Let’s face it, data centers are one of the biggest energy hogs on the planet, often consuming as much as 50 times the energy of an office building of equal size. It has also been suggested that they are responsible for up to 5% of all global greenhouse gas emissions. Given the amount of their energy consumption, it is easy to see how even small improvements in energy efficiency can result in significant improvements to the environment.
Here we explore methods for making data center usage more sustainable and efficient. The first of these is the use of liquid immersion cooling technology.
What is liquid immersion cooling?
Liquid immersion cooling is a system for cooling data center hardware by submerging it in a thermal but non-conductive liquid that redirects heat into heat exchangers. This eco-friendly method prevents overheating more efficiently than air or water cooling. It has gained much traction in recent years, especially with the advent of cryptocurrency and high-performance computing.
A step up from air and water
Aside from increased efficiency and reduced energy consumption, liquid immersion cooling offers several advantages. Among these are easy installation and maintenance, less space usage and reduced operational costs.
The underlying principle of why this system is so efficient is that liquid is a much better conductor of energy than air. Liquid water, for example, conducts energy about 22.4 times as compared to air. But liquid type is also an important factor. Unlike with air and water-cooling systems, which were used in earlier generations of computers, liquid immersion cooling uses a dielectric liquid that absorbs heat through convection. Examples of this are mineral oil and virgin coconut oil, which have a high heat transfer coefficient, have a stable flow against disturbances and can cool components directly.
Single-phase vs. two-phase systems
There are two types of immersion cooling: single-phase (1-PIC) and two-phase (2-PIC). 1-PIC is where a dielectric liquid remains in the liquid state throughout the cooling process. Meanwhile, 2-PIC is where the dielectric liquid changes state and becomes a vapor.
Both liquid immersion cooling technologies eliminate the need for computer room air conditioning (CRAC), computer room air handler (CRAH) and chillers, with specific advantages over each other. For example, 1-PIC comes with a lower initial cost. However, when looking at total cost of ownership (TCO), the 2-PIC system is more favorable due to its slightly lower partial power usage effectiveness (pPUE).
With a 2-PIC system, 1.02 - 1.05 is an achievable yearly pPUE, depending on the climate, while 1.03 - 1.07 is possible for 1-PIC. Compared to the latter, 2-PIC offers greater cooling density (higher kW per rack unit), which can accommodate higher capacities per rack (over 250kW per rack). It also eliminates the need for a cooling distribution unit (CDU).
1-PIC servers are typically submerged in dielectric, hydrocarbon-based fluid similar to mineral oil with a comparatively higher boiling point. The liquid is in constant contact with the server boards, but it does not boil. It stays in its liquid state and is cooled in a forced flow manner by pumping the liquid past the heat sinks of the IT load, then through a heat exchanger in a CDU. Because it does not undergo a transformation from liquid to gas, it stays in one phase, or 1-PIC.
With 2-PIC, servers are immersed in a bath of dielectric, fluorocarbon-based liquid with a relatively low boiling point. This liquid is also in constant contact with the server boards. The heat boils the liquid, producing a gaseous vapor through phase change, hence the name 2-PIC. The gas is then condensed back into a liquid using water-cooled condenser coils at the top of the sealed rack chamber. Afterward, the condensed liquid is returned to the fluid in the bottom of the rack chamber to repeat the process.
Another consideration is server removal and maintenance. This is possible with both systems without disturbing and shutting down other equipment in the same bath. But there are differences in overall efficiency.
With a 1-PIC system, servers using hydrocarbon-based fluids will require a cleaning station to remove the excess fluid before work can be performed. On the other hand, the fluid used in 2-PIC will evaporate during removal from the bath and condense on the coils inside the system, which reduces fluid losses. Once removed, the server is ready to work on immediately. Typical fluid losses for 2-PIC systems are lower than 2% per year, maximizing efficiency.
The future of liquid immersion cooling
With pPUEs approaching unity, liquid immersion cooling is without a doubt the most sustainable and energy efficient method of cooling data centers. In today’s environmental, social, and corporate governance (ESG) market, liquid immersion cooling shows significant promise and is a strong contender in the race toward better and planet-friendly technology management.
Liquid immersion cooling technology is only the start. Read our upcoming blogs for more efficient and future-forward solutions in building a stronger, more sustainable data center industry.
