| Infrastructure | Refrigerant piping, heat rejection per unit or group | Chilled-water piping, pumps, chillers |
| Scaling | In unit steps | Centralised, scales well at larger capacity |
| Typical fit | Small to medium rooms | Medium to large facilities |
These are general tendencies, not rules; check each project's constraints.
Electrical implications
- CRAC units put compressor motor starting current on the board; CRAH units concentrate the electrical load in the chiller plant and pumps.
- Both need fans and controls on a supply that rides through transfer events, and a defined restart sequence.
Overview: data center cooling systems explained and chilled-water vs air-cooled.
Written by the Vision Matrix Institute editorial team. Worked examples use stated, illustrative assumptions; check them against your project data, the applicable standards and manufacturer datasheets before use.
Frequently Asked Questions
What does CRAC stand for?
Computer room air conditioner. It contains its own refrigeration circuit with a compressor, evaporator and, in direct-expansion units, a condenser connection.
What does CRAH stand for?
Computer room air handler. It has a fan and a chilled-water coil and relies on a central chiller plant for cooling.
Which is more efficient?
It depends on the whole system. CRAH units avoid per-unit compressors but need a chiller plant and pumps, so compare the efficiency of the complete heat-removal chain for the climate and scale.
Which is better for a small data center?
Small sites often use refrigerant-based units for simplicity; larger sites often favour chilled-water systems. Scale, climate and operations skills drive the choice.
Want to learn this properly?
This topic is covered in depth in our Electrical Design – Data Center Specialist program.
Ask us on WhatsAppLearn to do this on a full project in the Electrical Design – Data Center Specialist program, or read the data center design guide.