Abstract—Efficiency of energy resource use is a key factor for a sustainable energy future. By matching the exergy levels of supply and demand, Energy Quality Management (EQM) of building energy supply systems may achieve more efficient use of energy resources. Beyond this, environmental impact of energy supply systems is another essential issue. This work addresses the influence of EQM on CO 2 emissions in the operation optimization of a Distributed Energy System (DES). A multi-objective linear programming problem is formulated to reduce energy costs and increase the overall exergy efficiency. Total CO 2 emissions are evaluated for the optimized operation strategies of the DES. The operators of the DES can choose the operation strategy from the Pareto front, based on their priorities and also aware of effects on CO 2 emissions. Results demonstrate more efficient use of energy resources and reduction in CO 2 emissions through EQM, as compared with conventional energy supply systems. Index Terms – Distributed Energy System, Influence of Energy Quality Management on CO 2 emissions, Multi- Objective Operation Optimization. I. INTRODUCTION To address worldwide energy-related problems such as depletion of fossil fuels and global warming, increasing sustainability of energy systems is essential. The efficiency of energy resource use plays a key role in the development of a sustainable energy future [1]. Buildings are responsible for more than 40% of the total final energy consumption [2], most of which is used for low- quality demands, such as Space Heating (SH), Space Cooling (SC), and Domestic Hot Water (DHW). Exergy, derived from the Second Law of Thermodynamics, is a measure of the energy quality. It is the maximum amount of work that can be obtained from an energy flow as it comes to equilibrium with the reference environment [1, 3, 4]. In buildings, to keep the temperature of indoor air equal to 20°C, heat can be supplied at a temperature slightly higher than 20°C, and the required energy quality (the exergy fraction or quality factor, q) is very low (q ≈ 7%). To produce domestic hot water with a temperature of 45°C, the energy quality needed is slightly higher (q ≈ 15%). For the operation of different household appliances and lighting, the highest possible energy quality is needed (q ≈ 100%). However, energy supply systems are not structured in the same manner as their use, since the energy quality level of the supply for different uses in buildings is high (q ≈ 100%) by using fossil fuels and electricity [1]. Energy analyses do not take into account the degradation in quality occurring when high quality energy resources are used to satisfy low quality thermal demands. The matching of the quality levels of supply and demand should be made, if possible, by covering low exergy thermal demands with low exergy sources, e.g., solar thermal or waste heat from power conversion processes, and electricity demands with high exergy sources. Distributed Energy Systems (DESs) consisting of modular and small-scale technologies, are energy supply systems where energy is produced close to end-use [5]. Most of the studies in the literature were focused on the design and operation optimization of DESs focusing only on the economic factor [6, 7] or on both the economic and environmental factors [8, 9]. Beyond those, DESs may also provide a unique opportunity to show benefits from the Energy Quality Management (EQM), to match the quality levels of supply and demand. This is because that several energy resources, including renewable ones, with different energy quality levels may be involved to meet building demands with different exergy requirements. In such context, the waste of high quality energy resources can be avoided through EQM, thereby improving the efficiency of energy resource use. In our previous works [10, 11], EQM was involved in the operation optimization of a DES, by increasing the overall exergy efficiency, defined as the ratio of the total exergy required to meet the given energy demands to the total primary exergy input to the system. A Multi- Objective Linear Programming (MOLP) problem was formulated to reduce energy costs and increase the overall exergy efficiency of the DES. It was demonstrated a reduced waste of high quality energy resources by the optimized operation of the DES, as compared with conventional energy supply systems. Beyond this, the environmental impact of energy supply systems is another essential issue. The innovation of this work is the evaluation of the influence of EQM on CO 2 emissions in the operation optimization of a DES. As in [10, 11], a MOLP problem is formulated to obtain the optimized operation strategies of the DES. The objective is to reduce energy costs, and improve the overall exergy efficiency of the DES. Then, the total CO 2 emissions are evaluated under the optimized operation strategies of the DES obtained by the multi- objective optimization. The operators of the DES can Influence of Energy Quality Management on CO 2 Emissions in Operation Optimization of a Distributed Energy System M. Di Somma 1,2 , Y. Bing 3 , N. Bianco 2 , P. B. Luh 3 , G. Graditi 1 , L. Mongibello 1 , V. Naso 2 1 ENEA - Italian National Agency for New Technologies, Energy and Sustainable Economic Development – CR Portici – Portici – 80055 (Italy) 2 Dipartimento di Ingegneria Industriale (DII) – Università degli Studi Federico II – Napoli – 80125 (Italy) 3 Department of Electrical and Computer Engineering – University of Connecticut – Storrs – CT – 06269 (USA)