Laboratory and In-Situ Measurements for Thermal and Acoustic Performance of Straw Bales

Abstract

This paper investigates the performance of timber-framed walls insulated with straw bales, and compares them with similar walls containing expanded polystyrene (EPS) instead of straw bales. First, thermal conductivity, initial water content, and density of the straw bales were experimentally measured in a laboratory set-up, and the dependence of the thermal conductivity of the dry material on temperature was described. Then, the two insulation solutions were compared by looking at their steady and periodic thermal transmittance, decrement factor, phase shift, internal areal heat capacity and surface mass. Finally, the acoustic performance of both wall typologies was analyzed by means of in situ measurements in two-story buildings built in Southern Italy. The weighted apparent sound reduction index for the partition wall between two houses and the weighted standardized level difference for the façades were assessed based on ISO Standard 16283. The results indicate that the dry straw bales have an average thermal conductivity of k = 0.0573 W/(m·K), and their density is around 80 kg/m3. In addition, straw bale walls have good steady thermal performance, but they still lack sufficient thermal inertia, as witnessed by the low phase shift and the high periodic thermal transmittance. Finally, according to the on-site measurements, the results underline that the acoustic performance of the straw bale walls is far better than the walls adopting traditional EPS insulation. Overall, the straw bales investigated are a promising natural and sustainable solution for thermal and sound insulation of buildings.

Energy Sustainability of Rural Residential Buildings with Bio-Based Building Fabric in Northeast China

“…The bio-based wall construction includes in-fill straw bales and timber structural frames. As the thermal transmittance of straw bales is lower than 0.070W/mK [48,49], the thermal performance of the bio-based walls is significantly less than 0.20 W/m 2 K [50]. This is considerably superior to both the conventional wall construction and the construction standards in GB/T50824-2013.…”

A review of material properties and performance of straw bale as building material

“…Linear correlation in the range of 60-130 kg•m À3 was observed by Costes et al [16] using guarded hot plate method, and Shea et al [25] using heat flow meter method. However, studies from Marques et al [14], Reif et al [15] and Cascone et al [18] indicate a rather weak correlation between bulk density and thermal conductivity of straw bale. A non-linear relation was also suggested by Vė jelienė [34] where optimum thermal conductivity was observed in the density range of 50-80 kg•m À3 , and the thermal conductivity increase when their densities are fall below or exceed above that range.…”

“…2 summarizes the steady-state thermal conductivity measurements of straw bale against density from different studies. The majority of these measurements [14][15][16][17][18][19][20][21][22][23][24] were determined in accordance with guarded hot plate method, based on ISO 8302:1991. The other two steady-state methods which have been used in the straw bale studies are measurement using heat flow meter apparatus [25] based on ISO 8301, and measurements using small hot box apparatus [26][27][28] based on EN-ISO 8990:1994 or ASTM C1363-19 [29].…”

“…2 indicates no significant deviation of thermal conductivity from different sources of straw, e.g. barley [20,21], wheat [15,16,18,26,28] or rice [14]. Overall, straw with fiber oriented perpendicular or random to heat flow showed lower thermal Fig.…”

“…2. Measured Thermal Conductivity vs Density based on studies from Marques [14], Reif [15], Costes [16], DIBt [17], Cascone [18], D'Alessandro [19], Vejeliene [20], Laborel-Préneron [21], Samuel [22], Munch-Andersen [23], Shea [25], Conti [26], Buratti [27], Cornaro [28], Christian [29], Langmans [33]. conductivity compared to those arranged parallel, as observed by Munch-Andersen and Andersen [23], Christian et al [29], Langsmans et al [33], Vė jelienė [34] and Douzane et al [35].…”