Thermal analysis of above-grade wall assembly with low emissivity materials and furred airspace

Abstract

/npsi/ctrl?lang=en http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?lang=fr Access and use of this website and the material on it are subject to the Terms and Conditions set forth at http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=en NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. For the publisher's version, please access the DOI link below./ Pour consulter la version de l'éditeur, utilisez le lien DOI ci-dessous.http://dx.doi.org/10.1016/j.buildenv.2011.01.009Journal of Building and Environment, 46, 7, pp. 1403-1414, 2011 Thermal analysis of above-grade wall assembly with low emissivity materials and furred-airspace Saber, H. H.; Maref, W.; Swinton, M. C.; St-Onge, C. The material in this document is covered by the provisions of the Copyright Act, by Canadian laws, policies, regulations and international agreements. Such provisions serve to identify the information source and, in specific instances, to prohibit reproduction of materials without written permission. For more information visit http://laws.justice.gc.ca/en/showtdm/cs/C-42Les renseignements dans ce document sont protégés par la Loi sur le droit d'auteur, par les lois, les politiques et les règlements du Canada et des accords internationaux. Ces dispositions permettent d'identifier la source de l'information et, dans certains cas, d'interdire la copie de documents sans permission écrite. Pour obtenir de plus amples renseignements : http://lois.justice.gc.ca/fr/showtdm/cs/C-42 Abstract A 3D numerical model was developed to investigate the effect of foil emissivity on the effective thermal resistance of an above-grade wall assembly with foil bonded to wood fibreboard in a furred assembly having airspace next to the foil. This model solved simultaneously the energy equation in the various material layers, the surface-to-surface radiation equation in the furred airspace assembly, Navier-Stokes equation for the airspace, and Darcy and the Brinkman equations for the porous material layers. In this work, the furring was installed horizontally. In the first phase, the present model was benchmarked against the experimental data generated by a commercial laboratory for an above-grade wall assembly. The wall consists of a conventional wood frame structure sheathed with fibreboard and covered on the interior side with a low emissivity material bonded to wood fibreboard that is adjacent to a furred airspace assembly. The results showed that the predicted R-value was in good agreement with the measured one. After gaining confidence in the present model, it was used to predict the effective thermal resistance of the same above-mentioned wall but having Oriented Strand Board (OSB) sheathing in lieu of wood fibreboard sheathing. In the second phase, the mode...

Investigation of thermal performance of reflective insulations for different applications

“…It is surprising that the present prediction of the R-value is consistently higher than the measured R-value (in accordance of ASTM C-518 test method [12] using FOX-314 heat flow meter [13]) by approximately the same percentage for different reflective insulations. In a previous study [6], however, the prediction of the present model for R-value was in good agreement (within 1.2%) with the measured R-value in GHB (in accordance of ASTM C-1363 test method [11]) for a full-scale wall system (8' x 8') having a reflective insulation and furred-airspace assembly. So, the question is "why was the predicted R-value found to be consistently higher than the measured R-value by approximately the same percentage for different reflective insulations using the ASTM C-518 test method with FOX-314 heat flow meter?…”

“…After gaining confidence in the present model in predicting the R-value of specimen with horizontal orientation (see the pervious section) and specimen with vertical orientation (e.g. see [6]), it was used to quantify the contribution of reflective insulation to the R-value of specimen with different orientations.…”

“…airspace) absorbs and emits long-wave thermal radiation (e.g. surfaces of wood furring and drywall in furred-airspace assembly [5,6,7 and 8]). The amount of radiative heat transfer of this surface depends on its temperature and emissivity.…”

“…This test was conducted in accordance with ASTM C-1363 "Standard Test Method for the Thermal Performance of Building Assemblies by Means of a Hot Box Apparatus" [11]. Results showed that the predicted R-value of this wall system was in good agreement with the measured R-value [6].…”

“…Alternatively, the ASTM C-1363 test method using the GHB can be used to determine the effective thermal resistance of sample with thermal bridges [11]. The present model was benchmarked in previous studies against the experimental data that was obtained using the ASTM C-1363 test method in the case of full-scale wall assemblies (8 feet x 8 feet) with reflective insulation [6] and without reflective insulations [14, 15 and 16]. As the wall R-value is affected by the indoor and outdoor ambient temperatures and wind speed, the boundary conditions that were used to benchmark the present model were: (a) convective boundary with the measured indoor temperature and heat transfer coefficient on the interior surface, (b) convective boundary with the measured outdoor temperature and heat transfer coefficient on the exterior surface, and (c) adiabatic boundary condition on the other surfaces of the wall assembly (i.e.…”