Glycol is an important component in chilled water systems. It provides freeze protection, corrosion inhibition and stable heat transfer. However, glycol’s effectiveness depends on regular monitoring and maintenance. Over time, its protective additives deplete, and the fluid can become corrosive without visible warning signs.
This guide explains the role of glycol in chilled water systems, why maintenance matters and how to make data-driven decisions about testing and replacement to protect your industrial chiller investment.
Glycol is an organic compound in the alcohol family. It features two hydroxyl (–OH) groups attached to different carbon atoms. A common example is ethylene glycol.
It has a thick consistency, no color or odor at room temperature, and mixes easily with water. Glycol used in chilled water systems lowers the freezing point of water, preventing freeze-ups even in extremely cold conditions. Its high boiling point also helps maintain performance in high-temperature applications.
Its role goes beyond freeze protection, impacting system longevity and performance in the following ways:
Choosing the right glycol is essential for system compatibility, safety and performance. The two main types are ethylene glycol and propylene glycol.
When selecting a glycol for industrial chillers, it’s important to consider the unique properties and safety considerations of ethylene glycol, including the following:
Propylene glycol offers distinct advantages and trade-offs that make it suitable for specific applications and environments. It has lower toxicity and is considered safer for environments with potential human or environmental exposure. Propylene glycol is slightly less efficient in heat transfer and has higher viscosity, which may require pump adjustments. It is commonly used in food processing, commercial buildings and areas with stricter safety requirements.
Always match the glycol type and its corrosion inhibitor additives with the metals used in your system’s pipes, pumps and heat exchangers, ensuring they are chemically compatible. Mixing incompatible glycols or using automotive antifreeze instead of glycol in chilled water systems can cause fouling and corrosion.
Glycol-based chilled water systems need regular maintenance. Without it, the fluid’s protective additives are depleted, and its chemical balance can shift, leading to hidden corrosion risks and reduced system performance. Proactive testing and upkeep help ensure the glycol continues to protect your equipment and maintain efficient operation.
Glycol levels in chilled water systems should be tested at least once a year, and more often for critical or high-use systems. Use a refractometer to verify the glycol concentration and ensure the freeze point meets system requirements.
It’s also important to measure pH, reserve alkalinity and inhibitor levels to confirm the fluid is still providing corrosion protection. Additionally, testing for metals like iron and copper, as well as other contaminants, helps find early signs of corrosion or leaks before they become major issues.
Throughout its life cycle, glycol gradually loses its protective qualities as inhibitors are depleted, pH drops and reserve alkalinity diminishes. As glycol oxidizes, it produces organic acids that can accelerate corrosion if not properly managed. To maintain system health and meet compliance or warranty requirements, it’s essential to document all test results and maintenance actions, ensuring a clear record of fluid condition and service history.
For the most accurate assessment, laboratory analysis can show subtle changes in glycol chemistry that may not be detected through field testing alone. This proactive approach helps catch potential problems early, protecting your system from costly damage.
Have our certified techs perform a comprehensive analysis to maximize productivity and prolong the life of your system.
Knowing how to check glycol levels in a chiller is crucial. Waiting for visible problems can mean costly repairs. Glycol should be tested at least annually and replaced when tests indicate depleted inhibitors, a low pH or contamination. Replacement may be necessary every three to five years, but the frequency depends on the system’s conditions and maintenance.
The following are warning signs that indicate glycol needs to be replaced:
Key characteristics of the degradation process include oxidation leading to the formation of glycolic and organic acids. These acids then lower the pH and consume inhibitors. Once inhibitors are depleted, corrosion accelerates quickly.
Replacing glycol in a chiller system is a methodical process that ensures the system’s protection and optimal performance. Skipping steps can leave behind contaminants or incompatible fluids.
Start by shutting down the system and safely draining all existing fluid. Next, flush the system thoroughly with clean water or a recommended cleaning agent to remove any residual glycol, scale and accumulated debris. During this process, carefully inspect the system for leaks, signs of corrosion or any damaged components that may need repair before refilling.
Choose the appropriate type and concentration of inhibited glycol based on your system’s requirements and the local climate. Always mix the glycol with high-quality, deionized water to minimize scaling and ensure the inhibitors work effectively. Once prepared, fill the system and circulate the fluid thoroughly. To maintain optimal system performance, ensure you purge any trapped air to prevent oxygen from entering the system.
After refilling, test the glycol solution for proper concentration, pH and inhibitor levels to confirm the system is adequately protected. Be sure to document the date of service, the type of glycol used and all test results. Keeping detailed records gives you a clear maintenance history for future reference and compliance.
Proactive maintenance extends the life of your glycol and your chiller system. A structured program helps you catch issues before they become failures.
Common tasks include:
Avoiding these pitfalls can save your facility from expensive repairs and downtime.
Always use glycol that includes the correct inhibitor package for the specific metals in your system. Uninhibited glycol lacks the additives needed to protect against corrosion, which can quickly lead to system damage.
Don’t wait for visible problems to appear — glycol can become corrosive even when it looks clear. Corrosive glycol can silently damage pipes, pumps and heat exchangers long before any noticeable symptoms appear. Regular testing is essential to catch issues early, prevent costly repairs and maintain overall system health and efficiency.
Never mix ethylene and propylene glycol in a chiller system or different brands of glycol without performing a complete system flush. Incompatible mixtures can cause chemical reactions that reduce corrosion protection and may damage system components.
Always use deionized or low-mineral water when mixing glycol. Poor water quality can introduce minerals that promote scaling and reduce the effectiveness of corrosion inhibitors.
Expert support ensures your glycol system is protected, efficient and compliant with industry standards. Partnering with Chardon Laboratories gives you access to:
You can’t see when glycol has become corrosive. Don’t guess — test. Chardon Laboratories offers certified fluid analysis, expert system assessment and tailored maintenance programs to keep your chilled water system protected and efficient.
Contact us today for a professional fluid analysis and ensure the long-term health of your system.
