The Techs at HUG Hydronics have been working on an interesting case this week. We were called to investigate mold forming on a HUG Hydronics tank in a client’s cabin. Obviously this meant something was amiss and we took a sample of their water/antifreeze mix back to the lab. Its pH level was 6.1 (for reference the pH of the stuff we sell is 8.5) , it froze solid at zero degrees, and it had a moldy smell.
Antifreeze’s job in Hydronics Heating applications is to make sure things don’t freeze up, even when the application may be subjected to below freezing temps most likely to occur in jobs like driveway de-icing or solar water heating. But not all antifreezes are created for this job. Hydronics systems have 2 good choices for antifreezes; ethylene glycol, and the less toxic variety propylene glycol (the one we sell).
Angela D. Harris, in the article “The Dos and Don’ts of Hydronics System Glycol”, that appears in The News, Air Conditioning/Heating/Refrigeration, published on Sept. 24, 2020, quotes a specialist from Go Glycol Pros discussing the differences between the two glycols: “Propylene glycol is a less toxic fluid; however, ethylene glycol has a little bit better heat transfer, often at a lower cost,” said Rohr. “I would not recommend ethylene glycol in any system that has a domestic water exchange, but it is still common in industrial and commercial process demands.”
In this same article Harris also discusses what makes the heat transfer less efficient with antifreeze, “If a system is utilizing glycol, instead of pure water, that mixture has a different heat transfer rate with potentially five to 10 percent less efficacy than water due to its viscosity,” said Walter Timerson, HVAC technical educator at the Isaac Training and Education Center (ITEC). “Standard mixtures are 50/50 in most boilers, depending on the type of system, mixtures of 60/40 or 70/30 in snowmelt, ground source heat pumps, and solar water heating systems are common.”
HVAC antifreeze often comes pre-mixed with the right ratio of glycol to distilled water, and becomes a “heat transfer fluid” in your system; meaning that it’s the liquid that carries the heat to the cold areas to be warmed. Purchasing the right amount in the right concentrations is important to the functioning of your system. Some of this discussion can be viewed on our glycol propylene page, and can also be discussed with any of our Sales Techs.
Harris then notes that you need to check your Glycol yearly and that the “pH level should range between 8.0 and 10.0 to minimize corrosion and glycol degradation.” Any narrow range pH testing strips should be able to do the job. She continues by explaining that, “Any fluid with a pH below 7.0 should be replaced. For fluids between 7.0 and 8.0, adjustments can be made using a 50 percent solution of sodium hydroxide or potassium hydroxide.”
Every 3-5 years the glycol degrades enough that it will have to be completely replaced. You will know it is time if the pH is lower than 7.
Other cautions Harris offers are: Do not Mix antifreeze types, and to make sure to dispose of them properly.
Do’s & Don’ts of Glycol Storage and Disposal
DO keep new and waste antifreeze in clean, closed, and labeled containers that are in good condition with no leaks or defects.
DO NOT store glycol in old food or beverage containers, or store where pets and children could access the antifreeze.
DO clean up any spills immediately and report the spill when required.
DO NOT mix with other wastes (including other antifreeze chemicals) unless the recycler will accept that mixture.
DO store glycol in a well-ventilated area.
DO NOT pour glycol down the drain, into a septic system or onto the ground for disposal.
DO recycle or dispose of it properly.
Source: Michigan Department of Environmental Quality and U.S. Environmental Protection Agency
OK, now back to our mystery:
The next step was to interview those involved. We talked to the man who set up the HUG system. When he chose his antifreeze, he went to the hardware store and found something on the shelf that looked good. It was the wrong choice. Its pH was too low and it’s freezing point too high. We sell antifreeze that is perfect for this application, so our customers don’t have to guess what to use.
So in Just Ducky fashion, we helped him empty, clean, and refill his system with the right mix of propylene glycol.
And it should be one happy HUG Hydronics system :)