Key takeaways
- Europe’s size thresholds measure different things. The EU reporting rule counts 500 kW of installed IT power demand, Germany’s EnEfG 300 kW of non-redundant connection power, and the EED waste-heat duty more than 1 MW of total rated energy input.
- The EU database calculates four indicators from reported data: PUE, WUE, ERF and REF. Each has an ISO/IEC 30134 and EN 50600-4 counterpart, and the Commission reported EU averages of 1.36 for PUE, 0.58 m³/MWh for WUE and 0.86 for REF from the first reporting period.
- Binding PUE limits exist only in national law so far. Germany requires existing sites to reach 1.5 from 1 July 2027; a bill to relax that to 1.6 is not law.
- Several headline rules are not in force: the EU rating scheme adopted on 21 September 2026 is under scrutiny, EU minimum performance standards are in consultation until 14 December 2026, and Spain’s hourly 80% renewables condition is a draft.
- Every one of the 72 entries has a stable anchor, so you can link straight to a definition, for example https://scienceshot.com/data-centre-glossary#pue.
This glossary defines the terms a European operator, consultant or journalist meets across the data-centre stack, from the grid connection to the GPU. Each definition is paraphrased from the law or standard that sets it and links to that primary source. Where a term has no legal or standardised definition, the entry says so. Every entry also states what the term means for a European operator and, where ScienceShot has a deeper page, links to it.
Status labels describe legal or formal standing on 10 October 2026: in force, adopted but not in force, bill, proposal, consultation, standard, guideline or industry term. Rules change, so check the linked source before relying on a date. Corrections are welcome through the contact page.
Jump to a layer Grid and power Cooling Efficiency metrics Regulation Site and building Compute and network Thresholds compared
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Grid and power
From the connection request to the UPS output: the terms that decide when a site gets power, what it pays and how it counts green electricity.
Grid connection queue
The set of connection requests waiting for a transmission or distribution system operator to offer capacity at a point on the network. Under the EU's 2024 electricity market reform, distribution system operators must publish the capacity available for new connections in their area, including capacity already under connection request, and update it at least every quarter.
Why it matters for a European operator In congested hubs the queue, more than land or permits, sets the earliest date a site can be energised, so read the operator's published capacity before committing to a plot.
Firm and non-firm capacity
Firm capacity is connection capacity the network operator guarantees, faults aside. Non-firm capacity can be limited or interrupted by the operator under conditions agreed in advance; EU law expects such connections to be made firm once the network has been reinforced.
Why it matters for a European operator A non-firm offer can bring energisation forward, but its curtailment terms have to be covered by backup power, storage or workloads that can pause.
Flexible connection agreement
EU law defines it as a set of agreed conditions for connecting electrical capacity that limit and control how much electricity is injected into or withdrawn from the network. Regulators must set up a framework under which grid operators can offer such agreements in areas where capacity for new connections is limited.
Why it matters for a European operator It is the legal basis for asking a European grid operator for a curtailable connection while reinforcement is built; national frameworks may require the agreement to state its duration and the expected date for full firm capacity.
Bidding zone
The largest geographical area within which market participants can exchange energy without capacity allocation. One wholesale price applies across a zone in each market period. Some countries form a single zone, others such as Sweden, Norway and Italy are split into several, and Germany shares one zone with Luxembourg.
Why it matters for a European operator Your energy price, its daily spread and its carbon profile are set per bidding zone, so two sites in the same country can face different prices.
Day-ahead price
The price set in the daily auction that couples European power exchanges, Single Day-Ahead Coupling (SDAC), for each delivery period of the following day. Since delivery day 1 October 2025 the auction clears in 15-minute market time units.
Why it matters for a European operator Index-linked tariffs and many PPAs settle against it, and the spread between a day's cheapest and dearest periods is what flexible load can earn.
Grid carbon intensity (gCO2e/kWh)
Grams of CO2 equivalent emitted per kilowatt-hour of electricity, either as an average across the generation mix or at the margin, meaning the plant that responds to one more unit of demand. Published series also differ on whether they trace imports and whether they count lifecycle emissions.
Why it matters for a European operator Carbon-aware scheduling and emissions reports give different answers depending on the signal used, so put the signal and its source next to any figure you quote.
Location-based and market-based emissions (Scope 2)
The two methods the GHG Protocol sets for Scope 2 emissions from purchased electricity. The location-based method applies the average emission factor of the grids where the power is used; the market-based method applies the factors of the contracts a company chose, such as PPAs and guarantees of origin. The guidance dates from 2015 and has been through a public consultation on its revision.
Why it matters for a European operator ESRS E1 requires companies in CSRD scope to disclose gross Scope 2 emissions both ways, so data-centre customers may ask for both figures.
24/7 carbon-free energy (24/7 CFE)
Meeting every kilowatt-hour of consumption with carbon-free electricity in every hour of every day, wherever it is consumed, as defined by the UN-backed 24/7 Carbon-free Energy Compact. Annual matching is looser: a year's certificates can cover consumption at night or in winter.
