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This report critically evaluates the sustainability and circularity of data centres (DCs), identifying significant synergies and trade-offs in energy and water usage. It highlights the inadequacies of the Power Usage Effectiveness (PUE) metric, which conflates cooling and power provisioning, and proposes more nuanced metrics that account for compute efficiency, transformation efficiency, and cooling overhead. The findings reveal that while on-site water consumption can reduce cooling energy, it introduces complex trade-offs, particularly in the context of different electricity sources, emphasizing the need for improved metrics to better capture energy circularity and material efficiency in DC operations.
Current energy metrics for data centres obscure critical trade-offs between cooling efficiency and water consumption, leading to potentially misguided sustainability strategies.
This report analyses data centre (DC) sustainability and circularity, revealing existing synergies and trade-offs: The PUE is too coarse, mixing cooling and power provisioning. It wrongly attributes server fan consumption and transformation losses to IT energy. It does not measure compute but infrastructure efficiency, which is already outstanding. Compute energy, however, is exploding. Better energy metrics for DCs would thus cover i) compute efficiency, ii) transformation efficiency, and iii) cooling overhead. Trade-offs exist between cooling energy and water as well as on-site and upstream water: Consuming water on-site lowers the cooling energy, which also lowers the water consumed upstream in power generation. For'wet'electricity, there is little competition: It is worth spending more on-site energy to save both electricity and related upstream water. For'dry'electricity, there is a trade-off. Waste heat recovery brings energy circularity but has limited uses and is not the same energy quality, a fact not reflected by current metrics. A better metric would consider the avoided energy through heat recovery instead of the amount recovered. Material circularity can be achieved by interpreting the 9R framework in the context of DCs. Circularity-enhancing measures can be categorised into product design, process design and business models, choice of materials, and operating conditions. Together, they have effects across all circularity levels. The relation between DCs and the power grid is complex. Modern DCs present new challenges for the grid. Mitigation includes battery storage and onsite generation. These measures have, in turn, further consequences, both beneficial and detrimental. They can offer grid flexibility as well as innovations in the field of energy. But they also bring noise, pollution, and GHGs, and compete with the energy sector for resources.
