I was just visiting friends in Rice Lake Wisconsin who built a new home this fall.  He specified geothermal and the contractors installed a 4.5 ton Econar FA heat pump with a horizontal ground loops.  The contrators instructed my friends to go down to the local Menard's and purchase several pallets of windshield washer fluid to use to fill the ground loops?  I've never heard of this.  Is there any know issues with using washer fluid as the system's antifreeze?  Everything seemed to be functioning OK when I was there (it was -10F).

I have heard of this practice.

Can't say if it is ok or not.

I heard at a geo class put on by Carrier , that its exactly the same stuff , sold as washer fluid to make it seem more eco friendly

I'd be skeptical - the stuff is cheap, but formulation questionable - there may be alcohol, ammonia, who knows what else, and that may vary from batch to batch. I'd want a better handle on what's in it and its compatibility with geo plumbing.

For northern geo apps antifreeze is a vital quality, but also need conductivity and viscosity so as to maintain heat transfer and turbulent flow.

MSDS - good catch.

Here methanol is readily available,  we simply do the math to 20%  add it directly to purge cart, pop in a rit dye tab or two, add water and swirl.  When the pretty colors come back to the purge cart we continue for a time then check the mix with a hydrometer.
Eric

I like it!