Multi-objective optimization for sizing of a small-scale combined cooling, heating, and power generation (CCHP) system is performed. In multi-objective optimizing the s CCHP system, the three objective functions including the exergetic efficiency, total levelized cost rate of the system product and the cost rate of environmental are optimized, simultaneously. The environmental impact and thermoeconomic objective are minimized while the exegetic objective is maximized. A comprehensive emission assessment framework suitable for addressing of distributed cogeneration systems is formulated according to an electrical output-based emission factor approach and the environmental impact objective function are defined and expressed in cost terms. The economic analysis is conducted in accordance with the total revenue requirement (TRR) method. The genetic algorithm is applied to find the set of Pareto optimal solutions with respect to the aforementioned objective functions. In the present work, reliability and availability are introduced in the developed models of the system, so that redundancy is embedded in the optimal solution. In this regard, risk analysis is used as a decision-making tool for the selection of the final optimal solution from the obtained Pareto optimal frontier. The sensitivity of the optimal solution respect to variations of input parameters is analyzed. (C) 2013 Elsevier B.V. All rights reserved.