From the view of appropriate technology, this paper compares and analyzes the calculated thickness, feasible thickness, economic thickness, and appropriate thickness of the external wall insulation material with the highest contribution rate from the economic point of view, and obtains the relationship, curve, and model between the economic thickness and the appropriate thickness of the thermal insulation material. The purpose is to provide a reference basis and model for the optimal design of building energy-saving external walls. It inspires the architectural designers to consider the energy conservation of buildings from the economy’s perspectives and environment to get the optimal and environment-friendly energy-saving design method. The purpose is to provide a robust theoretical basis for guiding energy-saving housing investment and reducing the blindness of investment.

The urban traffic is a common concern in the large cities around the world, and th calls for high technology to improve its efficiency and reduce its costs. The underground traffic development is one solution used often in the metropolitan cities like Paris and London. In China, the ventilation system of the underground bidirectional BRT still needs more refinement to achieve the sustainable development, though the underground traffic system has developed very fast. The airfoil structure is adopted abroad to dilute the polluted air in the subway stations and increase the ventilation efficiency, yet it has not been applied in China. This paper studies the reduction of the piston wind loss by airfoil structure on the basis of piston principle, so as to improve the role of the piston wind in the ventilation process. In the mathematical simulation, it is also proved that this method can substantially increase wind energy by 63.27% per meter of the underground road, improving the ventilation efficiency of the underground BRT. Due to the failure to refine the parameter curve of the airfoil structure, the simulation data has some deviations. In future studies, in order to make up for the shortcomings of this study, it is necessary to use XFLR software to carry out refined parameter analysis of laminar airfoil.