Data Centers Adopt Cooling Towers for Energy Efficiency

As massive data flows flood into the cloud, fueling rapid digital economic growth, data centers are proliferating worldwide. However, the enormous computing power supporting these facilities generates staggering amounts of heat. Efficient heat dissipation has emerged as a critical challenge for sustainable data center operations. Cooling towers, long considered controversial for their water usage, are being reevaluated as essential components that may actually contribute to greener data infrastructure when properly implemented.

Data center cooling solutions vary significantly depending on multiple factors including facility size, computing requirements, regional energy costs, and data load density. The primary cooling approaches include:

• Water-cooled chillers: Systems incorporating chillers, pumps, cooling towers, and plate heat exchangers that dissipate heat through evaporation.
• Air-cooled chillers: Simplified systems using only chillers and pumps that rely on air for heat rejection.
• Direct evaporative cooling: "Swamp cooling" systems employing wet media that leverage water evaporation without mechanical refrigeration.
• Adiabatic cooling: Hybrid systems combining air and water cooling, using water-assisted cooling during peak demand periods.

Operators must consider both operational costs and environmental impact when selecting cooling solutions. Two key metrics guide these decisions: Power Usage Effectiveness (PUE) measuring total energy consumption relative to IT equipment usage (with 1.0 being ideal), and Water Usage Effectiveness (WUE) evaluating cooling system water consumption.

While cooling towers consume water through evaporation, industry experts argue this must be evaluated against broader energy system impacts. Tim Chiddix, Mechanical Engineering VP at Swanson Rink, emphasizes that cooling technology selection requires localized analysis considering climate conditions, energy infrastructure, and operational requirements.

A comprehensive evaluation must account for water consumption throughout the entire energy chain. Traditional power plants like coal facilities consume substantial water during electricity generation. While air-cooled systems reduce on-site water use, their higher energy demands indirectly increase water consumption at generation facilities. In many cases, mechanical evaporative cooling systems demonstrate superior overall efficiency compared to air-cooled alternatives.

For example, an air-cooled system consuming 1 MW annually versus a water-cooled system using 0.5 MW with 3,000 gallons per minute water consumption might actually conserve more water when accounting for the additional generation requirements of the less efficient air-cooled option.

A white paper co-authored by Chiddix and Brook Zion, "Data Center Water Usage in Denver, Phoenix, and Los Angeles: The Big Picture," examined whether reducing water consumption at individual facilities truly decreases regional water usage. The study found water's superior heat transfer capabilities make it more efficient than air for cooling, though effectiveness varies by climate with arid regions benefiting most.

Analyzing 1,500 kW sample data centers in three cities while incorporating local grid water intensity data from the National Renewable Energy Laboratory, researchers compared three systems: standard water-cooled chillers, air-cooled chillers, and evaporative cooling. Results showed air-cooled systems required significantly more energy (4,663,740 kWh annually in Denver versus 1,610,748 kWh for water-cooled systems), with nearly all water consumption shifted to power generation facilities rather than being eliminated.

Chiddix cautions that well-intentioned local regulations mandating reduced on-site water and energy use may inadvertently increase total resource consumption when accounting for power generation impacts. Water-cooled systems often prove more efficient, particularly when incorporating "free cooling" (or water-side economizer) modes that leverage cold outdoor air to chill water without mechanical refrigeration, potentially reducing energy needs by 75% or more during favorable conditions.

Variable flow technology allows operators to reduce water flow from cooling towers during cooler seasons, with adjustable fan speeds providing additional energy savings. Modular cooling tower designs offer further benefits, enabling capacity expansion aligned with server growth while controlling capital and operating expenses. Prefabricated modular systems also support faster deployment critical for time-sensitive data center projects.

As data centers continue expanding globally, comprehensive evaluation of cooling solutions must consider both direct and indirect resource consumption. When properly implemented with a systems-level perspective, water-based cooling solutions can deliver superior efficiency, supporting the development of sustainable digital infrastructure while conserving both energy and water resources.