Why it matters for a European operator No EU law requires hourly matching today. Spain's draft royal decree on data centres would require at least 80% renewable coverage in each operating hour, but it is still a proposal.
Power purchase agreement (PPA)
The EU Renewable Energy Directive defines a renewables PPA as a contract under which a buyer agrees to purchase renewable electricity directly from a producer. In practice it is either physical, with power delivered through the grid, or financial (virtual), settled as a price difference while the buyer receives the certificates.
Why it matters for a European operator EU data-centre reporting lists renewable energy from PPAs as its own line (ERES-PPA), so contract evidence feeds straight into your REF.
Guarantee of origin (GoO)
An electronic certificate whose sole function is to show a final customer that a given share or quantity of energy came from renewable sources. The standard size is 1 MWh, divisible into fractions since the 2023 revision. A GoO is valid for transactions for 12 months after the energy was produced and expires 18 months after production at the latest if not cancelled.
Why it matters for a European operator Certificates are the cheapest way to raise a reported renewable share, and EU reporting lists them separately (ERES-GOO), so buyers can see how much of a REF rests on certificates alone.
Uninterruptible power supply (UPS)
Equipment that keeps the IT load powered through supply disturbances and bridges the gap until generators take over, using energy stored in batteries or flywheels. IEC 62040-3 sets how UPS performance is specified and tested, with classes such as VFI, VI and VFD describing how far the output depends on the input supply.
Why it matters for a European operator EU reporting measures IT energy (EIT) at the output of every UPS feeding IT equipment, so UPS metering also fixes your PUE boundary.
Redundancy (N, N+1, 2N)
Notation for how much capacity exists beyond the baseline N needed to carry the design load: N+1 adds one spare unit, 2N duplicates the whole system. EU law defines data-centre redundancy as duplicating components or functions so that one set can take over if another fails or is taken down for maintenance.
Why it matters for a European operator EU reporting asks for redundancy levels in this notation for electrical infrastructure (high voltage, low voltage and rack level) and for cooling (room and rack level).
Busway (busbar trunking) (BTS)
An enclosed run of conductors that distributes low-voltage power along a row of racks, with tap-off units feeding individual racks. IEC 61439-6 covers busbar trunking systems rated up to 1,000 V AC or 1,500 V DC.
Why it matters for a European operator Overhead busway lets a hall change rack power without re-cabling, which matters as AI racks push densities far beyond what older distribution was sized for.
Low and medium voltage (LV, MV)
In EU product law, low-voltage equipment is rated between 50 and 1,000 V AC or between 75 and 1,500 V DC. Medium voltage is the distribution level above that, from which most large sites take their supply and transform down on site; the exact bands vary by country and grid operator.
Why it matters for a European operator The voltage at which you connect affects tariffs, who owns the substation and how long the connection takes, so settle it early with the grid operator.
Back-up generation (EDC-BG)
On-site generators, usually diesel or HVO-fuelled engines, that carry the site through a grid outage once the UPS has bridged the transfer. EU reporting counts their energy within total data-centre consumption but requires it to be measured separately as EDC-BG.
Why it matters for a European operator Generator energy appears in your reported totals, so long test runs or extended outages move your numbers.
Grid services from data centres (CBtG)
Functions a data centre provides to support the stability, reliability and resilience of the power system, such as peak demand shifting or firm frequency response. EU reporting asks whether a site provides them and the average battery capacity it offered to the grid through a market or contract (CBtG, in kW).
Why it matters for a European operator UPS batteries and movable workloads are assets that some grid markets pay for, and the reporting fields make that participation visible to regulators.
Cooling
Air, liquid and the temperature classes that set how much of the year a site can run without chillers.
Air cooling: CRAC and CRAH units (CRAC, CRAH)
Room-level units that cool and condition the air in a computer room. A computer room air conditioner (CRAC) is a packaged unit, typically with its own refrigeration circuit; a computer room air handler (CRAH) moves air across a coil supplied with chilled water from a central plant.
Why it matters for a European operator The unit type decides where compressor energy sits in your PUE and how much you gain from raising supply temperatures.
Hot and cold aisle containment
Enclosing either the cold aisle in front of the racks or the hot aisle behind them so that supply and exhaust air cannot mix. It builds on the hot aisle and cold aisle layout, in which rows of racks face each other intake to intake.
Why it matters for a European operator Containment is among the first retrofits an air-cooled hall considers when it needs a lower PUE, because it allows warmer supply air and lower fan energy.
Direct liquid cooling (DLC)
Cooling in which liquid flows through cold plates attached to the hottest components, usually GPUs and CPUs, and carries their heat out of the server without passing it through room air. Heat from memory, drives and power supplies is still removed by air unless the design covers them as well.
Why it matters for a European operator DLC makes rack densities beyond air-cooling practice workable, and its warmer return water is easier to reuse in heat networks.
