Liquid Immersion Cooling (LIC) in Data Centers: Innovation & Opportunities

Liquid cooling solutions have emerged as an innovative and sustainable way for digital infrastructure providers to reduce their energy and resource use, alongside other sustainability benefits. Our Excess Heat Utilization from Data Centers Steering Group is running and we plan to launch a new one on the Liquid Immersion Cooling, led by members such as Asperitas and Submer. This article is authored by Razi Ahmadi from our Innovation Labs team — as part of our series highlighting the work of our Steering Groups.

Key Takeaways

• Data centers are rapidly growing and consequently, energy consumption is increasing
• Cooling systems are responsible for circa 40% of the energy consumption within data centers
• Traditional cooling systems like air-cooling, despite their benefits, are not practical for the future
• Liquid cooling systems, due to their higher heat transfer capacity, will be a more feasible alternative
• Liquid immersion cooling (LIC) solutions submerge computing elements into dielectric fluids
• LIC increases the rate of heat transfer, reducing the energy consumption and carbon footprint
• Dielectric liquids applied in LIC are categorized as single-phase and two-phase, and have particular applications based on their properties
• Liquid immersion cooling is an efficient and sustainable cooling approach that provides new opportunities to utilize excess heat

Around the world, the significant demand for 5G connectivity, cloud-based gaming, the Internet of things (IoT), and other technological developments are fueling rapid growth within the information and communications technology (ICT) infrastructure. This development, in turn, is leading to greater energy consumption within data centers (DCs), while also incentivizing the computing industry to improve the processing efficiency of their devices and other products. Research demonstrates that an average of 40% of a DC’s entire energy consumption is directly consumed by the cooling system. This fact poses a sobering wake-up call for DC operators to further enhance current cooling systems, capitalize on new technologies, and develop new approaches to DC cooling. At the moment, most cooling systems are based on air cooling, popularized by its general ubiquity and key benefits such as cost and operational conditions. A survey by the Uptime institute revealed that approximately 56% of the DCs are using precision air cooling while 30% are using basic room-level cooling and only 14% are utilizing liquid cooling systems.

Limitations and alternatives for air-cooling

Despite their popularity, however, air-cooled systems have constraints that limit the ability of such systems to reach higher efficiency in DCs. Such limitations include the lack of an intelligent and practical heat removal system from IT devices and managing airflow inside the DCs, in addition to the low heat capacity. Since the main role of cooling devices is to keep the temperature within the desired range of operation to prevent malfunctioning and hot spots on the computing components, it is beneficial to consider the main features of liquid cooling as a practical alternative. Liquid cooling systems provide significant benefits over air-cooled systems, including larger heat transfer capacity (for instance the specific heat capacity of water within the room temperature is 4184 Jkg-1K-1 whilst air is 1012 Jkg-1K-1). This makes liquid cooling much more efficient and appealing for large-scale DCs, not only to accelerate the heat removal from the hot components, but also to reduce energy consumption, costs, and noise.

Among liquid cooling techniques, the liquid immersion cooling (LIC) system applies a specific liquid with a high capacity of heat transfer. In this process, all computing facilities (servers, central processing units, etc.) will be submerged into a non-conductive liquid bath. Consequently, all IT devices will directly transfer heat into the coolant, which will prevent the creation of hot spots. This differs from the conventional cooling solutions such as water cooling, as the liquids in such systems flow through pipes to prevent possible damages to computing elements.

For DCs that implement a LIC system, fans and other air-cooled systems that adversely affect the cooling energy consumption are not required, therefore leading to reduced costs, energy consumption, and improved power usage effectiveness (PUE) which greatly increases DC competitiveness and provide new opportunities. Fans are also the primary source of noise and dust on computing elements in air-cooled DCs. With LIC systems, however, their design and the equipment employed not only maximize energy efficiency gains, but also eliminates a significant amount of the noise and makes them immune from dust, leading to relatively easier maintenance.

Innovative fluids - differences between dielectric liquids

The liquid used in immersion cooling is not merely water; it has specific properties that should be properly understood. For one, they should have low electrical conductivity; as a result, dielectric liquid is applied in this cooling system. Dielectric liquids are categorized as single-phase and two-phase, which offer different properties based on application. With single-phase, dielectric liquids circulate inside the bath, and heat is transferred from the hot components to the coolant. During all this process, the liquid will experience no phase change. In the next step, the hot liquid is pumped into the heat exchanger, removing the heat before the cooled liquid is returned to the bath. And this highlights another great advantage of the LIC system, which is the possibility to utilize the excess heat in an efficient manner.

For a two-phase cooling system, a liquid with a low boiling point is added that circulates inside the bath. By absorbing heat from the hot devices, the working liquid will boil and the vapor will transfer the heat. On top of the tank, accumulated vapors will lose heat via heat exchange processes (condensing) and the liquid will then recirculate into the process. Two-phase immersion cooling can provide notably more uniform temperature distribution on the server surface utilizing the latent heat transfer, which decreases energy consumption.

Overcoming barriers to adoption

Computing elements are producing huge amounts of heat while operating, and it is crucial to utilize cooling devices in a professional manner to prevent any possible hot spots. One of the main challenges that liquid cooling faced was the complexity of the system during installation, this challenge has been addressed for current LIC systems, with both installation and maintenance becoming relatively easy. Undoubtedly, fears about liquid cooling system leaks have long been the biggest barrier to wider adoption, but with the LIC system this has almost disappeared with the new innovations and engineered structures.

Last but not least, liquid immersion cooling systems may seem to be costly in comparison to air-cooled systems. This mostly originates from the wider adoption of air-cooled systems and their earlier development. However, by considering the huge impact of the LIC system on the reduction of power consumption and the opportunities for waste heat recovery, liquid immersion cooling is more cost-effective in the long term.

When considering the many positive effects of an immersion cooling system and ensuring reliability in comparison to other air or liquid-based cooling approaches, this system is set to eventually replace conventional cooling systems, not just in hyperscale DCs, but also DCs of various sizes including edge facilities. Yet, immersion cooling requires further development in terms of the working liquids used and improved design of packed servers that can fit into the liquid bath, which can greatly open new fields of operation and efficiency. One solution to this is chassis-level precision-immersive cooling whereby the chassis containment acts as a fluid reservoir, requiring much less liquid than full immersion, and can be incorporated within conventional data hall rack layouts.

Data centers are developing faster than ever and rack densities are increasing which is resulting in higher energy consumption while the importance of cooling systems becomes even more evident. By taking into account all the positive impacts and also the challenges, the liquid immersion cooling system is a sustainable and realistic approach that provides an energy-efficient system that results in a reduction of carbon emissions which is directly contributing to the SDIA’s roadmap that is paving the way towards sustainability.

Moreover, the LIC system will enable DCs to benefit from the excess heat in a proper and efficient way. The SDIA and many of our members are working to do just that in our upcoming Liquid Cooling Steering Group, which we plan to launch in 2022. The main goals of this group are to analyze different aspects of liquid immersion cooling as a sustainable technology and come up with novel business cases. Find out more about the Roadmap and join us in making this vision a reality.

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