Warm Water Cooling and AI: The Future Is Here but It’s Not Chiller-Free

Summary

Wall Street panicked over “hot water cooling” when Jensen Huang announced that the Vera Rubin platform can run on 45°C water without chillers. Warm water cooling is not new. Single-phase direct liquid cooling has enabled warm water operation for more than a decade.

What is changing is not the need for cooling but how facilities rely on chillers.

The Market Reaction Followed an Established Design Direction

When NVIDIA CEO Jensen Huang said that the Vera Rubin platform could operate with water at 45°C, requiring “no chillers,” the reaction was immediate.

Headlines framed it as a turning point for data center cooling. Markets followed suit, with investors quickly selling stocks of companies associated with traditional mechanical cooling.

Warm Water Cooling Is Mainstream, Not Revolutionary

Operating servers with warm water is not new. ASHRAE standards have supported elevated water temperatures since 2011. Direct liquid cooling (DLC) systems have delivered this capability at scale for over a decade.

NVIDIA’s announcement simply validates this approach. AI platforms are increasingly being designed to tolerate higher inlet temperatures. That trend has been building quietly for years as liquid cooling moves heat management closer to the silicon. Vera Rubin continues to elevate rack densities into the 150kW+ range, with sustained utilization. At these densities, DLC is critical to effective operation.

Single-phase DLC has become the de-facto technology for AI deployments due to system simplicity, interoperability and support for multi-vendor procurement. Hyperscalers are adopting it en masse. The same approach appears in supercomputers, NeoClouds and other large-scale data centers.

Reality Check. Chillers Are Not Going Away

Warm water cooling reduces chiller dependency, but it does not magically eliminate the need for mechanical cooling.

True chiller-free operation requires ambient conditions that can reliably supply 45°C water. Hot and humid regions still need chillers. Even moderate climates face reduced free-cooling effectiveness during extended heat waves above 35°C.

The limiting factor is temperature delta. The difference between facility water temperature and ambient air. As this delta shrinks, heat rejection efficiency declines, requiring higher pump power and larger heat exchangers.

Table: Example temperature differences between ambient air and facility water.

A fourfold increase in delta fundamentally changes system performance. Data centers are designed for worst-case conditions therefore the need for mechanical cooling will remain, simply as a risk-management tool for the hottest days of the year.

Advanced Engineering Enables Warm Water Cooling

Direct liquid cooling makes warm water operation possible. Facility shortcuts cannot achieve the same results. DLC uses water-based coolants, which transfer heat roughly 3,000 times better than air. Unlike air, DLC also targets heat at its source, primarily the processors.

This capability depends on precision cold plates, manifolds, pipe routing, flow control and leak mitigation within the Technology Cooling System (TCS). The TCS captures heat at the rack level while Coolant Distribution Units (CDUs) transfer that heat to the Facility Water System (FWS) for rejection to ambient air.

Maximizing performance of the TCS relies on improving components like the CDU, manifold, pipping and coldplates. Designs vary in operating temperatures based on workload, climate and reliability requirements but the principle remains: engineering excellence makes warm water cooling feasible even as power densities rise.

Cooling Value Is Moving Toward the Silicon

As these new DLC designs are being manufactured, the reality is that capital investment in cooling is shifting from heat rejection towards the CDU & TCS. Quite simply, this is because they enable more efficient infrastructure design.

CoolIT has led this transition for 25 years. Our system level view of the entire TCS including CDU gives us a unique perspective on the efficiency gains occurring with the adoption of DLC. Our professional services team have supported the design and installation of many warm water-cooling deployments and will continue to do so in the future. Regardless of individual component performance, optimising the TCS in its totality is critical for operators to realise the efficiency gains from DLC while also adopting the latest AI ITE.

For more information on CoolIT’s end-to-end direct liquid cooling products, visit: https://www.coolitsystems.com/products/