Why Glycol Stability Matters in Liquid-Cooled Systems

As AI and high-performance computing (HPC) drive rack densities higher, liquid cooling has become essential infrastructure in modern data centers. Direct-to-chip (DTC) Technology Cooling Systems (TCS) are increasingly used to manage rising thermal loads, but they introduce a less visible operational risk: maintaining the biological stability of the cooling loop.

Many operators still view propylene glycol (PG) as a passive additive introduced during startup to protect the system over time. In reality, glycol concentration is a dynamic variable that directly impacts cooling system health, efficiency and reliability.

When glycol stops protecting the system

One of the biggest misconceptions in liquid cooling is that coolant chemistry remains stable once a loop is charged. Maintaining the proper glycol concentration is critical to preventing microbial contamination.

Water alone is highly vulnerable to microbiological growth, which is why glycol is added to technical cooling loops. However, propylene glycol is only biostatic – meaning it inhibits bacterial growth – at concentrations of 25% v/v or greater. Below that threshold, glycol can become a carbon source, effectively serving as food for microbes.

At suboptimal concentrations, the very fluid meant to protect the system can instead fuel microbial growth.

Laboratory incubation data show a clear relationship between glycol concentration and microbial proliferation. Systems with 0% glycol show the fastest growth, while systems maintained at 30% concentration consistently suppress microbial activity across organisms including E. coli, S. pyogenes, C. albicans and S. aureus. Intermediate concentrations between 1% and 10% offer inconsistent protection and can still permit measurable biological activity.

For operators, the takeaway is straightforward:

• Maintaining glycol at protective concentrations helps reduce microbial colonisation and biofilm formation. 
• Operating below recommended levels can accelerate biodegradation and create downstream system issues.

The impact of biodegradation

Glycol degradation typically occurs in two ways: thermal degradation and biodegradation. Both can affect coolant performance, but biodegradation creates unique operational risks because microbial activity can quickly compromise loop efficiency.

Biofilm and clogging

As microbes multiply, they form biofilms that adhere to system surfaces. In DTC cooling loops, these films can coat cold plates and narrow microchannels, creating an insulating barrier that reduces heat transfer efficiency. Over time, buildup can restrict flow and limit cooling performance at the chip.

CO2 and air entrainment

Microbial metabolism also produces carbon dioxide (CO2). Even in lower-oxygen environments like DTC loops, biodegradation can generate gas that contributes to air entrainment, trapped gas pockets and flow disruptions – further reducing thermal transfer efficiency.

Monitoring beyond glycol percentage

Measuring glycol concentration is essential, but it is only one indicator of loop health. Protecting high-value computing infrastructure requires a broader monitoring strategy that includes:

• Glycol concentration – Confirms the system remains above the 25% biostatic threshold 
• Microbial counts – Identifies contamination before biofilm buildup occurs 
• pH and reserve alkalinity – Measures buffering capacity and corrosion risk 
• Conductivity – Tracks dissolved salts and contamination ingress 
• Pressure differential – Detects early signs of blockage or pump performance issues 
• Copper and iron levels – Indicate active corrosion inside the loop 

Together, these measurements provide a more complete picture of coolant health and system performance.

A more proactive approach

In AI-driven facilities, uptime depends on more than compute power – it depends on the chemistry supporting thermal management behind the scenes.

A reactive maintenance model is no longer enough. Continuous monitoring allows operators to detect coolant degradation early, optimise dosing and maintain consistent cooling performance over time.

Solutions like 3D TRASAR™ Technology for Direct-to-Chip Liquid Cooling help shift coolant management from periodic inspection to real-time optimisation, supporting greater efficiency, equipment protection and long-term loop stability.

The takeaway is clear: glycol management is not a maintenance afterthought – it is a critical operational function that directly impacts the reliability and resilience of liquid-cooled data centre infrastructure.

Ecolab is a global leader in fluid management and cooling technologies for data centres and high-performance computing. Visit Ecolab's website to learn how they can partner with your organisation to maximise cooling system performance and lifespan from design to operation.