Energy efficiency and operational running cost continue to be key drivers of innovation. Furthermore, when we consider that current mechanical cooling technology is responsible for up to 55% of a Data Centre’s energy consumption, industry demand is rising for more efficient solutions. Could immersion cooling be the answer?
Drawing on general media comment, customers are still unsure about this technology. Typically, liquid and electricity are known as a potentially high-risk combination, and many are uneasy about such pairing in technology. However, in order to allay any misconceptions, it is important to understand all the facts, not least the potential this technology might offer us.
So, what is immersion cooling?
To explain in simple terms, immersion cooling is achieved by submerging the hardware (IT rack mounted equipment) in a non-conductive liquid (known as dielectric) to cool it rather than circulating cold air over or through it. The liquid is circulated through cool heat exchangers to maintain the low temperature.
There are three types of immersion cooling:
1. Single-phase circulation: The equipment is directly immersed in the Dielectric liquid (hydrocarbon synthetic oil), the heat is transferred to the fluid, the liquid is cooled via a water-cooled heat exchanger and then returned to the immersion tank (see fig.1 below).
Fig 1. Single-Phase Liquid Immersion Cooling System
2. Two-phase immersion: The equipment is submerged in a liquid (fluorocarbon based) that has a low boiling point (50°C), the fluid boils on the surface and rising vapour passively disperses the heat. NB. More expensive than single phase.
Fig 2. Two-Phase Liquid Immersion Cooling System
3. Direct-to Chip Cooling: This method of immersion cooling is a little different but can be implemented using either single-phase or two-phase cooling technologies. The system releases heat from the components by pumping the liquid through the cold plates attached to the rack components. The liquid utilised can be either Dielectric or non-Dielectric as it does not come into direct contact with the electronic components.
What are the benefits of immersion cooling?
- Negligible risk of hot spots: The submersion of the equipment reduces the possibility of hot spots.
- Long thermal ride through: In terms of traditional air cooling, should there be an air flow reduction due to a fan failure, etc, the hardware will rapidly overheat possibly leading to component failure or even system shutdown before the problem can be rectified. Immersion cooling facilitates longer cooling periods due to the thermal mass of the liquid.
- Cost efficiency: Eliminating the need for fan supplied air and fans, the cost of energy consumption and maintenance is drastically reduced. Additionally liquid cooling systems require less floor space and 95% of the waste heat generated can be more easily recovered and reused in commercial heat networks reducing the carbon footprint of the facility.
- The system can run at higher chilled water temperatures: This would be typically 60 °C as opposed to 30degC for an average system. This higher-grade heat allows for improved heat reclamation and use in a heat network.
- Density and space requirements: Immersion and other “liquid cooling” systems can allow rack loads to be deployed more densely as the water medium is more efficient at removing heat. Therefore the “white-space” requirement in a liquid cooling data hall could be greatly reduced in comparison to an air cooled system of the same power deployment.
What are the drawbacks?
- Resilience: Will need to consider what resilience is required in the central distribution unit (CDU), a unit that uses local valves and pumps to remove heat from the liquid cooling system. Will there be a transitional period with both air cooling and on-chip cooling?
- Return temperatures: What impact will the high chilled water return temperatures have on the Chillers, new or existing? Mechanical cooling systems will need to be modified to achieve greater temperature changed across the chilled water system, although less water will need to be pumped than in a traditional data centre chilled water system.
- Complex installation: A professional installation is required. Novel and unfamiliar technologies can introduce risk into a project.
- Expensive to install: Potential improvements in energy efficiency are likely to save money in the long run, however installation costs are less clear cut. Systems that use both air and water, could result in high installation costs.
- Equipment failure: If any part of the immersion system fails, it can damage the hardware, therefore proper consideration will need to be given to system resilience. Back-up systems such as UPS (Uninterruptible Power Supplies) could inflate the overall cost of the installation.
Why use this technology in data centres?
Immersion cooling can reduce overall mechanical cooling electricity demand by circa 70-80% (Craig, as cited in Pressley, 2021) depending on how efficient the installation already is. This efficiency could be comparable with with IDEC (Indirect Evaporative Cooling) systems that use a significant amount of water during high external ambient temperatures. Conservation of water is a is an important sustainability factor.
Higher operating water temperature make rejection of heat easier in warmer climates therefore this form of cooling is relatively efficient regardless of where the Data Centre is located, and as such allows for a more flexible deployment. This is particularly important for areas with high annual ambient temperatures, although in some climates this could be accompanied with increased evaporative cooling and associated water consumption.
Reduction to climate impact
As mentioned in sustainability above, immersion cooling, when deployed correctly is likely to be more power efficient than traditional cooling methods and there are numerous ways to eliminate water wastage through the incorporation of dry coolers.reuse waste heat offsetting energy that would be used elsewhere.
Retro fitting immersion cooling systems to existing Data Centre installations
This can be tricky, there are several barriers to retro fitting immersion cooling to air cooled data centres.
- An existing Data Centre installation will require your IT team to manage both systems while the transition takes place which can be quite challenging.
- Dielectric liquid is a preferred for the system because it does not conduct electricity however there are some systems that use chilled or warm water which may increase the risk electrocution if there is a leak.
- As with any fluid, there may be a risk of corrosion over time.
- Immersion cooling systems, unfamiliar to contractors, can be challenging to install, maintain, and troubleshoot without the help of professionals which can incur additional maintenance costs.
It would be crucial to obtain advice from an immersion cooling specialist when thinking of retro fitting immersion cooling systems. Apart from the above points, the condition of the current technology may not allow for the transition and could require a substantial upgrade to the installation. Additionally, in order to keep costs down, the current rack arrangement may require repositioning which could impact floor space. These considerations may prove cost prohibitive with your present infrastructure.
It is also important to note that not all vendors support immersion cooling at present, although it is highly likely that this will change very soon. Therefore, it is still necessary to check with suppliers that their products can support immersion cooling or that the manufacturer will support their warranties.
Indeed, due to its efficiency and long-term energy cost saving, it is strongly expected that Immersion Cooling will become the most dominant cooling technology in Data Centres in the not-too-distant future.
How is JDA responding to these changes in technology?
Working in partnership with Immersion Cooling technology providers, we design our Data Centre systems to be “Liquid Cooling Ready” and, in doing so, we future proof systems to allow for possible changes with minimal impact to the Data Centre rack and equipment installation.
If you would like to discuss your current and future Data Centre system requirements, please get in touch. Our multi-disciplined Mission Critical team draw on over 15 years of knowledge and expertise in this specialist field.
Pressley, A. (2021, May 18). How is immersion cooling technology helping data centre operators to fulfil their sustainability goals? Intelligent Data Centres. https://www.intelligentdatacentres.com/2021/05/18/editors-question-how-is-immersion-cooling-technology-helping-data-centre-operators-to-fulfil-their-sustainability-goals/