Abstract
This article analyses the connection of the two types of floors on the ground (floors on joists and self-supporting floors), with the external wall made of a hemp–lime composite for the occurrence of thermal bridges. Several factors that may affect the heat transfer in the junction were taken into account: the level of the floor on the ground, the wall thickness, the thermal conductivity of the composite, and the location of the timber frame construction. The technology of using hemp and lime is relatively new, and there is a lack of such analyses in the literature. The two-dimensional (2D) heat-transfer in the described construction joints was analyzed based on the finite-element method with the use of the THERM 7.4 software. The results were presented as averaged and linear thermal transmittance coefficients dependent on the above mentioned factors. The possibility of surface condensation was also checked. The differences in the values of the thermal transmittance of the junction between the two variants of ground floors reached around 0.13%–1.67% and the values of linear thermal transmittance factor reached approximately 2.43%–10.13%. The junctions with the highest floor level showed a decrease in the thermal transmittance value by about 3.00%–5.77% and in the linear thermal transmittance, by about 21.98%–53.83%, compared to the junctions with the lowest floor level. Calculations showed that almost all analyzed junctions are free from surface condensation causing mould growth, because the minimum temperature factors f0.25 were higher than 0.78 (except for junctions with the lowered floor levels). The junction with a floor on the timber joists showed better thermal parameters than the junction with a self-supporting floor in each of the analyzed variants. By increasing the level of floor insulation, it is possible to limit the thermal bridges and improve the thermal properties of the junction.
Highlights
The building and construction sector accounts for about 40% of world energy consumption and about 25% of global greenhouse gases emissions [1]
The graphs (Figure 7a,b) show the changes in the average thermal transmittance coefficient for the ground junction with all the design variants of the analysed walls filled with hemp–lime composites characterized by a thermal conductivity coefficient of 0.08 W/(m·K), depending on the level of the floor ground
In the case of the floor on joists, the thermal transmittance coefficients were lower by 0.0003 W/(m2 ·K)–0.0019 W/(m2 ·K), while for the self-supporting floor, the coefficients were lower by 0.0006 W/(m2 ·K)–0.0024 W/(m2 ·K), relative to junctions with the timber frame placed on the inside of the wall (taking into account both the wall thickness of 350 and 400 mm, but with the same value of λ = 0.080 W/(m·K))
Summary
The building and construction sector accounts for about 40% of world energy consumption and about 25% of global greenhouse gases emissions [1]. Another study on the occurrence of thermal bridges in typical constructions showed that improved building envelope details minimizing thermal bridges can result in up to 10% energy savings, which is comparable to increasing the insulation levels and using triple-glazed windows [26]. Another unfavorable phenomenon related to thermal bridges is the change in the temperature distribution and its reduction on the surface of the partitions. The results presented in the article may be helpful in the design of buildings using this technology
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