Numerical Heat Transfer Attic Model Using a Radiant Barrier System

A two-dimensional, steady-state finite-element model was developed to simulate the thermal effects of the application of an attic radiant barrier system (ARBS) inside a ventilated residential attic. The attic is ventilated using the exhaust air from an evaporative cooler. The study uses a k-ε turbulent model to describe the velocity and temperature distributions in the attic. The ambient temperature and solar isolation densities on the outside inclined attic surfaces are used as driving functions for the model. The model also included the appropriate heat exchange modes of convection and radiation on these outside surfaces. Several recirculation zones were visually observed in the attic flow pattern. Also, the use of the ARBS seems to lower the heat transfer through the ceiling by 25–30%, but this effect decreases significantly as the outside ventilation rates are increased through the attic space. The 2D model revealed some interesting temperature distributions along the attic surfaces that could not have been predicted by the one-dimensional models. The lower emissivity ARBS seems to raise the temperature of the inclined attic surfaces as well as the temperature of the exhausted ventilation air.