Immersion cooling
Cooling in which whole servers sit in a dielectric liquid. In single-phase systems the liquid stays liquid and is pumped through a heat exchanger; in two-phase systems it boils on the hot components and condenses on a coil above the bath.
Why it matters for a European operator Fluid choice carries regulatory and supply risk, since many two-phase fluids are fluorinated, so check fluid data sheets against EU chemicals and F-gas rules before you commit.
Coolant distribution unit (CDU)
The unit that separates the liquid loop serving the IT equipment from the facility water loop, transferring heat between them through a heat exchanger and controlling flow, pressure and temperature on the IT side. ASHRAE calls the IT-side loop the technology cooling system (TCS) and the building loop the facility water system (FWS).
Why it matters for a European operator The CDU's approach temperature decides how warm your facility water can run, and therefore how many free-cooling hours and how much usable heat you get.
Rear-door heat exchanger (RDHx)
A rack rear door with a built-in coil that cools server exhaust air before it returns to the room, using chilled water or another coolant. Passive doors rely on the server fans; active doors add fans of their own.
Why it matters for a European operator It is a common way to add higher-density racks to an existing air-cooled hall without moving to direct liquid cooling.
Chiller
A machine that produces chilled water with a refrigeration cycle and rejects the heat either to outside air (air-cooled) or to condenser water and a cooling tower (water-cooled). Its efficiency is given as a coefficient of performance (COP), the heat removed per unit of energy put in.
Why it matters for a European operator Chiller run hours drive much of the cooling energy in a conventional plant, so design work focuses on how many hours a year the climate and water temperatures let you leave them off.
Free cooling (economiser)
Cooling the data centre with outdoor conditions instead of the refrigeration cycle, either by bringing filtered outside air into the hall (air-side economiser) or by cooling the water loop through a heat exchanger, dry cooler or cooling tower (water-side economiser).
Why it matters for a European operator Warmer permitted supply temperatures add free-cooling hours in any climate, which is why setpoints and economiser design are decided together.
Evaporative cooling and cooling towers
Cooling that removes heat by evaporating water, either by wetting the incoming air or in a cooling tower, where atmospheric air cools warm water by direct contact. The lowest temperature it can approach is the wet-bulb temperature.
Why it matters for a European operator It saves electricity by spending water, shifting load from your PUE to your WUE, and EU reporting now records both.
Wet-bulb temperature
The temperature a thermometer with a water-saturated wick reaches when air flows over it and evaporation cools it to equilibrium. It is the floor that evaporative cooling can approach, and it is never higher than the ordinary dry-bulb air temperature.
Why it matters for a European operator Design wet-bulb on the hottest humid days, more than average air temperature, sets the capacity of evaporative coolers and cooling towers.
ASHRAE air-cooling classes A1 to A4 and H1
Environmental classes for air-cooled IT equipment in ASHRAE TC 9.9's Thermal Guidelines for Data Processing Environments, fifth edition. The recommended inlet range for classes A1 to A4 is 18 to 27 °C; the allowable dry-bulb ranges are 15 to 32 °C for A1, 10 to 35 °C for A2, 5 to 40 °C for A3 and 5 to 45 °C for A4. Class H1, added for high-density air-cooled servers, has a recommended range of 18 to 22 °C and an allowable range of 15 to 25 °C.
Why it matters for a European operator ASHRAE describes the allowable range as where vendors test that equipment works, with no statement about reliability, so write into your SLAs which range applies.
ASHRAE liquid-cooling classes W17 to W+
ASHRAE's liquid-cooling classes, named after the maximum facility water supply temperature: W17, W27, W32, W40, W45 and W+ for above 45 °C, with a 2 °C minimum for all. W17 and W27 typically use chillers and a cooling tower, with an optional water-side economiser; W32 and W40 usually run without chillers in most locations; W45 and W+ are typically operated without chillers.
Why it matters for a European operator The class you design to decides whether you need chillers at all and whether your waste heat is warm enough for a district heating network.
IT intake air temperature setpoint (TIN)
The average setpoint temperature the cooling system is commanded to deliver at IT equipment air intakes, across all computer rooms and averaged over the year. It is one of the KPIs in-scope EU data centres report.
Why it matters for a European operator It shows how much of ASHRAE's recommended 18 to 27 °C range a site actually uses, which bounds the free-cooling hours it can get.
Average waste heat temperature (TWH)
The annual average temperature of the fluid that cools the IT equipment, measured where the heated fluid enters the heat exchangers at the computer room boundary, or at the heat recovery exchanger where there is one.
Why it matters for a European operator Heat buyers care about temperature: low-grade heat usually needs a heat pump before a district network can use it, which changes the economics of reuse.
Cooling degree days (CDD)
A measure of how far and for how long outdoor temperature exceeds a base temperature over a year. For EU data-centre reporting it is calculated for the site's location with the Eurostat and JRC method, a base of 21 °C and open-access data.
Why it matters for a European operator It gives the EU database a climate correction, so a southern site's PUE can be read against its weather instead of against a Nordic peer.
