Determining the Thermal Resistance of Enclosed Reflective Airspace

Enclosed airspaces of various effective emittances exist in the building envelope walls, roofs, and double/triple glazing windows, curtain walls skylight devices. Assessing energy performance a component with enclosed reflective requires evaluation all modes heat transport inside airspace. The thermal resistance (R-value) depends on dimensions orientation airspace, emittance temperature surfaces that bound To best our knowledge, existing methods used around world to evaluate airspace (e.g., ISO 6946, AUS/NZ 4859, based U.S. NBS data) are one-dimensional assume isothermal conditions hot cold surfaces. In actual applications, however, temperatures both vary (i.e., they non-isothermal), transfer takes place via conduction, convection surface-to-surface radiation. some cases, is absent or negligible, as case for downward flow situations small difference between Radiation significantly reduced by presence low-emittance surface path. One goals this study answer question “is it good assumption use determining/reporting R-value different applications?” A complete includes impact bounding materials can now be undertaken multiple convective described computational fluid dynamics. addition providing relatively airspaces, adequacy popular simplifying assumptions evaluated. This paper describes process used, along examples variation aspect ratio, realistic boundary radiative analysis completed research shows affects calculated R-values reflected less than 3%. was demonstrated five conventionally considered heat-flow directions from 0 0.82.