Performance analysis of a new ejector expansion refrigeration cycle (NEERC) for power and cold: Exergy and energy points of view

Abstract

In the present work, a new CO2 refrigeration cycle, with the ejector expansion cycle serving as a harvesting tool of gas cooler wasted heat, is investigated. An attempt has been made to harvest and utilize the low-grade wasted energy, in the gas cooler component of the refrigeration basic cycle, through a transcritical carbon dioxide Rankine cycle. The work produced by the new cycle is used to drive the compressor and the feed pump, hence reducing the consumption work input and, as a result, it will enhance the performance characteristics of the whole system. The system operating and performance characteristics are investigated theoretically by energetic and exergetic methods. The simulation results were obtained by a computer FORTRAN program, where REFPROP 9 database was used to get the refrigerant thermodynamic properties. The simulation results showed that the proposed new refrigeration ejector expansion cycle (NEERC) had higher coefficient of performance and higher system second law efficiency in compare to the basic ejector expansion refrigeration cycle (BEERC). An enhancement of 12% in the COP and exergy efficiency of NEERC was found in comparison with BEERC when the cooling capacity and operating conditions of the two systems were the same. The increase of COP of NEERC and its efficiency along with the reduction of power consumption make it more practical for the use in residential air conditioning and cooling applications. A techno-economic analysis to compare ORC with Rankine cycle is provided. The results indicated that Rankine cycle for transcritical CO2 refrigeration cycle is more appropriate and has an advantage over the use of ORC. In addition, the small scale Rankine cycle combined with BEERC is economically viable for countries where the electricity price is above 15 c€/kWh.