Evaluating heat recovery systems to mitigate thermal stratification in large-space buildings during heating seasons

• A heat recovery system is introduced using a heat pump and ceiling radiant panels. • The system captures and redistributes heat from the upper regions of large spaces. • Thermal stratification is reduced significantly, with a 45% drop in temperature gradient. • The occupied area temperature rises by 5.4°C, and pressure gradients drop by 23% • The effects of varying heat recovery temperatures on system performance are analyzed. Large-space buildings often experience thermal stratification during winter heating, with higher temperatures at the top and lower temperatures at the bottom, resulting in heat waste. Additionally, air infiltration caused by buoyancy further degrades thermal comfort. This study proposes a heat pump heat recovery system using ceiling radiant panels to recover heat from the upper space and improve indoor thermal conditions. A case study was conducted on a large building at a railway passenger station, and a CFD model was used to simulate the system under various radiant panel temperatures. The results show that the system significantly reduces thermal stratification, with a maximum reduction of 45% in the building’s temperature gradient. The temperature in the occupant zone increased by up to 5.4°C, and pressure gradients were reduced by up to 23%. The system also reduced air infiltration heat loss by 18.9% and the heating demand by 13.1%. Further analysis revealed that indoor temperature gradient, pressure gradient, air permeability, and the heating demand were positively correlated with the radiant panel temperature, while heat recovery was inversely proportional to the recovery temperature. The best performance was achieved with a recovery temperature of 12°C, where air infiltration was lowest and heat recovery was maximized. At a radiant panel temperature of 18°C, the comfort of occupant zone is optimal, with the temperature reaching its highest point. Additionally, the heat recovery system can also enhance the coefficient of performance (COP) of the heat pump system and reduce power consumption. When the radiant panel temperature is 12°C, the heat recovery system achieves optimal energy efficiency, saving up to 18.0% of power consumption. This study validates the effectiveness of the system in reducing thermal stratification and improving thermal comfort, providing valuable reference for the design and renovation of HVAC systems in large space buildings.