Appropriate technology aims to achieve the optimal comprehensive benefits. The improvement of comprehensive benefits depends on the betterment of every benefit and the overall balance between benefits. Through value engineering evaluation, this paper transforms qualitative method into a quantitative method, and uses the new method to compare the comprehensive benefits of technical schemes for energy saving of external envelope of residential buildings, laying the basis for improving technical schemes. Multiple functional indices were determined, and organized into a hierarchical structure. The relative weight of each index was calculated through analytic hierarchy process (AHP). Drawing on the principle of value engineering, function coefficient, cost coefficient, and value coefficient were calculated for examples, and subjected to empirical comparison and analysis. After that, the technical schemes were contrasted, analyzed, and improved, according to the numerical value of the value coefficient. The proposed evaluation system provides a theoretical guide for making investment decisions on energy-saving residential buildings, and avoiding blind investment.

According to the climate characteristics in Hot Summer and Cold Winter (HSCW) zone, this study summarizes the special strategies for retrofitting the Existing Residential Buildings (ERB) in four aspects: envelop reformation, external environment improvement, energy saving behavior and renewable energy utilization. Then this study constructs the evaluation system frame of energy saving effect through 3 factors which are architecture design, construction and economic investment to comprehensively assess the practical effect of transforming. This research chooses a classical residential building in Huzhou as a case study and adopts the technologies to rebuild and uses the above evaluation system to figure out the most suitable reforming project. We hope our study about the reconstruction technologies and evaluation system can give some reference to renovation of existing residential buildings in other regions in China.