Understanding the Freeze Protection Properties of Different Glycol Types
When temperatures drop below freezing, the water circulating through HVAC systems and industrial processes faces a serious risk of solidifying. Ice formation can rupture pipes, damage chillers, and interrupt production. To avoid these issues, facilities rely on glycol-based antifreeze solutions that provide dependable freeze protection.
Glycol is a colorless, odorless liquid commonly used in cooling and heating systems to lower the freezing point of water. By mixing glycol with water in the proper ratio, operators can keep fluids moving smoothly through equipment even at freezing temperatures. The result is a stable system that maintains heat transfer efficiency and prevents costly downtime.
Among the many chemicals used for this purpose, two stand out: ethylene glycol and propylene glycol. Each offers distinct physical properties, benefits, and safety considerations that make it suitable for different industrial applications. Understanding these main types of glycol is crucial for engineers, facility managers, and maintenance teams who want to ensure effective and economical freeze protection in a variety of environments.
What is Glycol and How It Works in Freeze Protection
Glycol is a versatile chemical compound used across various industries to prevent water from freezing inside pipes, coils, and chillers. It acts as an antifreeze by lowering the freezing point of water, allowing fluids to circulate freely at lower temperatures. This property is especially valuable in HVAC systems, refrigeration, and industrial cooling loops where maintaining consistent temperature control is essential.
Chemically, glycols are odorless liquids belonging to the alcohol family. Their molecular structure includes hydroxyl groups, which form hydrogen bonds with water molecules. This interaction disrupts water’s ability to crystallize, delivering reliable freeze protection. As glycol concentration increases, the freezing temperatures of the solution drop, providing greater protection in colder environments.
Glycol also influences other physical properties of the mixture, such as viscosity and heat transfer. A higher glycol concentration increases the fluid’s viscous liquid nature, which may reduce heat transfer efficiency but improves resistance to freezing. Because of this balance, the correct glycol-to-water ratio must be carefully determined to match each system’s operational requirements and climate conditions.
The Two Main Types of Glycol: Ethylene and Propylene
There are two main types of glycol used for freeze protection in industrial applications: ethylene glycol and propylene glycol. While both are colorless, odorless, and viscous liquids, they differ in toxicity, performance, and appropriate usage across different industries.
Ethylene Glycol
Ethylene glycol is the most commonly used glycol in industrial processes and cooling systems. Produced from ethylene oxide, it is an essential raw material in the manufacture of polyethylene terephthalate (PET), which is used in plastics, fibers, and paints. Ethylene glycol provides excellent freeze protection and superior heat transfer characteristics, making it ideal for chillers and large-scale HVAC systems operating at lower temperatures. However, it has a sweet taste and is toxic to humans and animals if ingested, so it must be handled with care to prevent leakage or contamination in food or pharmaceutical facilities.
Propylene Glycol
Propylene glycol, on the other hand, is considered safer for food industries and pharmaceutical environments. It is also an odorless, colorless, viscous liquid, but it has higher viscosity and slightly less efficient heat transfer at lower temperatures than ethylene glycol. Its low toxicity allows it to be used in systems where incidental human contact might occur, such as in schools, hospitals, and different industries that require safety over efficiency.
Both glycols serve as dependable antifreeze agents, but selecting between them depends on factors such as toxicity, cost, environmental impact, and the specific system in which they will be mixed and circulated.
Comparing Physical and Chemical Properties
Both ethylene glycol and propylene glycol share similar chemical structures and are effective in freeze protection, yet their physical properties and performance vary significantly under different temperatures. Understanding these differences is crucial when designing or maintaining cooling and heating systems.
Viscosity and Heat Transfer
As temperature decreases, glycol solutions become more viscous, meaning they flow less easily. Propylene glycol typically exhibits higher viscosity than ethylene glycol, which can slightly reduce heat transfer efficiency in HVAC systems and industrial processes. While this may increase pump energy requirements, propylene glycol’s safety profile makes it preferable where human exposure or food contact is possible. Ethylene glycol, with its lower viscosity, generally offers better flow and more efficient coolant performance, particularly at lower temperatures.
