Heat transfer modeling and system performance assessment of an innovative thermosyphon radiator integrated with air source heat pumps for sustainable heating applications

• A novel thermosyphon radiator improves ASHP efficiency and comfort. • The radiator eliminates the need for water pumps, reducing energy consumption . • The heat transfer model captures complex “boiling-condensation” phenomenon. • A modular approach enables flexible simulation/optimization of the ASHP system . • A case study shows stable indoor temperatures with improved energy efficiency. Air source heat pumps (ASHPs) are a key technology for achieving low-carbon buildings, with indoor heating terminals playing a crucial role in determining system efficiency and occupant comfort. Traditional air- and hydronic-based heating terminals often face challenges, such as uneven heat distribution, increased energy consumption, and inconsistent thermal comfort. This study proposes a novel thermosyphon radiator for ASHPs, which offers high heat transfer efficiency, rapid thermal response, and eliminates the need for water pumps. The heat exchange between the refrigerant and thermosyphon fluid forms a complex system involving simultaneous boiling and condensation. To model this “boiling-condensation” phenomenon, a combination of distributed and lumped parameter methods was employed to accurately capture phase changes while enhancing computational efficiency. A simulation demonstrated that the radiator’s working temperature increases with heat input. The use of thermosyphon fluids with high boiling heat transfer coefficients, such as pentane, improves radiator performance, raising the working temperature by 3 to 5 °C compared to water. Mathematical models for other system components were developed, enabling a modular approach for simulating the entire system. The model’s reliability was validated through a field test, showing prediction errors below 10 %, confirming its accuracy. Using this model, system performance was evaluated under various conditions. Additionally, a case study in Taiyuan revealed that the system achieved an average coefficient of performance of 2.67 throughout the heating season, 23.6 % higher than the system with traditional radiators. These findings highlight the potential of thermosyphon radiators to enhance ASHP efficiency and contribute to more sustainable heating solutions.