Experimental and Analytical Investigations of Simultaneous Heat and Moisture Transport through Glass Fiber Insulation

Abstract

Glass fiber insulation is one of the most commonly used building materials in residential wall cavities. In the normal conditions under which buildings operate, the moisture content in this insulation may locally vary from that of a very dry to a fully saturated state. This gives rise to many mechanisms for moisture trans port in the insulation. This article looks at all the possible mechanisms through which moisture is transported. This is done through two series of experiments and detailed numerical analysis The experiments include investigations on water vapour transport in the presence of thermal gradients and drying of fully saturated speci mens through evaporation. Physical quantities measured include history of heat flux, boundary temperatures and relative humidities and transient moisture distributions. The simultaneous heat and moisture transport processes are mathematically described through a pair of conservation equations In a finite difference method, these equations are used for detailed numerical analysis of the processes. The numeri cal analysis makes use of the experimental data to derive consistent values for a set of moisture transport properties, representative of a sample of medium density glass fiber insulation. The properties include thermal conductivity as a function of mois turc content, vapour permeability as a function of temperature, moisture diffusivity as a function of moisture content and temperature, heat capacity and hydraulic con ductivity as functions of moisture content and sorption isotherm. A sensitivity anal ysis and an independent experiment on the drying of a randomly wet specimen sup port the results obtained from the numerical analysis