Rethinking Glycol Use in Closed-Loop Data Center Cooling Systems

Key Takeaways

• Many data center cooling specifications still reflect inherited design assumptions developed before today’s density, efficiency, and liquid-cooling demands.
• Corrosion resiliency should start with a closed-loop water treatment strategy that manages actual risk factors such as dissolved oxygen, entrained air, water chemistry, contaminants, filtration, and monitoring.
• As cooling requirements evolve, teams should reevaluate whether 25% propylene glycol belongs in technology water loops by default or whether it has simply been carried forward from prior projects.
• Glycol can be valuable when freeze protection is required, but it should not be treated as a substitute for root-cause corrosion control.
• Engineers, owners, and operators should separate corrosion treatment from freeze protection so fluid selection reflects the actual operating risks of each loop.

Many data center technology water loop specifications still carry forward design assumptions that were established before today’s density, efficiency, and liquid-cooling demands. If a specification had worked for a major hyperscale operator, it became a safe reference point for the next project. One of the most important to revisit is the routine use of 25% propylene glycol when the loop has no clear freeze-protection requirement. Corrosion resiliency should start with a closed-loop water treatment strategy designed to control the loop’s actual risk factors, including dissolved oxygen, entrained air, water chemistry, contaminants, filtration, and monitoring. If glycol is specified mainly as a corrosion-resiliency habit, teams may be accepting penalties in heat transfer, pumping energy, maintenance, and lifecycle performance without addressing the conditions that actually drive corrosion. Owners, designers, and OEMs should be asking whether glycol belongs in the loop because the application truly requires freeze protection, or because the specification has simply been carried forward. 

What Does Glycol Actually Do in a Cooling Loop?

Glycol lowers the freezing point of water-based heat-transfer fluids, making it useful when a cooling loop faces legitimate freeze exposure. In many data center cooling specifications, however, glycol is accepted because it is familiar rather than because the application clearly requires it.

Specifying glycol is not inherently wrong, but its primary function is freeze protection. If a technology water loop operates year-round inside a conditioned data center environment, the specification should identify a specific freeze-risk scenario before accepting the performance tradeoffs that come with a glycol blend.

As propylene glycol concentration increases, specific heat generally decreases, meaning the fluid carries less heat per pound per degree of temperature change than water. Viscosity also increases, especially at lower temperatures and higher concentrations, which can increase pressure drop and pumping requirements. ASHRAE Handbook data shows aqueous propylene glycol solutions becoming more viscous as concentration rises and temperature falls.

In applications with real freeze exposure, those tradeoffs may be justified. But as AI infrastructure increases pressure on cooling performance, efficiency, and sustainability, the industry has an opportunity to revisit long-standing assumptions and determine whether they remain aligned with current operating conditions.

Does Glycol Prevent Corrosion in Closed-Loop Systems?

Glycol does not, by itself, prevent corrosion in closed-loop systems. Inhibited glycol can help manage corrosion risk in the right application, but it cannot eliminate the root causes of corrosion or substitute for oxygen control, chemistry management, filtration, and monitoring. When a glycol specification is inherited rather than questioned, facilities may end up relying on a substance to solve a problem it was not primarily intended to solve.

Corrosion in closed-loop systems is an electrochemical process, not a single water-quality defect. The NIH Office of Research Facilities technical bulletin on closed-loop water systems explains that corrosion requires several conditions, including an anode, cathode, electrolyte, and electrical connection, and that corrosion can reduce efficiency, reliability, system longevity, and maintenance performance.

That is why a glycol specification alone is too blunt an answer. A stronger corrosion strategy starts by specifying how the loop will control oxygen, chemistry, contaminants, and particulates over time—not by assuming glycol will provide that protection by default.

Where Do Most Current Cooling Specifications Fall Short?

Many teams still approach corrosion control as a set of inherited requirements rather than a response to the loop’s actual risk profile. PG25, inhibitors, testing, filtration, and maintenance can all have a role, but they should be tied to specific corrosion drivers—not carried forward as independent checklist items. Oxygen control, water chemistry, filtration, and monitoring each address a different part of the problem. Glycol does not perform all of those jobs.

Glycol, inhibitors, testing, filtration, and maintenance each have a legitimate role in closed-loop system care. The problem comes when they are treated as separate checklist items instead of parts of a coordinated water treatment strategy. To improve corrosion control, that strategy should focus on the causes of corrosion—not only on monitoring conditions or managing symptoms after they appear.

The common barrier is risk avoidance. Engineers and owners are understandably reluctant to move away from specifications used by major market leaders, particularly in mission-critical environments. A root-cause treatment strategy gives teams a more defensible way to ask whether PG25 is actually required for the loop in front of them. 

How Should Data Center Teams Evaluate Glycol Usage Going Forward?

Data center teams should evaluate glycol use by first specifying the closed-loop water treatment system the application actually needs.

Once corrosion control is addressed at the source, the freeze-protection question becomes clearer: does this loop need glycol to prevent freezing? If the answer is yes, glycol may be appropriate. If the answer is no, the team should evaluate the specification against a different set of criteria:

 

• What water treatment system is required to manage the loop’s actual corrosion drivers?
• How will dissolved oxygen and entrained air be measured, controlled, and prevented from re-entering the loop?
• What chemistry limits, treatment methods, and inhibitor-monitoring practices are required for the materials in the loop?
• What level of filtration is needed to manage magnetite, scale, debris, and corrosion byproducts?
• What monitoring plan will confirm that oxygen, chemistry, particulate, and inhibitor conditions remain within acceptable ranges over time?
• Does the glycol specification reflect current operating conditions, or was it carried forward from a prior project?

  

This gives teams a more practical decision path: specify treatment for corrosion resiliency first, then decide whether freeze protection still requires glycol.

When glycol is not required for freeze protection, reducing or eliminating it may offer several practical benefits:

 

• Improved heat-transfer performance by relying on water’s higher specific heat compared with glycol blends.
• Lower pumping energy because water has lower viscosity than propylene glycol mixtures.
• Reduced maintenance complexity by removing the need to manage glycol concentration, degradation, and inhibitor compatibility where those controls are not needed.
• Simpler wastewater and disposal planning during flushing, maintenance, or decommissioning because glycol-containing fluids may require special handling and cannot be assumed suitable for ordinary discharge.
• Clearer sustainability accounting by avoiding an additive that may increase energy demand and create additional waste-management considerations without solving the root corrosion problem.

Conclusion

Data center growth is forcing the industry to revisit long-standing assumptions about power, cooling, density, resilience, and sustainability. The strongest organizations will align treatment strategy, fluid selection, and operating risk so technology water loops support long-term reliability, efficiency, sustainability, and performance.

Glycol remains important where freeze protection is required. However, in continuously conditioned environments, facilities should explore the benefits of specifying closed-loop water treatment systems to address the actual causes of corrosion. Then, determine whether glycol is still needed for freeze protection based on the loop’s operating conditions.

 

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About the Author

Dean Freije

Vice President, Sales - EasyWater®, a Watts Brand | [email protected]

 

With more than 20 years of experience in the water treatment industry, Dean has been instrumental in driving EasyWater’s growth and expanding its market presence since joining the company in 2005. A recognized leader in commercial and industrial water treatment, Dean specializes in strategic business development, sales leadership, and advanced treatment solutions for domestic water, HVAC, and high-purity water systems. He is passionate about helping customers solve complex water challenges through innovative technologies that enhance system performance, reliability, and operational efficiency.