Choosing the Right Cooling Path for AI-Powered Data Centers

As AI and other high-performance computing workloads continue to surge, data centers are being pushed to new levels of power density. Traditional air-cooling methods are no longer sufficient to manage the intense thermal output of today’s GPU-rich environments. For many operators, liquid cooling isn’t just a consideration—it’s a necessity.

While hyperscalers have led the way, many data center operators are still exploring what liquid cooling entails and how to implement it effectively. There are four main cooling approaches to consider: hot/cold aisle containment, rear-door heat exchangers, direct-to-chip cooling, and full immersion. Each comes with its own infrastructure requirements and trade-offs. Understanding these differences is key to choosing the best solution.

1. Hot/Cold Aisle Containment (Traditional Air Cooling)

This tried-and-true method involves arranging server racks so that cold air intakes face a cold aisle, while hot air exhausts face a hot aisle. CRAC and CRAH units feed cool air into the cold aisle, while hot air is directed back to the cooling units.

This method helps prevent hot and cold air from mixing and is relatively efficient—but its capabilities top out at about 15–20kW per cabinet. That makes it increasingly inadequate for AI and high-density environments.

2. Rear-Door Heat Exchangers

Rear-door heat exchanger technology offers a practical entry point into liquid cooling. Mounted at the back of a rack, these units capture hot air before it enters the room and transfer the heat to chilled water via a coil.

They’re room-neutral, meaning the air discharged into the data hall is at ambient temperature. Rear-door heat exchangers can handle densities of 85–90kW per rack, with some solutions supporting up to 200kW in specialized setups. However, claims of higher capacities should be carefully vetted to ensure compatibility with the intended application.

3. Direct-to-Chip Cooling

Also known as direct liquid cooling, this method applies fluid directly to cold plates within the server to remove heat from the processor before it’s expelled as hot air. There are two variations:

• Single-phase cooling uses water or a coolant that absorbs heat and cycles it through a CDU, where it’s transferred to a larger loop and recirculated.
• Two-phase cooling involves a liquid that boils upon heat absorption, then condenses back into a liquid and returns to the chip.

Direct-to-chip cooling typically supports 100–120kW per rack. However, it only targets the chip, not the rest of the cabinet. Therefore, it’s often used in combination with other cooling technologies, such as rear-door heat exchangers.

4. Immersion Cooling

In full immersion setups, servers are completely submerged in dielectric fluid that absorbs and removes heat. The fluid is then cycled through a cooling system—usually involving a heat exchanger or direct liquid-to-liquid loop—before returning to the tank.

While immersion cooling is highly effective, it complicates maintenance. Removing equipment from fluid requires special handling and drying time, making it less suitable for environments with frequent hardware changes. As a result, immersion cooling has found its niche in static applications like bitcoin mining.

An emerging option is two-phase immersion, where the dielectric fluid boils upon contact with heat sources. The resulting vapor condenses and recycles automatically, allowing easier maintenance. However, this approach is still early in adoption.

Planning for Success

Once a team selects a liquid cooling path, the next step is successful deployment. This requires careful coordination and planning beyond just the technology selection.

For example, many teams jump into procurement before fully understanding how the components will integrate. This can create challenges later, especially when the installation contractor isn’t familiar with secondary fluid loops, which are separate from the primary building cooling loop but essential for heat removal.

Post-installation considerations are just as critical. Equipment like CDUs are more sensitive to contamination than traditional CRAC/CRAH units. This means attention must shift to microscopic-level risks, such as bacterial growth or corrosion. These are often managed using fluid additives and inhibitors.

Designing for Scale

Operators managing multiple facilities should also consider how to standardize their cooling approach. Engaging a supply chain partner with broad reach and liquid cooling experience can help create consistent, replicable designs. A good partner can provide not just drawings and components, but full installation and commissioning packages —essentially a turnkey playbook for each deployment.

Standardization helps reduce variability, streamlines installation, and saves time and money across multiple sites.

Cooling with Confidence

As rack densities rise, liquid cooling is becoming a cornerstone of modern data center infrastructure. But success requires more than adopting a new technology, but also understanding each method’s benefits, limitations, and operational fit.

With the right strategy, data center teams can confidently introduce liquid cooling into their environments - unlocking greater efficiency, resiliency, and scalability to meet the performance needs of AI and tomorrow’s compute-intensive workloads.