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Glycol Treated Closed Loops

Updated: Nov 8, 2019

Some closed loop systems require protection from freezing. Untreated water expands when frozen, so it goes without saying that exposing water in a closed loop system to freezing conditions can result in a very costly rupture.


Glycol is the industry standard for freeze protection in most closed loop applications. Closed loop systems can be completely filled with glycol and water, or just the coils can be isolated and treated for protection.



Types of Glycol

Typically, two types of glycol are used for closed loops. The two major types of glycol used are ethylene and propylene.


Ethylene glycol is often used for HVAC applications. It offers the most efficient heat exchange medium. Propylene glycol was developed to replace ethylene glycol under circumstances when potable water and food could be exposed. In some locations, propylene glycol must be used because it is more friendly to the environment. Ethylene glycol should not be used if there is a risk of contaminating potable water, food processing, or any products to be consumed by humans.


While glycol protects the loops from freezing, it does reduce the efficiency of the fluid. For example, a 20% ethylene glycol solution results in a 6% loss of heat transfer, whereas 40% glycol solution results in a 14.5% loss of heat transfer.