Selection of natural refrigerants for heat pumps in district heating systems
Heat pumps designed for district heating (DH) systems, utilizing natural refrigerants, are emerging as transformative technologies for decarbonizing urban energy networks. This study focuses on evaluating the theoretical performance of such heat pumps using different natural refrigerants and examining their integration into district heating systems. By analyzing potential heat sources, district heating temperature requirements, and capacity demands of existing or potential new DH systems, the research establishes boundary conditions that guide heat pump theoretical performance analysis of heat pump. It identifies the best-performing refrigerant options under the specified conditions. Thermodynamic performance analyses are conducted using Engineering Equation Solver (EES) to model and simulate heat pump cycles for selected natural refrigerants. Key refrigerant properties including critical temperature and pressure, coefficient of performance (COP), volumetric heating effect (VHE), and operating pressure range are assessed to ensure compatibility with DH system requirements. The insights gained from these analyses are used to compare refrigerant performance tailored to meet specific DH requirements. This study presents a comprehensive analysis of COP across three generations of district heating systems, examining the effects of heat source temperature and system design parameters on refrigerant performance. The results reveal that R717 consistently demonstrates dominant performance in the basic cycle, achieving the highest COP values among the evaluated refrigerants. Additionally, RE170, R600, and R600a also exhibit strong performance, particularly with the integration of an internal heat exchanger (IHEX), which enhances efficiency across all generations. Overall, this research provides valuable insights into the performance characteristics of various refrigerants, highlighting the critical role of cycle design in optimizing heat pump performance.