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planning:thermal_protection:thermal_protection_works:thermal_protection_vs._thermal_storage [2018/11/22 12:11] – cblagojevicplanning:thermal_protection:thermal_protection_works:thermal_protection_vs._thermal_storage [2022/02/15 19:57] (current) – admin
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 In some publications, including various articles on the internet, emphasis is placed on the influence of the thermal storage capacity of buildings, claiming that improving the thermal insulation of external walls is pointless or even damaging. Allegedly, the effects of the thermal storage capacity of a wall and the heat gains from solar radiation are insufficiently, or not at all, taken into account by scientists.  In some publications, including various articles on the internet, emphasis is placed on the influence of the thermal storage capacity of buildings, claiming that improving the thermal insulation of external walls is pointless or even damaging. Allegedly, the effects of the thermal storage capacity of a wall and the heat gains from solar radiation are insufficiently, or not at all, taken into account by scientists. 
  
-The author of this article has already dealt with this topic systematically in 1987, under the same title. In the meantime, many new findings have become available, all of which support this publication. The full (German) version of the summary given here can be ordered from the following link: [[http://passipedia.passiv.de/passipedia_de/_media/picopen/faxb.pdf|[Feist 2000] Feist, Wolfgang: Ist Wärmespeichern wichtiger als Wärmedämmen? (Is thermal storage more important than thermal protection?) Passivhaus Institut, Darmstadt 2000]]\\+The author of this article has already dealt with this topic systematically in 1987, under the same title. In the meantime, many new findings have become available, all of which support this publication. The full (German) version of the summary given here can be ordered from the following link: [[https://shop.passivehouse.com/de/products/ist-warmespeichern-wichtiger-als-warmedammen-90/|[Feist 2000] Feist, Wolfgang: Ist Wärmespeichern wichtiger als Wärmedämmen? (Is thermal storage more important than thermal protection?) Passivhaus Institut, Darmstadt 2000]]\\
 \\ \\
 ===== The main facts ===== ===== The main facts =====
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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.
 +
     * 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.
 +
     * 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 %).
 +
     * 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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 <WRAP center 60%> <WRAP center 60%>
-<latex>  
 $$\rho c \dfrac{\delta T}{\delta t} = - div\,(- \Lambda\,grad\,T )$$ $$\rho c \dfrac{\delta T}{\delta t} = - div\,(- \Lambda\,grad\,T )$$
-</latex> 
 </WRAP> </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).
  
-  * Differences in the temperature (gradient //grad//, on the right) propel a heat flux which increases proportional to the relevant component of the thermal conductivity tensor <latex> \Lambda </latex>. ((The most general formulation with which the thermal conductivity can vary for different spatial directions (e.g. in a perforated brick) is represented here. If the thermal conductivity is invariant with respect to direction (isotropic), the scalar value of the conductivity <latex> \lambda </latex> applies instead of the tensor <latex> \Lambda </latex>. The specific heat capacity <latex>\rho c</latex> and thermal conductivity <latex>\Lambda</latex> can depend on the location, without significantly changing the character of the equation. If the coefficients also depend on the temperature (e.g. gases), the equation becomes non-linear – however, even then the numerical solution can still provide useable results under certain conditions.)) (<latex> q = -\Lambda \,grad\,T </latex> is the heat flux).+  * Differences in the temperature (gradient //grad//, on the right) propel a heat flux which increases proportional to the relevant component of the thermal conductivity tensor $\Lambda$. ((The most general formulation with which the thermal conductivity can vary for different spatial directions (e.g. in a perforated brick) is represented here. If the thermal conductivity is invariant with respect to direction (isotropic), the scalar value of the conductivity $\lambda$ applies instead of the tensor $\Lambda$. The specific heat capacity $\rho c$ and thermal conductivity $\Lambda$ can depend on the location, without significantly changing the character of the equation. If the coefficients also depend on the temperature (e.g. gases), the equation becomes non-linear – however, even then the numerical solution can still provide useable results under certain conditions.)) ($q = -\Lambda \,grad\,T$ is the heat flux).
  
