Why the Future of Data Center Cooling Is Hybrid

Just as hybrid powertrains bridge the EV era, air cooling remains essential to high-density AI infrastructure alongside liquid cooling.

Key takeaways:

• The Hybrid Reality: AI workloads drive rapid liquid cooling adoption (direct-to-chip, CDUs), but air cooling remains essential for non-liquid components, white space ambient control, and standby resiliency. 

• Modular CRAC Evolution: Replacing monolithic legacy CRAC units with modular, variable-speed systems — such as the AIRSYS Optima2™ platform — optimizes part-load efficiency and simplifies white space retrofits.

• CRAH & Fan Walls: Perimeter water-based cooling handles high-density thermal loads while navigating low-GWP refrigerant restrictions.
• Edge & Modular Precision: Systems like AIRSYS UniCool™ and UniCool-Edge™ extend precision thermal management into high-density modular and edge deployments.

Pure electric vehicles have stolen a lot of the limelight recently in the auto-industry.

But despite all of their advantages, from simpler engineering to potentially lower climate impact, they have not eclipsed fossil-fuel alternatives yet. The reliability and predictability – especially in rugged environments – means there will likely be a role for petrol and diesel engines for a long time to come. Especially when that trusted technology is married to electric batteries in hybrid designs arguably combining the best of both worlds.

Similarly in data center circles, liquid cooling solutions increasingly dominate the thermal agenda especially when it comes to high-density AI workloads. Direct‑to‑chip cooling, higher water temperatures for efficiency, and advanced distribution architectures all point toward a future where liquid carries a greater share of the IT load.

Yet even in the most forward‑leaning facilities, experts agree air cooling still remains indispensable. Certification and advisory organisation Uptime Institute points out that traditional workloads, and traditional data center designs, will continue to be required well into the future. “Compared to AI training and high-performance computing (HPC) hardware, IT that supports business-critical applications (e.g., databases) typically has lower thermal density and a higher resiliency objective,” Uptime states.

And for all of its efficiency and flexibility, just like the idea of using an electric car for a remote desert crossing, liquid cooling has some inherent resiliency challenges: “The volume of the liquid coolant is also much less than that of the air in the data hall, affording less time for standby generators to start and synchronize before taking over the cooling load following a power outage,” Uptime explains.

The real question for the industry is not whether air cooling will survive, but how, just like in the car industry, it must evolve to support hybrid environments. The future will likely see a diverse menu of cooling options. According to analyst firm Dell’Oro, the data center thermal management market is: “projected to grow at a 20 percent CAGR and reach the value of the UPS market by the end of the decade, underscoring cooling’s evolution from a supporting function into a primary determinant of data center design”.

 From Product Silos to Integrated Air-Cooling Strategies

To understand this air evolution, progressive data center operators are shifting their focus from individual units to a holistic, site-wide air-cooling strategy.

It is no longer about deploying isolated hardware; it is about how computer room air conditioners (CRACs), computer room air handlers (CRAHs), fan walls, and packaged direct expansion (DX) systems integrate into a singular, coherent thermal strategy.

Traditional refrigerant‑based CRAC units remain foundational, particularly in retrofit scenarios. Meanwhile, CRAH systems and fan walls — which leverage facility chilled water instead of localized refrigerant — handle larger air‑cooling loads in modern data halls without the constraints tied to traditional DX refrigerants. In addition, advanced systems like Airsys UniCool™ and stackable UniCool-Edge™ units extend these exact same precision cooling principles into modular and edge deployments.

Ultimately, these air-based systems do not operate in a vacuum. They sit alongside chillers, coolant distribution units (CDUs), and liquid-cooled racks in a unified thermal ecosystem.

Modernization: The Power of Modular Retrofits

The transition to high-density compute does not mean conventional facilities are no longer relevant. Instead, the industry is seeing classic DX CRAC platforms updated with modern, system-level modularity.

