Increasing Heat Pump Efficiency Through Expansion Turbine Integration: A Comparative Study of Refrigerants and Process Cycles

The growing demand for energy efficient thermal systems highlights the importance of optimizing heat pump performance. This study investigates the replacement of conventional expansion valves with expansion turbines in heat pump processes, allowing partial recovery of compressor work. Process simulation software was used to investigate different refrigerants, process parameters and cycle configurations to evaluate potential improvements in system performance. The focus was on propane (R290), a refrigerant of increasing importance due to its environmental benefits and favorable thermodynamic properties. The results show significant improvements in the coefficient of performance (COP) of heat pumps by up to 24%, particularly at lower operating temperatures where systems typically lose efficiency due to the large temperature rise. By integrating an expansion turbine, COP improvements were observed across the operating range, with the most significant improvements at colder heat source temperatures. In addition, this approach extended the efficient operating range of the heat pump system, allowing it to operate more effectively under challenging conditions. These findings contribute to the development of more sustainable and efficient energy systems, especially for large heating applications such as industrial and district heating, as well as high temperature heat pumps.