From cooling loop to heat network: the technical path of data-centre waste heat
Temperatures, hydraulics, heat pump COP: how older 3G networks and modern 4G networks differ in waste-heat integration.
TL;DR
- Air cooling delivers waste heat at max. 30 °C; liquid cooling at 60–65 °C.
- Classical district heating networks (3G) require 70–130 °C supply — without a heat pump, direct feed-in is usually not possible.
- Modern 4G networks (55–70 °C) allow more direct integration and lower system cost.
- A heat pump's COP falls to 2.5–3.5 when feeding classical district heating — careful economic analysis is essential.
- Hydraulic balance and return temperature are the critical planning parameters.
1. Background
Data centres produce waste heat continuously — independent of weather and season. That makes them theoretically ideal as a base-load heat source. The challenge lies in the temperature level. A district or local heat network is typically operated with supply temperatures of 70 to 130 °C. Exhaust-air or warm-water temperature must be raised using specific heat pumps until it reaches the network level.
2. Data
| Cooling type | Waste-heat temperature | Heat pump needed? | Direct feed-in 4G network |
|---|---|---|---|
| Air cooling | ≤ 30 °C | Yes, large lift | No |
| Warm-water cooling | 45–60 °C | Depending on network | Conditional |
| Liquid cooling (direct contact) | 60–75 °C | No (for 4G network) | Yes |
Sources: Umweltbundesamt; VDI/Ingenieur.de; velasolaris.com
With direct-contact liquid cooling, the water heats to about 60 °C — this heat can be used directly for many purposes without needing a heat pump and additional electricity. Older district heating networks (3G: 80–110 °C) however require active temperature lifting. The Norderstedt reference illustrates the complexity: the high temperature level of the district heating network (supply up to 81 °C, return around 55 °C) posed a particular technical challenge that was resolved through an innovative concept at a COP of about 3.
3. Implications for energy providers
The key is knowing your own network level. Anyone already on a 4G transformation pathway can integrate data-centre waste heat with significantly lower heat-pump cost. For feed-in into cold local heat networks or adjacent direct supply, high COP values of 3.5–6 are possible because only moderate temperature lifts are required. Also note: the hydraulic balance of the existing network must accommodate a decentralised source.
4. Where P2H connects
P2H modules run water-cooled architecture with 60–75 °C supply. This makes them directly compatible with 4G networks and usable in 3G networks with a small heat-pump stage. Limits exist for very old high-temperature networks (> 100 °C supply) and sites with insufficient return temperature — a site assessment by the heat-network operator is prerequisite in any case.
5. Outlook
Existing district heating networks are likely to reduce supply to 70–80 °C over the coming years — made possible by better heat emitters and insulation standards in the building stock. The further this retrofit progresses, the more economic direct integration of data-centre waste heat becomes — no heat pump, no additional electricity demand.
Sources
- Umweltbundesamt: Data-centre climate control. https://umweltbundesamt.de/themen/klima-energie/fluorierte-treibhausgase-fckw/stationaere-kaelte-klima-waermepumpenanlagen/anwendungen/rechenzentrumsklimatisierung
- VDI / Ingenieur.de (2025): Using data-centre waste heat sensibly. https://www.ingenieur.de/technik/fachbereiche/energie/abwaerme-aus-rechenzentren-sinnvoll-nutzen/
- Stadtwerke Norderstedt / Kraftanlagen.com (2024). https://www.kraftanlagen.com/rechenzentrum-wird-zur-waermequelle-fuer-das-fernwaermenetz-von-norderstedt/
- velasolaris.com (2025): Data-centre waste-heat utilisation — COP values. https://www.velasolaris.com/abwaermenutzung-rechenzentren/