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Stirling engines have many unique advantages including higher thermal efficiencies, preferable exhaust gas characteristics, multi-fuel usage, and low noise and vibration. On the other hand, heat pump systems are very attractive for space heating and cooling and industrial usage. There are several environmental merits of Stirling-driven vapor-compression (SDVC) systems. A design method for the SDVC, which is based on mathematical methods for Stirling and Rankine cycles, has been developed. The model treats a kinematic Stirling engine and a scroll compressor which are coupled by a belt. The measured performance of an actual system well agreed with the calculated results. The attractive SDVC performance using conventional and alternative refrigerants was shown. From the calculated Total Equivalent Warming Impact, TEWI and operating costs, it became clear that the SDVC system with the alternative refrigerant has a higher potential as the future air-conditioning system.

Solar-driven generators which have closed cycles are proposed. The cycles consist of isentropic and two isobaric processes. Two types of the cycle engines are designed based on the concept. The cycle performance is calculated for normal and improved cases with the theoretical background. From the results, the improved closed cycle promises a high performance for the solar application. Actual engines are currently designed to achieve the 20% system efficiency.

A small size engine, SD01 has been developed since 1989. For the purpose of cultivating the advantageous properties of the SD01 engine, its cylindrical cam mechanism was modified. The modification was able to operate the Stirling cycle stably and silently. The modified SD01 coupled with an electric motor was reconstructed as a hermetic cooler. The attractive Stirling cooler was evaluated on the conditions of a cooling mode. Moreover, with an aid of the enhanced design concept for the SD01 machine, a small size Vuilleumier machine for heat pump applications was designed and constructed.