   * The negative divergence of the heat flow is the change of the heat content in the infinitesimal volume element.   * The negative divergence of the heat flow is the change of the heat content in the infinitesimal volume element.
  
-  * This is the same as the temporal change in temperature <latex>\(\frac{\partial T}{\partial t}\)</latex> multiplied by the heat capacity   <latex>\rho c</latex>(left side of equation).+  * This is the same as the temporal change in temperature $\frac{\partial T}{\partial t}$ multiplied by the heat capacity $\rho c$(left side of equation).
 This equation has proved to be consistently effective in physics and technology. Such different things like heat transfer in stars, in semi-conductor devices, brake pads and many others can be calculated in good correlation with measurements. This equation also applies in building physics – and the calculations made using it correspond just as well with building physical measurements as shown in [[planning:thermal_protection:thermal_protection_works:Thermal protection vs. thermal storage#Theory and practice (measurement)|the following example]]. This equation has proved to be consistently effective in physics and technology. Such different things like heat transfer in stars, in semi-conductor devices, brake pads and many others can be calculated in good correlation with measurements. This equation also applies in building physics – and the calculations made using it correspond just as well with building physical measurements as shown in [[planning:thermal_protection:thermal_protection_works:Thermal protection vs. thermal storage#Theory and practice (measurement)|the following example]].
  
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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", 
 + 
   * 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.
 +
   * 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.
 +
   * 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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 ===== Literature ===== ===== Literature =====
  
-**[Feist 1987]** Ist Wärmespeichern wichtiger als Wärmedämmen? 1. Auflage, IWU 1987; 2. Auflage, Passivhaus Institut, 2000 ({{:picopen:faxb.pdf|PHI's list of publications}})\\+**[Feist 1987]** Ist Wärmespeichern wichtiger als Wärmedämmen? 1. Auflage, IWU 1987; 2. Auflage, Passivhaus Institut, 2000 [[https://shop.passivehouse.com/en/products/ist-warmespeichern-wichtiger-als-warmedammen-90/|Link to PHI Publication]]\\
 (**“Is thermal storage more important than thermal insulation?”**, 1st edition, IWU 1987; 2nd edition, Passive House Institute, 2000)\\ (**“Is thermal storage more important than thermal insulation?”**, 1st edition, IWU 1987; 2nd edition, Passive House Institute, 2000)\\
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 (**“Passive houses in Central Europe”**; Dissertation, University of Kassel, 1993)\\ (**“Passive houses in Central Europe”**; Dissertation, University of Kassel, 1993)\\
 \\ \\
-**[AkkP 5]** Energiebilanz und Temperaturverhalten; Protokollband Nr. 5 des Arbeitskreises kostengünstige Passivhäuser, 1. Auflage, Passivhaus Institut, Darmstadt 1997 ({{:picopen:faxb.pdf|PHI's list of publications}})\\+**[AkkP 5]** Energiebilanz und Temperaturverhalten; Protokollband Nr. 5 des Arbeitskreises kostengünstige Passivhäuser, 1. Auflage, Passivhaus Institut, Darmstadt 1997 [[https://shop.passivehouse.com/en/products/05-energiebilanz-und-temperaturverhalten-24/|Link to PHI Publication]]\\
 (**“Energy balance and temperature behaviour”**; Protocol Volume No. 5 of the Research Group for cost-efficient Passive Houses, 1st edition, Passive House Institute, Darmstadt 1997) (**“Energy balance and temperature behaviour”**; Protocol Volume No. 5 of the Research Group for cost-efficient Passive Houses, 1st edition, Passive House Institute, Darmstadt 1997)
  
planning/thermal_protection/thermal_protection_works/thermal_protection_vs._thermal_storage.1542885105.txt.gz · Last modified: 2018/11/22 12:11 by cblagojevic