Skip to main content
BSS/OSS Academy

Architecture · Data centre

Sustainable AI data centres: the metrics, the rules and the certificates

AI data centres use large amounts of energy and water, and in Europe a growing share of what they must measure and report is set by law. This page is a short overview of a large subject: the five numbers used to measure a site, the rules that apply, what green-building certificates add, and where teams most often go wrong.

Part 1 · Metrics

Five numbers that matter

Each is defined in a part of ISO/IEC 30134 (International Organization for Standardization / International Electrotechnical Commission), the international series on data centre key performance indicators. Cards marked EU reported are among the four indicators EU data centres must report under Delegated Regulation (EU) 2024/1364; Carbon Usage Effectiveness is not one of them.

PUE, Power Usage Effectiveness

EU reported

Power Usage Effectiveness

How much of the site’s energy reaches the information technology (IT) equipment rather than cooling, power losses and lighting.

Total data centre energy ÷ IT equipment energy. 1.0 would mean no overhead at all.

With AI racks: Liquid cooling can bring it down, but it says nothing about whether the graphics processing units (GPUs) are doing useful work.

ISO/IEC 30134-2 · Source: European Commission: Commission Delegated Regulation (EU) 2024/1364 on the first phase of the establishment of a common Union rating scheme for data centres (read 2026-11-08)

WUE, Water Usage Effectiveness

EU reported

Water Usage Effectiveness

How much water the site uses for each unit of IT energy.

Water taken in ÷ IT equipment energy, in litres per kilowatt-hour.

With AI racks: Evaporative cooling improves PUE but uses water; closed-loop liquid cooling uses little water but can need more energy in hot climates.

ISO/IEC 30134-9 · Source: European Commission: Commission Delegated Regulation (EU) 2024/1364 on the first phase of the establishment of a common Union rating scheme for data centres (read 2026-11-08)

CUE, Carbon Usage Effectiveness

Carbon Usage Effectiveness

How much carbon dioxide the site’s energy use emits for each unit of IT energy.

Carbon dioxide emissions from the data centre’s energy ÷ IT equipment energy, in kilograms per kilowatt-hour.

With AI racks: Set mostly by the grid and the power contracts, not the building: a low PUE on a fossil-heavy grid still gives a poor CUE.

ISO/IEC 30134-8 · Source: ISO/IEC: ISO/IEC 30134-8 Carbon usage effectiveness (CUE) (read 2026-11-08)

ERF, Energy Reuse Factor

EU reported

Energy Reuse Factor

The share of the site’s energy that is reused outside it, usually as heat for a district heating network.

Energy reused outside the data centre ÷ total data centre energy, from 0 to 1.

With AI racks: Warm-water liquid cooling returns hotter water than air cooling, which makes the heat far easier to sell.

ISO/IEC 30134-6 · Source: European Commission: Commission Delegated Regulation (EU) 2024/1364 on the first phase of the establishment of a common Union rating scheme for data centres (read 2026-11-08)

REF, Renewable Energy Factor

EU reported

Renewable Energy Factor

The share of the site’s energy that comes from renewable sources.

Renewable energy ÷ total data centre energy, from 0 to 1.

With AI racks: Large AI sites usually buy renewable energy by contract rather than generate it on site, so check what is being counted.

ISO/IEC 30134-3 · Source: European Commission: Commission Delegated Regulation (EU) 2024/1364 on the first phase of the establishment of a common Union rating scheme for data centres (read 2026-11-08)

Two figures can only be compared when they use the same definition, the same measurement points and the same period. A design-stage PUE and a measured annual PUE are not the same number.

Part 2 · Rules and certificates

What the law requires vs what you choose

Required by law, where it applies

Germany: Energy Efficiency Act (EnEfG) § 11

Data centres in Germany that the Act covers.

Sites opening from 1 July 2026 must reach a PUE of 1.2 or lower and reuse at least 10% of their energy, with planned shares of 15% and 20% for sites opening from July 2027 and July 2028. Older sites must reach 1.5 from July 2027 and 1.3 from July 2030. Electricity must be 100% renewable on balance from 1 January 2027. Text as published, read on 8 November 2026; an amendment has been proposed.

Source: Bundesministerium der Justiz: Energieeffizienzgesetz (EnEfG) § 11 Klimaneutrale Rechenzentren (read 2026-11-08)

EU Taxonomy (activity 8.1, data processing and hosting)

Only sites presented as a sustainable investment under EU finance rules.

The operator must have put the European Code of Conduct on Data Centre Energy Efficiency practices in place, checked by an independent audit.

Source: European Commission: Commission Delegated Regulation (EU) 2021/2139 (Climate Delegated Act), Annex I, activity 8.1 (read 2026-11-08); European Commission Joint Research Centre: Assessment framework for data centres in the context of Activity 8.1 in the Taxonomy Climate Delegated Act (read 2026-11-08)

Chosen: green-building certificates

Voluntary. Each mainly assesses design and construction; buildings in operation have separate schemes. A certificate does not replace the measured figures the law asks for.

LEED

Leadership in Energy and Environmental Design

US Green Building Council (USGBC)

Levels: Certified, Silver, Gold, Platinum

Usually asked for by: Investors and tenants, especially US-based ones.

Source: US Green Building Council: LEED rating system (read 2026-11-08)

BREEAM

Building Research Establishment Environmental Assessment Method

BRE (Building Research Establishment), UK

Levels: Pass, Good, Very Good, Excellent, Outstanding

Usually asked for by: UK and European investors, and some UK planning authorities.

Source: BRE Group: BREEAM (read 2026-11-08)

DGNB

Deutsche Gesellschaft für Nachhaltiges Bauen

German Sustainable Building Council

Levels: Silver, Gold, Platinum for new buildings; Bronze also for existing buildings

Usually asked for by: German and continental European investors and tenants.

Source: DGNB: Assessment and award (read 2026-11-08)

Part 3 · AI

What AI changes

  • Liquid cooling moves the trade-off

    Dense GPU racks push sites from air to liquid cooling. That changes how energy and water trade against each other, so PUE and WUE have to be read together.

  • Heat reuse becomes realistic

    Warm-water cooling returns heat at temperatures a heating network can use. Reuse quotas such as Germany’s already apply to new sites.

  • Grid flexibility is harder

    Training jobs swing power draw quickly across thousands of GPUs. Offering to cut load when the grid asks has to be planned around jobs that lose work when they stop.

  • PUE is not AI efficiency

    A perfect PUE says nothing about how much useful work each watt of IT energy does. That needs measures such as tokens per watt.

Part 4 · Traps

Common traps

  1. 01

    Treating a design-stage certificate as proof the site runs efficiently.

    The certificate scores the design; the measured annual figures can be worse, and the law asks for those.

  2. 02

    Chasing points.

    Cheap credits lift the rating without changing energy, water or carbon, the things that matter for a data centre.

  3. 03

    Comparing PUE figures that use different definitions or boundaries.

    A "1.2" from one site and a "1.3" from another may not be comparable at all.

  4. 04

    Reporting without metering that can back the figures up.

    Mandatory reports and audits then rest on estimates, and fixing the metering after opening is costly.