The design optimisation of a hybrid Stirling-organic Rankine cycle driven micro-CCHP utilising biomass fuel and exhaust waste heat to produce power, cooling and heating is presented. Four objectives have been formulated from thermodynamic and economic points of view to optimise the design of the system including the energy utilisation efficiency, exergy efficiency, primary energy savings and artificial thermal efficiency of the system. While the cooling ratio and frequency of the Stirling engine prime mover have been selected as the decision variables. The non-dominated sorting genetic algorithm II (NSGA-II) has been deployed to solve the optimisation problem and produce a Pareto frontier of the optimal solutions. Further, using the TOPSIS approach, the optimal design parameters have been selected from the Pareto set. The study constitutes the first attempt to holistically optimise such a hybrid micro-CCHP in a robust manner. The results of the study optimise the design of the proposed system and this design will be used as basis, in the future, to carry out a dynamic simulation of a scaled-up case study.
Under optimal conditions, the design parameters are found to be frequency and cooling ratio of 29.11 Hz and 0.238, respectively and the performance indicators; energy utilisation efficiency, exergy efficiency, primary energy savings and artificial thermal efficiency are 0.85, 0.57, 0.51 and 0.62, respectively. The optimum SE-ORC based micro-CCHP system will produce 3.2 times more heating than cooling.
Keywords Biomass fuel, Micro-CCHP, Optimisation, TOPSIS, Hybrid prime mover