The trade-off relationship between two economic viewpoints of the annual total cost and the payback period is investigated for the installation of cogeneration systems. For this purpose, a multiobjective optimal unit sizing method is proposed based on e-constratint and fractional programming methods. In this method, design variables such as numbers and capacities of equipment and utility maximum contract demands are determined so as to minimize both the annual total cost and the payback period in consideration of systems' annual operational strategies corresponding to seasonal and hourly energy demand requirements. Through a numerical study carried out on microturbine cogeneration systems installed in a hotel, the aforementioned trade-off relationship is clarified, and it is also found that the payback period can be shortened with making the annual total cost slightly worse by determining the numbers and capacities of equipment properly.
