Not all liquid is water when it comes to cooling

As the autumn days shorten, and the temperatures drop, the heatwaves across Europe in Summer ‘22 are becoming a distant memory. That may not be a good thing. The temperature extremes we witnessed are likely to continue and data centre operators need to be prepared.

When temperatures reach 40°C the amount of energy required to cool a data centre increases as the ambient temperature goes up. This poses a particular issue for traditional air-cooled data centres who can see their energy usage – and costs – skyrocket. The use of cooling towers and other evaporative cooling techniques for heat rejection are popular with larger data centres because of their high efficiency and large cooling capacity. However, they use evaporation which consumes vast amounts of water.

Water usage is becoming a controversial topic as many regions are starting to face regular drought conditions. Public pressure is being put on data centre owners to reduce their water usage. We saw that firsthand this summer when Thames Water announced they were going to launch a review of the impact of data centres on water supplies in and around London.

What has become obvious to me as a result of these discussions is that greater clarity is needed on how and why data centres use water in their facilities. Water has always been a part of the cooling infrastructure, whether it is circulating in the technical space underfloor and through air handlers or via a chilled water loop cooling the air that was moving around the room. Data centre operators should rightly be scrutinised for the type of water being used, non-potable vs potable, as well as the quantity given many data centre operators do not report on their water usage.

This type of water usage, however, primarily supports traditional air-cooling methods and technologies. Air cooling has long been the default standard within the industry, but its limits are quickly being reached. Accelerating chip thermal design power, as well as the rise of artificial intelligence, high performance computing and machine learning, are all pushing air cooling beyond its limitations.

This is where liquid cooling technologies come in. Precision immersion liquid cooling circulates small volumes of a harmless dielectric compound across the surface of the server removing almost 100% of the heat generated by the electronic components. This technology can significantly reduce or eliminate water usage from the cooling system design. Because they use warm water (up to 45⁰C) in a closed secondary loop for heat rejection, simple dry coolers can be used in most climates to reject the heat.

One of the challenges in the discussion about water usage within the industry is that the terms water cooling and liquid cooling become interchangeable, but they are not. After all, water is liquid, but not all liquid is water. Even the study that triggered discussions about data centre water usage this summer conflated the two terms. The lead analyst on the report from GlobalData was quoted as saying, “We have reached an environmental crunch point in the resources needed to run data centres. Switching to liquid cooling can cut a data centre’s electricity usage, but water is an increasingly scarce resource in drought-stricken parts of Europe and the US.” While the two halves of his statement are independently true, the implication leaves one to believe that all liquid cooling is water cooling.

Thankfully, when it comes to water usage, the industry is taking steps to remedy the problem. A self-regulatory initiative from the Climate Neutral Data Centre Pact has set a limit of 0.4 liters of water per kilowatt-hour of compute power (0.4l/kWh) deployed to ensure their members will rate among the most efficient globally for their use of water. Last year, Google announced they will replenish 120% of the water they consume across their offices and data centers by 2030. These are all positive steps in the right direction. Combined with solutions like liquid cooling that can be implemented now, the industry is looking to play its part the next time there is a major drought.