Glossary

Coolant Distribution Unit (CDU)

A CDU is the control point for a liquid cooling loop. It moves heat out of racks while protecting IT equipment from unstable flow, pressure, or water quality.

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Definition

A coolant distribution unit, or CDU, manages coolant for liquid-cooled servers and racks. It controls flow, temperature, pressure, filtration, and heat exchange between the IT equipment loop and a facility or external heat-rejection loop.

The CDU is often the boundary between sensitive electronics and broader cooling infrastructure. On one side it supplies controlled coolant to cold plates or manifolds. On the other side it transfers heat to facility water, seawater exchangers, dry coolers, or chillers.

Why it matters

Liquid cooling only works if coolant arrives at the right temperature, pressure, and flow rate. Too little flow overheats equipment. Too much pressure stresses fittings. Poor water quality causes corrosion, biological growth, or blocked channels.

In dense AI systems, thermal margins can be narrow. A CDU helps keep cooling predictable and gives operators a place to monitor conditions before failures escalate.

How it works

A CDU usually contains pumps, heat exchangers, valves, filters, sensors, and controls. Coolant returning from servers carries heat. The CDU transfers that heat across an exchanger, then sends cooled fluid back to the racks.

Rack-level CDUs serve one or a few racks. Row-level or facility-level CDUs serve larger zones. Choice depends on heat load, redundancy, installation constraints, and maintenance strategy.

Common misconceptions

A CDU is not just a pump. It is a control and protection system for the thermal environment.

CDUs reduce risk when designed and operated well, but liquid cooling still needs commissioning, monitoring, service procedures, and materials compatibility.

See Direct Liquid Cooling, underwater cooling costs, and What Is a Subsea Data Center?