Glycol In Process Cooling: When You Need It, How To Specify It, And How To Avoid Freeze-Ups

Glycol is not optional when your cooling system operates in winter, uses outdoor pipework, or relies on free cooling. Get the glycol mix right and your system runs reliably, avoids burst coils, and stabilises production. Get it wrong and you face slush formation, low flow alarms, blocked plate heat exchangers, and expensive downtime. This guide gives you a straight, practical overview of when glycol is required, what concentration to specify, the real-world costs involved, and how to maintain a dependable glycol programme.

What Glycol Actually Does

Glycol mixed with water provides three key protections:

• Freeze protection for exposed pipework, evaporators, coils, and headers
• Burst protection during idle periods or overnight temperature dips
• Corrosion resistance from inhibitor packages that protect mixed-material circuits

It stabilises free cooling operation by preventing slush formation, reduces biofouling risks, and protects components during low ambient conditions.

When You Need Glycol

Use water only when:

• All pipework is fully indoors
• No part of the system sees below 7°C to 8°C
• There is zero freeze risk

You need glycol when any of these are true:

• Outdoor pipework or exposed coils
• Leaving fluid temperatures below 7°C
• Overnight free cooling or extended shoulder-season free cooling
• Intermittent operation or shutdown periods
• Corrosion protection required for mixed materials

Comfort cooling often runs fine on water. Process cooling, breweries, plastics, and data centres generally don’t.

Standard industrial glycol systems can safely operate down to around -8°C to -10°C leaving temperature.

Specialist systems with appropriate insulation, refrigerant choice, and coil design can run colder, but always maintain a safety margin of at least 3°C to 5°C from the measured freeze point of your fluid.

Never run setpoints tight to the theoretical freeze point. That’s how you produce slush, block plates, and ruin heat exchangers.

Energy Impact, Pump Sizing, and Capacity Derate

Glycol changes how a system behaves. Expect:

• Higher viscosity
• Higher pump head
• Slightly lower heat transfer efficiency
• Reduced chiller capacity at the same setpoint
• Potential low flow alarms if winter viscosity isn’t calculated properly

When sizing pumps or recommissioning systems:

• Recalculate flow and head for the glycol mix
• Check NPSH and motor kW
• Confirm the pump has winter headroom
• Consider VSD control

Poorly sized pumps are one of the biggest causes of alarms and nuisance shutdowns during the first cold snap.

Maintenance Schedule and Testing

There’s no fixed replacement interval; condition dictates timing, not a calendar.

Solid programme:

• Test glycol twice per year: pre-winter and pre-summer
• Check concentration using a refractometer (ensure it’s calibrated for the right glycol type)
• Test pH and inhibitor levels
• Monitor microbiological activity
• Carry out partial refresh every 3-5 years in clean systems
• Replace fully if inhibitors can’t be stabilised or metals are rising in lab results

Corrosion issues are almost always caused by neglected inhibitor levels or incorrect top-ups.

Common Glycol Problems and What the Alarm Actually Means

• Low flow alarms in winter: viscosity has increased; pump duty not estimated correctly
• Slush forming in coils/plates: setpoints too close to freeze protection margin
• High dp across the plate HX: corrosion debris or fouling
• Unstable pH: incompatible glycols mixed or inhibitors depleted
• Dilution: topping up leaks with water removes inhibitors even if freeze point looks OK

Sector-Specific Guidance

Breweries

25% to 35% propylene glycol for fermentation and crash cooling. Outdoor pipework and free cooling nights justify the higher end.

Food Processing

Food-grade propylene glycol recommended. HACCP and intermittent cleaning/washdown cycles make freeze protection critical.

Plastics and Injection Moulding

20% to 30% glycol for low setpoints and outdoor chiller positioning. Size pumps for winter viscosity.

Data Centres

25% to 35% glycol optimises free cooling hours across the year. Corrosion management and coil performance need balancing.

Real-World Costs to Plan For

• Initial fill volume plus spare drums
• Pumping energy increase
• Slight capacity derate
• Semiannual testing
• Inhibitor dosing
• Occasional filtration
• Eventual partial or full refresh

The biggest saving comes from preventing freeze-ups. One burst coil can cost more than years of proper glycol management.

Practical Specification Checklist

• Confirm lowest fluid temperature anywhere in the loop
• Select type of glycol and concentration
• Add 3°C to 5°C safety margin
• Verify materials compatibility
• Recalculate pump duty for cold conditions
• Consider derate impact on chiller capacity
• Plan testing and dosing schedule
• Ensure safe handling, spill kits, and disposal routes

Next Steps and Support

If you want your system protected for winter, we can test your glycol mix, confirm freeze margins, optimise pumps for winter duties, and calibrate your controls.

Book your glycol health check and winterisation service now.
📞 0121 820 8946
📧 [email protected]
🌐 www.evolution-cooling.com