Optimal structural design of residential cogeneration systems in consideration of their operating restrictions

An optimal structural design model of a residential cogeneration system, known as combined heat and power, considering various kinds of operating restrictions is developed from the energy-saving viewpoint. As principal operating restrictions of cogeneration units, a constant power output operation, a daily start–stop operation, and a continuous operation are focused on. The developed model results in a mixed-integer linear programming problem and the selection and multi-period operation are simultaneously optimized. Moreover, the model is applied to the structural design of a residential cogeneration system, consisting of a cogeneration unit and its peripheral devices, for simulated energy demands in a Japanese residence. The candidates for a cogeneration unit are a gas engine employing a constant power output operation, a polymer electrolyte fuel cell employing a daily start–stop operation, and a solid oxide fuel cell employing a continuous operation, and the candidates for peripheral devices are an electric water heater and an air-cooled heat exchanger. The optimization results reveal that the selection of the cogeneration unit is influenced more by their operating restrictions than by the consistency in the heat-to-power ratios of the cogeneration unit and energy demands. In addition, it is found that the selection of the peripheral devices varies with the selected cogeneration unit and energy demands.