Is Your CDU Ready for the Heat? AI Server Cooling Validation with Preen

In high-density AI environments, Cooling Distribution Units (CDUs) serve as the critical thermal management interface. With GPU-accelerated servers pushing rack power densities toward the 120kW threshold, the thermal load exceeds the capacity of conventional air-based solutions. This paradigm shift to liquid cooling necessitates robust CDU validation to ensure thermal stability, as the space and energy penalties associated with legacy cooling are no longer sustainable for modern AI infrastructures.

How CDU Works

CDUs are the thermal heart of AI infrastructure, actively circulating coolant to cold plates to eliminate thermal throttling and ensure peak performance.

While Liquid-to-Liquid CDUs lead hyperscale efficiency with redundant pumps and heat exchangers, Liquid-to-Air (L2A) CDUs leverage high-pressure fans and pumps to bridge liquid cooling into legacy air-cooled facilities. For edge or water-constrained deployments, refrigerant-based CDUs utilize integrated compressors for standalone thermal management.

Regardless of the architecture, whether driven by pumps, fans, or compressors, precision power validation is mission-critical for maintaining maximum uptime under extreme AI workloads.

CDU Testing Items
1. Power Resilience and Redundancy Testing
In the R& D and OQC phases of CDUs, leveraging programmable AC power sources to replicate complex data center grid conditions is essential for validating internal PSU stability. By simulating voltage fluctuations, frequency shifts, and grid disturbances, engineers can ensure continuous power delivery to control boards and pump drives under extreme scenarios.
Furthermore, for redundant power architectures, our solution rigorously verifies seamless transfer, inrush current tolerance, and protection logic, securing maximum availability and electrical resilience for high-density AI infrastructures.

2. Functional Components Testing of Pump and Compressor Systems
A programmable AC power source is indispensable for simulating the rated voltage, frequency, and phase conditions required to validate the electromechanical performance of CDU components. This testing rigorously verifies startup torque and inrush characteristics for redundant pumps in Liquid-to-Liquid systems, high-pressure fan arrays in Liquid-to-Air configurations, and integrated compressors in refrigerant-based architectures.
By confirming steady-state current, dynamic load response, and precise power consumption, our solution ensures that pumps and fans achieve specified flow rates while compressors operate within thermal limits. Such validation is critical for AI liquid cooling, where consistent coolant circulation is the only defense against the extreme thermal loads of high-density GPUs.

3. Aging Test
Simulating extended operation helps uncover issues such as component wear, coolant leakage, or thermal cycling effects, all of which are crucial to long-term reliability. Taken together, these test items ensure that CDU systems can continuously support high-density AI server environments while maintaining performance, safety, and compliance with industry requirements.

Real-Case Application

Preen power’s AFV-PLUS-33120, a three-phase 120 kVA programmable AC power source, delivers low-THD output with tight voltage and load regulation, ensuring stable and repeatable test conditions for CDU electrical module validation.

Its independent phase voltage control and programmable phase-angle adjustment enable accurate simulation of voltage dip and sag, as well as split-phase configurations, including single-phase three-wire and single-phase two-wire systems. This capability allows realistic simulation of power conditions used in AI data center deployments, supporting comprehensive verification of CDU input tolerance, load balance, and protection behavior under various operating scenarios.