Refrigerants and the F-gas Regulation (F-gas)
Refrigerants are the working fluids in chillers and direct-expansion units, and many are fluorinated greenhouse gases. Regulation (EU) 2024/573 replaced Regulation (EU) No 517/2014 as the EU F-gas law, and EU data-centre reporting asks operators to list the refrigerant types used to cool the computer rooms.
Why it matters for a European operator The EU Taxonomy's data-centre criteria cap refrigerant global warming potential at 675, and F-gas restrictions shape which plant you can buy and service over its life.
Efficiency metrics
The ratios regulators and customers ask for, anchored in the ISO/IEC 30134 and EN 50600-4 series and in the EU reporting regulation.
Power usage effectiveness (PUE)
Total data-centre energy divided by the energy used by the IT equipment over the same period, normally a year. EU reporting calculates it as EDC/EIT. The metric is standardised in ISO/IEC 30134-2, whose second edition was published in January 2026, and in EN 50600-4-2; German law calls it Energieverbrauchseffektivität.
Why it matters for a European operator Germany's EnEfG sets binding PUE limits, 1.5 from 1 July 2027 for existing sites, and the Commission reported an EU average PUE of 1.36 from the first reporting period.
Partial PUE and mixed-use PUE (pPUE, mPUE)
Variants of PUE for part of a facility or a shared building. Partial PUE is the usual industry name for a PUE-style ratio drawn around one zone or subsystem instead of the whole site; check how the boundary was set before comparing two figures. ISO’s catalogue description of the 2026 edition of ISO/IEC 30134-2 says it adds an mPUE variant for data centres in mixed-use buildings.
Why it matters for a European operator Neither is an EU reporting indicator, yet both help explain a site's PUE to auditors when the hall shares plant with offices or other tenants.
Total energy and IT energy (EDC, EIT)
The two meter readings behind PUE in EU reporting. EDC is all energy entering the data centre, including electricity, fuels for cooling and back-up generation, measured before the supply transfer switchgear. EIT is measured at the output of every UPS feeding IT equipment, the category 1 method of EN 50600-4-2, or at the PDUs where there is no UPS.
Why it matters for a European operator Moving the IT meter from UPS output to rack PDUs changes PUE, so record the category used; operators must keep records of measurement points and devices for at least 10 years.
Installed IT power demand and rated IT load (PDIT)
Installed IT power demand is the sum of the nominal power demand of the network, server and storage equipment installed in the computer room, in kW. Rated IT load is the maximum IT load the power and cooling infrastructure can handle while providing the intended service availability; EU reporting accepts it when installed demand cannot be determined.
Why it matters for a European operator This is the figure that decides whether you cross the EU's 500 kW reporting threshold, and it is a different quantity from the connection capacity German law uses.
Water usage effectiveness (WUE)
Water entering the data-centre boundary divided by IT energy. EU reporting expresses it in cubic metres per MWh of IT energy, numerically the same as litres per kWh, and asks for potable water as a separate figure; the method follows EN 50600-4-9, and ISO/IEC 30134-9 specifies the same KPI internationally.
Why it matters for a European operator The Commission reported an EU average WUE of 0.58 m³/MWh from the first reporting period, and the rating scheme it adopted, not yet in force, would give each site a WUE class.
Carbon usage effectiveness (CUE)
A key performance indicator for the CO2 emitted by a data centre during the use phase of its life cycle, specified in ISO/IEC 30134-8. The standard defines how the indicator is measured, calculated and reported, and introduces measurement categories; EN 50600-4-8 is the European counterpart.
Why it matters for a European operator CUE is not among the EU database indicators, and its value depends on the emission factor chosen, location-based or market-based, so always state which.
Energy reuse factor (ERF)
The share of a data centre's total energy that is reused outside its boundary, mostly as heat. EU reporting calculates it as EREUSE/EDC, measured under EN 50600-4-6 at the point where heat is handed to the other party, after subtracting any reused heat that cools the data centre itself. ISO/IEC 30134-6 defines the same ratio.
Why it matters for a European operator Germany requires new data centres to reuse at least 10% of their energy and France treats the waste-heat duty as met at an ERF of 0.20, while across the EU only about 1.8% of data-centre heat was reused in the first reporting period.
Energy reuse effectiveness (ERE)
The Green Grid's metric for reuse: total facility energy minus reused energy, divided by IT energy. It equals PUE multiplied by (1 minus ERF), so it can fall below 1.0 when a lot of heat is reused.
Why it matters for a European operator ERE is not used in EU or German law; when a vendor quotes an ERE below 1, convert it back into PUE and ERF before comparing it with regulatory figures.
Renewable energy factor (REF)
The share of total data-centre energy that comes from renewable sources. EU reporting calculates it as ERES-TOT/EDC, where the renewable total is the sum of guarantees of origin, PPAs and on-site generation, each reported separately and measured under EN 50600-4-3. ISO/IEC 30134-3 defines the same factor.
