Optimization of Wall Thickness Based on a Comprehensive Evaluation Index of Thermal Mass and Insulation

The thermal performance of buildings in the south of China focuses on thermal mass design, while in the north it favors thermal insulation design, which makes it impossible to achieve a balance between the thermal mass and insulation. Here, a comprehensive evaluation index is developed to measure the thermal performance of a building’s external envelope, which aims to find out the optimal range of the wall thickness under the influence of the thermal mass and insulation, and to seek the correct balance between a building’s energy consumption and the thermal performance of walls. In this paper, four dimensions, namely the heat transfer coefficient, thermal inertia index, attenuation degree, and delay time, are discussed, and the weight coefficients of each subfactor are calculated and isotropically treated to create comprehensive evaluation indicators. Then the distribution laws of the composite index values of common building materials in different climatic zones are examined. The result shows that the correlation coefficient (R 2 ) between M and building energy consumption is about 0.7736–0.8215, which is higher than 0.3494–0.384, the heat transfer coefficient, and is more accurate in predicting building energy demands. Furthermore, through the analysis of the thermal improvement rate and the building energy-saving rate, the suitable wall thickness of commonly used building materials in different climate zones is determined, and the application prospects of the research results are described. With the above research findings, the thickness ranges of walls can be determined at the initial period of building design by combining regional environmental factors and material characteristics to provide a reference for building energy-saving design.