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planning:thermal_protection:thermal_protection_works:thermal_protection_vs._thermal_storage

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planning:thermal_protection:thermal_protection_works:thermal_protection_vs._thermal_storage [2015/01/02 14:56] – wolfgangfeist@googlemail.complanning:thermal_protection:thermal_protection_works:thermal_protection_vs._thermal_storage [2019/02/21 10:18] – cblagojevic
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 Furthermore, these statements can be checked by everyone, even regarding the topic of “thermal insulation", for example:\\ Furthermore, these statements can be checked by everyone, even regarding the topic of “thermal insulation", for example:\\
     * What happens, when the heating system of an old building breaks down in winter? The author himself experienced that: the temperatures can sink to below zero – the water in the flower vase froze.     * What happens, when the heating system of an old building breaks down in winter? The author himself experienced that: the temperatures can sink to below zero – the water in the flower vase froze.
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     * And what happens when the heating in a Passive House breaks down? Even at minus temperatures, such an insulated house cools down very gradually. Two to four days later it is still pleasantly warm. And even after two weeks the temperature doesn't fall below 14°C. The few interior heat sources have a moderating effect on the temperature in the house.\\     * And what happens when the heating in a Passive House breaks down? Even at minus temperatures, such an insulated house cools down very gradually. Two to four days later it is still pleasantly warm. And even after two weeks the temperature doesn't fall below 14°C. The few interior heat sources have a moderating effect on the temperature in the house.\\
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 Incidentally: by using statistical methods something can be said about the reliability with which energy can be saved through better insulation. In the meantime, savings of 80% on average have been statistically proved in random samples of hundreds of Passive Houses in contrast with ordinary constructions)) beyond any scientific doubt that Incidentally: by using statistical methods something can be said about the reliability with which energy can be saved through better insulation. In the meantime, savings of 80% on average have been statistically proved in random samples of hundreds of Passive Houses in contrast with ordinary constructions)) beyond any scientific doubt that
     * The thermal protection of the external envelope (U-value) and the air exchange are mainly responsible for the heating energy consumption of a house in Central Europe.     * The thermal protection of the external envelope (U-value) and the air exchange are mainly responsible for the heating energy consumption of a house in Central Europe.
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     * Irradiation on external wall surfaces in the average heating period is usually an insignificant effect with very small energy gains, which is reduced even more by the heat radiation into the cold sky. However, the passive use of solar energy can be considerably increased through measures such as a selective coating or a transparent (translucent) insulation.     * Irradiation on external wall surfaces in the average heating period is usually an insignificant effect with very small energy gains, which is reduced even more by the heat radiation into the cold sky. However, the passive use of solar energy can be considerably increased through measures such as a selective coating or a transparent (translucent) insulation.
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     * After all, the influence of the thermal storage capability of the external walls is extremely small (less than 0.5 %).     * After all, the influence of the thermal storage capability of the external walls is extremely small (less than 0.5 %).
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     * The heat capacity of the interior building components facing towards the interior has a perceptible influence on the temperature stability and thus on summer comfort – the interior walls and intermediate ceilings are important.\\     * The heat capacity of the interior building components facing towards the interior has a perceptible influence on the temperature stability and thus on summer comfort – the interior walls and intermediate ceilings are important.\\
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     * For external building components, it is the insulation that is effective against heat losses. Whether internal or external - insulation is always efficient. However, the prevention of constructive thermal bridges and airtightness are essential for the effective functioning of the insulation.     * For external building components, it is the insulation that is effective against heat losses. Whether internal or external - insulation is always efficient. However, the prevention of constructive thermal bridges and airtightness are essential for the effective functioning of the insulation.
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     * The thermal storage capacity of the external building components is insignificant.     * The thermal storage capacity of the external building components is insignificant.
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     * The absorptivity of the external surface for solar energy and the emissivity of the surfaces for long-wave heat emission is important only to a small extent.\\     * The absorptivity of the external surface for solar energy and the emissivity of the surfaces for long-wave heat emission is important only to a small extent.\\
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 Both are described by the basic equation for heat transport. This has been known in physics since 1822, when [[http://en.wikipedia.org/wiki/Joseph_Fourier|Joseph Fourier (Wikipedia page)]] proposed his [[http://en.wikipedia.org/wiki/Conduction_%28heat%29#Fourier.27s_law|law of Heat Conduction (Wikipedia page)]]. This equation describes the interaction of thermal storage and thermal conduction in fixed materials. Both are described by the basic equation for heat transport. This has been known in physics since 1822, when [[http://en.wikipedia.org/wiki/Joseph_Fourier|Joseph Fourier (Wikipedia page)]] proposed his [[http://en.wikipedia.org/wiki/Conduction_%28heat%29#Fourier.27s_law|law of Heat Conduction (Wikipedia page)]]. This equation describes the interaction of thermal storage and thermal conduction in fixed materials.
  
