To meet the increasing demand for small high efficient domestic heat pumps with a good total cost of ownership performance, a next generation of heat pumps is required. This article is dealing with the development of a new compressor technology for domestic heat pumps. After identification of the main losses in mechanical driven low capacity heat pump cycles, it became clear that a concept with a (semi-)free piston compressor has the potency to improve the efficiency significantly. An evaluation showed that none of the existing free-piston designs meets essential requirements like low internal friction, small size integrated electromotor and hermetic design suitable for all refrigerants, including ammonia. Therefore TNO designed a complete new free piston compressor making use of the following two design philosophies: balancing mechanical forces by using symmetry and reducing motor size by use of transmission ratio based on elastic deformation and the peak shaving effect of the energy contents (kinetic and elastic) of the compressor running in a natural frequency mode This paper describes the background, the design steps and the final design of the new torsion compressor technology.
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