"New Wave": why water cooling in the data center is gaining popularity

    According to Stratistics MRC forecasts , by 2023 the cost of the water cooling technology market in the data center will reach $ 4.55 billion. Under the cat we understand the reasons for the growth in demand for such developments and talk about the technologies that are developing in this area.

    / photo Rolf Brink CC / Immersion cooling system

    One of the reasons for the growth of the market is an increase in the volume of data processed. According to an IDC study , by 2025 the amount of data generated by mankind will be 163 zettabyte. As data volumes grow, so does the load on servers in data centers, especially in those that deal with high-performance computing (HPC). To cool such systems, conventional air installations are no longer enough.

    For example, to cool Google tensor processors (TPU), which are sharpened by TensorFlow, the IT giant had to use waterfor the first time. Due to the fact that the new generation of processors (TPU 3.0) is different power and high power consumption, air cooling was not applicable to them.

    Why air cooling is inferior to water

    Clive Longbottom, Service Director at Quocirca, an analytic company, notes that air is not so good as a heat transfer fluid: compared to water, it is 50 to 1000 times worse to remove heat from equipment.

    In addition, traditional air cooling units take up more space and consume more energy. And this affects the bills for electricity. Therefore, in the machine rooms of data centers, where the density of equipment is constantly increasing, it becomes unprofitable to use air for cooling. For this reason, the fans in the data center of the US National Security Agency replaced the system of immersion cooling (we wrote about other alternative solutions in one of the posts ).

    Vali Sorell, President of Sorell Engineering, a company engaged in technical building design and engineering communications, and Mark Hourican, Managing Partner of the Syska Hennessy Group consulting company, believe that the data center industry is not yet ready to take and completely refuse from “investing in the air” and completely switching to water cooling. In this case, you will have to completely rebuild the entire infrastructure of the data center, which is quite expensive.

    However, companies that have to work with large loads are already developing and using liquid cooling systems.

    About liquid data center cooling technologies

    Immersion cooling. One of the many liquid cooling technologies is immersion cooling (which we have already described in a blog ). The technology involves the complete immersion of equipment in a special oil environment. The main advantage of the technology is that the oil has a higher thermal conductivity than air. This helps the system more efficiently absorb heat and remove its excess.

    In 2015, Horizon Computing presented a system for immersion cooling: the company developed a special boxfor servers, which is filled with mineral oil. The design of the box maintains the optimum temperature of the equipment by convection. Such a “container” is able to work on the street without air conditioners, and the low cost of manufacturing and the simple design of the box allow it to be used without changing the infrastructure of the data center.

    Indirect liquid cooling. This technology is already used in the data center Facebook: in early June, the company demonstrated how the new cooling system made the data center in North Carolina more energy efficient.

    Facebook representatives say that in some data centers use the freecooling is not possible due to harsh environmental conditions and high levels of air pollution (with this problem, such as fightingin China). Therefore, the company decided to develop an indirect liquid cooling system.

    The system is based on evaporative cooling technology. Water for the system is cooled in a special heat exchanger, evaporating through a special membrane layer. Then it cools the air inside the data center, while maintaining the optimum temperature of the servers (the technology operation scheme can be viewed in a post from Facebook blog ).

    Testing of the system showed that it can reduce water consumption in the data center by 20% (in places with hot and humid climates) and by 90% (in temperate and cold climates).

    / photo poolie CC

    Heat exchangers on the back of the server rack.In this case, the cooled water flows directly to the rack with the equipment, removing excess heat. Lenovo uses this technology in its Neptune project: heat exchangers are already used by 30% of the company's customers for their HPC systems.

    In addition to the mentioned heat exchanger, the Neptune project includes a heat exchange module (Thermal Transfer Module) and a Direct to Node Cooling system.

    The module uses liquid from the heat-absorbing reservoir to transport excess heat from the processor to the area with rarefied air through special tubes. The system has a compact size, so it allows to reduce the traditional rumble in the server. And the direct cooling system delivers cold water straight to the node and "removes" excess heat from key components of the system.

    Future water cooling technology

    As they say industry experts Sorell and Huriken, air cooling fully cede their place of water when its use is absolutely unprofitable or impossible (eg, because of the physical constraints of data centers). However, experts predict that the transition will not be a one-time. Hybrid technologies will be spread first (for example, systems based on evaporative coolers , like on Facebook), and then the transition to direct cooling with water will be made.

    Lenovo also hopesthat the application of water cooling will go beyond the HPC-systems and will become popular among ordinary data centers. To do this, the company will work to reduce the cost of their implementation. Their goal is to make water cooling systems cheaper and more affordable for regular companies.

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