Large-scale ammonia-butane high-temperature heat pump demonstrator: Development of fundamental numerical models and experimental validation

A cutting-edge thermal pilot plant at the Fraunhofer IEG facility of Bochum proves the technical viability of high-temperature heat pumps that employ seasonal mine thermal energy storage as a heat source. The system injects 500 kW of thermal power into the conventional district heating grid, reducing fossil fuel-related CO2 emissions by up to 4800 tons annually. In this study, we detail the installed ammonia and butane high-temperature heat pump system and describe the six-months on-site data collection, characterized by the system operating for the first time at supply temperatures above 90 ◦ C, reaching 120
C. We define a system of four numerical models developed to predict the performance, the electrical and thermal powers of the high-temperature heat pump
system under several operating conditions. The models, two steady-state and two dynamic, thoroughly described, are developed respectively with Visual Basic for Applications, Matlab, OpenModelica, and Dymola. The results indicate that the steady-state models exhibit especially low percentage errors on total coefficient of performance and produced thermal power, respectively 0.19% and 1.31% for the Visual Basic for Applications code and 3.40% and 0.59% for the Matlab code. The dynamic behavior of the plant is accurately represented by the OpenModelica model, furthermore Dymola offers a closer approximation to the installed system, requiring accurate initialization and parametrization. The developed models serve as a foundational framework for the installed thermal plant, capable of adaptation to other systems, enabling broader application and further advancements in high-temperature heat pump technologies, particularly in planning and digital twin representation.