Performance assessment and multi-objective optimization of a geothermal-based tri-generation system in hot Summer Continental Climate: Tianjin case study

Abstract

Considerable interest in the investigation of energy supply systems that effectively utilize renewable energies is being aroused due to the shortage of fossil energy and serious environmental pollution. Geothermal energy is a considered as a promising alternative to fossil energy due to its advantages of large reserves, good stability, and strong sustainability. This paper developed a geothermal-driven tri-generation system to generate power and supply heating and cooling demand. The tri-generation system is composed of an absorption refrigeration cycle, a heat exchange cycle, and an organic Rankine cycle. The paper begins with an introduction to the thermodynamic, economic, and environment models of the presented system. The effects of the geothermal water parameters on the system performance were originally investigated based on the actual data of a sports center (zero energy building). This building is located in Jiefang South Road, Tianjin, which belong to Hot Summer Continental Climate. In addition, the multi-objective optimization of this system was carried out based on the TOPISIS decision-making method considering economic and environmental criteria. The minimum payback period and maximum carbon emission reduction were chosen as the optimization factors. Finally, the optimal temperature of geothermal water is obtained and the exergy analysis was performed under the optimal conditions. The results indicate that the presented system possesses an optimal geothermal water temperature of 83 °C. Under this temperature, the total thermal efficiency in cooling season and heating season were 41.17 % and 84.93 %, respectively. The exergy efficiency in cooling season and heating season were 47.28 % and 62.23 %, respectively. Our proposed system has equivalent annual operating cost of 12.9 k$/year, with a payback period (PBP) of 2.57 years and carbon emission reduction of 2379 ton/year. The condenser and evaporator need to be improved in terms of large exergy loss rate and low exergy efficiency.