Liquid cooling and NABERS: Improving Australian data centre efficiency ratings

Author: Mark Deguara, Technology Innovation Leader

Australian data centre operators are adding higher-density compute within constrained power and cooling capacity. As a result, cooling architecture can directly affect the data centre energy efficiency rating facilities achieve.

NABERS Energy for Data Centres measures operational performance, covering the energy used to provide cooling and power services to IT equipment. Liquid cooling can reduce that overhead by capturing heat closer to high-power components and reducing the energy needed to transport and reject it. The resulting NABERS performance depends on the efficiency of the full cooling system, from chip-level heat capture through coolant distribution and heat rejection.

How does cooling affect a NABERS data centre energy efficiency rating?

NABERS Energy for Data Centres provides a one-to-six-star operational benchmark. Its three rating scopes are Infrastructure, IT Equipment and Whole Facility. For many data centre operators, particularly colocation providers that control cooling and power delivery without controlling tenant IT equipment, Infrastructure provides the clearest measure of facility efficiency.

The infrastructure assessment includes air conditioning, ventilation, process cooling, in-rack fans, lighting, power conditioning and distribution, and associated backup energy. Liquid-cooling pumps, heat exchangers and heat-rejection equipment serving the rated data centre can contribute to the infrastructure energy being measured. However, specific classifications and meter boundaries should be confirmed with a NABERS Accredited Assessor or NABERS.

An Infrastructure or Whole Facility assessment uses twelve continuous months of acceptable operational data. Reference designs, CFD modelling, and equipment specifications can guide design decisions. This data centre energy efficiency rating reflects how the facility performs once operating.

For liquid-cooled data centres, NABERS emphasises the energy consumed across the thermal path: capturing heat at the rack, moving it through the cooling system, and rejecting it from the facility.

How liquid cooling can improve infrastructure efficiency

Direct-to-chip liquid cooling captures heat at the chip and transfers it through a liquid loop. This can reduce the energy required for air movement while allowing higher coolant temperatures that increase economiser hours and reduce compressor operation.

Increasing a technology cooling system supply temperature by 20°C can cut cooling-system energy use by 30%–40%, depending on climate and system conditions. Heat-rejection design is critical: pump efficiency, coolant temperatures, and reliance on mechanical refrigeration can increase or reduce the overall benefit.

These considerations become more significant as rack density rises. With advanced chips like NVIDIA’s Vera Rubin, cooling architecture influences both available compute capacity and infrastructure energy consumption.

Liquid cooling architecture choices that affect NABERS performance

A liquid cooling system’s impact on data centre energy efficiency ratings depends on how coolant is distributed and heat is rejected. Three design choices are especially relevant to NABERS performance.

1. CDU and hybrid architecture

Coolant Distribution Units (CDUs) connect the technology cooling system with the wider facility cooling infrastructure. Liquid-to-liquid CDUs transfer captured heat to facility water, while liquid-to-air systems such as Heat Dissipation Units (HDUs) reject it into the data hall. HDUs can support retrofits where facility water is unavailable, although the room cooling system must then remove that heat.

Hybrid environments may also combine direct-to-chip accessories, conventional air cooling, and rear-door heat exchangers (RDHx) to accommodate different rack densities and customer requirements.

2. Cooling-loop temperatures

Connecting liquid cooling to a shared chilled-water loop can simplify some retrofits, but legacy air-cooled equipment may require colder water and limit economisation opportunities. A dedicated higher-temperature loop offers greater flexibility, but adds plant and integration requirements.

3. Chillers and heat rejection

Chillers and heat rejection complete the thermal path. Warm-water liquid cooling can reduce mechanical refrigeration under suitable conditions, while dry, free, adiabatic and evaporative approaches create different energy and water profiles.

This is particularly relevant in Australia, where water performance should be assessed separately from NABERS data centre energy efficiency ratings. A closed technology cooling loop does not determine total facility water consumption; that depends largely on how heat is ultimately rejected.

Design the NABERS measurement boundary with the cooling system

Liquid cooling introduces equipment and energy flows that need to be accounted for in the NABERS measurement boundary. In brownfield and mixed air/liquid facilities, CDUs, pumps, chilled-water systems, and heat-rejection equipment may cross existing electrical and mechanical boundaries.

The current NABERS data centre energy efficiency ratings do not identify CDUs, direct-to-chip cold plates, or liquid-loop pumps as individual categories. Equipment serving the rated data centre would generally fall within process cooling or infrastructure energy where applicable, but specific classifications and meter boundaries should be confirmed with a NABERS Accredited Assessor or NABERS.

For specifiers and consultants, this means defining meter locations, CDU and pump energy, shared cooling loads, facility-water allocation, and flow and temperature measurements during design. Contractors and integrators can support the assessment through validated meter maps, calibrated sensors, verified controls, and accessible trend data. Building these requirements into the cooling design gives operators a clearer record of facility performance throughout the NABERS assessment period.

Look beyond PUE to understand the energy impact

Data centre operators can complement PUE with measures like absolute energy consumption, cooling power, IT fan power, rack density, utilisation, and Water Use Effectiveness (WUE). Water should be tracked separately as NABERS Energy performance does not establish the water efficiency of the cooling system.

NABERS has announced work to develop a Data Centre Water Efficiency Framework to address that gap, with work underway to establish appropriate water-efficiency metrics and methodology for data centres. If water performance is incorporated into future NABERS assessment, cooling-system water use will become an even more important design consideration.

With higher-density computing changing the cooling requirements of Australian data centres, liquid cooling can support a stronger data centre energy efficiency rating by reducing the infrastructure energy required to capture, transport, and reject heat.
The result depends on decisions across the cooling architecture: CDU configuration, operating temperatures, pumps, controls, chillers, heat rejection, metering and commissioning. Considering those elements alongside the NABERS measurement boundary gives operators a stronger basis for evaluating liquid cooling investments.

Schneider Electric offers a comprehensive liquid cooling portfolio that spans direct-to-chip heat capture, coolant distribution, and facility-level heat rejection. Explore Schneider Electric’s Liquid Cooling Hub to learn about comprehensive direct-to-chip architectures. For a closer look at how to select and design the right system for your facility, download the Liquid Cooling System Architecture Guide.