In this study, both energy and exergy analyses and sustainability assessment of a thermal energy storage system with a solar-ground coupled heat pump installed in a 120 m2 house are performed. The actual operating data taken from the literature are utilized for model validation. The system considered here mainly consists of a solar collection system, an underground thermal storage system, an indoor air conditioning system, and a data collection system. First, energy analysis is employed to the system and its components, and the rates of energy input (solar radiation), energy storage, collector heat loss, and other heat loss are found to be 4.083 kW, 1.753 kW, 1.29 kW, and 1.04 kW for a 5 h working time, respectively, while the energy efficiency of the system is calculated to be 42.94%. Exergy analysis of the entire system is then conducted for various reference temperatures varying from 0°C to 25°C with a temperature interval of 5°C. As a result of this analysis, the rates of the maximum exergy input, exergy storage, and exergy losses are determined for a reference temperature of 0°C to be 0.585 kW, 0.24 kW, and 0.345 kW, respectively. Finally, the maximum exergy efficiency of the system is obtained to be 40.99% and the maximum sustainable development using sustainability index, which is a function of exergy efficiency, is calculated to be 1.6946 for a reference temperature of 0°C. Furthermore, the energy and exergy results are illustrated through Sankey (energy flow) and Grassmann (exergy loss and flow) diagrams.
Assessment of sustainability of different renewable energy systems based on life cycle exergy analysis
