The choice of water as the refrigerant brings various positive properties. In addition to good thermodynamic suitability, this includes aspects such as environmental compatibility, availability, the possibility of direct process steam utilization, and safety classification. However, using water as a refrigerant presents technical challenges for developers. This particularly concerns the significant temperature increase during compression, which goes far beyond the intended temperature range without cooling the refrigerant, complicating the compressor design.
One focus of the project is therefore on enhancing a screw compressor for the targeted temperature range. Screw compressors are robust, market-leading displacement machines suitable for achieving the temperature lift in a single compression stage while simultaneously injecting liquid cooling water into the compression chamber. Accordingly, the development of an appropriate material, bearing, and sealing concept, as well as the optimization of injection parameters, are central to the compressor enhancement. Simulative and experimental results will contribute to the compressor development throughout the project, leading to gradual improvements during the project duration.
The compressor, initially tested in air and steam cycles in early experiments, will then be tested at Fraunhofer IEG in a closed heat pump circuit with approximately 400 kW thermal maximum capacity under laboratory conditions. The aim is to generate process heat at an industrial temperature and pressure level, albeit with a total capacity of the system lower than the actual industrial demand. The potential for scaling the heat pump to industrial size for future utilization is also a central aspect of the project. The experimental data obtained will be used to calibrate simulation data, allowing for the subsequent determination of the suitability, efficiency, and size of the heat pump for integration into industrial processes via simulation.