How to reduce water consumption in data center cooling systems

In data centers, water consumption is almost exclusively dedicated to the cooling needs of IT rooms. Most data centers use a chilled water loop to absorb the heat generated by IT equipment. The water is cooled by electrically powered chillers or, sometimes, by fresh outdoor air through a free chilling system. The cold water, which is used to blow cooled air onto IT equipment, heats up as it exits the IT rooms, returns to the chillers, and so on. The chilled water circuit operates in a closed loop. Therefore, initial water consumption only occurs during the commissioning of the data center.

Systems like free cooling allow data centers to be cooled without using water. They directly capture fresh outdoor air to blow it into the IT rooms.

Water consumption in data centers only increases when outdoor temperatures rise above a certain threshold and the need for cooling becomes greater: under these conditions, in addition to existing cooling installations (chillers, free chilling, or free cooling), a water droplet spray system (called adiabatic cooling) can cool the air by a few additional degrees.

With this method, which avoids oversizing installations and higher electricity consumption, some of the water evaporates. And the figures can be considerable: in its 2022 environmental report, Microsoft, for example, announced that it consumed 6.4 million m³ of water for all its data centers worldwide, equivalent to 2,500 Olympic swimming pools 2 meters deep. Google, for its part, revealed that all its data centers would have consumed 15 billion liters of water in 2021. The intensification of digital uses and the densification of servers within IT rooms (with the development of AI, for example) lead to ever-increasing cooling needs.

Just a few years ago, water was not considered a precious resource, especially in temperate regions of the world. Data center operators therefore prioritized increasing water consumption over electricity consumption to cool IT rooms. However, ongoing climate change has made water a scarcer resource, and its competing uses are becoming increasingly numerous, particularly in high-density areas: water for human consumption, water for hygiene, water for agriculture, industrial water, etc.

To reduce water consumption related to adiabatic cooling, many alternatives or bypass solutions are available today.

To reduce cooling needs, data center operators are notably working on:

• The increase in IT room operating temperatures, with equipment capable of withstanding higher operating temperatures than before;
• Improving the management of cold and hot air flows in IT rooms;
• The urbanization of rooms to rationalize spaces and limit the volumes to be cooled.

But these solutions do not solve everything: cooling remains necessary. The data center sector is therefore constantly seeking innovations to generate the least possible environmental impact and limit water consumption:

• Increased cold production by refrigeration units: this solution considerably increases the electricity consumption of chillers but ensures the required cooling capacity without consuming water.
• River cooling: depending on the geographical location of the data center, it is possible to use surface water for its cooling. The water extracted is discharged without being stored. There is therefore no depletion of groundwater or rivers. However, it is necessary that the discharged water, which is warmer, does not disturb natural ecosystems, and authorization is required.
• Direct Liquid Cooling: a water loop passes directly through the core of the servers to cool them. This system is very efficient because it is closest to the heat-producing equipment, water consumption is zero because it is a closed loop, but this system requires specific IT equipment.
• Immersion cooling: IT equipment is immersed in tanks of water or oil that effectively dissipate the heat produced. This cooling method does not consume water (closed circuit) but requires material and organizational adaptations, and new skills.

Furthermore, data centers, like other types of buildings, can also, with adequate treatment and filtration, implement the reuse of certain waters, or even rainwater harvesting. With the risk, in the latter case, of facing criticism related to the capture of water that no longer flows into groundwater.

We can no longer do without digital services. On the contrary, uses tend to intensify, and IT equipment to densify. This is particularly true with the development of artificial intelligence, which requires considerable computing power. This implies ever more servers, data centers, and therefore increased cooling needs.

While alternatives to adiabatic cooling exist, and can even be combined, not all these alternatives are necessarily possible or relevant depending on the data center's location (geographical location, dedicated building or not, etc.), its surroundings (presence of surface water, use of waste heat for heating, etc.).

More broadly, it is necessary to conduct upstream studies for new construction and renovation projects to size them as accurately as possible and determine solutions that reduce the environmental footprint. It is also important to evaluate environmental impact transfers when selecting an alternative cooling solution. For example, reducing water consumption by increasing electricity consumption in a country where electricity is produced by burning fossil fuels, leading to additional greenhouse gas emissions, is not virtuous.

By Jessica Le Goff, Sustainable IT Project Manager, APL Data Center.