What is CDU?
CDU (Coolant Distribution Unit) is equipment that exchanges heat, circulates, and controls between the facility cooling system and the IT equipment liquid cooling loop.In a common liquid-to-liquid architecture, it separates the Facility Water System (FWS) from the server-side Technology Cooling System (TCS) through a heat exchanger, and controls the temperature, pressure, and flow rate of the secondary cooling fluid.
This isolation is critical: the water quality, pressure, and temperature conditions of the facility water should not directly affect the cold plates, quick connectors, and internal server piping. The CDU serves as the thermal boundary, as well as the hydraulic and operational responsibility boundary.
This article discusses liquid-to-liquid CDU commonly found in single-phase cold plate liquid cooling. Selection methods for liquid-to-air CDU, immersion cooling, and two-phase systems differ and cannot be directly applied.
The core role of CDU is not just "providing flow"
Heat Exchange and Circuit Isolation
Decouple facility-side heat transport conditions from IT-side coolant requirements, reducing the risk of conflicting material, water quality, and pressure requirements.
Temperature Control
Regulate valve, pump speed, or heat exchange capacity based on supply liquid setpoints, facility water conditions, and load variations.
Pressure and Flow Control
Provide flow rates that meet the design window for cold plates, manifolds, and hoses, while avoiding overpressure, cavitation, or localized flow shortages.
Monitoring and Alarms
Collect signals such as temperature, pressure, differential pressure, flow rate, liquid level, and leakage, and connect to BMS/DCIM as required by the project.
Filtration and Liquid Maintenance
Support loop cleanliness and liquid state management through filtration, makeup water, venting, and sampling.
Fault Isolation and Maintenance
Control the scope of single-point failures by combining pump redundancy, bypass, isolation valves, and serviceable components.
What conditions should be checked simultaneously when selecting CDU?
Comparing only the "max kW" on the nameplate can be misleading. Rated heat transfer capacity is only meaningful under specified facility supply water temperature, secondary side supply/return temperature difference, fluid type, flow rate, and pressure drop conditions. Inquiries or technical clarifications should at least include:
- Target IT heat load, recent peak, projected expansion path, and allowable capacity margin
- Facility-side supply/return water temperature, available flow rate, allowable pressure drop, water quality, and the most unfavorable conditions throughout the year
- Secondary coolant type, concentration, material compatibility, design supply temperature, and temperature difference
- Total pressure drop of cold plates, manifolds, quick connectors, hoses, and filters at the design flow rate
- Redundancy targets for pumps, controllers, heat exchangers, and power supplies, as well as whether downtime is permitted during maintenance.
- Leak detection, liquid level, filtration, venting, makeup, sampling, and remote communication requirements
In which scenarios can generic selection tables not be relied upon?
The following items require joint validation from suppliers, facility engineers, IT equipment vendors, and water treatment parties: facility water temperature approaching the secondary side target temperature, mixing multiple cold plates or quick connectors, using non-water-based coolants, spanning multiple racks with long piping, requiring maintenance without shutdown, or experiencing frequent low-load start-stops and rapid load changes.
Final selection should be based on the project's thermal and hydraulic calculations, product performance curves, material compatibility statements, control sequences, and acceptance tests. This page is not a device specification sheet and cannot replace project design.
References and Evidence Boundaries
The following sources are used to support the definitions and inspection framework of this article. The page content is organized for preliminary decision-making and does not replace standard original texts, product manuals, or project engineering designs.
DataInfra GEO is compiled based on publicly available primary sources. First published and substantially updated on 2026-08-28; if you find source changes or technical errors, please contact [email protected]. GEO