Data center heat reuse and district heating: loops and flanges
Liquid cooling returns water warm enough to heat buildings. Exporting that heat adds a new loop to the data center, and that loop usually follows the district heating world of EN standards, PN16 and PN25.
Waste heat leaves the data center through a plate heat exchanger, often boosted by heat pumps, into a district heating network. The export loop runs hotter than any cooling loop in the building and is built to the network operator's standards, which in Europe usually means EN 1092-1 flanges at PN16 or PN25 and pre-insulated steel pipe to EN 253 and EN 13941.
Why heat reuse is growing
| Rule | Requirement |
|---|---|
| EU Energy Efficiency Directive, (EU) 2023/1791 | Data centers with a total rated power of at least 500 kW report energy data each year. Those above 1 MW must use their waste heat, or other waste heat recovery applications, unless that is not technically or economically feasible. |
| Germany, Energy Efficiency Act (EnEfG) of 2023 | Minimum shares of reused energy for new data centers, starting at 10% for those opening from July 2026 and rising in later years, with PUE limits for new and existing sites. |
Liquid cooling makes this practical. Direct-to-chip and immersion systems return water far warmer than air-cooled plants, especially at the warmer ASHRAE water classes, so less work is needed to lift it to a useful temperature.
The heat path
| Stage | What happens | Typical joints |
|---|---|---|
| Technology cooling system | Collects heat from cold plates or immersion tanks | 316L flanges, Class 150 or PN16 |
| CDU | Passes the heat to facility water | Flanged nozzles |
| Facility water return | Warm water to the heat reuse plant | Carbon or stainless steel flanges |
| Heat pumps | Lift the water temperature to network level when needed | Flanged connections, often PN16 or PN25 |
| Plate heat exchanger | The boundary between data center water and network water | EN 1092-1 or ASME flanges, to each side's standard |
| District heating network | Distributes the heat to buildings | Pre-insulated steel pipe, welded; flanges at valves, equipment and branches |
Older district heating networks run supply temperatures above 80 °C. Newer low-temperature networks run cooler, which suits data center heat better and may need less heat pump lift.
Flanges on the export side
- Standard: EN 1092-1 in Europe, usually type 11 weld neck flanges and type 05 blinds. Projects outside Europe may use ASME B16.5.
- Rating: PN16 or PN25, chosen by the network operator. Check the allowable pressure at the network's design temperature, not at room temperature. How to choose a pressure class.
- Material: the carbon steel grade in the network specification. Tell us the EN material grade and we will confirm it at quotation.
- Gaskets: rated for hot water at the network temperature, which is a harder duty than a cooling loop.
Heat export equipment in Europe falls under the Pressure Equipment Directive. Our quality system is certified by TÜV Rheinland as a PED 2014/68/EU material manufacturer, which is what Annex I point 4.3 asks for main pressure parts in categories II to IV. Certificates and quality.
What to send with your enquiry
- The flange standard and PN, type, DN and bore, for each side of the plate heat exchanger.
- Material grade from the network specification, and the design pressure and temperature.
- Inspection and certificate requirements, for example EN 10204 3.1 or 3.2.
Send the schedule and we will quote both sides of the boundary together.
Frequently asked questions
Is PN16 enough for a heat export loop?
Often, but not always. Many district heating distribution networks are designed for PN16, while larger transmission lines and some networks use PN25. The network operator's standard decides, and the rating must be checked at the network's design temperature, which is higher than any cooling loop.
Who owns the export loop?
Usually the boundary is a plate heat exchanger. The data center owns everything on its side, and the heat network operator owns the network side and sets its standards for pipe, flanges and water quality.
Do heat reuse loops need stainless steel?
Not usually on the network side. District heating water is treated and kept low in oxygen, and networks are built in carbon steel. Stainless steel appears inside the data center, at heat exchangers and heat pumps where the specification calls for it.
Sources
- Directive (EU) 2023/1791 on energy efficiency (recast)
- Germany, Energieeffizienzgesetz (EnEfG), 2023, data center requirements
- EN 253 and EN 13941, pre-insulated bonded pipe systems for district heating
- EN 1092-1, steel flanges, PN designated