Ground Source heating

[Big Pete]

Wandering a bit away from Seafaring here.

On my last trip at Sea we had a Russian Electrician onboard who was telling me about a Domestic Heating system from Scandinavia that the Captain on another ship had installed in his house. He said it took no external power to run, and transferred the Heat from the Ground into the house in multiple stages. Generating totally Free heat, but with a high Capital cost.

I puzzled ove this for a while, and the only way I can see that this is possible would be some sort of ground source heat pump.
I can see that this might work using the heat in the House to drive an Ammonia Adsorbtion cycle, the heat source would be at such a low temperature that the difference between the input and output temperatures could only be very low, so you would require multiple cycles in a tandem or cascade arrangement to bring a house up to a living temperature. Also, if the house and the ground were initially at the same temperature you must have some initial source of Heat to start the system.

Does anyone know of such a system or have any alternative suggestion as to how it could be done?

BP