When glycol loops go bad

David McKune, corporate account manager of Ecolab EU, a global sustainability leader offering water, hygiene and infection prevention solutions and services, discusses the hidden risks of ignoring coolant health in AI-era data centres.

As AI workloads increase, rack power densities are rising. Racks that once drew a few kW are now routinely operating at tens and, in specialised cases, hundreds of kW. 

That density is driving a rapid shift to liquid cooling architectures that remove heat at the chip. Many of those deployments rely on propylene-glycol blends in secondary or row loops to control freeze/boil points and protect pumps and plumbing.

And glycol works well doing this — until it doesn’t.

When glycol loops are pushed to new temperature and duty extremes, small chemistry and cleanliness issues stop being nuisances and become operational threats. Field experience across early direct-to-chip (D2C) rollouts shows a worrying pattern – a sizeable share of sampled glycol loops begin life out of ideal specification.

The practical consequences are familiar to HVAC pros who’ve seen scale, corrosion and biological fouling in chillers – except cold-plate channels are far less forgiving than a condenser pipe. A single particle or a localised corrosion spot can reduce flow through a cold plate, raise local temperatures, and cascade into performance loss, warranty exposure, and expensive rack rework.

Several factors make modern glycol loops more vulnerable than traditional facility systems:
• Tighter hydraulics. Cold plates and rack manifolds contain sub-millimetre passages. Even tiny particulates or deposits can restrict flow.
• Higher sustained temperatures and thermal cycling. Elevated and variable return temperatures accelerate inhibitor consumption and chemical reactions that change fluid properties over time.
• Mixing and logistics variability. Glycol fills are often performed from multiple totes and by different crews; concentration and inhibitor packages can vary across fills unless intake is strictly controlled.
• Microbial risk in stagnant zones. Warm, low-flow dead legs invite biofilm that reduces heat transfer and resists remediation.

Each of these can translate into clogged channels, accelerated corrosion, biofouling, and, ultimately, leaks or unplanned downtime. Today, these outcomes are operationally acute rather than theoretical.

Regional considerations

The technical fundamentals are global, but regional realities change priorities. In Europe, tightening environmental and wastewater rules, strong corporate ESG targets, and a focus on circular water use mean operators must think harder about flush-water handling, biocide  selection, and documented discharge approvals. Demonstrable telemetry and auditable commissioning records make regulatory conversations far smoother and support claims around WUE and lifecycle impact.

In the Asia-Pacific region, hyperscale growth and constrained site conditions multiply the operational challenge. Tropical climates limit free-cooling windows in some markets, while rapid roll-outs in water-stressed locales make freshwater conservation a higher priority. Distributed edge deployments across APAC also mean many small sites with limited on-site expertise, increasing the appeal of telemetry and standardised commissioning playbooks that can be applied repetitively.

Likewise, the Middle East and Africa present a distinct mix of opportunity and risk. Many European design houses and integrators work extensively in MEA, and a significant portion of recent European investment is backed by Middle Eastern capital — yet local operating conditions and water regulations can differ markedly from Western or APAC norms. In parts of the Middle East, extreme temperatures and constrained freshwater supplies make closed-loop performance and alternative water sourcing essential design considerations. 

In Africa, rapid growth and varying levels of local technical capability mean commissioning discipline and capacity building are often as important as the technical solution itself. There is also a noticeable gap in local knowledge and operational experience in some markets – a gap industry partners and experienced service providers are well placed to bridge.

Put simply, Europe’s regulatory lens, APAC’s scale and site constraints, and MEA’s water and capability profiles raise different imperatives, but all benefit from the same engineering discipline – documented commissioning, continuous monitoring and planned wastewater handling.

A handful of practical controls reduce risk dramatically when applied consistently.

1. Treat the loop like a process plant at day one.
Pre-commissioning is the most cost-effective risk control: hydrotest → staged filtration → flush → verify. Use “procedure water” meeting defined conductivity/turbidity targets, and document acceptance before handover.

2. Staged filtration to protect small passages.
Begin with coarse filtration to remove construction debris, then progress to finer filtration. A practical final filtration target in many D2C projects is in the low single-digit micron range; staged filtration avoids premature filter clogging while protecting narrow cold plates.

3. Flow-rate discipline during flushing and layup.
Industry practice points to flushing velocities (eg ~3–5ft/s in many line sizes) that mobilise sediments and ensure effective mass transfer. Low-velocity flushing leaves particulates adhered and increases the risk of later blockages.

4. Validate materials compatibility and chemical choices.
Glycol concentration, inhibitor chemistry, and elastomer/metal choices must be selected together. Avoid improvised cleaning chemistries and engage a water-treatment specialist to choose agents that remove organics without attacking wetted materials.

5. Instrument the process and create verifiable records.
For commissioning, fit flushing skids and loops with calibrated flow meters, filter ΔP gauges, pressure gauges, turbidity or colorimetric sensors, conductivity and pH meters, plus sample ports at representative locations. These instruments prove that acceptance criteria were met and create an auditable trail for handover — invaluable under regulatory scrutiny or for multi-site rollouts.

Continuous monitoring is essential

Handheld lab tests are useful but episodic. The industry is moving to minute-by-minute coolant telemetry that monitors pH, conductivity, temperature, turbidity (or particulate proxies), refractometry for glycol concentration, flow and filter ΔP which are streamed into operations dashboards. 

Continuous visibility does three things:
• Detects gradual drift (inhibitor depletion or glycol dilution) before a lab sample would.
• Catches transient events (a sudden turbidity spike during maintenance) that would otherwise be missed.
• Bridges commissioning and operations, turning acceptance criteria into ongoing KPIs and triggering defined remediation playbooks rather than ad-hoc “do something” responses.

In regulated markets, telemetry also supports compliance reporting and demonstrates proactive stewardship of water and chemical use which is a growing expectation among corporate customers and public authorities.

Dosing, automation and wastewater

Automated chemical dosing is common in large utility loops, but for many rack-level D2C architectures, telemetry primarily provides monitoring and operational insight; chemistry interventions are typically procedural and governed by site protocols. Pre-commissioning flush water must be handled responsibly — capture, treat or coordinate discharge with local authorities and document the composition of procedure water and any biocides used to avoid permitting delays.

Take aways

If you come from traditional chiller or tower ops, think of D2C glycol loops as process-grade systems living close to very expensive electronics. That means commission like a process plant, instrument deliberately, and operationalise telemetry. Start with a pilot telemetry deployment and a rigorous commissioning checklist. The payoff is fewer rack-level surprises, longer equipment life and reliable scale.

The bottom line is glycol is a reliable tool for modern cooling but when pushed to new extremes by AI workloads, it demands engineering rigour. 

Continuous visibility into coolant health turns a potential liability into a manageable engineering discipline, enabling data centres worldwide, from Europe’s regulation-intensive sites to APAC’s rapid roll-outs and the unique demands of the Middle East and Africa, to scale compute without sacrificing uptime or sustainability.