Is immersion cooling the answer to sustainable data centers?

While air-based cooling is available for server racks drawing more than 20 kilowatts (kW) in common data center designs, these designs are near their density limits and require expensive redesign to go further – leading data center owners and operators to look toward liquid cooling, and particularly immersion cooling, for facility projects.

Data centers have started to use liquid cooling for more than just building supercomputers in a small footprint. Liquids can more efficiently transfer heat than air, helping to address the challenges of air-cooling systems, especially as computing densities increase. Liquid cooling delivers cooling directly to the server rack, thereby densifying to support 100kW per rack or more.

As data centers grow in power, they generate more heat and cooling requires more energy. As a result, there’s an emerging need at the same time for energy conservation, supported by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). With liquid cooling systems bringing cooling as close as possible to the chip, the heat exchange is improved – meaning higher temperature liquid can be used to accomplish the cooling necessary for proper chip performance.

Chiller usage for producing cooling water can then be reduced or even eliminated. When a data center system does not require a chiller in most, if not all, environments, energy conservation is immediately accomplished, in addition to the benefits of densification to achieve high-performance computing.

How immersion cooling benefits sustainability

One liquid cooling technology is immersion cooling, where the hardware is fully submerged in a heat transfer dielectric fluid (a much better heat conductor than air) to transport heat away from the equipment.

A full immersion cooling solution can support sustainable data centers by offering great energy savings potential as well as improving water usage effectiveness. Because the whole board is immersed, all heat gets absorbed by the liquid and no residual heat is released to the data hall.

Yet there are some challenges in retrofitting a server with a liquid-cooled solution. Equipment life cycle expectations, manufacturer’s warranty, and thermal performance will vary for server design, heat transfer fluid, tank design, and operating temperatures. Immersion cooling uses specialized tanks, making it difficult or prohibitively expensive to convert existing data centers to liquid cooling. While readymade liquid-cooled equipment can be purchased, the equipment is costly.

And while there are a number of techniques to strategically apply liquid cooling to an existing server like cold plates, the best these typically can achieve is picking up around 80% of the heat off a server. This means the data center room will still experience some heat rejection from the servers, storage, and network equipment that needs to be picked up with a secondary liquid-cooled system like rear door heat exchangers or an airside system cooling the associated computer room.

So, while a great deal of energy and water savings can be achieved through a dedicated liquid cooling solution, many data center owners may still need to choose a hybrid environment.

As more companies drive sustainable change through corporate initiatives and commitments – and legislation drives more interest in sustainable solutions – this can be expected to change over time, with liquid cooling becoming more acceptable in the industry.

Making headway in Europe and the Nordics

For example, we recently talked with a company that has worked with a data center provider to convert a data center to a full immersion cooling solution on a small scale in the Nordics. The solution is attractive because of the opportunity for such high temperatures on the immersion cooling heat rejection side, making it possible for heat reclaim into a district heating system.

But when companies are building a business case for this, they will still likely look at airside and determine what must be done to comply with regulations.

An interim step could be water-to-water heat pumps. These are being used more frequently in Europe to elevate water temperature so that it is more useful in a heat reclaim situation, particularly when considering district heating systems.

Other considerations for the future of liquid cooling

Today, we are installing chilled water-cooling systems that use refrigeration and water, while also providing taps to accommodate water-cooled equipment. This offers flexibility to migrate gradually into the data halls and eventually, can make certain data halls or potentially entire data centers, specific to liquid-cooled solutions.

Currently, the industry is seeing a move away from raised floor air dispersion distribution systems – and going to flooded room cooling, which is typically deployed in non-raised floor environments, is on the rise. When using this concept of no raised floors, data center owners can look at different ways to introduce cooling water piping into a project that doesn’t require the wholesale installation of raised floors.

Another consideration is the height of the data center. There are several different things to look at – including providing trenches that bring liquid cooling into a space and hook up to the equipment, whether it's an immersion tank or racks. The trench would serve as a containment, so the liquid can be detected and directed out of the room at the same time. This offers a double benefit that could impact data center design.

Over the coming years, we can expect that new designs will be tested using no raised floors, and new ways of using water cooling will be introduced.

Summary

Decisions are made by businesses on IT selection using cost-benefit or total cost of ownership analysis based on many factors, including capital cost, operating cost, as well as progress on corporate goals like sustainability. With the advent of AI, immersion cooling has the promise to provide owners with sustainability options as they examine the continuum of cooling and computing choices in front of them.

How Ramboll can help

As companies navigate the evolving landscape of sustainable data centers, our experts can assist in assessing total cost of ownership (TCO) and implementing effective cooling and computing solutions. By staying ahead of industry developments and offering insights, we support businesses in making informed decisions that align with their corporate goals, including sustainability objectives in the era of AI.