The impact of temperature and relative humidity dependent thermal conductivity of insulation materials on heat transfer through the building envelope

Abstract

The accurate value of thermal conductivity of building insulation materials and the coupled heat and moisture calculation of the envelope structure are crucial for the analysis of energy consumption in building and the selection of air conditioning equipment. Currently, the thermal conductivity given in the relevant manuals is a fixed value at normal temperature and dry state. Studies have shown that temperature and moisture content are key factors influencing the thermal conductivity of insulation materials. The moisture transfer process in the building envelope has a significant impact on the heat transfer process, especially in extremely hot and humid areas. Therefore, this study experimentally determined the influence of temperature and humidity on the thermal conductivity of common building insulation materials. The influence of moisture transfer and thermal conductivity coupled with temperature and relative humidity on the sensible heat, latent heat and total heat passing through the building envelope has been analyzed through numerical simulations. The results show that the thermal conductivity of the most commonly used building insulation materials increases with increasing temperature and humidity, but the degree of change is different. Thermal conductivity varies depending on the temperature from about 8.8% to 21.4% (temperature is from 20 °C to 60 °C). Thermal conductivity varies depending on relative humidity from 14.8% to 186.7% (humidity is from 0% to 100%). In extremely hot and humid areas, when the thermal conductivity of five insulation materials changes with relative humidity, they have a greater impact on the heat transfer of the wall. In summer, the heat transfer through the wall when considering the transfer of moisture in the wall and the change of thermal conductivity with relative humidity is from 1.5 to 1.9 times, as much as the heat transfer through the wall when only considering the wall heat transfer and the thermal conductivity is a fixed value.