Technical guides: recovery of waste heat from data centers

Waste heat is the thermal energy produced by a process for which it is not the primary purpose. It is described as "fatal" (unavoidable) because, when it is not recovered and used, it is simply dispersed into its environment and therefore wasted.

In the same way as power plants, waste recovery centres, or industrial production sites, data centers are among the producers of waste heat. In data centers, it comes mainly from IT equipment, but also from cooling infrastructure. It can be recovered to heat residential buildings, offices, public facilities (swimming pools, gyms, etc.), and more. However, data center operators must first seek to reduce their energy consumption before considering the reuse of waste heat.

It should be noted that, according to the current state of the art, liquid cooling (immersion, direct-to-chip, etc.) is the system most conducive to heat recovery. However, its use remains marginal, and several years will be required before its large-scale deployment.

The French Energy-Climate strategy aims to quintuple the recovery of waste heat delivered to networks and to recover 25 to 29 TWh of waste heat by 2035. In 2021, 898 heating networks were deployed in France. In ten years, they have contributed to reducing greenhouse gas emissions by almost half compared to individual gas boilers.

Data centers represent significant sources of waste heat. In 2020, the potential for recoverable waste heat via data centers was estimated at 1 TWh, or the equivalent of 100,000 homes. By 2030, given the increase in the number of data centers, the potential for recoverable waste heat could represent 3.5 TWh.

This is why the European Energy Efficiency Directive (Directive (EU) 2023/1791) requires data centers with a capacity of more than 1 MW to recover their waste heat, unless it is not technically or economically viable. In parallel, like the European Union Code of Conduct for Data Centre Energy Efficiency, the non-mandatory standard "Data centre facilities and infrastructures" (ISO 50600-2-1 July 2021) now incorporates local energy synergies.

Data center operators must therefore work hand in hand with local heat demanders. This particularly includes local authorities, inter-municipal cooperation bodies (EPCI), or energy unions, which "hold the responsibility for creating and operating public heating and cooling networks," to integrate the waste heat generated by their sites into local energy strategies.

To align their respective challenges and constraints (economic, regulatory, etc.), data center operators and local authority representatives must commit to a long-term process of co-constructing projects based on dialogue, mutual understanding, and transparency. Whether it involves creating a heat distribution network or a data center, several years of planning and implementation are required.

These projects, which are more of a marathon than a sprint, always start with an assessment of the current situation. For local authorities, this involves identifying heat needs in the area and evaluating the potential for waste heat recovery from data centers (or other producers) already present or planned. For their part, data center operators, in the interest of synergy with their host territory, must first quantify the recoverable waste heat and evaluate the inlet and outlet temperatures. This will also help local authorities identify possible uses.

Regarding the establishment of new data centers, these early exchanges will also make it possible to optimize the future location based on the potential for waste heat use in the area, while taking into account, of course, the necessary proximity to power and telecom networks to supply the data center.

Finally, a heat exchange agreement will allow for the contractual sale or provision of energy from the heat producer to the public network (or under concession) of the territory.