Long-term hygrothermal performance of white and black roofs in North American climates

2012

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Section: Effect Of Inclination Angle and Direction Of Heat Flowmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Investigation of thermal performance of reflective insulations for different applications

2012

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“…The design of building envelope roof and wall systems with the intent of achieving energy savings can necessarily help reduce building operating loads and thus the demand for energy over time [1,2]. A straightforward means of reducing building operating costs is to limit heat transmission and thus energy loss through the building envelope.…”

Section: Introductionmentioning

confidence: 99%

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

2013

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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.

“…In Europe, however, buildings are responsible for 40-50% of energy use and the largest share of energy in buildings is heating [3]. The design of building envelope roofing and wall systems with the intent of achieving energy savings can necessarily help reduce building operating loads and thus the demand for energy over time [4,5]. This evidently can be achieved by increasing the thermal resistance (R-value) of the building envelope.…”

Section: Introductionmentioning

confidence: 99%

Practical correlations for thermal resistance of horizontal enclosed airspaces with upward heat flow for building applications

2013

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/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.2012.12.016 Building and Environment, 61, pp. 169-187, 2013-03-01 Practical correlations for thermal resistance of horizontal enclosed airspaces with upward heat flow for building applications Saber, Hamed H. AbstractThe thermal resistance (R-value) 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. A In this paper, previous studies undertaken by the author that focused on determining the Rvalue for vertical enclosed airspaces and horizontal enclosed airspaces with downward heat flow are extended to investigate the effect of the aspect ratio on the R-value of horizontal enclosed airspaces under an upward heat flow condition for different airspace thicknesses and having a wide range of values for effective emittance, mean temperature, and temperature differences across the horizontal airspaces. The R-values predicted from numerical simulation are compared with those provided in the ASHRAE table. Considerations were also given to investigate the potential increase in the R-values of enclosed airspaces when a thin sheet is placed horizontally in the middle of the airspace and whose surfaces have different values of emissivity. Thereafter, practical correlations are developed for determining the R-values of horizontal enclosed airspaces for future use by modellers, architects and building designers. The simplicity of these correlations for horizontal airspaces with upward heat flow along with those that were previously developed for vertical airspaces and horizontal airspaces with downward heat flow suggests that these correlations could be included in the ASHRAE Handbook of Fundamentals.