HPC and AI in Supercomputing Centres: Green Today, Greener Tomorrow (SCA25 Workshop on Energy Efficiency, LRZ)
Leibniz Supercomputing Centre · Dieter Kranzlmueller
A keynote deck from LRZ summarising more than a decade of hot-water-cooled supercomputers in Munich and the lessons for AI infrastructure.
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Overview
This keynote by Dieter Kranzlmueller, given at the SupercomputingAsia 2025 (SCA25) energy-efficiency workshop in March 2025, summarises more than a decade of hot-water-cooled supercomputers run by the Leibniz Supercomputing Centre (LRZ) in Munich and the lessons for AI infrastructure. The deck traces systems from SuperMUC (2012) to SuperMUC-NG Phase 2.
LRZ systems run direct hot-water cooling at up to 45 C with 100% free cooling year-round and a PUE of 1.03. By contrast, air-cooled DGX A100 racks in a water-cooled rack at MCML show PUE 1.65-1.80. Air cooling overhead is cited as about +30% for fans and +30% for cooling infrastructure. In the water-versus-air comparison, thermal conductivity is about 23x, specific heat about 4x and volumetric heat capacity about 3,500x.
The deck lists the operational levers LRZ uses: frequency scaling, power capping, waste-heat use, adsorption chillers and glycol-free cooling. The lessons include DVFS averaging 68% of nominal frequency, power capping and sleep modes, a 100% renewable contract, glycol-free cooling, waste-heat use and adsorption chillers, and job-level power reporting.
As a limitation, this is a conference slide deck with no detailed measurement method, and the results belong to LRZ's own climate and systems. It is nonetheless useful as operator evidence for warm-water design targets. Copyright belongs to the author and institution.
Key points
- LRZ systems run direct hot-water cooling at up to 45 C with 100% free cooling year-round and a PUE of 1.03.
- Air-cooled DGX A100 racks in a water-cooled rack at MCML show PUE 1.65-1.80.
- Air cooling overhead is cited as about +30% for fans and +30% for cooling infrastructure.
- Lessons: DVFS averaging 68% of nominal frequency, power capping and sleep modes, 100% renewable contract.
- Further lessons: glycol-free cooling, waste-heat use and adsorption chillers, job-level power reporting.
- Water versus air: thermal conductivity about 23x, specific heat about 4x, volumetric heat capacity about 3,500x.
- Systems span from SuperMUC (2012) to SuperMUC-NG Phase 2.
Using it in design
- Let liquid-cooled design templates allow facility supply temperatures up to 45 C with dry-cooler-only heat rejection, and show the resulting PUE.
- Contrast this in reports with air-cooled AI racks so users see the efficiency penalty of air.
- Expose frequency scaling and power capping as parameters in operating scenarios.
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Who should read it
HPC centre designers and operators planning warm-water cooling and AI infrastructure efficiency.
Related standards
- ASHRAE W-classes
Publication details
- Authors
- Dieter Kranzlmueller
- Publisher
- Leibniz Supercomputing Centre
- Year
- 2025
- Document number
- SCA25 workshop keynote, March 2025
- Event
- SupercomputingAsia 2025 (SCA25) energy-efficiency workshop
- Document language
- English
- Source type
- Scientific
- Access
- Free to read
- Licence
- Copyright retained; citation only — the publisher’s terms apply to the original document
Citation
Dieter Kranzlmueller (2025). HPC and AI in Supercomputing Centres: Green Today, Greener Tomorrow (SCA25 Workshop on Energy Efficiency, LRZ). Leibniz Supercomputing Centre. SCA25 workshop keynote, March 2025. SupercomputingAsia 2025 (SCA25) energy-efficiency workshop. https://ee-workshop.for.lrz.de/wp-content/uploads/2025/03/SCA25-WorkshopEnergyEfficieny_LRZ.pdf
Events on this subject
- Data Centre World Frankfurt
- SC26 – International Conference for High Performance Computing, Networking, Storage and Analysis
- iMasons Climate Accord Summit
All content and rights belong to the respective authors and publishers. SoSo CAD provides only the citation, its own summary and a link to the source, and is not responsible for the sources' content.
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