basics:building_physics_-_basics:thermal_bridges:tbcalculation:ground_contact:ground_contact
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basics:building_physics_-_basics:thermal_bridges:tbcalculation:ground_contact:ground_contact [2016/08/16 13:13] – [Temperature and thermal conductivity of the ground] mschueren | basics:building_physics_-_basics:thermal_bridges:tbcalculation:ground_contact:ground_contact [2022/01/18 15:29] (current) – [Thermal capacity of the ground] yaling.hsiao@passiv.de | ||
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Heat flow through the individual components of a building is determined by the temperature difference between the inside space and the outside. In the case of components in contact with the ground, heat flow depends on the temperature field prevailing in the ground. Although this depends directly on the temperature of the outdoor air, it is also influenced by radiation exchange of the ground surface. In **AkkP 27** it is suggested that on average the surface temperature is about 1 K higher than the outdoor air temperature. Thus for example, snow that falls during temperatures around freezing point initially does not remain as snow on the ground. Nonetheless, | Heat flow through the individual components of a building is determined by the temperature difference between the inside space and the outside. In the case of components in contact with the ground, heat flow depends on the temperature field prevailing in the ground. Although this depends directly on the temperature of the outdoor air, it is also influenced by radiation exchange of the ground surface. In **AkkP 27** it is suggested that on average the surface temperature is about 1 K higher than the outdoor air temperature. Thus for example, snow that falls during temperatures around freezing point initially does not remain as snow on the ground. Nonetheless, | ||
- | Heat follows the path of least resistance. 100 m of earth with a thermal conductivity of 2.0 W/(m•K) has a U-value of just 0.02 W/(m 2•K), so the relevant heat exchange only takes place towards the outside air. The heat flow caused by the temperature difference between the inside and the outside environment accordingly travels from the ground towards the surface through the building envelope, therefore the ground should be regarded as an additional component layer of the affected building component, the thermal conductivity of which influences the U-value of the component. However, the heat transfer resistance can no longer be determined in accordance with R = λ/d because the ground around a building does not represent a homogeneous building component layer. As a consequence, | + | Heat follows the path of least resistance. 100 m of earth with a thermal conductivity of 2.0 W/(m•K) has a U-value of just 0.02 W/(m 2•K), so the relevant heat exchange only takes place towards the outside air. The heat flow caused by the temperature difference between the inside and the outside environment accordingly travels from the ground towards the surface through the building envelope, therefore the ground should be regarded as an additional component layer of the affected building component, the thermal conductivity of which influences the U-value of the component. However, the heat transfer resistance can no longer be determined in accordance with R = λ/d because the ground around a building does not represent a homogeneous building component layer. As a consequence, |
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==== Thermal capacity of the ground==== | ==== Thermal capacity of the ground==== | ||
- | In building physics, the thermal capacity of a material is given by the specific thermal capacity c. this defines the amount of energy that is required in order to increaser | + | In building physics, the thermal capacity of a material is given by the specific thermal capacity c. This defines the amount of energy that is required in order to increase |
{{ : | {{ : | ||
- | The amplitudes of the sinsoidal | + | The amplitudes of the sinusoidal |
{{ : | {{ : | ||
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**Further literature on the topic of skirt insulation: | **Further literature on the topic of skirt insulation: | ||
- | **[AkkP 48]** Using Passive House technology for retrofitting non-residential buildings/ Heat losses towards the ground ; Protocol Volume No. 48 of the Research Group for Cost-effective Passive Houses, 1st Edition, Passive House Institute, Darmstadt 2012 ({{:picopen: | + | **[AkkP 48]** Using Passive House technology for retrofitting non-residential buildings/ Heat losses towards the ground ; Protocol Volume No. 48 of the Research Group for Cost-effective Passive Houses, 1st Edition, Passive House Institute, Darmstadt 2012 [[https:// |
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===== Transient or steady-state Ψ-values? ===== | ===== Transient or steady-state Ψ-values? ===== | ||
- | For calculating thermal bridges in the area in contact with the ground, a steady-state approximation suffices in many cases and dynamic simulation can be dispensed with. Although dynamic simulations provide more accurate results, they also incur additional effort. Moreover, on account of the usually only imprecisely known thermal characteristics of the ground, the expected accuracy of a one-dimensional or two-dimensional transient numerical calculation is not so high that this extra effort can also be justified (except in the case of large or research projects). Frequently, the Ψ-values calculated in a steady-state manner are therefore also used as harmonic Ψ-values (see the Ground worksheet in the [[planning: | + | For calculating thermal bridges in the area in contact with the ground, a steady-state approximation suffices in many cases and dynamic simulation can be dispensed with. Although dynamic simulations provide more accurate results, they also incur additional effort. Moreover, on account of the usually only imprecisely known thermal characteristics of the ground, the expected accuracy of a one-dimensional or two-dimensional transient numerical calculation is not so high that this extra effort can also be justified (except in the case of large or research projects). Frequently, the Ψ-values calculated in a steady-state manner are therefore also used as harmonic Ψ-values (see the Ground worksheet in the [[planning: |
==== Further literature ==== | ==== Further literature ==== | ||
- | **[AkkP 27]** **Heat losses through the ground**; Protocol Volume No. 27 of the Research Group for Cost-effective Passive Houses, \\ 1st Edition, Passive House Institute, Darmstadt 2004 ({{:picopen: | + | **[AkkP 27]** **Heat losses through the ground**; Protocol Volume No. 27 of the Research Group for Cost-effective Passive Houses, \\ 1st Edition, Passive House Institute, Darmstadt 2004 |
===== See also ===== | ===== See also ===== |
basics/building_physics_-_basics/thermal_bridges/tbcalculation/ground_contact/ground_contact.txt · Last modified: 2022/01/18 15:29 by yaling.hsiao@passiv.de