Selecting the Appropriate Liquids
Liquid cooling is making an impact in the tech world, allowing high-output accelerators and tight datacenter arrangements to remain cool, yet startup Accelsius believes we’re utilizing the wrong fluids. Their findings suggest that alternative cooling liquids could significantly reduce datacenter operational expenses by enabling data centers to increase their water temperatures by approximately 14° C above the standard. By replacing single-phase coolants with two-phase ones, such as those utilized in refrigerators and air conditioning systems, Accelsius asserts they can manage facility water temperatures as high as an impressive 54° C, or even 59° C if you are willing to enhance the flow rate.
Increasing the Temperature Threshold
Gaining a few degrees may not seem significant, but Accelsius argues that for each 1° C increase, you can save around 4% in annual energy costs. With datacenters expanding and electricity prices climbing, that adds up to considerable savings. “There’s not a lot you can do with excess 30° C waste heat,” stated Accelsius CTO Rich Bonner to GadgetLad, “but once you reach 50°-60° C, you’re at temperatures suitable for showers.”
Old Techniques for Techies
Two-phase coolants aren’t a novel concept in datacenter cooling. Back in 2021, Microsoft was submerging server chassis in bubbling pools of fluoroketones and hydrofluoroethers to maintain cool temperatures. ZutaCore is also employing these for direct-to-chip cooling innovations. Accelsius’s strategy may appear similar to a typical datacenter liquid cooling configuration, circulating liquids through manifold racks connected to servers and other equipment. The main difference? Their two-phase coolants are particularly effective at extracting heat from accelerators.
Accelsius’ Approach
In a whitepaper provided to GadgetLad, Accelsius demonstrates that modifying a Dell PowerEdge XE9680L with its NeuCool two-phase coolant led to a reduction in temperatures by a remarkable 19° C at the cold plate and 9°–14° lower at the system level. “It’s your call on how to utilize it,” Bonner remarked. “Operate at higher facility water temperatures, maybe eliminate the chillers, and boost your datacenter computing power, or consider overclocking your processors to the limit.”
Coolers: Dry vs. Evaporative
Increasing water temperatures in a facility results in less heat to expel. Rather than using evaporative coolers that consume significant water, dry coolers — essentially industrial radiators — can be utilized. These dry coolers are primarily effective in cooler months, as they require a significant temperature differential between facility water and air for optimal performance. In warmer seasons, the assistance of traditional water-absorbing coolers may still be necessary.
Challenges to Tackle
Accelsius is facing difficulties with universal cold plates and compatible CDUs. Existing systems like Nvidia’s NVL72 with 72 GPUs and 36 CPUs present challenges. Universal cold plates could simplify matters by allowing OEMs to create a single platform capable of handling either single- or two-phase coolants. Their technology doesn’t rely on boiling any refrigerants in wells, opting instead for skived fins, similar to single-phase systems.
CDU Compatibility
CDUs are essential parts of any liquid-cooled system, functioning as both a pump and a heat exchanger. The issue? Two-phase coolants necessitate specialized CDUs. Nvidia rack systems currently have soaring power demands, and Accelsius’ largest in-row CDU is only suitable for a single 250 kW rack. Bonner hints at a unit capable of over 350 kW and a 2.4-megawatt powerhouse on the horizon, anticipated next year.
Environmental and OEM Issues
Two-phase systems have often depended on coolants originally designed for other applications. Popular options such as 3M Novec, associated with health hazards, have faced production halts, prompting researchers to develop safer alternatives. Accelsius’ NeuCool formula holds A1 safety certification, meaning it is non-flammable and non-toxic. Securing OEM cooperation has been challenging. Liquid-cooling suppliers have needed to provide support agreements to alleviate buyers’ concerns about potentially ending up with expensive, non-functional servers.
OEM Support Challenges
Retrofitting servers for liquid cooling is not the problem. It’s servicing them when issues arise. In the absence of OEMs like Dell or Lenovo onboard, fingers tend to point towards liquid-cooling suppliers when something goes awry. Bonner’s vision? “We aim for a two-phase system you can purchase from Dell or Supermicro.”
Conclusion
“Rational Thinking Prevails, For Now”
Accelsius is entering the arena with an innovative two-phase methodology, offering cooler savings and increased operational temperatures. However, with challenges in OEM support and custom configurations, the cooling revolution is still in its preliminary stages. Stay alert, this one is just beginning.
