Performance investigation and exergoeconomic optimization for a solar-driven direct heating and cooling system

Abstract

Integrating solar energy with direct heating and cooling (DHC) systems can improve system efficiency and reduce polluting gas emissions. To assist buildings in better selecting a DHC system, an exergoeconomic analysis and optimization model combined with building loads and environmental parameters is proposed. The exergoeconomic optimization model is applied to a novel DHC system based on transcritical carbon dioxide heat pump (TCHP) and solar energy. The sold electricity ratio and operating time ratio are defined to transform the building loads and environmental parameters into specific operating conditions of the system. The compressor discharge pressure is optimized to obtain the lowest total unit exergy cost (UEC) of the DHC system. The exergy, energy, and exergoeconomic performance of the DHC system are analyzed under optimal conditions. The results indicate that when the compressor discharge pressure in the heating mode and cooling mode are 7.31 MPa and 8.93 MPa, respectively, the DHC system has the lowest UEC, 0.629 $/kWh. The total UEC is reduced by 43.56% compared to the reference system. Under optimal configuration, the exergy and energy efficiency of the DHC system are 1.81% and 40.30%, respectively. The sensitivity analysis shows that the exergy and energy efficiency, the total UEC, and the UEC in the heating and cooling modes are positively correlated with the sold electricity ratio. The above results demonstrate that the exergoeconomic optimization methods can provide better assistance in selecting the DHC system.