Direct liquid cooling is now gaining momentum in mainstream data centers — for many good reasons.
As servers get faster, they generate more heat, and that increases the need for innovative approaches to cooling that go beyond the limitations of conventional air-cooled approaches. One of these innovative approaches that is gaining a lot of traction is direct liquid cooling.
Direct liquid cooling, or DLC, transfers heat away from processors and other heat-generating system components via contact with a liquid-cooled heat sink rather than using just air in the heat-exchange process. In one approach to DLC, used by the company CoolIT, a metal plate, or a cold plate, functions as a heat sink. This plate is placed in direct contact with the processor casing surface. Liquid flows through sealed micro-channels in the plate to capture heat from the processor, and then flows on to a heat exchanger, which dissipates the heat. The cooled liquid coming out of the heat exchanger travels back through the system, and the cycle repeats itself.
While it has been around for decades for various use cases — including supercomputing systems and desktop systems with accelerators — direct liquid cooling is gaining traction in enterprise data centers and service provider environments. The title of a paper by 451 Research pretty much says it all: “The Tide is Turning Toward Liquid Cooling in Datacenters.”
Market research validates this view of the growing momentum for liquid cooling. A report by the research firm Global Market Insights projects that the data center liquid cooling market will jump to $2.5 billion by 2025, up from $750 million in 2018.
A thirst for throughput
So why is direct liquid cooling gaining traction? One reason is an unquenchable thirst for higher throughput for artificial intelligence and high performance computing. To meet to this demand, new generations of technology bring faster Intel® processors and more dense racks, and that equates to more heat with the need for more efficient approaches to cooling.
Over the years, as Moore’s Law played out and the capacity and performance of processors grew, system builders continued to keep things cool with air-based approaches. But now we have reached the point where processor capacities and wattages are starting to bump up against the limits of conventional approaches to cooling. The more we push for higher performance in systems, the more wattage we require in processors, and that equates to more heat. Liquid cooling is one of the ways to deal with that heat in an efficient and cost-effective manner.
Let’s talk watts. Air cooling has worked for systems with CPUs that top out around 150 watts, which is what we have had for the past decade or so. But today, we are seeing more systems with CPUs that run at 200W and above and accelerators that run at 300W, with plans for even higher-wattage processors. These higher-wattage processors will be increasingly important for many computationally intensive artificial intelligence workloads that use hardware accelerators, including machine learning, deep learning and applications like high-frequency training and fraud detection.
Collectively, these trends are causing people to take a closer look at liquid cooling, which is a more efficient way to cool processors. It’s also a more efficient way to cool high-density storage and systems deployed at the network edge, according to 451 Research.
“DLC will largely take off because the existing technology — air cooling — will hit its limitations and inflict pain on major buyers of infrastructure in the form of lost performance or higher costs (or both),” the firm says in its report on the tide turning to DLC. What’s more, the data centers that we build today will likely still be in service in the late 2020s and early 2030s, so they have to be built with future cooling needs in mind. “It is for these reasons that 451 Research views DLC as a must-have in the datacenter operator’s toolset if it wants to keep pace with infrastructure requirements.”1
Liquid cooling in a new supercomputer
Among the organizations that have opted for liquid cooling is the Texas Advanced Computing Center (TACC), with new supercomputer Frontera. The primary system, supplied by Dell EMC, will have more than 8,000 dual-socket Intel® Xeon® nodes with 205W processors. Frontera will also include a small accelerated subsystem, to support molecular dynamics and machine learning applications.
Frontera, which debuted at No. 5 on the latest TOP500 list, leverages DLC-cooled Dell EMC PowerEdge C6420 servers and Dell EMC Isilon unstructured data storage in combination with 2nd-generation Intel® Xeon® Scalable Platinum processors, Intel® Optane™ DC Persistent Memory and a high-performance Mellanox HDR 200Gb/s InfiniBand interconnect.
For the system’s 448,448 cores, the racks leverage DLC technology from CoolIT, a Dell EMC partner. CoolIT’s Direct Contact Liquid Cooling technology uses the exceptional thermal conductivity of liquid to provide dense, concentrated cooling to targeted surface areas. The technology uses warm or room-temperature water to cool CPUs, eliminating the need for chilled water and reducing the cost of cooling by as much as 56 percent over traditional cooling methods.
Dell EMC now offers DCLC technology from CoolIT in the PowerEdge C6420 server, a density-optimized workhorse for artificial intelligence and high performance computing workloads. Liquid cooling allows the server to support higher wattage processors for increased performance and energy efficiency.
Direct liquid cooling is coming to a data center near you as one of the keys to enabling the use of higher-wattage processors and more powerful computing systems. As 451 Research notes, “DLC is quickly becoming a relevant consideration for enterprises and service providers, moving beyond the classic supercomputing use case.”1
To learn more
For a closer look at liquid cooling in HPC servers, see the Dell EMC-CoolIT solution brief and watch the Dell EMC video featuring CoolIT Systems CEO/CTO Geoff Lyon.
 451 Research, “The Tide is Turning Toward Liquid Cooling in Datacenters,” July 2018.
 Global Market Insights, Inc., “Data Center Liquid Cooling Market worth over $2.5bn by 2025,” February 04, 2019.
 HPCwire, “TACC’s ‘Frontera’ Supercomputer Expands Horizon for Extreme-Scale Science,” August 29, 2018.
 TOP500, “Frontera – Dell C6420, Xeon Platinum 8280 28C 2.7GHz, Mellanox InfiniBand HDR,” June 2019.
 Dell EMC solutions brief, “Improve Power Efficiency with Dell EMC PowerEdge and CoolIT Systems Rack DCLC,” 2017.