Still using air to cool your servers? Boy, you’re out of date! By now, everyone’s using liquid cooling… Or at least they should be, according to a very authoritative prediction I had from an IBM systems consultant I spoke to in 2009.

“We’ll see a return to liquid-cooling in most IT solutions,” he said, at an IDC conference in London. I guess I shouldn’t name him, but he reckoned that in ten years’ time, we’d be using liquid cooling pretty much here, there and everywhere.

We’re one year past that deadline, and the vast majority of racks in most data centers are still cooled by air. But still, every year since I had that prediction from IBM, someone has told me that liquid cooling will be widespread.

This year, engineer Robert Tozer promised that liquid cooling is inevitable at DCD’s Keeping IT Cool online event (in August 2020, still available online here). And this time round, there are liquid cooling systems that are practical: they can be added in small increments as needed.

In 2009, the argument was that companies wanting to become more efficient would invest in big liquid cooling systems to make use of waste heat: “Water-cooling is a better way to recycle the heat energy,” said my friend from IBM. “If you cool by air it is much harder to capture and condense it.” To harness that energy, it must be transferred to liquid, so it is more efficient to use liquid cooling directly, he said.

In 2020, Tozer predicts things are more imperative. We’ve now reached a point, he argues, where the energy density in our racks is becoming so great that only liquid can remove it efficiently enough.

Already, high-end processors produce so much heat that the only way to radiate it into an airstream is with a giant heatsink, said Tozer. “Look at the size of the chip compared to the size of the heatsink. As the density goes up, you literally cannot fit the heatsink into your 1U server.”

“Average rack power densities are 7kW, and that’s pushing up against the limits of what can be achieved in a conventional air cooled data center,“ said Malcolm Howe from engineering firm Cundall, in another DCD webinar. You can fill a data center with 7kW racks and still get rid of the heat, he said.

What happens next is new applications like AI bring higher density. Howe is already seeing 24kW racks: add some of those to a hall of 7kW cabinets and there simply isn’t enough air cooling to keep their temperature steady.

“It’s not stopping there”, said Kao’s CTO Gerard Thibault in that webinar. “We’re seeing potentially 125kW per cabinet.”

When applications like that arrive, data centres need a way to add higher levels of cooling to specific racks – running both alongside each other – and that’s exactly the way liquid cooling systems are being designed now.

Chassis level cooling from vendors like Iceotope builds a circulating system within the rack, so each blade can have its electronics immersed in liquid. Others, like Submer and Asperitas, are putting systems in baths of oil.

Tozer thinks that operators will need to run test systems, understand the science and serve their leading edge customers. Kao Data, for instance is already teaming up with Iceotope to run their chassis level liquid cooling systems in its Harlow facility.

This time, it looks like liquid cooling really is coming, said Tozer: “The driving force is chip densities. Businesses require the chip to do things – and if businesses require it, it will happen.”

Image: With thanks to the European OCP Experience Center.