Thermodynamic analysis and multi-objective optimization of a novel power/cooling cogeneration system for low-grade heat sources

A novel power/cooling cogeneration system based on an ammonia-water power cycle is proposed and investigated. The cooling capacity of the conventional combined system is much improved since an absorption-ejector refrigeration cycle is introduced. Besides the novel combined system could get more high-grade work at the same time obtain amounts of refrigeration due to the unique coupling mode. A mathematical model of the novel system is developed for system simulations under steady-state conditions. The results show that the thermal efficiency and the exergy efficiency are 21.34% and 38.95%, respectively. Exergy analysis shows that the exergy destruction mainly occurs in the recovery heat exchanger, followed by boiler and rectifier, respectively. Parametric study shows that the absorber temperature, the cycle high pressure, the temperature at boiler outlet and the extracting ratio have significant effects on the system performance. In addition, a multi-objective optimization using NSGA-II method is carried out to obtain the final optimums of the proposed system. The optimization results show that the exergy efficiency and the overall capital cost rate are 37.24% and 0.69408 $/h, respectively, and the thermal efficiency versus the overall capital cost rate are found to be 20.99% and 0.73351 $/h.