The role of the moisture in the outside-wall with reference to the heat-household of a building

"Under comparable conditions, older constructions, that were produced about the turn of the century, 3-once require 2 presently until less space-heat-energy than that was produced in the last 5 to 10 years after the point of view of the unit of heat-transfer. Although miscellaneous differences (heat-bridges) pass coolness-ribs regarding the construction-construction, etc..) the elevated energy-consumption-values with conventional calculations don't let themselves explain. As well as the Unit of heat-transfer-theory, as is not also the theory about non-stationary heat-performance of buildings in the situation, that to justify only approximately up to 300 per cent of amounting energy-consumption-increases.

in 1953, non-stationary k-Werte were determined by the Eidgenössischen-Material-Prüfanstalt (EMPA) for 5 years at attempt-little houses. It took place, extremely correct temperature and energy-measurement as well as the recording of the moisture-changes.

It will determine that the moisture in the stonework in the summer to - and in the winter decreases. With the desiccation, the value of the heat insulation got worse by 30 per cent. [1] Neither the non-stationary calculation also as the legally stipulated unit of heat-transfer - is theory experimentally sufficiently proved.
The different dampness-salaries for the stonework with its respective energy-streams, this Heat-storage-ability just as they Temperature-code number becoming in the calculations taken not into account. In an attempt-transaction 1954/55, it was determined that the outside-stonework dry off in the winter and the moisture increases in the summer. [1]

It is assumed that a moisture-increase the heat-code number in the stonework-construction approximately by 5 to 6 percent (Max). 10 percent) can make worse. According to volume-size, where waters or air-steam-mixtures are in the wall-construction, these values could be much bigger. See to this the material-values in the table 1.

The heat and dampness-transportation-processes in buildings are strongly connected normally. This especially clearly appears on the insulation with the dampness-influence from prefabricated parts. In graphics, the increase of the heat-conductivity is shown by three different construction-materials in dependence on the water-salary. (Form 1, [2]

While the heat-management mineral wall-creator, as with the here represented pore-concrete, rises linearly with the water-salary, the increase with Polystyrol is - hard-foam easily progressive. Surprising is the strong increase of the heat-conductivity of mineral-wool already with very small water-salary. [2]
The influence of the moisture on the insulation becomes also with Eichler / Arndt described, here influences with what in coast-proximity, weather-sides and hit-rain and other is named. Concrete numbers, as this has an effect, are not named. [3]

The physical states, steam, water and ice (winters) occur in a wall-construction. The phase-postponement becomes pores, capillary, through the temperature, material-structure, Salt, and Pressure decide. No constant conditions are available in the stonework. You/they constantly change qualitative and quantitative. Energy-streams are available, where additionally the wall-construction-material through the heat-conductivity of this Air, Air-steam-mixture, Water and in the winter through ice is influenced.

Table 1: selected material-values

One can recognize that so itself with moist sand and also at stonework the specific heat-capacity increases. The more heat a material can store, all the more lazily, it responds with the Aufheizung and cooling. The dampness sand has the same heat-capacity so approximately as from wood. However, also the heat-conductivity changes, which with moist sand and increases so at stonework. Another value, this Temperature-code number or temperature-conductivity a [m²/s] should find observation here. It is the measurement for the reproductive-speed of a temperature-alteration in a body. A temperature-alteration plants all the more quickly away the bigger the heat-conduction is and the smaller the specific heat-capacity and the density is. Wet sand shows clearly more favorable values here.
How already aforementioned, different dampness are available in a wall-cross-section, like kernel-dampness, condensation, Spritzwasser and other, that changes also in its expansion or doesn't exist at times. [6] with it alters also the physical conditions for itself in the construction-material. There are sections within the wall-cross-section consequently, where a higher heat-storage and Heat-conductivity be available, the values are lower with others. Hike the frost-point into the inside of the stonework in the winter, reduces the heat-storage and the heat-conductivity for itself so increases itself. This has an effect adversely on the insulation of the outside-wall.

