Dynamic performance evaluation of an R718 high-temperature heat pump within the GEOSYN project
High-temperature heat pumps (HTHPs) offer a viable solution for reducing greenhouse gas (GHG) emissions in hard-to-abate industrial sectors by replacing fossil fuel-based boilers to supply heating for various thermal processes. This paper presents the modelling and simulation results of an HTHP that uses geothermal energy as the heat source. The study is part of the ongoing GEOSYN project, which aims to develop and demonstrate an R718 heat pump integrated with a heat-powered chiller to enhance the utilization of geothermal energy sources. The HTHP is designed to operate at an evaporator temperature of approximately120 °C, delivering a temperature lift of up to 80 K. The system employs a newly designed four-stage reciprocating compressor with intercooling between each stage. The overall performance and environmental benefits of the R718 HTHP in the context of its application to the textile industry were investigated based on a system dynamic model along with the proposed control strategy. Field measurements from a geothermal plant in Tuscany (Italy) were used for the dynamic analysis of the proposed system, in addition to the varying steam load profile of the selected case study requiring steam at 185 °C. The results show that the proposed HTHP system can achieve an average coefficient of performance (COP) of 3.48, along with a reduction in operating costs and GHG emissions of up to 64% and 96%, respectively, compared to a natural gas-fired boiler. Furthermore, the proposed control strategy effectively maintained the discharge temperature within the compressor’s safe operating limits. The findings contribute to the advancement of HTHP technology by providing insights into control strategies and integration with geothermal energy sources.