Why it matters for a European operator The Commission reported an EU weighted average REF of 0.86 from the first reporting period, and Germany requires 100% renewable electricity on a balance-sheet basis from 1 January 2027.
Cooling efficiency ratio (CER)
A key performance indicator for how efficiently a data centre uses energy to control the temperature of its spaces, specified in ISO/IEC 30134-7 and in EN 50600-4-7. The standard defines its measurement, calculation and reporting, and does not apply to cooling systems that are not powered by electricity, such as heat-driven absorption chillers.
Why it matters for a European operator German operators report cooling-system efficiency under EN 50600-4-7 in their annual register submission, and CER isolates cooling performance from the IT load that PUE folds in.
Server efficiency and utilisation (ITEEsv, ITEUsv, CSERV, CSTOR)
ISO/IEC 30134-4 defines ITEEsv, the energy-efficiency capability of the installed servers based on benchmark data, and ISO/IEC 30134-5 defines ITEUsv, how heavily those servers are actually used; both parts were amended in 2025. EU reporting adds two capacity KPIs: CSERV, server capacity based on SERT active-state performance, and CSTOR, storage capacity in petabytes.
Why it matters for a European operator PUE says nothing about the work the IT does, and these indicators let the EU database relate energy to installed computing capacity.
Regulation
EU and national rules, each marked with its legal status on the date this page was last checked.
EED Article 12
The data-centre article of the recast Energy Efficiency Directive (EU) 2023/1791. It requires owners and operators of data centres with installed IT power demand of at least 500 kW to publish the information in Annex VII every year, trade secrets excepted. It excludes centres used for, or serving exclusively, defence and civil protection, creates the EU database, and asks Member States to encourage sites of 1 MW or more to take into account the best practices of the EU Code of Conduct.
Why it matters for a European operator It is the legal root of every EU data-centre obligation so far, and its paragraph 5 is what led to the minimum performance standards now under consultation.
Delegated Regulation (EU) 2024/1364
The Commission act that fixes what in-scope data centres report to the EU database: 7 identification items in Annex I, 24 KPIs in Annex II, and the four indicators PUE, WUE, ERF and REF calculated in Annex III. Reports were due by 15 September 2024, then by 15 May 2025 and every year after, each covering the previous calendar year.
Why it matters for a European operator Its annexes, more than the Directive's broad Annex VII, are the checklist your metering has to satisfy.
European database on data centres
The EU-level database set up under EED Article 12(3). Operators submit to it directly or through a national scheme where one exists, such as Germany's register. Individual site data stay confidential to the Commission and the Member State concerned, and only aggregates at Member State and EU level are published.
Why it matters for a European operator Site data you submit stay confidential in the database, while the Directive's own Annex VII publication duty is separate, so check what your national rules require you to publish yourself.
500 kW threshold and other size thresholds
The EU reporting threshold covers data centres with installed IT power demand of at least 500 kW. Other thresholds measure different quantities: Germany's EnEfG starts at 300 kW of non-redundant rated connection power, France applies 500 kW of installed power assessed per SIRET business number, and the EED waste-heat duty uses more than 1 MW of total rated energy input.
Why it matters for a European operator The same site can be in scope in one country and out of scope in another, so record installed IT demand, connection capacity and total rated input separately; the comparison table below sets them side by side.
EED waste-heat duty (Art. 26(6))
Member States must ensure that data centres with a total rated energy input above 1 MW use their waste heat or other waste-heat recovery applications, unless a cost-benefit assessment shows this is not technically or economically feasible.
Why it matters for a European operator Total rated energy input is a whole-facility figure, so the heat duty and the 500 kW IT reporting threshold can catch different sites, and national laws such as France's set the practical test.
EU rating scheme for data centres (C(2026) 3472)
A Commission delegated regulation adopted on 21 September 2026, catalogued as C(2026) 3472, that would turn reported data into electronic labels with PUE and WUE classes. Parliament extended its scrutiny by two months on 6 October 2026, and on 10 October the procedure was awaiting a committee decision with no Official Journal publication. If it enters into force as drafted, the EU database would issue labels by 15 August 2027 and each year after.
Why it matters for a European operator Labels would be built from the data you already report, so the quality of this year's metering is what a future label will show.
EU minimum performance standards (MPS)
Possible binding EU minimum performance standards for data centres, which EED Article 12(5) asked the Commission to assess. A public consultation and call for evidence opened on 21 September 2026 and closes on 14 December 2026, and the Commission plans a legislative proposal for the second quarter of 2027.
Why it matters for a European operator Operators can still shape the indicators and thresholds through the consultation, and any figure presented today as an EU minimum is speculation.
Energieeffizienzgesetz (EnEfG)
Germany's Energy Efficiency Act, whose data-centre section applies from 300 kW of non-redundant rated connection power. It has required an energy or environmental management system since 1 July 2025, validated or certified from 1 January 2026 at 1 MW or more (300 kW for public bodies), annual reporting to the federal register by 31 March, renewable electricity coverage of 50% since 1 January 2024 rising to 100% from 1 January 2027, and disclosure of directly attributable energy use to customers.
