Having run a lot of numbers, it looks like some of the bottleneck in closed ground loops is the PE pipe that is used.  The conductivity is about 1/2 of the soil around it though I realize the soil must then diffuse that. 

I stumbled into a couple products that have "nano particle" (trendy BS term today) optimization to double the thermal conductivity of the material.  Obviously the less excavation, pipe, and/or improved performance can all affect the bottom line.  I have not received anything back on pricing so I have no clue if it is then 5X the cost? 

Anyone using anything other than standard old HDPE SDR11 pipe for the geo field?  Would you even consider something else? 

If this special pipe is infused with copper, I might question long term life expectancy. 

I would be leery of it. HDPE works well, the pipe is relatively thin wall. But if you want to try it out...let us know how it works.

They have quite a resume' of installations and sounds like it has been out there for quite a while. However, if everyday designers are not familiar, I tend to wonder if they priced themselves at a point that only people that NEED it will pay for it...

The limiting factor is always the conductivity of the ground bringing the heat to the ground, thus the pipe is not the needle ear.

"Having run a lot of numbers, it looks like some of the bottleneck in closed ground loops is the PE pipe that is used. The conductivity is about 1/2 of the soil around it though I realize the soil must then diffuse that."

And that is why slinkies and multi pipe race tracks can shorten trenches.

I did find out this magic pipe is about 55c/ft for 3/4". I figured it was priced pretty high. Probably too high to make financial sense unless in a really confined space.