A Numerical Investigation of Repeating Thermal Bridges from Metal Fasteners in Offsite Manufactured Timber Frame Closed Panels for Exterior Walls

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.

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The The Occurrence of Thermal Bridges in Hemp-Lime Construction Junctions

Periodica Polytechnica Civil Engineering ◽

10.3311/ppci.13377 ◽

2019 ◽

Cited By ~ 6

Author(s):

Magdalena Grudzińska ◽

Przemysław Brzyski

Keyword(s):

Energy Efficient ◽

Composite Structures ◽

Building Materials ◽

Thermal Transmittance ◽

Timber Frame ◽

Energy Efficient Buildings ◽

Moisture Condensation ◽

Thermal Bridges ◽

Frame Construction ◽

Insulating Properties

Thermal bridges increase heat losses in buildings and reduce the temperature of the internal envelope surface, causing moisture condensation and mould growth. This is an important issue for building materials based on organic components such as a hemp-lime composite, as they are particularly susceptible to biological degradation.The hemp-lime composite is used as a filling in timber frame construction. The increased cross-section of wooden elements together with the geometry change in the construction joints can form thermal bridges. The paper presents numerical analyses of temperature distribution in the area of construction elements connections, taking into account several variants of junctions: external walls, corners, and window placement in a wall. The thermal parameters of hemp-lime composites used in the analyses were obtained from the authors’ own research.Despite relatively good insulating properties, timber elements have a noticeable influence on the local increase of the heat transfer in hemp-lime composite structures, forming thermal bridges in the partitions themselves and in the construction nodes. However, the linear thermal transmittance coefficients in the presented joints were not very significant (in the range of 0.026 ÷ 0.092 W/(m·K) depending on the type of connection), proving the usefulness of this type of construction in energy-efficient buildings.

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Numerical investigation of the effect of vacuum insulation panels on the thermal bridges of a lightweight drywall envelope

Journal of Facade Design and Engineering ◽

10.3233/fde-160047 ◽

2016 ◽

Vol 4 (1-2) ◽

pp. 3-18 ◽

Cited By ~ 4

Author(s):

Dimos A. Kontogeorgos ◽

Ioannis A. Atsonios ◽

Ioannis D. Mandilaras ◽

Maria A. Founti

Keyword(s):

Numerical Investigation ◽

Vacuum Insulation ◽

Thermal Bridges

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An Analysis of Repeating Thermal Bridges from Timber Frame Fraction in Closed Panel Timber Frame Walls: A Case Study from Wales, UK

Energies ◽

10.3390/en14041211 ◽

2021 ◽

Vol 14 (4) ◽

pp. 1211

Author(s):

Francesco Zaccaro ◽

John Richard Littlewood ◽

Carolyn Hayles

Keyword(s):

Thermal Performance ◽

Energy Use ◽

Design Stage ◽

Performance Gap ◽

Thermal Transmittance ◽

Timber Frame ◽

Operational Energy ◽

Thermal Bridges ◽

Detrimental Impact

Calculating Repeating Thermal Bridges (RTBs) for Timber Frame (TF) closed panels that could occur in Offsite Manufactured (OSM) Modern Methods of Construction (MMC), such as exterior walls for nearly-to-zero operational energy dwellings to be constructed in Wales, United Kingdom (UK) is discussed in this paper. Detailed calculations for linear RTBs due to the TF components are often neglected when evaluating thermal transmittance (known as U-values hereafter). The use of standard TF fractions does not allow the designer to perceive their detrimental impact on RTBs and consequent U-values for exterior walls. With the increase of the thermal performance of exterior walls and as such lower U-values due to ever-tightening Building Regulations, specifically related to the energy use and carbon emissions from the space heating of dwellings, then the impacts of RTBs requires more investigation. By not calculating the potential of linear RTB at the design stage could lead to a performance gap where assumed U-values for exterior walls differ from manufacture to onsite. A TF detail from the Welsh manufacture has been chosen as a case study, to develop and apply a methodology using manufacturing drawings to evaluate TF fraction and their effect on the thermal performance.

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