What Is A Cdu (Coolant Distribution Unit) In Data Centers? August 4, 2026 A Coolant Distribution Unit (CDU) is the interface between a data center's central chilled water plant and its rack-level liquid cooling infrastructure. CDUs receive chilled water from the facility cooling system, use a heat exchanger to isolate facility water from the IT equipment cooling loop, and distribute controlled liquid to the racks. Understanding what CDUs do — and what they don't do — is essential for anyone designing or evaluating a liquid cooling deployment. What a CDU Actually Does A CDU performs four critical functions in a liquid cooling system: System isolation: separates the facility chilled water loop from the IT cooling loop using a heat exchanger, preventing contamination of the facility system and allowing different fluid types or pressures on each side Flow and pressure control: maintains correct flow rates and pressures to the rack-level cooling components — direct-to-chip cold plates, in-row heat exchangers, or rear-door heat exchangers Temperature regulation: controls the supply temperature to IT equipment to keep components within thermal operating limits Monitoring and control: provides data on flow rate, supply and return temperatures, and system pressure for integration with DCIM and building management systems "CDUs are the control point — they connect high-performance computing to the larger cooling system without compromising reliability on either side. But they're only as effective as the chiller system upstream."— Paul Johnson, G&D Chillers How CDUs Fit Into the Full Cooling Architecture System Layer Function Chiller plant (G&D Chillers) Removes heat from the facility loop; produces stable chilled water supply CDU Interfaces facility loop with IT equipment loop; controls flow and temperature to racks Rack manifolds and distribution Carries cooling fluid to individual servers or chassis Cold plates / direct-to-chip Removes heat directly from processors and GPUs Where G&D Fits in Liquid Cooling Systems G&D Chillers does not manufacture CDUs. What G&D provides is the upstream chiller system that CDUs depend on for stable, reliable cooling. CDU performance is directly tied to the quality of the chilled water supply: Stable supply temperature from the chiller translates to consistent IT equipment thermal management Reliable chiller operation prevents the temperature excursions that cause CDU bypass or IT equipment throttling Efficient chiller systems (oil-free TurboCor compressors, flooded evaporator design) maintain their performance characteristics under the continuous, high-load operation data centers demand Redundancy in CDU Deployments CDUs are typically deployed with redundancy appropriate to the criticality of the workload they serve. Common configurations include N (single CDU per zone — acceptable only for non-critical loads), N+1 (one standby CDU per zone — standard enterprise practice), and 2N (fully duplicated CDU infrastructure — mission-critical and hyperscale deployments). A common misconception: 'the CDU handles cooling.' In reality, the CDU manages and distributes cooling. The chiller system removes the heat. A CDU connected to an undersized or unstable chiller plant will not perform reliably regardless of its own specifications. Frequently Asked Questions Do all liquid-cooled data centers use CDUs? CDUs are the standard approach for chilled water-connected liquid cooling. Immersion cooling systems work differently — the servers are submerged in dielectric fluid which is cooled through a heat exchanger to the chilled water loop. The chiller plant serves both, but the rack-level distribution differs. What fluid runs on the IT side of the CDU? Typically deionized or treated water on the IT side, operating at slightly higher temperatures than the facility chilled water supply (often 60-80 degrees F on the return side). Specific fluid requirements depend on server hardware specifications. Talk with our engineers about designing a system that integrates chillers, CDUs, and high-density cooling -> Contact us