Will liquid cooling for data centers live up to the hype?

03.05.2023 686 3

Martin Deshev

Sustainability and energy prices are big topics across every industry around the world, and it’s no exception for data centers. There’s a lot of talk about how to continue to achieve peak performance whilst lowering costs.

Cooling plays a big part in achieving this goal. It’s also one of the most complicated and expensive aspects in every data center. Naturally, it’s a very dynamic niche with a lot of innovations and ideas floating around, and for a while now liquid cooling has been slowly emerging as a leading trend among data center operators. There has been a lot of active development of various liquid cooling methods and some very ambitious forecasts about the future of this approach. But is it going to live up to the big hype?

Big ambitions

According to the Data Center Thermal Management Market Analysis in late 2022, conducted by Omdia, the interest for liquid cooling is quite high and will continue to rise. Revenue purely in just the liquid cooling market could reach $3 billion by 2026. The compound annual growth rate will reach 50.4% for the five years between 2021 and 2026.

“Fueled by the need to run compute-intensive workloads, cloud service providers’ investment has had a particularly positive impact on the market’s growth potential,” said Dr. Moises Levy, senior principal analyst for data center power and cooling for London-based Omdia, to DataCenterKnowledge (DCK).

About two-thirds of data centers in the US experience higher peak demands now. The power density is around 15kW per rack, DCK notes additionally. To look for solutions, data center operators have turned to… data for help. And it turns out that data centers use a lot of resources to cool off. Not really a big surprise. But what is surprising is that many of those resources can be optimized and reduced.

For example, in 2021, Google’s data centers used 4.3 billion gallons of water. That’s the water needed for 29 golf courses in the southwest US every year. But Google is investing in technologies and approaches to reduce both water and energy consumption. And in that same 2021, Google reduced its CO2 footprint for data centers by a combined 300 000 tons, says Urs Hölzle, senior vice president of Google’s technical infrastructure.

The IT giant and other data center operators are all exploring options to further improve their results. “Liquid cooling systems may or may not be the ideal solution for a data center project. The selection of liquid cooling instead of air-cooling systems has to do with various factors, including specific location, climate (temperature/humidity), power densities, workloads, efficiency, performance, heat reuse, and physical space availability,” according to Dr. Moises Levy, senior principal analyst for data center power and cooling at Omdia.

Liquid cooling is not new

Liquid cooling isn’t a new technology by any means. The IT industry has been developing and exploring it for years. According to DataCenterDynamics (DCD), liquid cooling entered the IT industry way back in the early 1960s. Back then the IBM enterprise computer System/360 made history with a lot of firsts with some of them still being used to this day. For example, parts of the S/360 code and… hybrid cooling. The System did use a mix of air and liquid cooling.

The main concept and components are used by desktops even today, too, and over the years this idea evolved for servers and data centers as well. If originally liquid cooling was dealing only with CPU heat, now the majority of components can be cooled by this method. Hardware manufacturers are actively working on making components that can be liquid cooled and not just by slapping a heat sink on them; they are also making components that can be fully submerged in liquid, but more on that later.

The liquid used for cooling brings many benefits. One of them is that there’s less need to keep the entire server room at a lower temperature. Data centers use a lot of energy to cool the air in the server rooms to make it easier for the components to cool off, especially when air cooling is used. Raising the temperature in the room by 2-4 degrees Celsius might not affect hardware too much and allow to continue to perform well, but also this could help save a lot of resources – and liquid cooling might be a good way to achieve this balance with less effort!

There’s another factor that we need to consider, DCK notes. The fact that hardware is becoming more and more powerful, and air cooling can’t keep up with this demand without severe drawbacks like higher energy consumption, bigger fans, and more noise. And data centers are already noisy enough! Liquid cooling can help solve these issues. It can’t be a complete fits-all solution, but it can certainly take big parts of the cooling efforts and help reduce energy consumption and noise, while keeping the footprint and costs more acceptable.

There’s more than one approach

As we mentioned, there’s more than one liquid cooling solution. In fact, these days there are dozens of variations and combinations. We will skip the consumer versions and focus on the developments for data centers. Even in this small arena, there are quite a few options. We can segment them into a few smaller groups.

The first one is Direct-to-Chip. As the name says, it focuses on the cooling the main chips – CPUs and GPUs. That happens with a plate placed on the chip and the liquid takes the heat away from it as it passes through it. The drawback is that it leave residual heatso fans are still required to remove it from the rack, although at a lesser cost. The benefits are the cheaper setup and the ability to use regular water or special dielectric liquids.

There’s another version of this type of cooling. The first one is called Single Phase as the liquid doesn’t change form. The Two-Phase liquid cooling is, yep, you guessed it, when the fluid changes state – most often to gas and then back to liquid. The benefit is less risk of leakage and damage, but the drawback is the need for additional equipment for the state-change and thus increased maintenance costs.

Next, we have immersion cooling. That’s the big trend now. And, of course, it also has several versions. The basics are the same though – the components are submerged in the liquid directly. There’s no heatsinks or anything else between the liquid and the chips and the board. Some designs submerge only parts of the servers while others submerge the entire server.

There are more variations. For some designs, simply submerging the components is enough to keep them cool depending on factors like ambient temperature, average heat from the server during peak loads, etc. Other designs incorporate liquid circulation and various approaches to cool it off before it returns in the tub with the hardware. Depending on the design, the cooling noise can be significantly less than fans or virtually completely silent.

There’s a possibility to use a Two-Phase liquid cooling for immersed solutions, too. There are different approaches for achieving the state change; it could be with a coil and condense which could again be near silent or another approach. The additional equipment needed could make this approach more difficult and costly to maintain, but it can also be more effective for some setups.

And yes, there’s more. Another, much rarer approach, is fully submerging the entire data center. Obviously, this only works at specific locations and for very small footprints. It’s a rare option, but it’s out there.

The future is liquid

There’s no doubt that liquid cooling will continue to evolve and become more effective. As more data centers adopt it, more innovations will come to fruition as there’s money in the market – and that doesn’t just mean new liquid cooling equipment or hardware that’s better optimized for it.

Companies are focusing a lot of effort on the development of better liquids for cooling. A recent innovation is vegetable oil. And no, it’s not exactly the same type you use to dress your salad. It’s a specially made product by Cargill. It’s made with 90% soya oil, and it has the goal to replace petroleum-based coolants for data centers. Because it’s made from plants, it is CO2 neutral and has a 10% better heat capacity than synthetic fluids, Cargill claims. The company also says the oil passes safety standards with a high flash point and can’t self-ignite. Spills are also easy to clean with soap and water without additional detergents. Recycling obviously is also easier.

Other companies are specially focused entirely on immersion cooling solutions. One of them is LiquidStack which will build an entire R&D lab in the US. It will focus entirely on this niche, and it will look to the future because AI (artificial intelligence) is coming. This technology will need even more powerful hardware. Of course, this leads to more heat and a rising need for even better cooling, so, liquid cooling comes at a perfect time as a great solution. There’s a lot of room for innovation in this niche and nearly every aspect can be improved and evolved. Thus, we can expect that the liquid cooling market is indeed in a great position to be a very dynamic and interesting place for the next few years. Much to the benefit of the companies involved in it and the data centers which are going to get access to even more options and solutions for every need and configuration.