This deliverable reports on the system-level testing of a hybrid cooling solution combining two-phase direct-to-chip liquid cooling with traditional air-based cooling.

The tests were originally planned to be done in ZutaCore facilities, nonetheless due to RISE’s expertise and diverse suite of advanced sensors, the experiments were conducted at RISE labs in alignment with HEATWISE objectives, under controlled but realistic environmental and operational conditions. The main objective of this task was to assess the performance, reliability, and operational behavior of the integrated system, simulating actual usage scenarios, including troubleshooting, break-fix operations, and runtime performance under variable IT workloads. The testing aimed not only to evaluate the system’s thermal and energy efficiency but also to provide critical insights into the feasibility of hybrid cooling deployment in commercial data centers. The system was additionally evaluated for repeatability, reliability, and scalability, with a focus on optimizing energy efficiency. The setup and methodologies were shaped according to the requirements and deliverables defined in WP3 (deliverable D3.2) in which the potential waste heat was assessed based on historical data, and WP4 in which CFD simulations and experimental studies on data centre pilots were conducted to evaluate and optimize cooling efficiency (deliverables D4.1 and D4.2).

Key outcomes include thermal performance: when using Hybrid cooling the CPU temperatures reduced compared with the CPU temperatures when using air cooling only, eliminating thermal throttling, energy efficiency: CPU power savings was demonstrated across the test servers and reduced demand on air cooling. Reliability: Stable operation without critical errors; predictable thermal behavior under varying workloads and optimization opportunities: Improved heat recovery potential, , and integration of adaptive fan control. These outcomes directly support the HEATWISE project’s key performance indicators by demonstrating ≥20% primary energy savings per server (PES), progress toward a Power Usage Effectiveness (PUE) of 1.05, and enhancement of the Energy Reuse Factor (ERF) toward 95%. Collectively, the findings validate hybrid cooling as a scalable, sustainable pathway for energy-efficient and heat-reusing data centers in line with HEATWISE objectives.