Chapter 01 · Foundations

Methodology

This chapter describes the thermodynamic foundations, the calculation model, data sources, feasibility logic, verification procedures, and standards references of the Ardor reports. The methodology follows CEN/CENELEC EN 50600-4-6 (Energy Reuse Factor) and Delegated Regulation (EU) 2024/1364 and is aligned with the BfEE waste heat platform.

At a Glance

Waste heat (MWh/a) = IT load (MW) × PUE × 8,760 h × η_capture. The facility coefficient η_capture is assigned by cooling type (air, hybrid, liquid) and can be overridden by measured operational data. The recovery fraction is checked against a proximity-based off-taker and classified as feasible, marginal, or not feasible. The result can be expressed as an ERF metric per EN 50600-4-6 and as a reporting quantity per Annex II of Delegated Regulation 2024/1364.

1. Thermodynamic Foundations

A data centre converts virtually all of its electrical energy input into heat. The IT load produces waste heat in the server hall; the cooling system, uninterruptible power supply, and auxiliary equipment produce waste heat at their respective operating levels. Total power intake P_tot equals total heat output over an annual average. Differences between input and output are in the single-digit percentage range and are absorbed by measurement uncertainty.

The heat usable by external off-takers is strictly less than the total heat output. It becomes usable only when it crosses the cooling system boundary as defined by EN 50600-4-6 and feeds into heat-consuming infrastructure (district heating network, industrial process, greenhouse, building heating). The difference between total output and externally usable heat is what we call the recovery fraction. It depends on cooling technology, supply temperature, spatial proximity to an off-taker, and temporal alignment of supply and demand.

2. Calculation Model

2.1 Core Equation

Waste heat (MWh/a) = IT load (MW) × PUE × 8,760 h × ηcapture

IT load is the average electrical active power of the IT payload in megawatts. It differs from the installed nameplate capacity by the actual utilisation rate and should, where available, be derived from the annual mean of measured active power.

PUE (Power Usage Effectiveness) is the ratio of total energy consumption to IT energy consumption. A PUE of 1.0 is the theoretical optimum; typical values range between 1.3 and 1.6. EnEfG § 11 targets a PUE ≤ 1.2 for new builds from July 2026.

8,760 h is the number of hours per year. At utilisation below 100%, availability is reduced accordingly. Ardor uses 8,760 h as the default assumption and allows operators to specify a measured or contractually agreed availability (typically 7,500 to 8,500 h).

η_captureis the recovery fraction of the waste heat. It is derived from the cooling type and reflects combined effects of temperature level, coupling losses, and practically achievable extraction rate. The default values are conservatively chosen and lie within the ranges reported by Pehnt et al. (2010) and Schlomann et al. (2020).

2.2 Default Values of η_capture by Cooling Type

Cooling Type	Temperature Range	η_capture Literature	η_capture Ardor
Air cooling	25 – 40 °C	30 – 50 %	50 %
Hybrid cooling (air and liquid)	40 – 60 °C	50 – 70 %	60 %
Liquid cooling (direct-to-chip)	60 – 80 °C	70 – 90 %	80 %

The Ardor default values lie within the literature ranges. Operators can specify alternative η_capture values via the assistant based on their own ERF measurements; in that case, the ERF metric is taken directly from the measurement and the default assumption is not used.

2.3 Worked Example: 10 MW, Air Cooling, PUE 1.4

Total power      = 10 MW × 1.4                 = 14 MW
Annual energy    = 14 MW × 8,760 h             = 122,640 MWh/a
Recoverable      = 122,640 MWh × 0.50          = 61,320 MWh/a
Households (≈)   = 61,320 MWh ÷ 20 MWh/household = 3,066

The household conversion factor of 20 MWh per household per year follows the Bitkom and AGFW convention for average residential heat consumption in Germany. This value is for illustrative purposes only and does not feed into regulatory reporting.

3. ERF and Standards Reference

The Energy Reuse Factor per CEN/CENELEC EN 50600-4-6 is the standard indicator of data centre waste heat utilisation. The numerator is the externally used thermal energy over the reporting period; the denominator is the total energy intake of the facility. The measurement boundary is at the handover point between the cooling system and the heat-consuming infrastructure.

ERF = Ereused,ext ÷ Efacility,total

In Annex II of Delegated Regulation (EU) 2024/1364, ERF is used directly as a reporting quantity. EU-wide reporting is due annually by 15 May via the national collection point of the competent authority. Ardor generates an ERF-compliant output per facility and can export it in the machine-readable format of the Delegated Regulation.

4. Feasibility Logic

Recoverable waste heat is an upper bound. Regulatory assessments additionally require an estimate of whether this heat can realistically be delivered to an off-taker in the foreseeable future. Ardor classifies each facility into one of three categories:

Category	Condition	Interpretation
feasible	Distance to network centre ≤ 3 km or within documented network extent	Feed-in realistic at accepted temperature; can be used as upper bound for ERF.
marginal	Distance ≤ documented network extent but > 3 km, or supply temperature < 40 °C	Feed-in technically possible, requires economic assessment; to be examined in cost-benefit analysis.
not feasible	Distance > network extent and no individual industrial off-taker identified	Exemption per § 17 EnEfG, Art. L.236-2 Code de l'énergie, or Art. 26 EED possible; documented as negative finding.

The distance check is performed based on the geocoded facility address against the respective national district heating dataset. Network extent per operator corresponds to the coverage areas stored in the dataset or a documented radius. Where no network coverage exists, Ardor performs a second-pass check for individual industrial off-takers (greenhouses, chemicals, food processing, paper/cardboard manufacturing) within a 5 km radius and assesses temperature compatibility.

