Novel geothermal driven CCHP systems integrating ejector transcritical CO_2 and Rankine cycles: Thermodynamic modeling and parametric study

摘要

With recent technical advances, Combined Cooling, Heating and Power (CCHP) system offers a practical and economical alternative to conventional energy conversion systems. Benefits of these systems are more marked with employing efficient thermodynamic cycle and using renewable energy resources. In this regard in the present work, a novel geothermal driven CCHP system, in which the ejector transcritical CO2 cycle is integrated with conventional Rankine cycle, is proposed (system a). The proposed system is then modified by replacing the gas cooler with an internal heat exchanger to make a more efficient CCHP system (system b). To investigate the first and second law performance of the proposed systems, thermodynamic models are developed and parametric analysis is carried out to examine the influences of design variables. The results indicated that, the gas cooler of conventional system can be replaced by an internal heat exchanger for a wide range of practical operating conditions and this replacement can improve the exergy efficiency, net output power and output cooling respectively by 30.9%, 49.1% and 75.8% at the expense of 39.1% reduction in heating output. Also a comparison is made between the two proposed systems in this work with similar systems (based on ejector transcritical CO2 cycle) proposed previously by other researchers and superiority of proposed systems in this paper is revealed and discussed.