Why it matters for a European operator Its register feeds the EU database, so German sites report through the national route, and its PUE limits apply on top of EU reporting.
EnEfG PUE and energy-reuse limits (§11 EnEfG)
Section 11 sets efficiency limits for German data centres. Sites that started operating before 1 July 2026 must reach an annual PUE of 1.5 or lower from 1 July 2027 and 1.3 or lower from 1 July 2030. Sites starting from 1 July 2026 must reach 1.2 and a share of reused energy, measured under DIN EN 50600-4-6, of at least 10%; the planned share rises to 15% for sites starting from 1 July 2027 and 20% from 1 July 2028, to be reached within two years of commissioning.
Why it matters for a European operator These limits are law today, so plan to them unless and until the amending bill is enacted.
EnEfG amending bill (Drucksache 21/8027)
A German government bill that would relax the §11 PUE limits for existing data centres to 1.6 from 2027 and 1.4 from 2030, keep 1.2 for new builds, and redefine a data centre from 500 kW of installed IT power. The Bundestag's summary of the hearing also lists moving the 100% renewable deadline from 2027 to 2030. It had a first reading on 24 September 2026 and a committee hearing on 5 October 2026, and on 10 October 2026 the Bundestag's procedure record still showed it as referred to committee, with no final vote.
Why it matters for a European operator Until it passes, the in-force limits apply; follow it, but do not plan a retrofit around it.
French data-centre rules (Code de l'énergie L236)
France requires data centres with at least 500 kW of installed power, assessed per SIRET number, to report annually by 15 May, and those with at least 1 MW to make use of their waste heat. Décret 2025-1382 treats the heat duty as met at an ERF of 0.20 or more, a level a ministerial order may raise to 0.40, and fines reach €50,000 per data centre.
Why it matters for a European operator Sites whose permits were filed before 1 January 2026 have until 1 October 2027 to complete a cost-benefit analysis of using their heat.
Irish data-centre connection policy (CRU)
The Irish energy regulator's decision of 12 December 2025 on connecting new data centres to the grid. Applicants must provide on-site or near-site dispatchable generation or storage matched to their requested import demand and match at least 80% of their annual demand with additional renewable-electricity projects; the duties scale with the size of the requested connection.
Why it matters for a European operator In Ireland a new data-centre grid connection now comes with generation and renewables obligations attached.
Dutch hyperscale siting rule (Bkl)
Dutch planning law bars municipal environment plans from allowing hyperscale data centres outside two designated areas: part of Het Hogeland in Groningen and the Agriport locations in Hollands Kroon. A hyperscale data centre is defined as more than 10 hectares of built floor area together with an electrical connection of 70 MW or more.
Why it matters for a European operator Projects below either threshold fall outside the ban.
Spanish draft royal decree on data centres
A Spanish draft royal decree on sustainable data centres, put to consultation from 27 August to 10 September 2026. As the energy ministry describes it, in-scope sites would need additional renewable supply covering at least 80% of consumption in each operating hour. Royal Decree-law 7/2026 only says such requirements may be set.
Why it matters for a European operator If adopted, annual certificate matching would no longer be enough for Spanish sites in scope, so check the Boletín Oficial del Estado for a final text before signing Spanish PPAs.
EU Code of Conduct on Data Centre Energy Efficiency (EU DC CoC)
A voluntary European Commission programme, run by the Joint Research Centre, in which operators commit to energy-efficiency practices set out in its Best Practice Guidelines. EED Article 12(4) asks Member States to encourage sites with installed IT of 1 MW or more to take those practices into account.
Why it matters for a European operator Its expected practices are the test in the EU Taxonomy's data-centre criteria, so participation also carries weight with lenders.
EU Taxonomy activity 8.1
Activity 8.1 of the EU Taxonomy climate delegated act, data processing, hosting and related activities, is a transitional activity when it implements all relevant expected practices of the EU Code of Conduct or CLC TR 50600-99-1, verified by an independent third party and audited at least every three years, and when its cooling refrigerants have a global warming potential of 675 or less.
Why it matters for a European operator Lenders and investors that report Taxonomy alignment will ask for this audit evidence.
CSRD and ESRS E1
The Corporate Sustainability Reporting Directive and its European Sustainability Reporting Standards. ESRS E1 covers climate, including energy consumption and mix (E1-5) and gross Scope 1, 2 and 3 emissions (E1-6), with Scope 2 disclosed both location-based and market-based. Directive (EU) 2026/470, the Omnibus I act published on 26 February 2026, limits mandatory reporting to undertakings with a net turnover above €450 million and more than 1,000 employees on average, with transposition due by 19 March 2027, and asks the Commission to revise the first set of standards by delegated act.
Why it matters for a European operator Operators outside CSRD scope may still receive E1 data requests from customers who are in scope, usually for energy and Scope 2 figures.
