Water is the most energy-efficient cooling medium available for data centers. However, like the Earth’s land, there is a finite amount of water. Restrictions on water use are rising as water scarcity is becoming a global concern.
Enhanced data center cooling systems are becoming more necessary as the demand for AI rises. Data center architects are designing modern data centers to use significantly less water, but replacing water cooling with traditional cooling methods increases energy demand.
This article explores how data centers can reduce their water footprint by adopting recycling methods, such as water reclamation and using natural resources.
Water reclamation
Water reclamation is the use of treated stormwater and wastewater. Once treated, data centers can use reclaimed water for their cooling systems, potentially recycling millions of gallons of otherwise wasted water annually.
Stormwater retention
Stormwater retention collects rain runoff from roads and rooftops into a basin or water tank. Rain runoff has contaminants and sediment, so filtration and treatment are necessary before integrating it into cooling systems. Water treatment involves filtering out impurities like sediment, chemicals and bacteria to mitigate blockages, microbial growth and corrosion within the system.
Underground basins minimize evaporation loss and further contamination. Flood zones are not ideal for data center locations. However, with proper supervision and planning, being near a flood zone can be beneficial. Basins can capture water from nearby areas prone to flooding, which would help drain the low-lying land and replenish the data center’s water supply.
The cooling capacity depends on the amount of water captured and the cooling system’s efficiency. Recycling water back into the holding basin can further minimize water loss, so long as the basin is large enough to avoid a temperature increase when the warm water reintegrates.
Wastewater reclamation
Buildings with kitchens and laundry facilities produce significant amounts of usable wastewater, or gray water, that is usually dumped into sewers. Data center cooling systems can use gray water. Advanced plumbing designs are necessary to isolate highly contaminated water, or black water. On-site treatment systems then purify gray water to meet the quality requirements of data center cooling infrastructure.
Data centers can also partner with public utilities, such as wastewater treatment plants, to use treated wastewater that would otherwise be discharged into natural waterways.
Geothermal cooling systems
Geothermal cooling is the most sustainable method, reducing water and energy consumption while providing year-round cooling capacity. Its efficacy depends on soil conditions, particularly moisture content. According to the National Renewable Energy Laboratory, underground soil temperature remains steady year-round, around 55 degrees Fahrenheit — or 12.8 degrees Celsius. Because this is far lower than the discharge temperatures of ITE cooling systems, transferring heat to the Earth is highly efficient.
Two fundamental types of geothermal cooling systems exist: well-based and water-based. Both methods recirculate water through closed-loop piping structures.
Well-based geothermal cooling
Well-based cooling requires minimal water consumption and works in locations with limited natural water sources.
Well-based geothermal cooling uses 150-foot to 500-foot-deep vertical boreholes. Pipes in the boreholes run through the data center and extend into the ground, creating a closed-loop system. The coolant absorbs heat as it circulates through the data center, and the heat transfers into the Earth when the coolant passes through the underground pipes.
Water-based geothermal cooling
Water-based geothermal cooling uses existing water sources, such as aquifers, lakes or underground reservoirs, as heat exchange mediums. This method offers cooling efficiency when suitable water sources are available and can be implemented as an open or closed-loop system.
An open-loop water-based cooling system circulates water from a natural source through a data center’s cooling system and heat exchangers. The water then returns to its source at a slightly higher temperature. A closed-loop water-based cooling system involves circulating coolant through pipes in natural water sources, where heat from the data center transfers into the natural water source — the coolant and natural water source never mix.
Water-based geothermal cooling requires less drilling than well-based cooling, but it depends on proximity to appropriate water bodies and must comply with environmental regulations regarding thermal discharge limits.
Using natural resources requires owner permission — private, corporate or government. Environmental studies and impact statements are also necessary to ensure rising water temperatures won’t harm fish or natural organic material. Once accomplished, however, it’s a highly efficient means of heat removal.
Robert McFarlane is the Senior Principal in charge of data center design for the international consulting firm Shen Milsom and Wilke LLC. McFarlane has spent more than 40 years in communications consulting and has experience in every segment of the data center industry.
