DataCenterChill synthesis · Based on the primary source listed below
Nvidia has published the cooling design for its Rubin generation of AI systems, and the number that matters to anyone building a facility is 45 degrees Celsius. That is the temperature the coolant is allowed to be when it arrives at the rack. The liquid leaves at roughly 55 degrees, and the mixture is three parts water to one part propylene glycol.
Warm water sounds like the opposite of cooling, and that is the point. A processor does not care whether the liquid touching it is cold, only whether heat is leaving faster than it is produced. Once the loop runs that warm, the outside air is cool enough to do the job for most of the year, which means heat can be rejected with dry coolers rather than a chiller. Nvidia says a site in a favorable climate can go without the chiller entirely, and that cooling water use falls from around 2.6 million gallons per megawatt each year to near zero.
The other change is that the fans are gone. Nvidia describes Rubin as its first fully liquid-cooled generation, with every chip and every networking component on the liquid loop. Removing server fans takes out a power draw worth roughly a tenth of server power, and it is a large part of why liquid cooling shows a net energy saving at high density rather than simply moving the heat somewhere else.
None of this is a new idea. European supercomputing sites have run warm-water loops for over a decade, and the industry's thermal guidelines have allowed it since 2011. What is new is that the vendor whose racks anchor most AI construction has made 45 degrees the design point across its rack-scale line, which means the dry coolers, the coolant distribution units, and the facility water system now have to be engineered to that number whether or not the operator planned for it.
Two things are worth holding at arm's length. The water figure is a comparison against cooling-tower designs in a favorable climate, so a hot or humid site will not see it. And Nvidia's own materials do not compare what this costs to build against a conventional air-cooled hall, which is the number an operator actually has to sign off.