Buildings represent one of the dominant energy-consuming sectors in industrialized societies. Combined heat, cooling and power (CHCP) systems are interesting for the supply of different energy services in urban districts and in big buildings, particularly in warm areas such as the Mediterranean countries. These systems utilize a fuel's energy better, because the cogenerated heat can be used for heating in winter as well as for cooling in summer with an absorption refrigerator. Furthermore, the use of thermal energy storage (TES) provides an additional advantage, which is the coverage of variable thermal demands while the production system operates continuously at nominal conditions. Thus, energy supply systems integrating the technologies of cogeneration, absorption refrigeration and thermal storage can provide substantial benefits from economic, energetic and environmental viewpoints. In this paper an optimization model is developed, using mixed integer lineal programming (MILP), to determine the preliminary design of CHCP systems with thermal storage as well as optimum operation for the different plant components on an hour-by-hour basis throughout the year. The objective function to be minimized is the total annual cost. The optimization model is applied to design a system providing energy services for a set of buildings constituted by 5 000 apartments located in the city of Zaragoza (Spain). The design methodology also takes into account the legal constraints imposed on cogeneration systems in Spain.