A closed-loop heat exchange system and related methods for harnessing subterranean heat energy from a subterranean zone having a passive heat transfer device with multiple operational modes for targeting hotspots within the subterranean zone and adjusting the rate of energy harnessed according to consumption demands. The system can also have at least one enhanced surface section for increasing the heat exchange efficiency and/or a variable pump for controlling the rate at which the working fluid travels through the passive heat transfer device.