Thermal Performance of Panels with High Density, Randomly Oriented Straw Bales

This paper describes the hot-box testing (based on ASTM C1363-11) of seven straw bale wall panels to obtain their thermal conductivity values. All panels were constructed with stacked bales and cement-lime plaster skins on each side of the bales. Four panels were made with traditional, 2-string field bales of densities ranging from 89.5 kg/m³–131 kg/m³ and with the bales on-edge (fibres perpendicular to the heat flow). Three panels were made with manufactured high-density bales (291 kg/m³–372 kg/m³). The fibres of the manufactured bales were randomly oriented.

The key conclusion of this paper is that within the experimental error, there is no difference in the thermal conductivity value for panels using normal density bales and manufactured high density bales up to a density of 333 kg/m³. However, because of lack of precision of the hot-box, no conclusions can be made on the true thermal conductivity of the high density bale panels. In addition, the panels tested were found to have significant voids between bales, and this is believed to have contributed to higher measured thermal conductivity values compared to those reported in the literature for normal density bale panels. Thermal properties may be affected for bales with higher densities than 333 kg/m³, therefore further testing is suggested.