Methodology
This chapter describes the thermodynamic foundation, the calculation model, the data sources, the feasibility logic, the verification procedures, and the standards reference of 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.
1. Thermodynamic Foundation
A data centre converts virtually all of its electrical energy input into heat. The IT load generates waste heat in the server room; the cooling system, the uninterruptible power supply, and auxiliary equipment generate waste heat at their respective operating levels. The total power consumption Ptot corresponds to the 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 offtakers 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 a heat-consuming infrastructure (district heating network, industrial process, greenhouse, building heating). The difference between total heat output and externally usable heat is referred to as the recovery share. It depends on the cooling technology, the supply temperature, the proximity to an offtaker, and the temporal alignment of supply and demand.
2. Calculation Model
2.1 Core Equation
IT load is the average electrical active power of the IT payload in megawatts. It differs from the installed rated 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 from 1.3 to 1.6. EnEfG Section 11 targets a PUE of 1.2 or below 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 the operator to enter a measured or contractually agreed availability (typically 7,500 to 8,500 h).
ηcapture is the recovery share of waste heat. It is derived from the cooling type and reflects the combined effects of temperature level, coupling losses, and the practically achievable extraction rate. The default values are conservatively chosen and fall within the ranges reported in Pehnt et al. (2010) and Schlomann et al. (2020).
2.2 Default Values of ηcapture by Cooling Type
| Cooling Type | Temperature Range | ηcapture Literature | ηcapture 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 fall within the literature ranges. Operating operators may enter a different ηcapture via the assistant based on their own ERF measurement; 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
The household conversion factor of 20 MWh per household per year follows the Bitkom and AGFW convention for the national average heat consumption of a residential unit. The value is for illustrative purposes only and does not enter 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 reuse. The numerator is the externally reused thermal energy over the reporting period; the denominator is the total energy intake of the facility. The measurement boundary lies at the handover point between the cooling system and the heat-consuming infrastructure.
In Annex II of Delegated Regulation (EU) 2024/1364, ERF is used directly as a reporting metric. 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 site 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 evaluation of whether this heat can realistically be delivered to an offtaker within a foreseeable timeframe. Ardor classifies each site into one of three categories:
| Category | Condition | Interpretation |
|---|---|---|
| feasible | Distance to network centre point ≤ 3 km or within documented network coverage | Feed-in realistic at accepted temperature; can be applied as upper bound of ERF. |
| marginal | Distance ≤ documented network coverage but > 3 km, or supply temperature < 40 °C | Feed-in technically possible, economic viability to be assessed; to be examined in cost-benefit analysis. |
| not feasible | Distance > network coverage and no industrial single offtaker identified | Exemption under Section 17 EnEfG, Art. L.236-2 Code de l'énergie, or Art. 26 EED possible; documented as a negative assessment. |
The distance check is performed based on the geocoded site address against the respective national district heating dataset. The network coverage per operator corresponds to the supply areas recorded in the dataset or a documented radius. Where no network coverage exists, Ardor performs a secondary check for industrial single offtakers (greenhouses, chemicals, food processing, paper/cardboard manufacturing) within a radius of up to 5 km and assesses temperature compatibility.
5. Data Sources
The data basis is structured by country and follows the publicly available district heating and industrial offtaker datasets of the respective member states. Third-party primary sources (BAFA, BfEE Platform, France Chaleur, RVO) are adopted unchanged. Derived attributes (temperature level, supply radius) are versioned with provenance and date.
| Country | District Heating | Regulation & Reporting | Status at Ardor |
|---|---|---|---|
| Germany | AGFW district heating map, Mainova, Stadtwerke | BAFA / BfEE Waste Heat Platform | Live (32 sites) |
| 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 sites) |
| Netherlands | Ennatuurlijk, Vattenfall NL, HVC, Stadsverwarming Purmerend, Eneco | RVO, Omgevingswet, Erkende Maatregelenlijst | Port in preparation (20 sites) |
| Ireland | SEAI District Heating, Dublin DHS | CRU, SEAI, EirGrid/ESB Networks | Preliminary (predominantly exemption documentation) |
| Italy | AIRU, A2A, Iren, Hera | MASE, GSE (decreto legislativo in consultation) | Seed data (6 sites) |
| Spain | ADHAC, Ecoenergies Barcelona, Veolia España | MITECO, Real Decreto in preparation | Seed data (6 sites) |
| Nordics (SE/DK/FI) | Stockholm Exergi, HOFOR, Helen, Fortum | Energimyndigheten, Energistyrelsen, Energiavirasto | Seed data (24 sites, SE/NO/FI) |
Non-EU sites in Norway and Switzerland are maintained under bilateral recognition. Their reporting does not count towards EED obligations but serves marketplace 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 site 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 from BAFA reporting | ± 5 % |
V3 is the target tier for all reports submitted to authorities. V1 is used only for public sample reports or for marketplace listings where the operator has explicitly authorised publication of a preliminary estimate.
Independent review is carried out 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 a minimum of ten years and disclosed to the competent authority upon request.
7. Link 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 reused waste heat verified per EN 50600-4-6. Issuance takes place after completion of the measurement period and after independent review. 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 Foundation
The methodology rests on two foundational studies 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 ranges published there form the basis of the ηcapturedefault values presented here.
For data centres, EN 50600-4-6 specifies the measurement boundary and the procedure for deriving the ERF metric. Ardor brings together the methodology at site level, the standards reference at measurement boundary level, and the reporting formats of Delegated Regulation 2024/1364 at reporting level.
9. Liability Notice
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 (Energieeffizienzgesetz, 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.