Abstract:This paper presents an exergy analysis combined with the life cycle assessment method to systematically and quantitatively evaluate the building envelope energy efficiency retrofit. Based on the second law of thermodynamics, the building energy consumption can be transformed into exergy. The method only analyzes the production stage and the operation stage, which represent a higher impact in terms of energy consumption and environmental impact in the building life cycle. A typical case of the existing building envelope energy efficiency retrofit in Ningbo city is analyzed. The results show that it takes 15 years for the cumulative saved energy consumption in the operation stage to reach the embodied energy of the newly added insulation materials in the production stage. For CO2 emissions, it takes 16 years. The cumulative saved exergy consumption would be difficult to reach the embodied exergy consumption in the life span after retrofit. So the embodied energy and CO2 emissions of the newly added insulation materials in the production stage should not be neglected. For the existing old building, it should be prudent to take any retrofit measures; and the energy and exergy efficiency and environment impact of the retrofit measures should be considered as a whole in analysis.