District heating substations integrating heat pumps: opportunities and experiences with hardware-in-the-loop testing procedures
This paper presents a comprehensive overview of a Hardware-in-the-Loop testbed and testing procedure applied for developing district heating substations integrating heat pumps. The study highlights the distinctive features of the testbed, offering an in-depth analysis of its capabilities to support the design and performance evaluation of the considered district heating substations. The paper delves into four different configurations demonstrating the flexibility of the Hardware-in-the-Loop approach, ranging from substations that include all components to those with some components emulated. The first case is a substation that includes heat pumps and two thermal energy storages while the second case includes a heat pump and a storage. The remaining two hybrid configurations both employ a real bidirectional substation: in the first, the heat pump is emulated based on numerical models, while in the second, real-time monitoring data are used from a heat pump located in a different facility. The described testing procedure emulates both the district heating network and thermal load according to realistic profiles, enabling the analysis of the district heating substation's operation under dynamic conditions that mimic real-world applications. The study involved a series of experiments designed to simulate real-world operational conditions, including peak load demands and partial load operations. Within this framework, various control methodologies, such as Rule-Based Controls and Model-Predictive Controls, were tested, analyzed in detail, and compared. Furthermore, the paper discusses the technical challenges encountered during the integration process, including system compatibility, control strategies, and maintenance requirements. Solutions, improvements, and best practices derived from these experiences are also presented, providing valuable insights for future implementations of similar systems. Overall, the laboratory tests underscore the potential of the implemented testing procedure in advancing sustainable energy solutions and improving the overall efficiency of district heating networks, particularly through the integration of heat pumps and the application of advanced control strategies.