Liquid Cooling Can Lower Data Center PUE, But That’s Not Its Main Draw

Liquid cooling vendors say their technology significantly reduces data center power consumption and Power Usage Effectiveness (PUE). Industry analysts and consultants agreed that it could in many cases improve PUE, but that wasn’t the main reason enterprises used liquid cooling in their data centers today.

The big driver for enterprises, they said, was bumping up cooling capacity in select places in the data center that need it, without having to change the entire facility’s cooling system.

“While reducing power is important, it’s not a driver for change right now for that segment,” Jennifer Cooke, a research director on IDC’s Data Center Trends and Strategies team, said. Data center investment drivers for enterprises today are agility and better responsiveness to business needs, not lowering utility bills, she said.

In some scenarios she witnessed, for example, enterprise data center operators installed hyperconverged equipment and used close-coupled liquid cooling for those specific racks, because hyperconverged infrastructure tends to need higher density than regular servers.

“Many enterprises deal with legacy equipment and different types of equipment, and they don’t want to disrupt a delicate ecosystem,” Cooke said. In those cases, a liquid-cooled rear-door heat exchanger is a common go-to solution specifically for higher-density racks.

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Most sales CoolIT Systems makes, for example, are with customers that have high-density compute infrastructure, the liquid cooling vendor’s CEO Geoff Lyon, said. CoolIT sells a direct-to-chip liquid cooling solution.

Liquid cooling can also be a good option for large service providers – colocation and cloud companies – who look to improve operational efficiencies as a matter of differentiation in the market. “They can be more profitable, and their job is to run a data center better than anybody else,” Cooke said.

What Kind of Savings, Exactly?

There’s little doubt that liquid cooling can be more energy efficient than air-based solutions.

When announcing its Neptune liquid cooling technologies in June, for example, Lenovo said one of the solutions, the rear-door heat exchanger, could turn a data center cooling infrastructure with PUE between 1.5 to 2.0 to one with PUE between 1.2 and 1.4. The direct-to-chip option could lower cooling PUE even further, to less than 1.1, the company said.

Dell EMC that its PowerEdge C6420 servers, liquid cooled with CoolIT Systems technology, could lower energy costs by up to 56 percent.

A third approach to liquid cooling, full immersion of the electronics in dielectric fluid, saves energy in two ways, Peter Poulin, CEO of GRC ( the immersion-cooling vendor formerly known as Green Revolution Cooling), explained: removing server fans, which are useless when submerged, usually cuts server power use by 15 to 20 percent (and sometimes even more); and powering GRC’s system requires 3 to 5 percent of the overall IT load, which is much less than the typical air-cooled system requirement of 30 to 70 percent.

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Overall, power savings resulting from switching to immersion in an already efficient air-cooled data center can be 30 to 35 percent, Poulin said. In an inefficient data center, it can be as much as 50 percent. From PUE standpoint, even an an extremely efficient air-cooled data center can cut its PUE from 1.35 to 1.1 by switching to liquid cooling, he said.

The Third-Party View

Industry analysts agreed that liquid cooling could be more energy efficient than traditional air cooling, but not always. The degree of savings would ultimately depend on the cooling technology used and the makeup of the individual data center in question, they said.

“Liquid cooling, in general, can improve PUE, but every solution is different,” Patrick Moorhead, president and principal analyst at Moor Insights & Strategy, said. “Some would reduce PUE. Some would increase it.”

“It eliminates the energy consumed by server fans; there is a significant reduction in HVAC power, as the need for air conditioners reduces,” Technavio analyst Venkat S. said. “We can also expect a small reduction in the power consumed by CPUs, due to continuous liquid cooling.”

Making a pure physics-based comparison, “the closer you can put the cooling to the heat source to remove the heat, the more efficient and effective it will be,” Greg Schulz, founder of the IT consulting form StorageIO Group, said.