Analysis on effect of cold air re-circulation on performance of heat collector units in Large-Scale Air-Source Heat Pumps (ASHPs)
Large-scale air-source heat pumps (ASHPs) are increasingly recognized as essential technology for promoting sustainable heating and cooling solutions in urban and industrial settings. They provide an efficient and environmentally friendly alternative to traditional energy systems. This study presents a comprehensive threedimensional computational fluid dynamics (3D-CFD) model designed to accurately capture the performance of heat collector of large-scale ASHPs under realistic environmental and operational conditions. Unlike previous models that often relied on simplified assumptions, this framework incorporates critical factors, such as, a: compressible flow, b: dynamic fan inlet and outlet temperatures, c: pressure variations along the fans, and d: variable mass flow rates influenced by fluctuations in air density. The model has been validated against experimental and numerical data from existing literature, demonstrating a strong agreement in volumetric effectiveness and flow characteristics. The results of this study provide valuable insights into the complex flow phenomena around the heat collector and their direct impact on the system performance. The impact of wind velocity (ranging from 0 m/s to 8 m/s) on the flow circulation around the device and the system's performance has been analyzed. As wind speed increases up to 5 m/s, efficiency declines due to enhanced vortex formation around the longer sides of the heat collector. This circulation of cold air to the inlets of the fans reduces system effectiveness. However, beyond this point, further increases in wind speed weaken these vortices, resulting in more stable airflow and improved system performance. Additionally, as the wind velocity increases from 0 to 8 m/s, it increasingly weakens the upstream vortex, resulting in improved working conditions for the fans located on the upstream side of the heat collector. These findings demonstrate a strong correlation between vortex behavior around the heat collectors and the overall operational efficiency of large-scale ASHPs.