Investigation of thermal performance of reflective insulations for different applications

Reflective insulations are being used in home attics, flat roofs, sloped roofs and wall systems of building envelopes. The present model, hygIRC-C, was used to investigate the contribution of the reflective insulations to the thermal resistance of specimens. The predictions of the present model were compared with test data of different sample stacks with different types of reflective insulations. In a previous study, the present model was benchmarked using test data obtained from a Guarded Hot Box (GHB) in accordance with the ASTM C-1363 test method. In this study, the test data was obtained from a different test method based on the heat flow meter in accordance of ASTM C-518 in the case of horizontal sample stacks with reflective insulations. Results showed that the predicted heat fluxes on the same area and same location of Heat Flux Transducers (HFTs) on the top and bottom surfaces of the sample stacks are in good agreement with the measured heat fluxes (within ±1%). The derived R-values using these heat fluxes are also in good agreements. Due to the combined effect of heat transfer by convection and radiation in the airspace (facing the reflective surface), these predicted and measured heat fluxes are greater than the area-weighted average heat flux of whole sample stack, which is needed to determine the effective R-value of the sample. As such, the derived R-value from the test data resulted in underestimation of the effective R-value of the sample stack. After gaining confidence in the present model, it was used to conduct parametric study in order to quantify the contribution of reflective insulations to the effective R-value for a sample stack with different inclination angles, different directions of heat flow (upward and downward) and for a wide range of foil emissivity. Furthermore, the present model was used to compare the predicted R-values with the listed R-values in the 2009 ASHRAE Handbook for enclosed air cavity (20 mm thick) of different effective emittance, inclinations and directions of heat flow.