The latest post on this topic by Beetle is:
Yes it sounds like a similar or the same system as 'earth tubes'. Apparently the cooling unit itself costs about the same as an evap aircon. and will be formally released in Nov. Not sure if it is the same system as the one you mention but we should have more details soon. The echoarchitect told us it releases dry cool air into the house through pipes that vent into the rooms.
I am not sure how long the pipes are, but I know we need a 120 mm slab with entry points into the house, & the tubes sit under the slab ( ). We will also install airvents to vent hot air into the roof space and cool the house down at night + 3 whirly birds on the roof. Sounds heavenly. The vents aren't perfect and will release some cold air back into the house as someone else has already posted on the forum.
We hope to have hydronic heating and currently have the solar panel & apricus system as part of our spec. The windows will be a combination of double glazed and comfort plus (larger panes of glass).
I will post our plan once we get it back with all the mod cons from the architect/builder.
Hope above is clearer than mud