REVERSIBLE HEAT PUMP-ORC PILOT PLANT – EXPERIMENTAL RESULTS AND FLUID CHARGE OPTIMIZATION

Abstract

The reversible operation of the heat pump process and the organic Rankine cycle as a Carnot battery has gained attraction of the scientific community in recent years. Despite numerous publications investigating the potential of such systems as a new energy storage technology, experimental results are scarce. The present work presents the outcomes on process level of a first experimental characterization of a reversible heat pump – organic Rankine cycle (HP-ORC) pilot plant designed for a maximum charging capacity of 15 kWel in heat pump mode and discharging capacity of 9 kWel in ORC mode. The experimental campaign comprised 150 stationary operating points. The plant yielded a maximum COP of 9.5 and a maximum ORC net efficiency of 4.4% for the defined boundary conditions of this experimental campaign. While the heat pump favors low temperature lifts for a high COP, high temperature gradients are favorable for ORC operation. Moreover, limitations on component and system level were determined. The challenging aspect of a proper fluid management of such reversible systems was identified as a crucial factor. Finally, the impact of fluid charge on ORC operation was experimentally evaluated and revealed significant optimization potential by means of an adequate fluid management.