I am planning a 2300sqft bungalow and had the engineers who are doing a Net-Zero home here  (LINK)  have look at the plans. There will be an ICF foundation and SIP wals and roof.
I asked them about Earth Tubes.
My take on tubes was that you used them to pull IN air through the ground for a bit of prewarming before it hit the HRV.
They suggested that i exhaust the low- value warm air from the HRV OUT through a series of tubes under the basement foundation, exiting around the perimeter of the foundation around the weeping tile with a bout 4 or 5 feet of 1-2 inch gravel with vents every six feet or so. They said I wouldn't get much heat from the ground at -30, and there may be an issue with mold in the pipe. Using the waste heat in the exhaust air to warm the foundation was a more efficient way to keep energy costs down.
Has anyone heard of this before?

bob