Thermal performance of wall assemblies with low emissivity

Building and Environment

2013

Many parts of the building envelope contain enclosed airspaces. The thermal resistance (Rvalue) of an enclosed airspace depends on the emissivity of all surfaces that bound the airspace, the size and orientation of the airspace, the direction of heat transfer through the airspace, and the respective temperatures of all surfaces that define the airspace. The 2009 ASHRAE Handbook of Fundamentals (Chapter 26) provides a table that contains the R-values for an enclosed airspace. The ASHRAE table is extensively used by modellers, architects and building designers in the design of building enclosures. T his table provides R-values for enclosed airspaces for different values of the thickness of the airspace, effective emittance, mean airspace temperature, and temperature differences across the airspace. The effect of the airspace aspect ratio (height/thickness of airspace) on the R-value is not included in the ASHRAE table. However, in a recent study on the R-value of reflective insulations using a numerical simulation model, it was shown that the aspect ratio of the airspace can affect the Rvalue of the enclosed airspace. The numerical simulation model used in this study had been benchmarked against experimental data obtained using two standard test methods: ASTM C-518 and ASTM C-1363.In this paper, a numerical simulation study was conducted, that was based on previous work focused on enclosed airspaces, to investigate the effect of the aspect ratio on the R-value of vertical enclosed airspaces of different thicknesses and having a wide range of values for effective emittance, mean temperature, and temperature differences across the airspace. The R-values predicted from numerical simulation are compared with those provided in the ASHRAE table. Considerations were also given to investigating the potential increase in R-values of enclosed airspaces when a thin sheet is placed vertically in the middle of the airspace and whose surfaces have different values of emissivity. Finally, practical correlations are developed for determining the R-values of an enclosed airspace for future use by modellers, architects and building designers. The simplicity of these correlations suggests that these could be included in the ASHRAE Handbook of Fundamentals.

Section: Comparison Between R-values Predicted By Model and Listed Insupporting

confidence: 83%

Section: Comparison Between R-values Predicted By Model and Listed Insupporting

confidence: 63%

Section: Comparison Between R-values Predicted By Model and Listed Inmentioning

confidence: 89%

See 1 more Smart Citation

Practical correlations for the thermal resistance of vertical enclosed airspaces for building applications

Building and Environment

2013

“…Many studies were conducted to determine the R-values of RI products, and wall and roofing systems incorporating RI products (Yarbrough 1983, Fairey 1985, Han et al 1986, Desjarlais and Tye 1990, Desjarlais and Yarbrough 1991, Medina 2000, Al-Homoud 2005, European Commission 2010, Saber and Swinton 2010, Craven and Garber-Slaght 2011, Saber et al 2011b,c, Vrachopoulos et al 2012, D'Orazio et al 2012, Saber and Maref 2012,b,c, Escudero et al 2013, Tenpierik and Hasselaar 2013, Saber 2013a.…”

Section: Introductionmentioning

confidence: 99%

Practical correlation for thermal resistance of low-sloped enclosed airspaces with downward heat flow for building applications

2014

HVAC&R Research

“…foil with low emissivity) were installed on the surfaces that bound the airspace (e.g. see references [20,[23][24][26][27][28][29]). …”

Section: Thermal Resistances Of Different Wall Specimensmentioning

confidence: 99%

Energy retrofit using vacuum insulation panels: An alternative solution for enhancing the thermal performance of wood-frame walls

Journal of Building Physics

Maref

Gnanamurugan

et al. 2013

Self Cite

Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. Questions? Contact the NRC Publications Archive team atPublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information. 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://doi.org/10.1177/1744259113505748Access and use of this website and the material on it are subject to the Terms and Conditions set forth at Energy retrofit using vacuum insulation panels: an alternative solution for enhancing the thermal performance of woodframe walls Saber, Hamid H.; Maref, Wahid; Ganapathy, Gnanamurugan; Nicholls, Mike http://nparc.cisti-icist.nrc-cnrc.gc.ca/fra/droits L'accès à ce site Web et l'utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D'UTILISER CE SITE WEB. NRC Publications Record / Notice d'Archives des publications de CNRC:http://nparc.cisti-icist.nrc-cnrc.gc.ca/eng/view/object/?id=2474b62a-855b-434e-b39b-52a41e2f8193 http://nparc.cisti-icist.nrc-cnrc.gc.ca/fra/voir/objet/?id=2474b62a-855b-434e-b39b-52a41e2f8193 ABSTRACTField monitorings of the thermal performance of residential 2 x 6 wood-frame wall systems that had been retrofitted using Vacuum Insulation Panels (VIPs) and extruded polystyrene foam (XPS) panels were undertaken in May 2011 -May 2012 at the Field Exposure of Walls Facility (FEWF) of NRC-Construction. The main objective of this research was to measure the steady-state and transient thermal performance of three wall assemblies (4 ft x 6 ft), two of which incorporated VIPs within an XPS Tongue and Groove (T&G) configuration and VIPs within an XPS Clip-On (C-O) configuration, and a third assembly incorporating only XPS. The three wall assemblies were installed in the FEWF for a one year cycle of exposure to outdoor natural w eather conditions. The results of the model calculations were in good agreement with the experimental data. Given that the VIPs could be punctured during the installation process (e.g. inadvertent use of f asteners in wall assembly) or could fail during normal operating conditions, additional model calculations were used to predict the thermal resistance (R-value) in cases where one or more VIPs failed.The model was also used to predict the yearly cumulati...