Hot-Box measurements of highly insulated wall, roof and floor structures

Abstract

The purpose of this study was to investigate how natural convection in air permeable glass wool insulation affects the thermal transmittance in walls, roofs and floor structures. The results can be used to evaluate the need for a convection barrier in thick mineral wool layers. Natural convection is affected by several parameters. In this study, the angle of inclination, the heat flow direction and the temperature difference across the test section have been studied. Thermal transmittance and temperature distribution measured by use of thermocouples placed inside the insulation cavity clearly showed convection in the insulation when the test section was in pitched roof and wall positions. An efficient measure to reduce the natural convection is to divide the insulation layer into two thinner layers by using a diffusion open convection barrier. A convection barrier is recommended by the authors both in wall and pitched roof structures if the insulation thickness exceeds 200 mm.

Thermal Performance of Insulated Constructions—Experimental Studies

“…The corresponding value perpendicular to the fibre directions was 2.6 × 10 −9 m 2 . These values are somewhat lower compared to the values reported by Gullbrekken et al [20]. The densities of the mineral wool of these studies are comparable.…”

“…Previously, Reference [16] calculated a Nusselt number of 1.07 (∆θ ie = 20) and 1.12 (∆θ ie = 40) based on Hot-Box measurements on a 200 mm mineral wool insulated timber frame. The similar Nusselt numbers for the 500 mm insulated wall of Gullbrekken et al [20] was 1.08 (∆θ ie = 20) and 1.15 (∆θ ie = 40). The Nusselt number of the 250 mm insulated wall is comparable with these previous studies.…”

“…A possible explanation is that wood-fibre insulation gives a lower practical air permeability of the insulated cavity due to a higher compressive strength, less flexibility and hence a better capability to fill the cavity. Previously the existence of such imperfections for mineral wool insulated constructions was presented by Reference [20]. However, the practical permeability of the insulated cavity was not measured.…”

“…However, limited literature is available concerning pitched roofs. A laboratory study of highly insulated mineral wool structures with insulation thickness of 500 mm was conducted by Gullbrekken et al [20]. Both inclination and temperature difference affected the thermal transmittance through the structure.…”

Integrated Measuring and Control System for Thermal Analysis of Buildings Components in Hot Box Experiments

“…Caruana et al [4] employed a hot box to investigate the thermal properties of a new building block (specimen dimensions equal to 165 × 190 cm), to improve its U-value without changing compressive strength, physical dimensions or manufacturing process. Gullbrekken et al [5] discussed how natural convection in air-permeable glass wool insulation affects the thermal transmittance in walls, roofs and floors. The study was carried out by means of a rotatable guarded hot-box (with a metering area equal to 245 × 245 cm).…”