Liquid cooling becoming essential as AI servers proliferate

“Facility water loops sometimes have good water quality, sometimes bad,” says My Troung, CTO at ZutaCore, a liquid cooling company. “Sometimes you have organics you don’t want to have inside the technical loop.”

So there’s one set of pipes that goes around the data center, collecting the heat from the server racks, and another set of smaller pipes that lives inside individual racks or servers. “That inner loop is some sort of technical fluid, and the two loops exchange heat across a heat exchanger,” says Troung.

The most common approach today, he says, is to use a single-phase liquid — one that stays in liquid form and never evaporates into a gas — such as water or propylene glycol. But it’s not the most efficient option.

Evaporation is a great way to dissipate heat. That’s what our bodies do when we sweat. When water goes from a liquid to a gas it’s called a phase change, and it uses up energy and makes everything around it slightly cooler.

Of course, few servers run hot enough to boil water — but they can boil other liquids. “Two phase is the most efficient cooling technology,” says Xianming (Simon) Dai, a professor at University of Texas at Dallas.

And it might be here sooner than you think. In a keynote address in March at Nvidia GTC, Nvidia CEO Jensen Huang unveiled the Rubin Ultra NVL576, due in the second half of 2027 — with 600 kilowatts per rack.

“With the 600 kilowatt racks that Nvidia is announcing, the industry will have to shift very soon from single-phase approaches to two-phase,” says ZutaCore’s Troung.

Another highly-efficient cooling approach is immersion cooling.

According to a Castrol survey released in March, 90% of 600 data center industry leaders say that they are considering switching to immersion cooling by 2030.

But immersion cooling does have its downsides. According to the survey, 38% of respondents are concerned about the potential for leaks, 31% say that it’s too time-consuming to implement, and 31% worry about maintenance challenges.

Colocation provider Equinix, which has more than 260 data centers in 72 markets, has liquid cooling already available at 100 of them — and continues to build new liquid-cooled facilities and retrofit older ones.

But it hasn’t seen much demand for immersion cooling yet, says Phil Read, the company’s senior director of data center services. “It’s definitely an area we’re monitoring,” he says. “It could be interesting in the future.”

Today, however, the technology still has some issues. For one thing, there’s the weight, he says. “You’re basically putting the weight of a small car on a data center floor.”

And then there’s the issue of the kinds of liquids that are used for immersion cooling. “Equinix has a strong sustainability posture and PFAS chemicals are very problematic for us,” he says. “But we see those used in immersion cooling — and in two-phase cooling as well.”

It’s not clear yet exactly how the industry will manage the power and cooling requirements of next-generation AI servers. Maybe AI will come up with some suggestions.