Why Glycol Matters: Freeze Protection & Maintenance

As the summer cooling season comes to an end and as temperatures drop in most parts of the country it is time to start thinking about freeze protection for your facility’s closed loop cooling systems and air handlers while they are offline for the winter. Propylene and ethylene glycol are the tools best suited for freeze protection in your facility’s systems.

Most of us have our first experience with closed cooling loops and glycol when we start driving. Your car’s radiator system is a simple closed cooling loop that is used to dissipate heat generated from the engine to the environment. Glycol is the heat transfer fluid of choice to prevent freezing due to its similar heat capacity to water and ability to depress freeze protection in fluid systems. While there are major differences between your automobile’s cooling system, your facilities fluid systems, and the materials they use, the principle of freezing point depression holds true.

Preparation for Glycol Treatment

Proper planning is essential for the effective treatment of a closed system.

Steps for Effective Preparation:

• Ensure that the system is free from particulate matter and shows no obvious signs of biological activity.
• To achieve optimal chemical treatment, it may be necessary to clean and passivate the closed loop prior to charging it with glycol.
  • Cleaning and passivation will provide effective corrosion protection and eliminate contaminants resulting from construction or previous inadequate treatments.
• Accurate knowledge of the system’s volume is imperative for administering the correct chemical dosage.
• HOH’s water treatment professionals can ascertain the volume of the closed loop with minimal disruption to your operations.

As a final precaution, all closed loops should incorporate filtration systems to remove suspended solids.

Selecting and Treating Glycol

Ethylene and propylene glycol can both be used for freeze protection. Ethylene glycol provides better freeze protection than propylene glycol; however, there has been a shift towards using propylene glycol over ethylene glycol since propylene glycol is considered non-toxic.

Most systems are treated with a 25 to 50% solution of glycol. Glycol has a heat capacity slightly lower than that of the heat capacity of water, meaning glycol-based fluids absorb less heat per unit mass, but can still offer sufficient heat transfer capabilities for most cooling applications.

It is recommended to add the concentration of glycol that the system was designed to operate with. This is necessary to achieve the desired freeze protection while ensuring proper heat transfer can occur and the system load is not affected.

The charts below depict the relative freeze and burst protection provided by ethylene and propylene glycol at various concentrations

Freeze & Burst Protection for Ethylene & Propylene Glycol by Volume

Glycol is commercially available in both concentrated and prediluted forms.

• In large systems, it may make better economic sense to buy concentrated glycol and dilute with makeup water that is softened or deionized on site.
• Prediluted glycol is available for smaller systems to avoid the added steps of treating city water to acceptable manufacturer’s specifications for dilution water.

It is critical to follow the manufacturer’s recommended specifications to ensure proper freeze protection is achieved, and to avoid any adverse effects with the inhibitor package.

Why Corrosion Inhibitors Matter

Glycol is available pretreated with corrosion inhibitors to simplify the treatment process and take the guesswork out of maintaining the correct treatment levels.

• Corrosion inhibitors are needed for glycol since glycol by itself provides no corrosion protection and can degrade over time with exposure to heat and oxygen.
• This can sour a glycol system and can develop a corrosive environment.
• The byproducts of glycol degradation are acidic in nature and will lower the pH of your closed loop and lead to corrosion and possible shortened asset life and unplanned maintenance and downtime.

Types of Corrosion Inhibitors

• Phosphate is a common corrosion inhibitor used in glycol.
  • Phosphate corrosion inhibitors should be avoided in systems with high hardness makeup water to avoid deposit formation on heat exchange surfaces.
• Azoles are commonly added to the solution, to provide corrosion inhibition for the yellow metal components (brass, bronze, copper) within the system.
• For systems with aluminum metallurgy, contact your HOH representative for specific recommendations.
• For systems with hard water makeup, nitrite and molybdate are suitable replacements for phosphate and are recommended for ferrous corrosion inhibition.

Caution should be used when using nitrite and molybdate corrosion inhibitors, especially if these systems are prone to high water loss. Increased makeup water can introduce oxygen and nutrients that can increase microbiological activity and degrade nitrite corrosion inhibitors. Molybdate should be avoided in systems with high water turnover due to cost and possible discharge restrictions.

Sustaining Glycol Systems

Once your system is treated with glycol it is imperative that the system is serviced on a regular frequency to maintain system reliability.

Routine Tasks:

• Routine laboratory analyses should be performed to ensure that organic acids, other organics, and soluble metals are kept within acceptable limits.
• Water loss is detrimental to closed loops. Any loss of water should be investigated at once and corrected.
• The best way to track water loss is with the use of makeup meter data.

Key Considerations for Laboratory Data:

• % Glycol: Required for adequate freeze protection in your climate. Maintain at least 25% glycol to keep your system biostatic.
• Glycol Mixture: Systems should contain only one form of glycol. Laboratory reports can indicate whether systems have had additions of incorrect material. For adequate freeze protection, propylene and ethylene glycol should not be mixed.
• Reserve Alkalinity: An indicator of the amount of protection available for the acidic products from the eventual breakdown of glycol.
• Iron & Copper: These ions should be closely monitored. An increase of these ions is indicative of corrosion in your cooling system.
• Inhibitor: Maintaining the recommended inhibitor levels will minimize corrosion.

Automated Glycol Feeders

An automated glycol feeder will take the guesswork out of maintaining the correct glycol concentration in your closed loop.

• Automated glycol feeders are available in a variety of sizes to fit your facility’s needs.
• These feeder systems keep pressure in the loop by adding glycol solution to make up for losses which occur due to bleed/relief valve leakage, evaporation, or loss from maintenance activities.
• Glycol addition is controlled by a pressure switch with adjustable set point and pressure differential.
  • When the pressure in the loop reaches the low set point, the pump begins to feed glycol into the system until the differential set point is achieved.

The HOH Advantage

Maintaining a glycol system can be a nuanced but rewarding experience. It often takes a significant amount of time, energy and capital to correct a fouled system. However, with proper preventative maintenance, monitoring, and quality material, a well running system should require little attention.

HOH Water Technology has been correcting and supporting industrial glycol systems in the Midwest for over 50 years. With a complete suite of cleaners, glycol products, and a full analytical chemistry laboratory, it is well equipped to serve your systems’ needs.

Since 1968, HOH Water Technology has provided a full range of water treatment chemicals, services and equipment to many industries across the Midwest to maximize asset life, prevent unplanned maintenance and downtime.

For a no obligation comprehensive audit of your facility contact HOH Water Technology at (800) 577-2211 or info@hohwatertechnology.com.