An improved combined ambient-air and earth exchange heat pump system includes a subterranean heat exchanger and an ambient-air heat exchanger, both refrigerant-based, which are adapted to be selectively operated individually, serially or in parallel for heating and cooling purposes. The system also includes...http://www.google.com.au/patents/US5461876?utm_source=gb-gplus-sharePatent US5461876 - Combined ambient-air and earth exchange heat pump system
