In this study, the design and optimization of combined cooling, heating, and power system is dealt with. In these systems, electricity, cooling, and heating are generating using just one primary energy source. The case study in this article is a residential complex in which the monthly energy, cooling, and heating demand is specified. The selection of size of components based on the maximum demand will lead to an increase in the capital cost in a unit. For this purpose, a system was designed in which the prime mover, heat recovery boiler, and absorption chiller is lower than the needed maximum. The difference in months with peak consumption is supplied with the help of absorption chiller and auxiliary boiler (and the national electricity network). In this study, the optimum capacities of each of the equipments are determined based on thermoeconomic method, in a way that the annual capital cost and energy consumption will be the lowest. The design was done for microturbine prime mover and reciprocating engine separately, and finally the optimum designs were investigated using exergy analysis, and were compared with a traditional energy supply system.