5. Data Sources

The data foundation is structured by country and follows the publicly available district heating and industrial off-taker datasets of the respective member states. Third-party primary sources (BAFA, BfEE platform, France Chaleur, RVO) are adopted unchanged. Derived attributes (temperature level, coverage radius) are versioned with provenance and date.

Country	District Heating	Regulation & Reporting	Status at Ardor
Germany	AGFW district heating map, Mainova, utilities	BAFA / BfEE waste heat platform	Live (32 facilities)
France	France Chaleur, Fonds Chaleur (ADEME), SNCU, Idex, Engie Solutions, Dalkia, Veolia	DGEC, Code de l'énergie L.236-2, Décret 2025-1382	Port in preparation (15 facilities)
Netherlands	Ennatuurlijk, Vattenfall NL, HVC, Stadsverwarming Purmerend, Eneco	RVO, Omgevingswet, Erkende Maatregelenlijst	Port in preparation (20 facilities)
Ireland	SEAI District Heating, Dublin DHS	CRU, SEAI, EirGrid/ESB Networks	Preliminary (primarily exemption evidence)
Italy	AIRU, A2A, Iren, Hera	MASE, GSE (Decreto legislativo in consultation)	Seed data (6 facilities)
Spain	ADHAC, Ecoenergies Barcelona, Veolia España	MITECO, Real Decreto in preparation	Seed data (6 facilities)
Nordics (SE/DK/FI)	Stockholm Exergi, HOFOR, Helen, Fortum	Energimyndigheten, Energistyrelsen, Energiavirasto	Seed data (24 facilities, SE/NO/FI)

Non-EU facilities in Norway and Switzerland are maintained under bilateral recognition. Their reporting does not count toward EED obligations but serves market-side representation.

6. Verification and Uncertainty

Report quality depends on the measurement basis. Ardor distinguishes three verification tiers and documents the tier used on every output.

Tier	Basis	Uncertainty Range
V1 Estimate	Publicly available facility data, operator declaration without measurement evidence	± 20 %
V2 Operator confirmed	Operator confirms IT load, PUE, and cooling from internal operational data	± 10 %
V3 Measured	ERF derived directly from submitted measurement protocol or BAFA filing	± 5 %

V3 is the target tier for all reports submitted to authorities. V1 is used only for public sample reports or marketplace listings where the operator explicitly authorises publication of a preliminary estimate.

Independent auditing is performed on request by a body accredited under ISO/IEC 17065 or by the competent national authority. Measurement protocols and audit reports are retained in versioned form for at least ten years and disclosed to the competent authority upon request.

7. Connection to the Waste Heat Certificate (WHC)

The methodology of this chapter is the calculation basis of the proposed Waste Heat Certificate (WHC). One WHC corresponds to one megawatt-hour of externally used waste heat verified per EN 50600-4-6. Issuance occurs after completion of the measurement period and independent audit. The serial number is unique; the certificate is transferable and terminally retirable. Details on the registry architecture are described in the position paper Waste Heat Certificates .

8. Scientific Basis

The methodology rests on two foundational works by Fraunhofer ISI and ifeu Heidelberg. Pehnt et al. (2010, ifeu Heidelberg) defined the national inventory methodology for industrial waste heat including temperature and utilisation classification. Schlomann et al. (2020, Fraunhofer ISI) updated the methodology and established the quantitative framework for the BfEE waste heat platform. The parameter bands published therein form the basis of the η_capturedefault values presented here.

For data centres, EN 50600-4-6 specifies the measurement boundary and the procedure for forming the ERF metric. Ardor brings together the methodology at the facility level, the standards reference at the measurement boundary level, and the reporting formats of Delegated Regulation 2024/1364 at the reporting level.

9. Liability Notice

Disclaimer

Reports generated by Ardor are produced using automated methods. The operator is responsible for the accuracy of the data and for regulatory-compliant submission. Ardor assumes no liability for the use of reports vis-a-vis authorities. All methods, data sources, and assumptions are documented and verifiable in every report. Questions and methodological feedback can be directed to /contact.

10. References

[01]Directive (EU) 2023/1791 of the European Parliament and of the Council of 13 September 2023 on energy efficiency (recast).
[02]Commission Delegated Regulation (EU) 2024/1364 of 14 March 2024 supplementing Directive (EU) 2023/1791.
[03]Directive (EU) 2023/2413 of the European Parliament and of the Council of 18 October 2023 (RED III).
[04]Energy Efficiency Act (EnEfG), Federal Law Gazette I, 18 November 2023.
[05]Loi n° 2025-391 du 30 avril 2025 (DDADUE), Journal Officiel de la République française.
[06]Décret n° 2025-1382 du 29 décembre 2025, Journal Officiel de la République française.
[07]CEN/CENELEC EN 50600-4-6: Information technology, Data centre facilities and infrastructures, Part 4-6: Energy Reuse Factor.
[08]Schlomann, B., Rohde, C. and Eichhammer, W. (2020). Evaluation of the German waste heat potential. Fraunhofer ISI.
[09]Pehnt, M., Bödeker, J., Arens, M., Jochem, E. and Idrissova, F. (2010). Use of Industrial Waste Heat. ifeu Heidelberg and Fraunhofer ISI.
[10]Ardor Institute (2026). Toward a Market for Waste Heat Certificates. Discussion Paper No. 1.
[11]Ardor Institute (2026). Waste Heat Certificates as a European Market Instrument. Discussion Paper No. 2.

Last updated: April 2026. Document version 1.0. Methodology review by BfEE Section 511 has been requested; feedback will be incorporated into the next revision.