Recent advances in refrigerant circuitry optimization of fin-and-tube heat exchangers for air source heat pump systems

With the growing demand for energy efficiency and the promotion of environmental policies, air source heat pumps (ASHPs) have garnered significant attention as energy-saving devices in building energy conservation. Fin-and-tube heat exchangers (FTHXs) are the key components of ASHPs, serving as the interface for heat exchange between the system and external heat sources or sinks. Their performance directly impacts the energy efficiency of ASHP systems. Optimizing the refrigerant circuitry of FTHX has emerged as a critical research focus for enhancing ASHP performance. Therefore, this paper provides a comprehensive review of the key technological advancements and challenges in circuitry optimization. In the first section, circuitry optimization methods are summarized and analyzed. Firstly, the effect of the non-uniform air velocity distribution on heat pump system performance is examined, and circuitry optimization methods addressing this issue are outlined. Then, circuitry optimization strategies for small-diameter heat exchangers are discussed. Additionally, the variable-circuitry heat exchanger technique aimed at enhancing the overall performance of the ASHP system is introduced. In the second section, four common types of heat exchanger simulation models are summarized, and the crucial role of intelligent algorithms in automating circuitry optimization is emphasized. Algorithm optimization can rapidly generate circuitry configurations that balance thermodynamic performance with manufacturability. In the third section, evaluation methods for circuitry design are discussed, considering thermodynamics, economics and multi-objective optimization. Finally, based on the current research status of circuitry optimization techniques and evaluation indicators, future development trends and improvement measures are proposed. This review aims to provide a guideline for the circuitry optimization of FTHX, thereby advancing the development of high-efficiency ASHP systems.