NVIDIA Rubin Liquid Cooling: Reducing Data Center Water Use to Near Zero

NVIDIA Rubin achieves 100% liquid cooling to eliminate water consumption

NVIDIA's Rubin generation AI infrastructure is the first to implement 100% liquid cooling, removing all fans from the system and utilizing a closed-loop liquid cooling methodology. By allowing cooling liquid to operate at temperatures up to 45°C (113°F), NVIDIA enables data centers to shift from evaporative cooling towers to dry-cooler-based designs, which can reduce facility water consumption from 2.6 million gallons per megawatt per year to near zero.

The efficiency of 45°C liquid cooling

Raising the operating temperature of the coolant allows heat to be rejected more efficiently into the outdoor air without the need for energy-intensive mechanical chillers. This approach provides several critical operational advantages:

• Energy Cost Reduction: Industry estimates indicate that raising chiller plant temperatures by just one degree can reduce cooling energy costs by approximately 4%. A 50-megawatt hyperscale facility can save over $4 million annually by transitioning to liquid-cooled infrastructure.
• Chiller-less Operation: In favorable climates, the 45°C architecture allows for "chiller-less" operation using outdoor dry coolers (large radiator coils). In these environments, mechanical refrigeration is only required for a small fraction of the year (approximately 1% in some climates).
• Performance Stability: Despite the higher coolant temperature, processors continue to operate at full performance. Coolant entering a chip at 45°C typically exits at 55°C after absorbing the heat load, while cold plates keep the silicon within validated operating limits.

Architectural shifts: From hybrid to full liquid cooling

Traditional liquid-cooled servers were hybrid systems where only the GPUs and CPUs had cold plates, while other components relied on air-cooled finned heat sinks. The Rubin architecture redesigns the entire server to be fully liquid-cooled, which results in several physical and operational changes:

• Increased Rack Density: Because they do not require space for airflow, fully liquid-cooled servers can significantly increase compute density. Systems that previously occupied six rack units can now fit into two.
• Noise Elimination: By removing all cooling fans, the system eliminates the noise levels that typically reach or exceed 85 decibels in traditional data centers.
• Simplified Infrastructure: The servers feature sealed front panels rather than the perforated bezels required for air intake, and the cooling loops are redesigned to route liquid to multiple high-power chips using a single inlet and outlet.

Technical specifications and implementation

The cooling system utilizes a mixture of 75% water and 25% propylene glycol. The liquid flows from a coolant distribution unit (CDU) to the servers in a closed-loop cycle. This closed-loop design ensures that once the system is filled, no new water is consumed for the cooling process.

Community insights and considerations

Technical discussions surrounding this announcement highlight both the potential applications and the remaining challenges of this architecture:

Waste heat recovery and district heating

Some experts suggest that the 45°C output temperature makes data centers viable candidates for district heating systems. By providing residual heat to nearby commercial or residential buildings, data centers could transform a waste product into a community asset.

Environmental and geographic constraints

While the system is highly efficient, its effectiveness is dependent on geography. The ability to operate without mechanical chillers depends on the ambient outdoor air temperature. In extreme climates (e.g., Phoenix, Arizona), chillers may still be necessary more frequently than in cooler regions (e.g., the Scottish Highlands).

Clarification on "Zero Water Consumption"

There is a distinction between the water used to fill the closed-loop system and the water consumed via evaporation. Traditional cooling towers consume massive amounts of water through evaporation to reject heat; NVIDIA's dry-cooler approach eliminates this evaporative loss, which is what is meant by "near zero" water consumption.