Are we talking heat pumps or a different passive heat exchanger system? Air-con/heat-pumps/refrigerators can extract heat from surprisingly cold sources as long as there's enough of them e.g. the city of Dremmen that extracts heat from the near freezing North Sea to heat water to near boiling point.

The original claim of a 30% saving seems like the jump from from air source to ground source heat pumps which are often quoted as giving back 3x or 5x the energy put in, respectively.