Exergy-based evaluation of a waste heat driven polygeneration system with CO2 as the working fluid

A waste heat driven polygeneration system that couples a supercritical power cycle with a transcritical refrigeration cycle is proposed and evaluated in this study. The stand-alone system using carbon dioxide as the working fluid produces power, refrigeration, and heating capacities simultaneously. Three scenarios of the system with different ambient temperatures (25-35 degrees C) are optimised using exergoeconomic approach to obtain the lowest average cost of the products. The obtained results show that the average product cost is the highest ($113/GJ) for the scenario with the ambient temperature of 30 degrees C, while the product cost is reduced to $82/GJ when the ambient temperature is 35 degrees C. Moreover, the pressure for merging the sub-systems influences the performance of the system significantly, and the variations of the operating conditions differ among the scenarios by increasing the merging pressure. Besides, a multi-objective optimisation is implemented for supporting decision-makers to find the optimal solutions.