Thermal and moisture performance of external thermal insulation system with periodic freezing-thawing

Abstract

The thermal and moisture performance of building envelope has an important influence on the energy consumption of buildings. In order to evaluate the thermal and moisture performance of external thermal insulation composite system (ETICS) with periodic freezing and thawing, a mathematical model considering the impact of water vapor, liquid water and solid ice on the heat and moisture transmission in multilayer walls is proposed. Two experiments are designed to verify the reliability of the model by measuring heat transfer characteristics, moisture transfer characteristics and ice content. The proposed model is applied to investigate the thermal and moisture performance of two insulation systems widely used in China under the natural climate conditions of Harbin (a severe cold region) for ten years in this article. The results show that most of liquid water is concentrated in the concrete layer, and freezing-thawing and temperature drop mainly occur in the insulation layer. Water content and ice content lead to an average increase of 15.5% and 14.6% in the heat transfer coefficient of the two insulation systems compared with that of their dry state, respectively, over the ten years, which leads to the heat transfer coefficient of the system 1 to exceed the specified value in the Chinese national standard. The annual energy consumption of the insulation system with freezing-thawing is on average 1 kWh/m2 of surface area higher than that without freezing-thawing. In addition, a correction coefficient model of heat transfer coefficient is proposed. The data shows that the correction coefficient model proposed in this article is reasonable, and the correction coefficient of the initial state is more suitable than the constant for thermal design of thermal insulation systems.