Solar-assisted biogas system with air-source heat pump for the energy-saving of indoor heating in north China

Abstract

To address the challenges associated with winter heating in high-latitude regions of China, solar-assisted biogas heating systems have emerged as the predominant focus of research due to their cost-effectiveness, accessibility, and environmentally friendly attributes. However, traditional solar-assisted biogas heating systems encounter issues of low efficiency and limited practicality resulting from unstable solar radiation and extreme ambient temperatures during the heating season. To improve the economy and stability of the system, this study proposed a novel operational control method for a small-scale energy station system in rural regions of North China, named Solar-Biomass-Air Source Heat Pump Hybrid Heating System (SBHP-HHS). The integration of solar energy, biogas energy, and air-source heat pump (ASHP) systems in this proposed work has shown to create effective complementarity and enhances the production efficiency of the existing system. Test and simulation studies have been carried out for this system. The layout of buildings and equipment within a university campus in Beijing is reconfigured and redesigned, incorporating an ASHP into the existing heat source configuration. To begin with, a mathematical model is established for the complementary heating system that incorporates solar energy, a biogas digester, and an ASHP. Subsequently, a dynamic simulation model is developed using the TRNSYS platform, and a corresponding operational control strategy for the multi-energy complementary heating system is proposed. Dynamic simulation and analysis of the newly implemented system are performed using the TRNSYS platform, focusing on energy flow and thermodynamic performance. Throughout the heating season, the solar-biogas integrated system achieves a remarkable assurance rate of up to 79%. Additionally, ASHP maintains a relatively high heating efficiency, coefficient of performance (COP) reaches 3.02. Finally, an economic evaluation of the multi-energy complementary system was conducted based on the annual cost method. This was compared with the clean approach of using only an ASHP unit. The results indicate that the SBHP-HHS is more economical when the anticipated useful life is 6 years or longer. The results indicate that the proposed can achieve significant energy-saving and carbon-reduction benefits in rural areas, catering to their heating needs.