Emergy analysis and optimization for a solar-driven heating and cooling system integrated with air source heat pump in the ultra-low energy building

Abstract

In this paper, a solar-driven heating and cooling system integrated with air source heat pump is designed and applied to the ultra-low energy building. The heat and electricity from the compound parabolic concentrated-photovoltaic thermal collector are fed to air source heat pump to increase the efficiency of the air source heat pump. Integrating energy, social, environmental, and economic benefits of the system in the whole life cycle, an emergy-based optimization method is adopted to obtain the optimal configuration of the compound parabolic concentrated-photovoltaic thermal collector. Under the optimal configuration, the emergy performance of the designed system is analyzed, and the monthly emergy performance and the influence of investment cost and solar irradiation on the emergy performance are discussed. The optimization results show that when the photovoltaic coverage ratio is 1.0, the total emergy consumed by the designed system is the lowest, 2.64 × 1016 seJ/y, which saves 9.96% of emergy compared with the reference system. The environmental load ratio, emergy sustainability index, emergy investment ratio, and emergy yield ratio under optimal configuration are 126.62, 0.021, 0.62, and 2.64, respectively. The emergy investment ratio and environmental load ratio in January are the highest, which are 0.28 and 100.09, respectively, while the emergy yield ratio and emergy sustainability index in May are the largest, which are 15.02 and 0.179, respectively. The environmental load ratio and emergy investment ratio are positively correlated with the annual investment cost, while the emergy sustainability index and emergy yield ratio are negatively correlated with the annual investment cost. The emergy optimization facilitates a better selection of building energy supply systems.