Size thresholds compared
The table puts the main European size thresholds side by side. Read the metric column first: the numbers are not interchangeable.
| Jurisdiction | Rule | Metric | Threshold | Status and source |
|---|---|---|---|---|
| EU | Annual reporting to the EU database (EED Art. 12, Reg. 2024/1364) | Installed IT power demand | 500 kW or more | In force |
| EU | Encouragement to take Code of Conduct best practices into account (EED Art. 12(4)) | Installed IT power demand | 1 MW or more | In force (soft law) |
| EU | Waste-heat use or cost-benefit test (EED Art. 26(6)) | Total rated energy input | More than 1 MW | In force, via national law |
| Germany | EnEfG data-centre definition and duties (§3 Nr. 24) | Non-redundant rated connection power | 300 kW or more | In force |
| Germany | Validated management system (§12(3)) | Non-redundant rated connection power | 1 MW or more; 300 kW for public bodies | In force |
| Germany | Amending bill 21/8027 definition | Installed IT power | 500 kW or more | Bill, not law |
| France | Annual reporting (L236-1) | Installed power, per SIRET number | 500 kW or more | In force |
| France | Waste-heat valorisation (L236-2) | Installed power | 1 MW or more; ERF 0.20 deemed compliant | In force |
| Netherlands | Hyperscale siting ban outside two areas (Bkl 5.161ba) | Built floor area and grid connection | More than 10 ha and 70 MW or more | In force |
Site and building
Resilience classes, floor areas and operator types as standards and EU law define them.
EN 50600 series
CENELEC's European standard series for data-centre facilities and infrastructures. Part 1, whose current edition is EN 50600-1:2026, sets general concepts, including a classification system based on availability, security and energy efficiency; the 2-x parts cover design of the building, power distribution, environmental control, cabling and security; the 4-x parts define KPIs such as PUE (4-2), REF (4-3), ERF (4-6), CER (4-7), CUE (4-8) and WUE (4-9).
Why it matters for a European operator EU and German law cite the 4-x parts by name for measurement, so they are the methods an auditor will check you against.
Availability Class (EN 50600)
The availability grade in EN 50600's classification system, chosen through a business risk analysis and applied to power supply, environmental control and cabling. There are four classes. The certification body TÜV NORD summarises them as follows: Class 1 has a single path with no redundant components, Class 2 a single path with redundant components, Class 3 multiple paths with one active, allowing maintenance during operation, and Class 4 multiple active paths and full fault tolerance.
Why it matters for a European operator It is the European, standards-based way to specify resilience in a tender or lease, and certification bodies audit against it.
Tier classification (Uptime Institute)
A four-level topology classification, Tier I to Tier IV, published and certified by the Uptime Institute, in which each level includes the requirements of the levels below. The Uptime Institute itself says a higher Tier is not better in general, only suited to a different kind of business operation.
Why it matters for a European operator Only the Uptime Institute certifies against its Tiers, and EN 50600 availability classes are the standards-based alternative for European specifications.
Computer room floor area (white space) (SCR)
The floor area that holds the data-processing, storage and telecommunications equipment delivering the data centre's IT services. EU reporting asks for it (SCR) alongside the total floor area of the structure (SDC), and operators commonly call it white space.
Why it matters for a European operator Power per square metre of white space ties the floor plan to cooling design, and colocation operators use the computer room area to state how much of a site their reported data cover.
Enterprise, colocation and co-hosting data centres
The three operator types in EU reporting. An enterprise operator runs the whole facility and the IT services it delivers; a colocation operator sells space, power, cooling, security and network access to customers who run their own equipment; a co-hosting operator also provides the servers, storage and part of the software.
Why it matters for a European operator Colocation operators report KPIs that depend on customer equipment, which is why the regulation lets them collect data from customers through an anonymous internal mechanism.
Hyperscale data centre
A very large data-centre campus, usually built for a single cloud or AI operator. There is no EU-wide legal definition; Dutch planning law is one place that sets one, at more than 10 hectares of built floor area with an electrical connection of 70 MW or more.
Why it matters for a European operator Read any hyperscale rule or statistic for its definition first, because thresholds differ widely between sources.
Compute and network
The IT side of the load: rack density, accelerators, interconnect and the markets where networks meet.
Rack density (kW per rack)
The electrical power drawn by the equipment in one rack, in kW, which equals the heat the cooling has to remove from it. A server with eight GPUs rated at up to 700 W each carries 5.6 kW of GPU power alone, before processors, memory, networking and fans.
Why it matters for a European operator Density decides whether a hall can stay air-cooled, needs rear doors or must move to direct liquid cooling, and it shapes floor loading and power distribution.
GPU thermal design power (TDP)
The maximum sustained power a GPU is designed to draw and dissipate, used to size power and cooling. NVIDIA lists the H100 SXM at up to 700 W and the PCIe version at 350 to 400 W, both configurable.
Why it matters for a European operator Size power and cooling from TDP times GPU count plus the rest of the server, and check which configurable power limit the customer will actually run.
