Dynamic modeling and analysis of a closed-loop steam compressor test rig for industrial heat pump applications
Heat pumps are expected to play a primary role in electrification of thermal users in the residential and industrial sectors. Dynamic compressors are widely used in large size heat pumps, thanks to their industrial replicability, compact size, affordable costs, and good performance in terms of efficiency. The instability, which may occur in a compressor installed in closed loop cycle such as in a heat pump, is quite different from the classic open loop configuration involving dynamic compressors. Therefore compressors should be tested before getting into operation to make sure that its thermodynamic behaviour is stable. This study investigates the dynamic behavior of a steam compressor integrated into an innovative closed-loop test rig. A dynamic model of the system, developed, represents the coupled interaction among a steam generator, expansion valve, compressor, back-pressure valve, and water bath cooler. A proportional integral controller regulates the vapor fraction within the cooler by modulating an environmental bypass valve to ensure stable operation during transients. The model is used to analyze the startup process, stability under varying compressor speeds, and controller response to disturbances. The results show that the system starts smoothly, reaches steady operation without oscillations, and maintains stability following rapid compressor speed variations. The compressor operating points remained within the valid map range, confirming accurate representation of its performance. The developed model provides a validated and flexible framework for the future design and experimental testing of steam compressors and advanced high-temperature heat pump systems. Future steps will encompass building a laboratory scale test rig to validate the model and to be a standard test rig for testing compressors in the future.