3D heat and air transport model for predicting the thermal resistances of insulated wall assemblies

A wall energy rating (WER) system has been proposed to account for simultaneous thermal conduction and air leakage heat losses through a full-scale insulated wall system. Determining WER requires performing two standard tests on a full-scale wall specimen: a thermal resistance test and an air leakage test. A 3D model representation of the wall specimen is developed to combine the results of these tests to obtain an accurate prediction of the wall thermal resistance (apparent R-value) under the influence of air leakage. Two types of wall configurations were tested and simulated. The first one was a standard 2 '' X 6 '' wood stud frame construction, made of spruce, spaced at 16 '' (406 mm) o/c in 2.4 m X 2.4 m full-scale wall specimens. The second wall configuration was similar to the first one except that it included through-wall penetrations. The cavities of the two types of wall configurations were filled with different types of insulation, namely glass fibre batts and two different types of open cell spray polyurethane foams (light density, 6.8 and 12 kg/m(3) nominal), a total of six walls. The present 3D model was used to predict the R-values of different types of wall assemblies (with and without air leakage). This model is a new hygrothermal tool that was recently developed and benchmarked against hygIRC-2D that was previously developed at the National Research Council of Canada, Institute for Research in Construction. The 3D version of this model was benchmarked by comparing its predictions of R-values for different types of wall assemblies against the measured R-values in the guarded hot box at no air leakage. Results showed that the present model predicted R-values of six walls to within +/- 5%. The 3D model was then used to investigate the effect of air leakage rate on the apparent R-values for these same walls. The results showed that the apparent R-values decreases linearly with air leakage rate less than similar to 0.1 L/(m(2).s). At air leakage rate greater than similar to 0.1 L/(m(2).s), the apparent R-values decrease asymptotically.