Does immersion cooling offer a route to the sustainable data centre?

As AI and machine learning technologies mature, and our appetite for ever more data and processing power continues to grow, demand for High Performance Computing (HPC), processing power and storage is mushrooming. 

This in turn puts increasing pressure on data centre capacity. McKinsey¹ reports that, in terms of power consumption, US data centre demand is set to grow from 17 Gigawatts (GW) in 2022 to 35 GW in 2030. 

The dilemma is that, against this growing demand for capacity, data centres must also deliver on their obligations to sustainability and net zero.

While computer technologists continue to find new ways to increase power density, fitting more processing and storage into ever smaller spaces, this may not be enough in the medium term to address this. A 2020 MIT Technology Review² article warns how we can no longer rely on Moore's law to keep putting more computing power on each wafer of silicon, and that there is no obvious short-term replacement technology other than an increase in server rack densities. 

In this context, reducing the environmental impact of existing data centre infrastructure is a key goal. Cooling is the biggest consumer of data centre power and space, after servers and IT equipment, so innovation in cooling technology has a critical role to play in resolving the data centre dilemma. 

This blog looks at immersion cooling as one such technology, weighs up its benefits and challenges, and considers whether the drive for data centre sustainability will be enough to take it from niche to mainstream adoption.

Immersion cooling works by placing IT equipment into a liquid agent which is a good conductor of heat but a poor conductor of electricity, as a means of dispersing heat.

There are two basic immersion cooling approaches: 

In single-phase immersion cooling, the tank is connected to a cooling distribution unit (CDU) that cools and recirculates the liquid, which always remains in a liquid state. 

Two-phase immersion cooling works by evaporation and condensation of the cooling liquid, using a heat exchanger such as a condenser coil. 

As a 2019 blog for Data Center Dynamics³ points out, immersion cooling is not new, having been used to cool high-voltage transformers for more than a hundred years, and in computer systems since the 1960s. Interest in liquid cooling, and immersion cooling in particular, has revived recently because of its potential to drastically reduce the power and size of IT cooling systems in addition to its increased cooling efficiencies compared to air cooling, especially at higher server rack densities.

Immersion cooling in its modern context is an emerging technology. 

The Open Compute Project published immersion cooling requirements⁴ as recently as 2022, so there is still work in progress to bring it into the mainstream. 

As a materials technology specialist, Henkel has a specific interest in the thermal interface materials used in immersion cooling. 

As with most means of dissipating heat, the efficiency of immersion cooling depends on how effectively heat is transferred from the source to the cooling agent, and thermal interface materials play a key role in this. 

Immersion cooling creates its own challenges, for example, traditional thermal interface grease solutions are likely to be soluble in the cooling liquid. 

Henkel is engaging and working through the implications of immersion cooling for thermal interface materials.

Immersion cooling offers benefits over other cooling methods that make it attractive to data centre providers looking to reduce costs, increase capacity and minimise environmental impacts

It is inherently more power-efficient than air cooling, and has the further advantage that it delivers direct cooling to the whole of the immersed server or other IT component. 

It requires fewer moving parts and electrical components than other methods.

Together, these attributes deliver a range of cost and sustainability benefits:

• Much lower power consumption for the same level of cooling 
• Greater component reliability from constant, consistent cooling of the whole item
• Lower total cost of ownership and operational costs
• Lower maintenance costs 
• Less noise

A 2022 article from Science Direct⁵ expands on some of these benefits. Immersion cooling remains a niche technology for now as there are also significant barriers to adoption, such as: 

• High capital costs for the required infrastructure 
• Retrofitting challenges in legacy data centres
• A potential need to redesign data centre layouts 
• Scarcity of cooling fluid & the skills needed to install and maintain the equipment
• The fluid currently required for two-phase cooling is harmful and not environmentally friendly

While these are significant challenges to immersion cooling moving into the mainstream, there is currently no obvious alternative that looks like it could deliver the step reduction in energy consumption data centres need. 

Immersion cooling is already a key enabling technology for Crypto Mining and green field sustainability deployments. Looking beyond overall data centre power consumption, there are specific factors driving the accelerated move to immersion liquid cooling systems.

Higher rack-power densities — Generative AI, ML & HPC workloads increase data compute performance needs. This in turn drives requirements for higher rack-power densities. As rack-power density increases, it becomes harder to cool efficiently with air cooling methods. Liquid-based methods, and primarily immersion cooling, may become the only viable solution.

Edge computing — Edge computing delivers more processing power and speed across a growing number of geographically widespread endpoints, by placing this capacity closer to the point of consumption. It's a market that is predicted to double in size between 2023 and 2028⁶.

Immersion cooling could greatly reduce the space footprint needed for a data centre, and deliver quieter data centres with less environmental impact. All of these are key criteria for delivering the small, local data centres that edge computing demands.

Sustainable, greener data centres — Immersion cooling technologies have the potential to play a key role in the data centre industry reaching its 2030 net zero target, while improving water usage effectiveness and reducing power consumption.

I'm keen to hear other thoughts on immersion cooling — reach out to me on LinkedIn, where I'll be glad to continue the conversation.