basics:building_physics_-_basics:thermal_bridges:thermal_bridge_definition
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basics:building_physics_-_basics:thermal_bridges:thermal_bridge_definition [2020/09/12 17:25] – [Effect on the building structure] wfeist | basics:building_physics_-_basics:thermal_bridges:thermal_bridge_definition [2022/07/30 14:50] (current) – [Effect on the building structure] wfeist | ||
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A general overview is possible if the procedure for determining the transmission heat losses $H_T$ of the building envelope is considered. The following equation in the norm DIN 14683 (Section 4.2) makes a distinction between one-dimensional, | A general overview is possible if the procedure for determining the transmission heat losses $H_T$ of the building envelope is considered. The following equation in the norm DIN 14683 (Section 4.2) makes a distinction between one-dimensional, | ||
<WRAP center 60%> | <WRAP center 60%> | ||
- | < | + | \begin{align} |
- | $$H_{T} = \underbrace{\sum_{i}A_{i}U_{i}}_{1d}+\underbrace{\sum_{k}l_{k}\varPsi_{k}}_{2d}+\underbrace{\sum_{j}\chi_{j}}_{3d}$$ | + | & |
- | \begin{tabular}{ll} | + | With\qquad&\\ |
- | where& \\ | + | A_{i}\qquad&\text{area of the building components, in $m^2$}\\\\ |
- | $A_{i}$ & area of the building components, in m^2\\ | + | U_{i}\qquad&\text{thermal transmittance of component $i$ of the building envelope, in $W/(m^2\cdot K)$}\\\\ |
- | $U_{i}$ & thermal transmittance of component $i$ of the building envelope, in W/(m^2\cdot K) \\ | + | l_{k}\qquad&\text{length of the linear thermal bridge $k$, in $m$}\\\\ |
- | $ l_{k} $ & length of the linear thermal bridge $k$, in m \\ | + | \varPsi_{k}\qquad&\text{thermal transmittance of the linear thermal bridge $k$, in $W/(m\cdot K)$}\\\\ |
- | $ \varPsi_{k} | + | \chi_{j}\qquad&\text{thermal transmittance of the point thermal bridge $j$, in $W/K$}\\ |
- | $ \chi_{j} | + | \end{align} |
- | \end{tabular} | + | |
- | </ | + | |
</ | </ | ||
Planar regular building components such as the roof areas and exterior walls have the largest share of the total heat flow. For these, heat transfer can be considered one-dimensional with good approximation. The reason for this is that no cross-flows occur in them on account of their homogeneous layered structure. The heat transfer coefficient is defined in the norm [DIN6946] and can be calculated with little effort using the familiar equation given below: | Planar regular building components such as the roof areas and exterior walls have the largest share of the total heat flow. For these, heat transfer can be considered one-dimensional with good approximation. The reason for this is that no cross-flows occur in them on account of their homogeneous layered structure. The heat transfer coefficient is defined in the norm [DIN6946] and can be calculated with little effort using the familiar equation given below: | ||
<WRAP center 60%> | <WRAP center 60%> | ||
- | < | + | \begin{align} |
- | $$U=\dfrac{1}{R}=\dfrac{1}{R_{si}+\frac{d_{0}}{\lambda_{0}}+\frac{d_{1}}{\lambda_{1}}+\dots+\frac{d_{n}}{\lambda_{n}}+R_{se}} | + | & |
- | + | With\qquad&\\ | |
- | \begin{tabular}{ll} | + | R_{si}\qquad&\text{inner heat transfer resistance , in $m^2 \cdot K/W$}\\\\ |
- | where& \\ | + | d_{n}\qquad&\text{thickness of the $n$-th component layer, in $m$}\\\\ |
- | $R_{si}$ & inner heat transfer resistance , in m^2 \cdot K/W \\ | + | \lambda_{n}\qquad&\text{rated value of the thermal conductivity of the $n$-th layer, in $W/(m\cdot K)$}\\\\ |
- | $d_{n}$ & thickness of the $n$-th component layer, in m\\ | + | R_{se}\qquad&\text{outer heat transfer resistance, in $m^2 \cdot K/W$}\\ |
- | $\lambda_{n}$ & rated value of the thermal conductivity of the $n$-th layer, in W/(m\cdot K) \\ | + | \end{align} |
- | $R_{se}$ & outer heat transfer resistance, in m^2 \cdot K/W \\ | + | |
- | \end{tabular}\\ | + | |
- | </ | + | |
</ | </ | ||
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The resulting condensation can penetrate further inside the construction due to the capillary action of the building materials, and the thermal conductivity may increase and thus the building component may almost be saturated. It will not be possible to avoid moisture damage to the building structure and mould growth may occur. However, large-scale damage is generally associated with errors in the planning, implementation and utilisation of buildings and is not a problem that is solely related to thermal bridges. These are only the points where the problems originate in the first place. Nonetheless, | The resulting condensation can penetrate further inside the construction due to the capillary action of the building materials, and the thermal conductivity may increase and thus the building component may almost be saturated. It will not be possible to avoid moisture damage to the building structure and mould growth may occur. However, large-scale damage is generally associated with errors in the planning, implementation and utilisation of buildings and is not a problem that is solely related to thermal bridges. These are only the points where the problems originate in the first place. Nonetheless, | ||
+ | |||
+ | In constructions suitable for passive house or EnerPHit-design, | ||
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<WRAP center 60%> | <WRAP center 60%> | ||
- | < | + | $$ |
f_{Rsi, | f_{Rsi, | ||
- | </ | + | $$ |
</ | </ | ||
basics/building_physics_-_basics/thermal_bridges/thermal_bridge_definition.1599924347.txt.gz · Last modified: 2020/09/12 17:25 by wfeist