-|{{ :picopen:waermeleitungsgleichung.png?300 }}|+ 
 +<WRAP center 60%> 
 +<latex>  
 +$$\rho c \dfrac{\delta T}{\delta t} = - div\,(- \Lambda\,grad\,T )$$ 
 +</latex> 
 +</WRAP>
 The heat equation in general formulation describes the time variation of a temperature field T(x,y,z) in fixed matter (e.g. in a solid body). The heat equation in general formulation describes the time variation of a temperature field T(x,y,z) in fixed matter (e.g. in a solid body).
  
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     * For normal building components, it turns out that to a great extent, the heat storage effect already averages out over a period of a few days (see the explanation in [[planning:thermal_protection:thermal_protection_works:Thermal protection vs. thermal storage#Stationary approximation|the next section]]).     * For normal building components, it turns out that to a great extent, the heat storage effect already averages out over a period of a few days (see the explanation in [[planning:thermal_protection:thermal_protection_works:Thermal protection vs. thermal storage#Stationary approximation|the next section]]).
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     * "Indirect" heat flows in the three space dimensions are even more important: These so-called thermal bridge effects can result in high additional heat losses, therefore they must be avoided meticulously if the insulation is to be effective.     * "Indirect" heat flows in the three space dimensions are even more important: These so-called thermal bridge effects can result in high additional heat losses, therefore they must be avoided meticulously if the insulation is to be effective.
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     * In simulations of complete buildings using Fourier's Law, the Passive House turns out to be a particularly energy-conserving solution for thermal comfort in winter as well as in summer [[planning:thermal_protection:thermal_protection_works:Thermal protection vs. thermal storage#Literature|[Feist 1993] ]].\\     * In simulations of complete buildings using Fourier's Law, the Passive House turns out to be a particularly energy-conserving solution for thermal comfort in winter as well as in summer [[planning:thermal_protection:thermal_protection_works:Thermal protection vs. thermal storage#Literature|[Feist 1993] ]].\\
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 -> How long are "long periods of time"? This depends on the system being considered. -> How long are "long periods of time"? This depends on the system being considered.
   * For a sheet of paper, one hour is "long",    * For a sheet of paper, one hour is "long", 
-  * for a 160 mm thick concrete ceiling three days are "long", + 
 +  * for a 160 mm thick concrete ceiling three days are "long", 
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   * however, for a several meter thick layer of earth, 6 years would be "long".\\   * however, for a several meter thick layer of earth, 6 years would be "long".\\
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   * If we want to keep tea or coffee hot, we use a tea-cosy or thermos flask – the alternative to insulation is not storage but constant energy expenditure for heating (tea-light or hot-plate).   * If we want to keep tea or coffee hot, we use a tea-cosy or thermos flask – the alternative to insulation is not storage but constant energy expenditure for heating (tea-light or hot-plate).
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   * In cold weather we put on insulating jumpers, stockings, hats etc.   * In cold weather we put on insulating jumpers, stockings, hats etc.
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   * In cold bedrooms, we keep beds warm by using “warm” duvets. Of course, the duvet itself is not warm, it is just very insulating, so that the human body loses less heat.   * In cold bedrooms, we keep beds warm by using “warm” duvets. Of course, the duvet itself is not warm, it is just very insulating, so that the human body loses less heat.
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   * Farmers are warned regularly about the occurrence of ground frost. Frost always occurs on the ground first because of the heat emitted into the night sky (in spite of thermal storage and solar radiation). The farmer can protect his plants with hay (insulation!) or sheeting (translucent insulation).\\   * Farmers are warned regularly about the occurrence of ground frost. Frost always occurs on the ground first because of the heat emitted into the night sky (in spite of thermal storage and solar radiation). The farmer can protect his plants with hay (insulation!) or sheeting (translucent insulation).\\
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planning/thermal_protection/thermal_protection_works/thermal_protection_vs._thermal_storage.txt · Last modified: 2022/02/15 19:57 by admin