Thanks to their numerous economic and environmental benefits, Distributed Energy Systems (DES) are considered as a sustainable alternative to traditional energy supply. To maximize the DES operators' profits while also containing emissions, daily operation is crucial. In this paper, the operation problem is addressed for a real DES in Italy by considering economic and environmental aspects. The DES consists of a Combined Heat and Power system, condensing and conventional boilers, and absorption and electric chillers. The end-users are an office building, a theater hall, and a residential building cluster, which is connected to the DES through a district heating network (DHN). A multi-objective linear programming problem is formulated based on the real constrains for devices and DHN with the aim to find the optimal operation strategies of the DES, which maximize the operator's profit and minimize the net CO2 emissions, while satisfying the users demand. The Pareto frontier is found through the weighted-sum method, by using branch-and-cut. The method is implemented for a winter day of December, by using experimental data for electrical and thermal demand of end-users. The results show that the optimization method is efficient in finding good trade-off solutions between economy and CO2 emissions. Moreover, the economic/environmental performances of the DES with optimized operation are much better than those found for the current operation strategies. In addition, the effects of the Italian white certificates scheme on the DES performances are also investigated. İ 2018 IEEE.