Study of heat and moisture transfer in internal and external wall insulation configurations

Abstract

Installing thermal insulation on the external walls of existing buildings is a common optimization method of reducing building energy consumption. Selecting the appropriate insulation configuration requires an understanding and comparison of the heat transfer characteristics of the internal and external configurations. In previous studies, the thermal characteristics of internal thermal insulation (ITI) and external thermal insulation (ETI) walls have mainly been compared from the perspective of dynamic heat transfer only, ignoring the effect of relative humidity. To analyze the relative humidity distribution and compare the heat transfer of ETI and ITI walls more accurately, a coupled heat and moisture transfer model, with temperature and relative humidity as the driving forces, was established to simulate a building envelope in a hot summer and cold winter (HSCW) zone. The ITI and ETI configurations were compared, revealing that indoor relative humidity significantly affects the heat transfer process. Under the indoor condition of 70% relative humidity, the ITI configuration lost more heat per unit area on an annual basis than the ETI wall configuration. In an HSCW zone, to reduce energy loads and save cost, the ETI configuration was more suitable. However, if air-conditioning systems are limited to the summer months and heat is not needed in the winter, the ITI configuration performs better. It is therefore recommended that the most suitable configuration of thermal insulation should be adopted according to the function and daily operation environment of the specific building.