Abstract

Accurate prediction of the effective thermal conductivity of loose fill fibrous building thermal insulation remains a challenging issue to date.  Most researchers considered the complex problem of heat transfer across a fibrous material to be the sum of heat transfer due to air conduction, solid conduction and radiation for which general empirical relationships were developed from reliable thermal conductivity tests. In this study, an experimental investigation of this hypothesis was undertaken by removing the air from a porous material, hence, theoretically leaving heat transfer due to solid conduction and radiation only. This hypothesis was tested by conducting steady state thermal conductivity measurements under vacuum conditions for coconut fiber and sugarcane fiber specimens. Test results indicated an average difference between the thermal conductivity at atmospheric conditions and under vacuum conditions of 0.0279 and 0.0231 W/m.K for coconut fiber and sugarcane fiber, respectively, over the density range tested. The experimental results were in agreement with the widely expressed opinion that air behaves as an independent individual contributor to the overall effective thermal conductivity of a loose fill fibrous material.

Key words: Fibrous insulation, thermal conductivity, loose fill insulation, effective thermal conductivity, air conduction.