Dialog: Initial Conditions
In this dialog the initial moisture and temperature distributions are defined (e.g. a dry component or one with trapped construction moisture).
You can specify
- for the initial moisture content:
- a constant initial relative humidity across the component
- a different initial water content in each layer
- an arbitrary initial moisture profile read from a file, specifying different initial water contents for different grid elements.
- for the initial temperature distribution:
- a constant initial temperature across the component
- an arbitrary initial temperature profile read from a file, specifying different initial temperatures for different grid elements.
"Constant Across Component":
For "Initial Moisture in Component" you can enter the desired value of the initial relative humidity in the text box (e.g. 0.8 for the practical moisture content, corresponding to the equilibrium moisture at 80% RH). WUFI then initialises the individual layers with a "Water Content" which it calculates from the entered RH, using the moisture storage function of the corresponding materials.
Note that this may result in different water contents in the different layers, as dependent on the different moisture storage functions of the different layer materials. However, this is a quite realistic initial condition, since it is the relative humidity which tends to assume a constant level across different layers in equilibrium, not the water content (this is because the relative humidity is uniquely related to the capillary pressure which tries to equilibrate).
The resulting water contents are displayed in the assembly table in the lower half of the
dialog, but they can not be edited in the table.
In the example shown in the screenshot, the specified initial relative humidity of 0.8 corresponds to an initial water content of 25 kg/m³ in the lime silica brick, but only 6.3 kg/m³ in the gypsum plaster which has a different moisture storage function.
For "Initial Temperature in Component" you can enter the desired value in the text box. All grid elements of the temperature field will be initialised with this value at the start of the calculation. Such a constant temperature profile will be adequate for most cases occurring in building physics since the temperature profile adapts to the prevailing boundary conditions in a few hours anyway.
Version notice: user-defined initial values can be entered in
WUFI Pro only.
"In each Layer":
For "Initial Moisture in Component" you can enter an individual "Water Content" for each layer of the assembly. Edit the relevant text boxes of the assembly table in the lower half of the dialog. This option is particularly useful for specifying construction moisture contents for the different layers.
If you have specified a "Typical Built-In Moisture" for the materials
in the Material Data dialog, just press the button
"Assign Typical Built-In Moisture" in order to fill the text boxes
with the respective values.
For "Initial Temperature in Component" there is no such option, since the temperature profile adapts to the prevailing boundary conditions in a few hours anyway and there is no point in specifying a step-like profile which is too crude for any detailed invetigation on the one hand and dissipates within a few hours on the other hand. If you want to employ a more sophisticated initial profile than a constant temperature, use the next option.
Version notice: the option "In each Layer" is only available in WUFI Pro.
"Read from File":
In this case WUFI reads the "Initial Moisture in Component" from a file which contains the desired initial moisture profile (e.g. as measured, or computed in an earlier WUFI run).
Enter the filename into the text box or open a "File" list from which you can select the file.
At the start of the calculation, WUFI then reads the initial moisture profile from the specified ASCII file. This file must consist of two columns. The first column contains the x-coordinates in meters, the second column, the corresponding moisture contents in kg/m³.
The x-coordinates need not be equidistant and need not be identical with the x-coordinates of the grid elements. WUFI evaluates the moisture content of an element by linear interpolation if necessary. [##decimal point?##]
This option also allows you to continue one calculation with another calculation. Write
the last calculated moisture profile to an ASCII file
and use it as the initialisation file for the next calculation.
For the "Initial Temperature in Component" you may specify an initial profile in exactly the same way as for the initial moisture.
Version notice: the option "Read from File" is only available in WUFI Pro.