Overview of a newly-installed high-temperature heat pump demonstrator coupled with high-temperature mine thermal energy storage

Abstract

The research aims to prove that renewable energy sources in the heating sector can enable the energy transition towards European and German CO2 reduction targets.To do so, at the premises of the Fraunhofer IEG Institute in Bochum a demonstrator for high-temperature heat pumps (HTHPs), coupled with seasonal high-temperature mine thermal energy storage (MTES), was developed.The goal is achieved by demonstrating the feasibility of the technology by connecting mine water present in a small flooded coal colliery (MTES) to solar parabolic trough collectors (SPTCs) and also to a HTHP system that serves the local district heating (DH) grid of Bochum south.The MTES, with an estimated water volume of approximately 20000 m3 is employed as seasonal storage for a 500 kW HTHP system that can reach a supply temperature of 120°C, as needed by the existing DH grid when the ambient temperature is lower or equal to -10°C.During the summer operation, the heat is injected into the MTES from the SPTCs to obtain a mine water temperature of 60°C; and in the winter operation, the heat is extracted through the HTHP until the mine water reaches the unheated temperature of 12°C at the end of the heating season.A literature review of the main components of the plant, the description of the installed system parts and performed tests are reported, along with the results of the successfully executed tests.