Freezing Point and Protection Levels
For equivalent concentrations, ethylene glycol provides a slightly lower freezing point than propylene glycol, resulting in stronger freeze protection in extreme climates. However, both types maintain dependable antifreeze performance when properly mixed with water and maintained. The effectiveness of the mixture depends on precise concentration and inhibitor balance to prevent oxygen-related corrosion and contamination.
System Compatibility and Risk
Regardless of glycol type, improper use or neglected maintenance can increase the risk of leakage, corrosion, or degraded protection. Facilities must carefully select inhibitors compatible with their chosen glycol and regularly test for concentration stability and pH balance to maintain long-term reliability.
Table 1: Comparison of Ethylene Glycol vs. Propylene Glycol
| Property | Ethylene Glycol (EG) | Propylene Glycol (PG) |
|---|---|---|
| Chemical Formula | C₂H₆O₂ (derived from ethylene oxide) | C₃H₈O₂ (derived from propylene) |
| Appearance | Colorless, odorless liquid | Colorless, odorless liquid |
| Toxicity | Toxic if ingested; sweet taste can attract animals | Low toxicity; safe for food and pharmaceutical use |
| Viscosity | Lower viscosity, better heat transfer | Higher viscosity, reduced flow efficiency |
| Freezing Point (50% mix) | ≈ -34°C (-29°F) | ≈ -32°C (-26°F) |
| Applications | Industrial systems, chillers, cooling plants | Food industries, HVAC systems, pharmaceutical settings |
| Environmental Risk | Higher contamination concern | More biodegradable, safer for disposal |
| Cost | Typically lower cost | Slightly higher cost due to purity standards |
In short, both glycol types provide dependable freeze protection, but ethylene glycol offers stronger performance in extreme cold, while propylene glycol prioritizes safety and environmental responsibility in sensitive industrial applications.
The Role of Specialized Glycols in Industrial Processes
Beyond the two main types used for freeze protection, there are additional glycol variations that serve critical roles in various industrial applications. Among them, triethylene glycol (TEG) stands out for its unique physical properties and effectiveness in specific industrial processes.
Triethylene Glycol (TEG)
Triethylene glycol is a colorless, odorless, and moderately viscous liquid produced from the reaction of ethylene oxide with water. It has a higher viscosity and boiling point than both ethylene glycol and propylene glycol, allowing it to function effectively at higher temperatures. TEG is widely used in gas dehydration systems, paints, cosmetics, and pharmaceutical manufacturing where moisture removal or controlled humidity is essential.
Glycols in Manufacturing and Product Formulation
In addition to freeze protection, glycols serve as intermediates in the production of polyethylene terephthalate (PET), a plastic resin used for bottles, fibers, and packaging materials. Their solvency and stability make them valuable in different industries, including cosmetics, cooling fluids, and industrial coatings. Because glycols are odorless liquids that mix easily with water, they are preferred in systems where uniform distribution and low volatility are important.
Broader Importance
From large-scale industrial processes to HVAC systems, the versatility of glycols makes them indispensable. Their balance of chemical stability, freeze protection, and heat transfer capability ensures consistent performance across various industries, especially where temperature control and safety are key operational factors.
Choosing and Maintaining the Right Glycol for Freeze Protection
Selecting the appropriate glycol and concentration for your system is essential to achieving reliable freeze protection and preventing long-term maintenance issues. The choice between ethylene glycol and propylene glycol depends on several factors, including toxicity, cost, operational temperature range, and the type of industrial applications involved.
Selecting the Correct Type
For industrial processes operating at lower temperatures, ethylene glycol typically provides stronger protection and better heat transfer. However, in environments where human contact or food safety is a concern—such as schools, healthcare facilities, or pharmaceutical plants—propylene glycol is the preferred choice because of its low toxicity and biodegradability. Decision-makers must carefully evaluate their operational temperatures and compliance requirements before selecting which glycol to use.
