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Dow ethylene glycol heat transfer fluid and propylene glycol heat transfer fluid are widely used in the HVAC industry to protect closed-loop and water-based heating and cooling systems from damage caused by freezing and corrosion. Other applications include:
Why Use Antifreeze Instead of Water in Hydronic Heating and Cooling Systems
While plain water is an efficient and inexpensive heat transfer fluid, it freezes at 32°F and the resulting expansion can produce pressures strong enough to damage coils and metal pipes. The addition of glycol antifreeze (such as Dowfrost HD™ propylene glycol, Dowfrost™ food grade propylene glycol or Dowtherm SR-1™ ethylene glycol) to water in hydronic heating and cooling systems, lowers the freezing point of your heat transfer fluid mixture. How much lower depends on the concentration of the glycol in your antifreeze mixture. For example, a glycol-water mixture with a concentration of 40% propylene glycol will have a lower freezing temperature than an antifreeze mixture containing 25% propylene glycol, because there is a higher glycol to water ratio in the mix.
For these reasons, we recommend using a high-quality glycol-based heat transfer fluid in your hydronic heating and cooling systems, such as Dowfrost HD, Dowfrost (Food Grade Antifreeze) or Dowtherm SR-1.
What is Inhibited Glycol?
Inhibited glycol is an antifreeze mixture enhanced with chemicals called inhibitors which prevent corrosion to your HVAC system. Corrosion (aggravated by heat, oxygen, chlorides, sulfates, metal impurities and other contaminants) can cause severe damage to your system leading to unscheduled shutdowns, high maintenance fees and even reduced system life. Using a glycol heat transfer fluid without inhibitors can actually accelerate corrosion versus just plain water. Since glycols produce organic acids as they degrade, especially when heated, these acids when left in the system will lower the fluids pH. With no corrosion inhibitors to buffer these acids, the corrosion rate of a solution of uninhibited glycol can be greater than that of plain water (which is highly corrosive). However, even purified water will cause serious corrosion problems unless treated with the proper level of inhibitors.
For these reasons, inhibited glycols are the heat transfer fluid of choice for the HVAC industry. You can read more about inhibited glycol vs. uninhibited glycol here.
Propylene Glycol Vs. Ethylene Glycol
The primary difference between propylene glycol and ethylene glycol are the toxicity and heat transfer characteristics.
Ethylene Glycol Properties
Ethylene glycol is the industry standard. It provides both excellent heat transfer and freeze protection. Having a low viscosity means its transport properties outperform propylene glycol at lower temperatures. While dye color may differ by supplier, DOWTHERM SR-1 Inhibited Ethylene Glycol is fluorescent pink in color with an operating temperature range of -60°F to 250°F (-51°C to 121°C) and provides freeze protection to below -60°F (-51°C) and burst protection to below -100°F (-73°C) depending on concentration. Due to its moderate acute oral toxicity, ethylene glycol is SARA and CERCLA reportable for spills and transport. In applications where toxicity is NOT a concern, ethylene glycol is often the heat transfer fluid of choice. Where low toxicity is desired, we would recommend propylene glycol.
Propylene glycol fluids are often selected because of their low acute oral toxicity vs. the moderate acute oral toxicity of ethylene glycols.
Ethylene Glycol Specifications(DOWTHERM SR1)
For more properties and specifications, click here to view the Ethylene Glycol Engineering and Operating Guide.
Propylene Glycol Properties
Propylene glycol is also used for its heat transfer and freeze protection properties. Similar to ethylene glycol, when inhibited, these glycols also protect HVAC systems against damage from corrosion. We offer two different types of propylene glycol, DOWFROST HD Inhibited Propylene Glycol, which is low in acute oral toxicity and DOWFROST Food Grade Inhibited Propylene Glycol which has the lowest oral toxicity. Dow's food grade propylene glycol is certified to be safe where contact with drinking water is possible, food processing applications where accidental contact with food or beverage products could occur, and applications where propylene glycol use is mandated by law.
While dye color may differ by suppler, DOWFROST HD Inhibited Propylene Glycol is bright yellow to green in color and has an operating temperature range of -50°F to 325°F (-46°C to 163°C). DOWFROST Food Grade Inhibited Propylene Glycol is water white, or colorless, and has an operating temperature range of -50°F to 250°F (-46°C to 121°C). Both DOWFROST and DOWFROST HD provide freeze protection to below -60°F (-51°C) and burst protection to below -100°F (-73°C) depending on concentration.
Food Safe Propylene Glycol Specifications (DOWFROST)
Propylene Glycol Specifications (DOWFROST HD)
For more properties and specifications, click here to view the Propylene Glycol Engineering and Operating Guide.
Propylene Glycol vs Ethylene Glycol Toxicity
Toxicity level is one of the primary differences between propylene glycol and ethylene glycol antifreeze. In applications where toxicity is NOT a concern, ethylene glycol is often the heat transfer fluid of choice. Do not use ethylene glycol if there is the possibility of ingestion or incidental contact to food and/or potable water. Report spills when required. Each state has different regulations that require release or spill reporting when a facility meets certain conditions or reportable quantities have been met or exceeded.
Where low toxicity is desired, propylene glycol fluids are often selected because of their low acute oral toxicity vs. the moderate acute oral toxicity of ethylene glycols.
Dow's food grade propylene glycol is certified to be safe where contact with drinking water is possible, in food processing applications where accidental contact with food or beverage products could occur, and in applications where propylene glycol use is mandated by law.
The Difference Between Propylene Glycol and Food Grade Propylene Glycol
Both propylene glycol and food grade propylene glycol are low in acute oral toxicity. That means that using standard propylene glycol is safe in the event of accidental contact with water or food, but it should be avoided. The ingredients in Dow Food grade or food safe propylene glycol are FDA certified for use as food additives. This means it is safe where contact with drinking water is possible and in food processing applications where contact with food or beverage products could occur.
What is Antifreeze?
HVAC systems are filled with a heat transfer solution that consists of an inhibited glycol-based heat transfer fluid (such as DOWFROST, DOWFROST HD or DOWTHERM SR1), at a specified concentration to provide adequate freeze protection, and water. We use glycol in addition to water to fill a system because plain water freezes below 32°F causing damage to the coils and pipes. When added to water, glycol lowers the freezing point of the water mixture. Dow recommends the use of high purity fill water, such as deionized water (di water), because the impurities found in hard water can cause damage to both the system and the inhibitors in the glycol itself. Learn more about the importance of good quality fill water here.
HVAC Antifreeze Alternatives (Substitutes)
We mentioned earlier that filling your HVAC system with plain water (or hard water) can result in system damage and will compromise the lifespan of the glycol itself. While hard water will provide superior heat transfer characteristics, it will also cause costly system damage due to corrosion and has extremely poor performance at low temperatures. For these reasons, we use a glycol-purified water solution in hydronic heating and cooling systems.
Other alternatives to inhibited glycol-based fluids that you may find are: