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Practical consequences of the altered thermal performance of the attic loose-fill insulation due to induced air movement

Mihail Serkitjis
Chalmers University of Technology, Dep. Of Building Physics, S-412 96 Guteborg, Sweden

Angela Sacic Kalagasidis
Chalmers University of Technology, Dep. Of Building Physics, S-412 96 Guteborg, Sweden

Abstract

The roof and attic floor are important parts of the building envelope in limiting heat losses and thus providing conditions for a good indoor climate. Under certain circumstances, e.g. high temperature gradients across the layer or air movement in the attic, the air convection (natural or forced) is taking place within the insulation. Due to the air movement, the thermal resistance of the insulation is decreased; however, the significance of this change is dependent on the insulation air permeability, which is generally related to the material density. Air movement in and around the attic affects not only the function of thermal insulation but also the moisture balance in the structure.
In order to estimate the influence of altered thermal resistance of the attic insulation on energy consumption of the building as a whole, a house with such insulation is simulated in the real climate conditions (represented by the Danish Reference Year, DRY). Following cases are studied: insulation with high air permeability, in the presence of forced (Case 1) and natural (Case 2) air convection. Simulations are performed with the building simulation computer code of integrated type, where structural details, materials, meteorological data, external and internal heat, air and moisture loads are designed in such details to represent the reality in a credible way. The indoor climate of the attic and adjacent dwelling are results of the interaction between the building envelope, occupants and the outdoor climate conditions. The air movement through the attic is calculated regarding the wind speed around it. The thermal performance of the insulation in the presence of air movement is evaluated by large-scale measurements.

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