[jnsaff2]

Well it does not have the heat pump. So you will only ever get the temperature the ground is at. In his case the temperature of the ground is 11C. Which I guess is fine for the greenhouse with the additional sun gain.

This is nowhere near enough for human habitation comfort let alone hot water.

[mcnugget]

Yea, the difference is in capex cost and capabilities so the best you'll get is the ground temperature. Ideally you put a ground source heat pump but the energy needed to run it is high, COP for a ground source heat pump is like 3-6, cop on earth tubes are like 30 because you're only running a fan but you get whatever temperature the ground is.