Rack densities are approaching 100 kW and climbing. Air cooling alone can’t keep up.
The arrival of AI and machine learning workloads has changed what data centers are being asked to do. CPUs and GPUs are generating heat at levels that traditional air cooling simply wasn’t built for. The industry has a clear answer: hybrid cooling, combining air and liquid cooling technologies to manage both low-density legacy equipment and high-density HPC in the same facility.
Hybrid cooling lets data centers scale up performance without a full infrastructure overhaul. For brownfield sites, that means a gradual, zone-by-zone transition toward liquid cooling while existing air-cooled infrastructure keeps running. For greenfield builds, it means designing from scratch with both efficiency and long-term growth baked in from the start.
The catch is that Direct Liquid Cooling (DLC) is a fast-moving space with few settled standards. Choosing the wrong technology, skipping CFD modeling, or underestimating the role containment still plays in a liquid-cooled environment can turn an efficiency initiative into an expensive problem. This white paper lays out exactly how to get it right.
What’s Covered Inside
How Hybrid Cooling Works
Air cooling handles lower-density and legacy equipment. Direct-to-Chip (DTC) liquid cooling targets the CPUs and GPUs generating the most heat. Both run simultaneously, alongside containment to manage the roughly 25% of residual heat that DTC doesn’t remove. We explain how the pieces fit together.
DLC Technologies: Who’s Leading and Who’s Lagging
A clear-eyed look at single-phase DTC, two-phase DTC, and immersion cooling, covering how each works, where each fits, and why single-phase DTC has become the industry’s preferred approach for HPC deployments in 2025.
Brownfield vs. Greenfield
The pros and cons of retrofitting an existing facility versus building new, including how hybrid cooling gets deployed differently in each scenario and what drives the choice between them.
CDUs: The Brains Behind DLC
How Cooling Distribution Units regulate liquid coolant temperature, protect cold plates from particulates and galvanic corrosion, adapt dynamically to changing HPC workloads, and the key differences between Liquid-to-Liquid and Liquid-to-Air configurations.
DLC Best Practices
CFD and Flow Networking Modeling requirements, rack sizing for HPC, power distribution planning, piping placement for both raised and slab floors, and why material compatibility inside the liquid cooling loop is more critical than most teams anticipate.
Introducing Composite AisleFrame (CAF)
Subzero Engineering’s new ground-supported infrastructure system built specifically for HPC and DLC deployments. 50% lighter than steel, with a lower Global Warming Potential, CAF combines containment, cabinet docking, cable management, and power delivery in a single scalable framework.
CURRENT INDUSTRY QUESTIONS
This white paper will answer
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How does hybrid cooling actually work, and how do air and liquid cooling divide the load? -
Which DLC technologies are leading the market in 2025, and which are still lagging? -
What are the real tradeoffs between retrofitting a brownfield site versus building greenfield? -
What do CDUs do, and how do you choose the right type for your deployment? -
What does containment’s role look like in a hybrid cooling environment?