Data center cooling systems and what they ask of a site

What a data center cooling system does

A data center cooling system moves heat out of the servers and then out of the building. Every design has two halves. One carries heat away from the servers, by air or by liquid. The other rejects that heat outdoors, through evaporation, chillers, or dry coolers.

The buyer’s mechanical engineer picks the design. The site limits which designs stay on the table. For how much water each design draws, see data center water usage.

Air cooling with chillers

Air cooling with chillers works by blowing cool air across the servers and returning warm air to cooling units. Chillers remove heat from a water loop that serves those units. Air-cooled chillers reject the heat to outdoor air with fans, so they use little water and more electricity.

What it asks of a site. Pad space for chillers, enough electrical capacity for their load, and room between the equipment yard and homes for fan and compressor noise.

Evaporative cooling

Evaporative cooling works by evaporating water, which carries heat away as it turns to vapor. Cooling towers and direct evaporative units both use this method. It uses the most water and often the least electricity.

What it asks of a site. A steady water supply, sewer capacity for the concentrated water the towers drain, and space for water treatment equipment. Towers also make noise and can release a visible plume.

Closed-loop systems

Closed-loop systems work by circulating water or coolant in a sealed loop that rejects heat through dry coolers. The loop needs little makeup water once it is filled. The coolers draw more electricity on hot days, because air alone carries less heat than evaporation.

What it asks of a site. A large yard or roof area for dry coolers, little from the water and sewer systems, and distance or screening for fan noise.

Liquid cooling at the rack or chip

Liquid cooling works by bringing coolant to the rack or directly to the chips. Rear-door heat exchangers cool at the rack. Cold plates and immersion tanks cool at the chip. These designs handle denser, hotter equipment than air can.

What it asks of a site. The heat still leaves through chillers, towers, or dry coolers, so the site must meet their needs, plus more power for each building, because denser racks draw more load.

Hybrid designs

Hybrid designs combine methods to balance water and electricity. Some campuses run dry for most of the year and switch to evaporative cooling in peak heat.

What the site decides

The site decides which cooling designs are practical.

• Water supply. Evaporative designs need a provider that can serve a large, steady demand.
• Reclaimed water. A reclaimed line can supply cooling water without drawing on drinking water.
• Wastewater capacity. The sewer system must accept tower drain water in volume and chemistry.
• Equipment space. Chiller and dry cooler yards need flat ground inside the setbacks.
• Distance from homes. Fan and tower noise travels, so layout and buffers matter. See data center noise.
• Local rules. A county or town may favor closed-loop designs or require disclosure of water use. See zoning and moratoriums.

The public record shows water and sewer lines, service areas, and ordinance text. It cannot show spare capacity or the terms for a large user. The water and sewer provider confirms those, and the mechanical engineer confirms what a design needs.

Questions

Which data center cooling system uses the least water?

Air-cooled chillers and closed-loop dry systems use the least water. They draw more electricity, especially on hot days.

Does liquid cooling remove the need for water?

No. Liquid cooling moves heat away from the chips well, but the building still rejects that heat outdoors. Whether that step uses water depends on the outdoor equipment.

Can a site change its cooling design later?

Sometimes. A new building on a campus can use a different design if the site has the water, sewer, power, and space for it. The mechanical engineer and the providers confirm what fits.