Glycol

Figure 2: 3D model of Propylene Glycol (C3H8O2)

HVAC Application

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      Glycol itself is not an effective corrosion inhibitor, and because of this chemical additives are preferred. As glycol decays over time, it produces organic acids that can decrease system pH, increasing corrosive tendencies and without corrosion inhibitor(s), will accelerate the deterioration of pipe, pumps and HVAC equipment. To avoid such issues, it is recommended that a concentration of glycol no less than 25% should be obtained. Water purity is also important for the longevity of a system. At elevated temperatures, oxygen, metal contaminants, and other impurities will increase the rate of glycol breaking down. Bacteria present can utilize glycol as a food source, leaving acidic byproducts that reduce concentrations. For these reasons manufacturers will typically dilute glycol with distilled water prior to shipment.

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      For HVAC applications in a well cleaned, concealed environment, glycol can last 15-20 years. With that being said these systems should be tested on a routine basis for concentration, glycolic acids, pH, etc. for preventative measures as if left unchecked, can lead to catastrophic failures. Glycol refractometers are handy tools utilized to determine the freeze points/concentration of glycol fluid solutions and can be used in the field as a quick verification method. Sending samples to the lab periodically will allow for a more thorough investigation. As water treaters, understanding the chemical and physical properties of glycol will allow us to better support these systems and provide useful testing, both in the field and in laboratory settings.