Abstract: A geothermal system includes a first circuit including a first heat exchanger exchanging heat with a controlled space, a second circuit including a second heat exchanger exchanging heat with an outdoor temperature sink that varies seasonally, a geothermal heat exchanging assembly arranged to exchange heat between a geothermal source and the fluid in both the first and second circuits and a pumping device allowing the first circuit to function as a heat pump. The flow in both the first and second circuits is seasonally reversible to alternately heat or cool the controlled space. An expansion motor connected in series with the second circuit in communication between the second heat exchanger and the geothermal heat exchanging assembly is driven by expansion of fluid in the second circuit to function as a Rankine cycle in either seasonal direction of the flow to power the pumping device in both seasonal directions.