Maintaining Proper Concentration and System Health
Once the glycol type is chosen, maintaining the correct concentration is crucial. Too little glycol reduces protection, while excessive amounts increase viscosity, reduce heat transfer, and raise energy costs. Regular testing for pH, inhibitor levels, and contamination helps ensure ongoing performance. Facilities should also check for leakage or system degradation, both of which can lead to corrosion and efficiency loss.
Depending on climate and usage intensity, glycol testing should be scheduled at least annually, or more often in cold climates. Proper maintenance ensures your freeze protection system remains efficient, reliable, and safe throughout its operational lifespan.
Also read: Glycol Contamination: Prevention and Solutions for Industrial Systems
ClearWater’s Expertise in Glycol and Freeze Protection Systems
Maintaining proper freeze protection is not just about selecting the right glycol; it’s about managing the entire closed loop system that supports your heating and cooling operations. At ClearWater Industries, we specialize in optimizing closed loop systems to ensure reliability, efficiency, and long-term protection against corrosion, contamination, and leakage.
Comprehensive Closed Loop Water Treatment
ClearWater’s Closed Loop Water Treatment Programs are specifically designed to protect HVAC systems, chillers, and process cooling loops where glycol mixtures are used for freeze protection. Our programs combine precise chemical control with ongoing monitoring to maintain optimal glycol concentration and system balance.
We address key challenges such as:
- Corrosion caused by improper inhibitor balance
- Reduced heat transfer from scale buildup or high viscosity
- Microbial growth in stagnant or poorly circulated loops
- Glycol degradation and pH instability
Specialized Treatment for Glycol-Based Systems
Glycol loops require unique chemical and operational oversight. ClearWater’s specialists provide:
- Custom inhibitor programs for specific metallurgy and glycol types
- Advanced glycol concentration measurement and pH analysis
- Preventive maintenance to detect early signs of leakage or system imbalance
- Non-destructive testing to identify corrosion before failures occur
Our technicians use data-driven tools and laboratory analysis to ensure every system performs efficiently, even during extreme freezing temperatures. By maintaining the correct glycol levels and inhibitor chemistry, we help prevent costly downtime and extend the lifespan of critical equipment.
Get Started
Protect your investment this winter. Contact ClearWater Industries for a comprehensive system evaluation, tailored treatment recommendations, and an ongoing maintenance plan that guarantees lasting freeze protection for your facility’s closed loop systems.
Learn more about Closed Loop Water Treatment Programs
Conclusion
Effective freeze protection begins with understanding the unique properties of each glycol type and maintaining the correct balance within your closed loop systems. Whether your facility relies on ethylene glycol for industrial efficiency or propylene glycol for safer food and pharmaceutical applications, proper monitoring ensures long-term reliability and performance.
Neglecting glycol maintenance can lead to corrosion, leaks, and reduced heat transfer efficiency, putting your operations at risk.
For expert guidance, system testing, and tailored glycol management solutions, contact ClearWater Industries (CWI) today. Our specialists will help you safeguard your system, maintain compliance, and achieve dependable protection through every season.
Frequently Asked Questions (FAQ)
Ethylene glycol is commonly used for freeze protection in cooling and heating systems, while triethylene glycol is primarily used in industrial processes such as paints, cosmetics, and gas dehydration. Triethylene glycol has higher viscosity and performs well at higher temperatures, making it suitable for moisture control and various industrial applications.
Yes, but only specific types. Propylene glycol is approved for food industries and pharmaceutical use because it is non-toxic and considered safe for incidental human contact. Ethylene glycol, on the other hand, is toxic and should never be used in applications where contamination is possible.
Contamination can alter viscosity, reduce freeze protection, and lead to corrosion. Over time, it may cause scaling, blockages, or bacterial growth within the system, increasing maintenance cost and operational risk. Testing and preventive maintenance are crucial to ensure fluid purity.
Common signs include sudden drops in glycol concentration, visible moisture or staining along pipe lines, and reduced heating or cooling performance. A miss in maintenance checks may allow small leaks to worsen, so regular inspection helps ensure early detection and repair.
Testing frequency depends on factors such as system type, temperatures, and environmental conditions. In most businesses, annual testing is recommended, but in colder regions or older systems, quarterly analysis helps identify early degradation or contamination before it affects protection.