does anyone know what if any system effect it has if ethelyne glycol gets added to a system filled with propylene glycol? say for example an existing loop has propylene glycol and a unit gets added or branch piping gets relocated and ethelyne glycol gets added.
They do blend together, EG is a slightly better transfer fluid and is common in larger commercial systems as a heat transfer fluid. EG is best kept away from potable water with double walled HX protection. PG may or may not require double walled HX, depends on your AHJ.
I have had some dealings with glycol in a geothermal closed loop system. I took several samples and they were different colors and mesured diferent freeze points. The major issues this customer was having was freezing water to water units. I sent all the samples to some company in Pensylvania and the one sample I had had a very high PH and lots of floating particles. I was told that different manufactures and different kinds of glycol will not mix and can cause corrosion and other adverse affects. Not sure who to believe.