Parametric energy analysis of alternative layouts for an R718 high-temperature heat pump – insights from the GEOSYN project
The recovery of medium- to high-temperature waste heat remains a significant challenge in industrial applications, particularly for high-temperature heat pumps, which often struggle to source heat at the required temperatures for effective operation. The GEOSYN Horizon Europe project addresses this issue by developing an innovative R718 high-temperature heat pump that harnesses medium-enthalpy geothermal energy, delivering 50 kW of process heat at 200 ºC to a local dairy plant and achieving a temperature lift of at least 80 K. Water offers several advantages as a high-temperature working fluid, including low cost, wide availability, zero environmental impact, non-toxicity, and non-flammability. However, it also presents significant challenges, such as high specific volume, large compression ratios, and high discharge temperatures, which must be addressed to fully exploit its potential. A preliminary energy analysis was conducted to assess how different system configurations respond to variations in key thermodynamic and technical parameters, including evaporation and condensation temperature levels, suction superheat, and the number of compression stages. Parametric analyses were performed to evaluate the effects on overall performance, compression ratios, volumetric heating capacity, and discharge temperatures. Open intercoolers yielded the highest COP of 3.87 under design conditions, though at the cost of increased system complexity. In contrast, closed intercoolers resulted in slightly lower performance but provided a more practical solution, effectively addressing the main technical challenges. These analyses provided a basis for component selection, particularly for the compressor, and for the initial performance evaluation, thereby guiding the design of the complete machine optimized for high-temperature industrial heat recovery