Data Center Cooling Systems Explained
Almost every watt the IT equipment draws becomes heat that must be removed. Here is how that heat leaves the building, the main system types, and why the cooling design and the electrical design cannot be done separately.
The heat path
- IT equipment turns electrical power into heat.
- Air (or liquid) carries that heat away from the equipment.
- Cooling units (CRAH, CRAC, in-row or rear-door units) transfer the heat to a refrigerant or chilled-water circuit.
- The plant (chillers, cooling towers, dry coolers, or outside air in some designs) rejects the heat outdoors.
Main system types
- Refrigerant-based units (CRAC): each unit has its own compressor. Simple to deploy, scale in units.
- Chilled-water systems (CRAH plus chillers): central plant, scales well at larger capacities. See CRAH vs CRAC and chilled-water vs air-cooled.
- Free cooling and economisers: use cool outdoor air or water for part of the year to reduce compressor use. Viability depends on climate.
- Liquid cooling: coolant removes heat directly at the chip or by immersion. See liquid cooling explained.
Managing the air
Airflow management decides how much of the cooling capacity is actually used. Separating hot and cold air stops recirculation and bypass; see hot aisle / cold aisle containment.
The electrical connection
- Cooling plant is a large share of the facility load, so it affects the transformer, switchgear and generator sizing. See load calculation.
- Cooling efficiency sets PUE; see PUE explained.
- Cooling must ride through power transitions, so its redundancy and restart behaviour matter as much as the IT supply.
Part of the data center design guide.
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
How are data centers cooled?
Heat from the IT equipment is picked up by air (or liquid), moved to cooling units, transferred to a chilled-water or refrigerant circuit, and finally rejected outdoors through chillers, cooling towers, dry coolers or direct air exchange, depending on the design and climate.
Why does cooling matter to electrical design?
Cooling plant is a large electrical load, so it sets part of the utility and generator demand, and its efficiency drives PUE. Cooling redundancy must also match the electrical redundancy target.
What is the difference between CRAH and CRAC?
A CRAC (computer room air conditioner) has its own refrigerant compressor; a CRAH (computer room air handler) uses chilled water from a central plant. See the dedicated comparison.
Is liquid cooling replacing air cooling?
Liquid cooling is used where rack power density is too high for air to handle efficiently, such as some AI deployments. Many facilities use a mix of liquid and air cooling.
Want to learn this properly?
This topic is covered in depth in our Electrical Design – Data Center Specialist program.
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