AI data centres are changing how heat is removed from servers. As computing equipment generates more heat in concentrated areas, liquid cooling is becoming an important part of data-centre design. But moving heat away from a processor with liquid does not, by itself, explain how the heat leaves the building.

That distinction matters for operators planning new capacity or reviewing existing cooling infrastructure. A liquid-cooled server rack may still depend on facility equipment that uses refrigerants. The refrigerant is further along the heat path, in the equipment that cools or rejects heat from the facility water system.

Understanding where each system begins and ends helps operators assess equipment needs, refrigerant requirements and F-gas obligations. It also prevents a common design misunderstanding: a coolant distribution unit (CDU) and a chiller perform different functions.

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From the processor to the facility water loop

In direct-to-chip liquid cooling, a cooling medium is brought close to heat-generating components, commonly through cold plates attached to processors. The liquid absorbs heat and carries it away from the IT equipment.

A CDU provides the connection between the technology cooling system (TCS), which serves the IT equipment, and the facility water system (FWS). In a common design, a heat exchanger in the CDU transfers heat from the TCS to the FWS while keeping the two liquid circuits separate. ASHRAE describes this separation as a common liquid-cooling arrangement in data centres. ashrae.org

The separation is useful because the liquids serving IT equipment and the facility may have different operating requirements. The CDU circulates and manages coolant for the IT-side loop, while the facility system receives the heat and carries it to the next stage of the cooling plant. NVIDIA’s DSX reference design similarly describes CDUs receiving facility water and using it to cool a separate technical-grade loop serving GPU cold plates. NVIDIA DSX Documentation

A CDU’s capacity is usually expressed in terms of the heat it can manage. In September 2026, LG announced that its 2.6-megawatt CDU had qualified as an NVIDIA DSX Ready CDU. The qualification means that the product met applicable requirements of the NVIDIA DSX reference design; it does not mean every data centre requires a unit of that size or uses the same layout. lg.com

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Heat still needs to leave the building

Once heat has moved from the server equipment into the facility water system, the facility must reject it. The method depends on the site and system design. It may involve outdoor heat-rejection equipment such as dry coolers, a cooling tower, mechanical chillers or a combination of systems.

NVIDIA’s DSX facilities reference design gives one example of how operating temperatures can affect that stage. It describes a 45°C liquid-cooling design point that expands the operating window for rejecting facility heat without full mechanical chilling. This is a design feature of that reference architecture, not a guarantee that every site can operate without chillers. NVIDIA DSX Documentation

Where a mechanical chiller is used, refrigerant has a role in the chiller’s refrigeration circuit. The European Commission describes a chiller as a system in which refrigerant cools a liquid—usually water—which is then circulated to cool air in a commercial or industrial facility. The facility water and the refrigerant therefore belong to different parts of the cooling system. Climate Action

This is why “liquid-cooled” does not automatically mean “refrigerant-free”. The term can describe how heat is taken from the IT equipment, while a separate system determines how the facility rejects that heat. Some designs may reduce reliance on mechanical chilling under their operating conditions; others may include chillers. The actual arrangement must be established from the site’s design documents and equipment specifications.

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Why the distinction matters for refrigerant planning

For operators, a useful first step is to map the whole heat path:

IT component → cold plate → technology cooling loop → CDU → facility water loop → heat-rejection plant

This map helps identify which equipment contains refrigerant and which equipment circulates liquid between heat exchangers. It also makes clear that changing the server-side cooling method does not, on its own, determine whether a facility needs refrigerant or how much.

The refrigerant question belongs to the equipment that contains the refrigerant—such as a chiller—not to the CDU simply because it forms part of a liquid-cooling architecture. A system inventory should record the equipment type, refrigerant, charge and location, along with the relevant service and replacement requirements.

That inventory also supports compliance checks. The EU F-gas Regulation covers listed gases and equipment containing them, or equipment whose functioning relies on them. Its HFC quota system applies to placing specified HFCs on the EU market, including HFCs in bulk and certain pre-charged equipment. The Regulation also sets separate restrictions for particular product categories. Fluorinated Greenhouse Gases – Climate Action

Those restrictions are specific to equipment type, refrigerant and other conditions. For example, the Commission lists restrictions applying from 1 January 2027 to certain stationary chillers: chillers with a rated capacity up to 12 kW using fluorinated greenhouse gases with a GWP of 150 or more, and chillers above 12 kW using gases with a GWP of 750 or more, subject to safety exceptions. These rules should be checked against the precise equipment category; they are not a blanket prohibition on every data-centre chiller. Climate Action

The EU’s HFC quota phase-down is another consideration for operators who need HFC refrigerants for equipment supply or service. The quota system limits the amount of covered HFCs that can be placed on the EU market. It does not, by itself, predict the price or availability of a particular refrigerant for an individual buyer. Those commercial questions depend on the product, supplier and transaction. climate.ec.europa.eu

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A practical review for data-centre operators

A structured review can help align cooling design with refrigerant compliance:

• Trace the heat path. Identify the server-side cooling method, CDU, facility water circuits and heat-rejection equipment.

• Separate the equipment roles. Record which components circulate coolant, which transfer heat between loops and which contain a refrigerant circuit.

• Check chiller specifications. Confirm the refrigerant, GWP, rated capacity and applicable product category before assessing restrictions.

• Plan servicing requirements. Record the refrigerant needed for installed equipment and confirm how maintenance supply will be arranged.

• Review refrigerant procurement. Confirm the supplier, product, applicable quota coverage and documentation for EU-market purchases or imports.

• Revisit the design assumptions. Check the supply and return temperatures, heat-rejection approach and any mechanical-chilling requirement in the actual engineering design.

These checks are relevant during new construction, equipment replacement and operational planning. They do not prescribe a particular cooling technology. Instead, they help the operator connect the IT cooling design to the facility plant and the rules applying to the refrigerants in use.

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Cooling is a system, not a single component

Liquid cooling can move heat away from high-density IT equipment through a dedicated cooling loop and CDU. The facility still needs to transfer that heat to an external sink. Depending on the site design, this may involve dry coolers, cooling towers, chillers or a combination.

For operators, the key is to assess the full system. Identify where refrigerants are used, verify the rules that apply to the equipment and plan supply and servicing requirements accordingly. A CDU milestone may signal progress in liquid-cooling technology, but it does not replace the need to understand the facility’s heat-rejection plant.

AFS Cooling supports businesses with refrigerant procurement, quota management and F-gas compliance. To discuss refrigerant requirements for your cooling infrastructure, contact AFS Cooling.