Substrate Barrier Effects for a R-19 Fibrous Insulation Batt

Abstract

This research investigates the effects on the total heat transfer when various substrate barriers are implemented at the bottom of a R-19 fiberglass insula tion batt. A plastic (polyethylene) vapor barrier and perforated and non-perforated radiant barriers are investigated. Heat transport in ceiling insulation is assumed to be transferred by these three mechanisms: conduction, radiation heat transfer, and mois ture transport (please note that convection heat transfer is not considered in this in vestigation). By modeling each of these three modes of heat transfer at the attic in sulation substrate, the total heat transfer into the house (summer conditions) can be obtained. Further modeling can determine the changes in the three individual modes of heat transfer once a substrate barrier is added. Summertime experimental data were collected at an occupied North Mississippi residence for cases with and without a vapor barrier at the substrate for R-19 fiberglass insulation. Predictions were made by a transient numerical/analytical model that simultaneously combines conduction and volumetric radiation heat transfer and moisture transport to obtain the total heat transfer at the substrate. Experimentally and predicted total heat transfer results are compared. Profiles such as temperature-time histories and vapor H₂O concentrations are presented to support the experimentally determined effects on the overall heat transfer at the substrate.