A cogeneration system driven by gas engine is proposed and studied. The cogeneration system can provide electricity generation and cooling/ heating for buildings. The cogeneration system has a large potential for energy saving and economical benefits. Primary energy rate (PER) and comparative primary energy saving are used to evaluate and compare the performances of the cogeneration system and conventional separate system. The comparative primary energy saving of the cogeneration system is more than 37% compared to conventional separate system at the required energy flows. The total annual income, the total annual saving and payback period of the cogeneration system are used to analyze its economy. The calculation result of economic analysis shows that the cogeneration system has a good economic benefits. (c) 2007 Elsevier B.V. All rights reserved.