I've been browsing this forum and I've noticed that a lot of people in the US use methanol as their antifreeze chemical in the ground loop. This is quite surprising to me here in the UK, as most people I ask say that there are problems of degradation and the fluid could need changing out avery 3 or 4 years. I would appreciate some comments on this question, as selection of the antifreeze can have a significant impact on loop design - particularly if the choice is ethylene glycol (most common in UK) whose viscosity increases rapidly as fluid temperature falls.
Technically, methanol seems a good choice as it is much easier to design the ground loop to remain well in the turbulent flow regime, and this leads to lower pumping losses and higher heat transfer into the fluid. In contrast, with ethylene glycol it would be very easy to get into a vicious circle of reducing heat transfer, leading to lower entry water temperature, leading to further increase in viscocity, leading to even lower heat transfer and also reduced flowrate, both of which lead to even lower entry water temperature. Not a good position to get into.
So the question is: has there been any experience in the US with degradation of methanol/water ground loop fluids? What concentration of methanol is typically used? Are any biocide additives used to avoid bacterial growth? And have there been any problems of corrosion in pumps, heat exchangers etc or other material incompatibility?
I appreciate that some districts may prohibit methanol use, so I am talking about districts where it is allowed.
Thanks for any feedback.
Jonathan
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