As artificial intelligence workloads continue to reshape data centre design, liquid cooling has become fundamental to supporting next-generation computing. Direct-to-chip (DTC) technology cooling systems (TCS) are increasingly being deployed to manage the rising thermal loads generated by high-performance computing (HPC) environments, offering more efficient heat removal at source.

However, as operators focus on cooling capacity, flow rates and hardware performance, one critical factor is often underestimated: coolant chemistry.

For many facilities, propylene glycol (PG) is treated as a static component of the cooling loop — a protective additive introduced during start-up and revisited only during scheduled maintenance. In reality, glycol concentration is an active operational variable that requires continuous oversight. If left unmanaged, it can become a source of system degradation rather than protection.

The challenge of passive glycol management

At its intended concentration, propylene glycol plays an important role in maintaining fluid stability. It helps inhibit microbiological growth and supports the overall protection of the cooling loop. However, that protection depends entirely on maintaining the correct concentration.

Propylene glycol is considered biostatic at concentrations of 25% v/v or higher, meaning that it prevents microbial growth. Below that threshold, its behaviour changes. Instead of suppressing microorganisms, glycol can become a carbon source that supports microbial activity.

This shift creates an operational blind spot. A cooling loop may appear healthy even while microbial contamination is actively developing within the system.

Laboratory incubation data reinforce this concentration-dependent relationship. Systems containing no glycol show rapid microbial growth, while those maintained at a concentration of 30% consistently suppress biological activity. Intermediate concentrations — particularly those between 1% and 10% — can still permit measurable microbial proliferation, creating conditions in which biodegradation can accelerate.

The takeaway is simple: glycol concentration is not merely a box to tick; it is a parameter that must be actively managed.

What happens when glycol breaks down

Glycol degradation can occur through thermal degradation or biodegradation, both of which can affect system performance. Biodegradation, however, can introduce a cascading series of operational issues that directly affect cooling efficiency.

As microorganisms metabolise glycol, they multiply rapidly and produce by-products that interfere with system operation.

Biofilm development

Microbial growth leads to the formation of biofilms on internal cooling-loop surfaces. In DTC systems, where cooling depends on efficient heat transfer through narrow channels and cold plates, these biofilms create an insulating barrier that reduces thermal performance. Over time, this build-up can restrict flow paths and increase system resistance.

Gas generation and flow disruption

Microbial metabolism can also generate carbon dioxide (CO₂). Even in low-oxygen environments, gas production can contribute to air entrainment, trapped gas pockets and flow interruptions, further reducing heat-transfer efficiency across the cooling loop.

In high-density computing environments, even small declines in cooling performance can create significant operational risks.

A smarter monitoring strategy

Protecting liquid cooling infrastructure requires operators to move beyond periodic coolant checks and adopt continuous system monitoring.

Although glycol concentration remains a core metric, operators should also monitor:

• microbial counts, to detect biological contamination at an early stage;
• pH and reserve alkalinity, to evaluate fluid-buffering capacity and corrosion potential;
• conductivity, to monitor dissolved solids and the ingress of contaminants;
• pressure differential, to identify early signs of fouling or flow restriction; and
• copper and iron levels, to detect active corrosion within the cooling loop.

Together, these indicators provide a more complete picture of cooling-loop health and allow operators to respond before system performance is affected.

From a maintenance task to an operational discipline

In modern liquid-cooled data centres, glycol management can no longer be treated as a routine maintenance task. It is a core operational discipline that directly affects system reliability, equipment longevity and uptime.

By using real-time monitoring technologies such as 3D TRASAR™ Technology for Direct-to-Chip Liquid Cooling, operators can shift from reactive troubleshooting to proactive fluid management. This enables them to maintain chemistry within target ranges, detect problems earlier and preserve cooling performance over time.

As AI infrastructure continues to scale, the facilities that succeed will be those that manage coolant chemistry with the same rigour they apply to computing, power and network performance.

In high-density cooling, long-term resilience depends on more than moving heat; it also depends on managing the chemistry that makes effective cooling possible.

This article is sponsored by Ecolab.