Design and performance evaluation of a solar-assisted biogas and air-source heat pump hybrid system for radiant heating applications

Energy and environmental crises have become critical challenges, making the efficient use of clean energy a focus of public attention. Although emerging clean energies have high economic and environmental values, these single energy sources are not well-developed. In colder climates, maintaining a stable fermentation temperature can be difficult, leading to the idling of many biogas digesters. Furthermore, despite extensive research on solar-assisted air-source heat pumps, these systems perform poorly in cold climates with low solar irradiance. To address these issues, this study investigates the integration of a solar-assisted biogas and air-source heat pump hybrid heating system (SBHP-HHS) for capillary radiant heating in rural North China, specifically adapted to local conditions. The system aims to utilize the combined benefits of various clean energy sources to improve system reliability in harsh climates. By combining experimental analysis with TRNSYS simulation, the system performance during the heating season in rural northern China was evaluated. Experimental results show that the hybrid system, utilizing the radiant capillary terminal, is capable of maintaining room temperatures above 20 degrees C, demonstrating its effectiveness. Simulation results show that the air-source heat pump achieves a coefficient of performance (COP) of 4.6. This efficiency level is generally favorable, ensuring stable operation. Additionally, the system achieves a solar-biogas hybrid utilization rate exceeding 75 % and a primary energy-saving rate of 78 %. Economically, the system offers an 8.23-year dynamic payback period and annual cost savings of 3055 CNY. Environmentally, it reduces CO2 emissions by 4263.6 kg annually. This study provides a solid experimental foundation for further research, offering empirical evidence to optimize system performance.