An energy-stream always takes place from the higher temperature to the lower. If you increase the air-temperature for itself at the outer surface of the outside-wall, so two energy-streams are available, one of interior and one from outside. The known amplitudes (temperature-curves), that overlap in the wall-cross-section somewhere and lift, come about with it. At a temperature-alteration, the pressure changes also in certain scope in the pores, cavities and capillaries. According to dew point, liquid thaws from or changes into an air-steam-mixture. The vaporization-heat of the water (0 ºC, 2500 kJ / kg) or the glaze-heat of the ice (333,4 kJ / kg) are still taken into account now that so the heat-reception and heat-depositing respectively, according to which which physical state appears, occur additionally locally. Alter the temperature again for itself in the wall-cross-section, so also the physical states change conceivably. Wintry Direkteinstrahlung and also the indirect in-radiation (only essentially more inferior just) cause an absorption of the heat-energy, that is stored over many hours and again slowly outside escapes. This was proved also in the attempt-transaction 2001 in Leipzig where a curve is represented for a day-section here.

Explanation: Score points in 1 = 7.00 o'clock until 23.00 o'clock, from 9.10 to 15.30 o'clock sunshine; Row 1 = area-temperature; Row 2 = temperature at the inside of the outside-wall; Row 3 = temperature in the wall (10 cm from outside); Row 4 = temperature at the outside-surface of the wall; Row 5 = air-temperature outside (protected)

"... It could be determined that a low temperature-increase also on days, if no sun shines, at the outer wall-surface takes place. This temperature is higher than this on that occasion in the wall-inside. In this time, a heat-stream lay additionally from outside inside before. On average a temperature-increase of 5 K occurred with 12 days. Time delayed took place a cooling, that stretched over a period of 10 to 18 hours, until the original level was reached..." [5]

Under the point of view of the higher heat-storage-ability could a moist wall-construction-material and the more inferior temperature-conductivity so additional Heat is stored for example in an outside-wall, with what also a delayed heat-depositing takes place. One is every moisture with a certain temperature Enthalpie assigned. Still, also the Teildrücke play a role here. (Comparisons to this the Mollier (h, s) - diagram of the contribution Atmospheric humidity.) At a complete dry wall, for example steel-plate, the moisture can be neglected under normal climatic conditions, if abandoned the temperature of the wall-surface and this of the surface of no fluctuations so only low quantity of condensate at the surface lasts and from-thaws. Heat-swappers work on this basis. However, the moisture is not picked up by the material. With more-layer-y wall-constructions, the variation-possibility is even bigger.

Besides the phase-postponement, also the individual dampness-conditions should be investigated practical Versuchensreihen since there will be critical and also optimal areas with certain dampness-shares, that also for the development of construction-material-systems and - constructions of interest should be.

The present legal u-Wert-Berechnung represents an ideal-condition (laboratory) under exclusion of climatic conditions. For coarse assessments for what this calculation-method was also developed and surely in the area of higher unit of heat-transfer sufficient.
Calculation of the unit of heat-transfer at an outside-wall.

Literature
[1] Energieverbrauchsanalysen von Hochbauten (Bossert/Nagel Januar 1980) aus Deutsche Bauzeitung 9/1982 S. 58-62 als pdf-Datei (308 KB)
[2] IBP - Software - WUFI - Grundlagen (2001) Fraunhofer Institut
[3] Eichler/Arndt; Bautechnischer Wärme- und Feuchteschutz, 1989
[4] Günter Meyer, Erich Schiffner; Technische Thermodynamik, Fachbuchverlag Leipzig, 1983
[5] Eingespeicherte Solarenergie bei einer Außenwand - praktische Versuchsdurchführung 2001 www.ib-rauch.de/bauphysik/waermsp.html
[6] Trocknung von feuchten Bauwerksteilen 2002 www.ib-rauch.de/Beratung/feuchtig.html