A few additional notes:
This drawing is not to scale. I got frustrated with Inkscape because it has programming bugs. The parallel pipes would need to be small diameter to transfer heat, and the black box would need a lot of surface area, possibly running the full length of the house to create enough buoyancy to compensate for the air resistance (pressure drop) of the small pipes.
If the water tanks are very deep and the A/C system runs in reverse in winter, it may work better on the south side of the building because it's easier to make a large black chimney, and the majority of heat transfer to and from deep underground would be from airflow through the small pipes, not thermal conductivity from the surface. After a couple years of use, it would reach approximately 75 F regardless of surface conditions.
I clicked around on the Australian site some more. There's a brief mention:
Air-to-water or air-to-ground (also called geothermal) exchangers are far more efficient. Heat exchange pipes are run through a body of water or deep into the ground where the temperature is relatively stable all year round.
on this page: http://www.yourhome.gov.au/energy/heating-and-cooling
but the diagram shows water-to-ground heat exchange. So it's possible that some people in Australia are running air underground for heat exchange with A/C and heat pumps.
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