Consider the traditional approach to retrofitting a 360 kW monolithic CRAC unit. Replacing it with another single “monster” unit presents extreme deployment challenges. A modern alternative, exemplified by modular designs like the Airsys Optima2™ CRAC platform, relies on deploying groups of smaller, independent modular blocks — such as multiple 60 kW units featuring variable-speed compressors and fans — to meet the same capacity. This design shift delivers two key advantages:

• Practicality of Deployment: Smaller, modular units are dimensioned to fit through standard doorways and into service elevators which helps to streamline the upgrade process.
• Operational Flexibility and Part-Load Efficiency: A modular multi-unit group can scale to match actual real-time demand. If the thermal load drops, the system can run a subset of units at their optimal, high-efficiency range via variable-speed controls. For example, a group of six units can run independently or in any group sequence depending on the load. Three units running at 20 kw is significantly more efficient than 1 unit running at 60 kw, or a 360 kw unit running at 180 kw because it is two-stage and that’s as low as it can go, even though the actual load demand is only 60 kw.

By utilizing modular configurations, operators inherently gain redundancy, allow for seamless unit rotation during maintenance, and gain the ability to scale investment directly alongside changing thermal profiles.

CRAH, Fan Walls, and the High-Temperature Shift

While modular CRACs may solve a retrofit challenge, CRAH and fan wall solutions have become the workhorses of large-scale, high-density air cooling in new builds.

By utilizing chilled water from centralized infrastructure — such as Airsys’ VectorCool-X™ centrifugal chillers — or dry coolers, these systems sidestep the refrigerant safety limits that restrict DX volumes inside the white space. Fan walls take this further by embedding coils and fans directly into the perimeter of the hall, moving large volumes of air more efficiently. As global refrigerant regulations tighten and low-GWP (global warming potential) options introduce new flammability considerations, water-based perimeter cooling offers a stable path forward.

The efficiency opportunity

Legacy air-cooled systems are recognized as being less efficient than liquid solutions, but that baseline inefficiency is precisely why they represent an opportunity for energy savings. You cannot optimize an architecture already running at peak theoretical efficiency; the greatest financial and operational gains come from tackling air-side inefficiencies.

Modern air-cooling platforms capture these immediate energy reductions through engineering levers including:

• Free-Cooling Optimization: Maximizing ambient outdoor air usage to completely bypass mechanical refrigeration for large portions of the year.
• Variable-Speed Compressors: Throttling capacity dynamically to match real-time thermal loads, eliminating the massive power spikes of legacy on/off cycling.
• Superior IEER Ratings: Optimizing equipment for high Integrated Energy Efficiency Ratio (IEER) performance under real-world, part-load conditions rather than just peak nameplate capacity.

Coexistence: Air and Liquid as Complementary Forces

The overarching reality of modern digital infrastructure is clear: no realistic, next-generation data center is exclusively air-cooled or exclusively liquid-cooled.

Liquid technologies, including direct-to-chip and immersion solutions, are non-negotiable for the hottest portions of the IT load, such as high-density AI clusters. But air remains responsible for cooling everything liquid cannot touch: memory modules, ancillary chassis components, power distribution units, and the overall ambient temperature and humidity of the white space.

Rather than fading into irrelevance, air cooling, just like conventional vehicle engines, is cementing its role as a strategic part of a hybrid future.

Optimize Your Thermal Strategy with Airsys

Navigating the complexities of hybrid data center cooling requires a partner that understands both sides of the thermal equation.

Airsys bridges the gap between legacy infrastructure and high-density environments with an innovative portfolio designed for seamless integration. From the groundbreaking, highly modular Optima2™ CRAC platform and the expansive range of the Optima-INV — ideal for transforming disruptive retrofits into efficient, scalable upgrades — to the stackable, space-saving UniCool™ and UniCool-Edge™ systems for edge deployments, AIRSYS provides precise control where it matters most.

Supported by ultra-efficient infrastructure like our VectorCool-X™ centrifugal chillers and advanced liquid CDUs, we ensure your facility achieves peak efficiency, maximum uptime, and a future-proof path forward.