Heat Transfer Analysis of Fiberglass Insulations With and Without Foil Radiant Barriers

Abstract

This work compares analytical results with experimental data for the total heat transfer through typical fiberglass insulations subjected to a time-varying incident radiative heat flux and with time-varying temperature boundaries. The insulation configurations and thermal environments analyzed are consistent with conditions that exist in residential attics during the summer months. A heat transfer analysis was performed, which treats the problem as one of coupled transient conduction and radiative heat transfer in a fully participating medium (absorbing, emitting, and scattering). Computations were performed for both isotropic and anisotropic phase functions and for both gray and nongray radiative transport. Temperature data recorded for summer-time conditions in FL and MS were used to describe the boundary conditions for the heat transfer analysis. The effect of foil radiant barriers on the overall heat transfer through the insulation also was studied. Calculations are presented that compare the foil radiant barrier and no-foil cases; the foil barrier is shown to reduce the total heat transfer by about 42%. All computations used the discrete ordinates solution method to solve the radiative transport equation and a control-volume based finite difference technique to solve the energy equation.