GPU interconnect (scale-up, scale-out)
The links that let many accelerators work as one machine. Scale-up links such as NVIDIA NVLink connect GPUs inside a server or rack at very high bandwidth, 900 GB/s per H100 SXM GPU; scale-out networks such as InfiniBand or Ethernet connect servers across the hall.
Why it matters for a European operator Cluster networks favour short cable runs, so AI training halls tend to pack many high-power racks close together.
Network latency
The time data take to travel between two points. Light in standard single-mode fibre covers about 200 km per millisecond, roughly 5 microseconds per kilometre one way, so distance sets a floor under round-trip time before any switching delay is added.
Why it matters for a European operator Latency-sensitive services stay close to users and exchanges, while batch work such as AI training can move to where power is available.
FLAP-D
Industry shorthand for Europe's largest data-centre markets: Frankfurt, London, Amsterdam, Paris and Dublin. Broker reports use it to track capacity and vacancy; some leave out Dublin and write FLAP.
Why it matters for a European operator Power and planning limits in these hubs recur in broker reports, which is why siting studies now look beyond them.
Internet exchange, meet-me room and cross-connect (IXP, MMR)
An internet exchange point (IXP) is a shared switching platform where networks exchange traffic directly; DE-CIX Frankfurt reports peak traffic above 18 Tbit/s. Inside a colocation site, networks interconnect in the meet-me room, and a cross-connect is the physical link between two customers or between a customer and a carrier.
Why it matters for a European operator Carrier density and exchange proximity help explain why the FLAP-D hubs stay in demand despite grid limits, and cross-connect fees are a recurring line in colocation contracts.
All terms A to Z
0-9 24/7 carbon-free energy (24/7 CFE) · 500 kW threshold and other size thresholds
A Air cooling: CRAC and CRAH units (CRAC, CRAH) · ASHRAE air-cooling classes A1 to A4 and H1 · ASHRAE liquid-cooling classes W17 to W+ · Availability Class (EN 50600) · Average waste heat temperature (TWH)
B Back-up generation (EDC-BG) · Bidding zone · Busway (busbar trunking) (BTS)
C Carbon usage effectiveness (CUE) · Chiller · Computer room floor area (white space) (SCR) · Coolant distribution unit (CDU) · Cooling degree days (CDD) · Cooling efficiency ratio (CER) · CSRD and ESRS E1
D Day-ahead price · Delegated Regulation (EU) 2024/1364 · Direct liquid cooling (DLC) · Dutch hyperscale siting rule (Bkl)
E EED Article 12 · EED waste-heat duty (Art. 26(6)) · EN 50600 series · EnEfG amending bill (Drucksache 21/8027) · EnEfG PUE and energy-reuse limits (§11 EnEfG) · Energieeffizienzgesetz (EnEfG) · Energy reuse effectiveness (ERE) · Energy reuse factor (ERF) · Enterprise, colocation and co-hosting data centres · EU Code of Conduct on Data Centre Energy Efficiency (EU DC CoC) · EU minimum performance standards (MPS) · EU rating scheme for data centres (C(2026) 3472) · EU Taxonomy activity 8.1 · European database on data centres · Evaporative cooling and cooling towers
F Firm and non-firm capacity · FLAP-D · Flexible connection agreement · Free cooling (economiser) · French data-centre rules (Code de l'énergie L236)
G GPU interconnect (scale-up, scale-out) · GPU thermal design power (TDP) · Grid carbon intensity (gCO2e/kWh) · Grid connection queue · Grid services from data centres (CBtG) · Guarantee of origin (GoO)
H Hot and cold aisle containment · Hyperscale data centre
I Immersion cooling · Installed IT power demand and rated IT load (PDIT) · Internet exchange, meet-me room and cross-connect (IXP, MMR) · Irish data-centre connection policy (CRU) · IT intake air temperature setpoint (TIN)
L Location-based and market-based emissions (Scope 2) · Low and medium voltage (LV, MV)
P Partial PUE and mixed-use PUE (pPUE, mPUE) · Power purchase agreement (PPA) · Power usage effectiveness (PUE)
R Rack density (kW per rack) · Rear-door heat exchanger (RDHx) · Redundancy (N, N+1, 2N) · Refrigerants and the F-gas Regulation (F-gas) · Renewable energy factor (REF)
S Server efficiency and utilisation (ITEEsv, ITEUsv, CSERV, CSTOR) · Spanish draft royal decree on data centres
T Tier classification (Uptime Institute) · Total energy and IT energy (EDC, EIT)
U Uninterruptible power supply (UPS)
W Water usage effectiveness (WUE) · Wet-bulb temperature
How to cite and how this page is kept current
Cite an entry with its anchor, for example ScienceShot, “European data-centre glossary”, https://scienceshot.com/data-centre-glossary#erf, checked 10 October 2026. Definitions paraphrase the cited laws and standards; standards text is not reproduced. Legal status is rechecked when a tracked rule moves, and the regulation tracker carries the dated history.