Duplex Stirling machines

The duplex Stirling concept - in which a Stirling engine drives a Stirling cycle heat pump - presents a major technological advantage over other types of heat pumps. The free-piston free-displacer device has nominally three moving parts in a single pressure enclosure, the same working fluid in both the engine and heat pump sections, freedom from halogenated hydrocarbons, all this in a highly efficient, well matched system. Over the past five years Sunpower has successfully developed and demonstrated various forms of duplex Stirling devices, ranging from gas fired refrigerator systems having 50W capacity to a residential heat pump having a 10kW capacity. This paper describes some of these projects, and presents an update of this new and very promising technology.