Initial conditions in DELPHIN 6.1

1. Overview

A numerical simulation such as DELPHIN requires initial conditions for the calculated state variables. In the case of a coupled heat and moisture transport calculation, these are the temperature (more precisely, the internal energy) and the moisture mass. DELPHIN uses two types of initial conditions:.

Default setting for the entire structure
Individual settings

2. Default settings

The default values are set on the simulation settings page (see figure below).

Figure 1. Button to switch to the simulation settings

After clicking on the highlighted button, the settings dialog is displayed. The red arrow points to the initial temperature and the blue arrow to the initial relative humidity. The moisture content itself is calculated from this relative humidity using the moisture storage function of each material.

Figure 2. Standard initial conditions for the entire structure

These values apply to the entire structure. In DELPHIN, 20°C and 80% r.H. are used as default values. These are also the conditions proposed in the ISO 15026 5.5 standard. Only if it can be guaranteed that all building materials were delivered and stored in a dry condition can a different value be entered here. ISO 15026 proposes 50% r.H. here (also in DIN 4108-3).

3. Individual settings

The individual settings allow you to specify a separate initial condition for each element. The dialog is located in the lower right corner of the main window.

Figure 3. Area for setting and changing initial conditions in the main window

Here you can add specific initial conditions by clicking on the green plus button. This opens the following dialog box.

Figure 4. Dialog box for an initial condition for temperature

The name must be specified by the user and should reflect the use of this particular condition.

The type determines which variable is set with which value:

Heat
- Temperature in degrees C
Humidity
- Volumetric moisture content in m³/m³
- Moisture mass density in kg/m³
- Mass-related moisture content in kg/kg
- Relative humidity in %
- Capillary pressure in Pa
VOC
- VOC mass density in mg/m3
Salt
- Solution mass density in kg/m3 and mol/kg
- Volumetric solution content in m3/m3 and mol/kg
- Salt mass density in kg/m3 and salt type

For air transport, the initial condition is set to the normal pressure of 101325Pa.

Various values are possible for moisture. The moisture mass density is used directly. The other values are converted internally. The relative humidity and capillary pressure can be converted into a mass using the moisture storage function (sorption isotherm or absorption curve). The values should not exceed the saturation moisture content of the material (ThetaEff) for which the condition is set.

4. Example

An internally insulated brick wall is used as an example here. The structure is shown in the following image.

Figure 5. Construction

The standard initial condition is 20 °C and 80 % RH. Here, 10 °C is to be set as the temperature for the exterior materials (brick wall and exterior plaster). In addition, the brick wall is to be assumed to be already saturated. This allows the drying behavior of an already damaged structure to be investigated. First, take a look at the material properties of the brick. To do this, double-click on the material name in the list on the right-hand side of DELPHIN (1).

Figure 6. Main window with material list and open material dialog

The material data dialog is displayed. Now click on the “View” button (2). This opens the properties dialog. You can also click on ‘Edit’ instead. This opens the same dialog. The only difference is that when you open it with “View,” the material properties cannot be changed. This prevents accidental changes to the material properties.

Figure 7. View of the material properties

As you can see, the brick has a saturation water content (theta effective) of 0.212m³/m³. This is the maximum value you can set as the initial condition. With the density of water being 1000 kg/m³, you can also calculate the corresponding water mass density of 212 kg/m³. You can use either of these values as the initial condition.

Now create a new initial condition by clicking on the green plus button described in the section above. First, we create the temperature condition.

Figure 8. Initial condition for temperature

Then create the condition for the moisture content.

Figure 9. Initial condition for brick moisture (saturation)

The images above show the contents of both dialog boxes. The names of the conditions have also been chosen appropriately so that they are easier to identify in the list. Finally, both newly created conditions are displayed in the “Condition List” dialog box.

Figure 10. List of newly created initial conditions

Like interfaces and materials, the entries are displayed in gray and italics because both conditions have not yet been assigned to the construction. This is the next step. To do this, select the condition (1), then select the area in the construction (2) and click on the green assignment button (3).

Figure 11. Assignment to the construction

In this example, the temperature is to be assigned to the exterior plaster and the brick layer, and the moisture content only to the brick layer. You can check the positions by clicking once on an initial condition in the assignment list. The assigned area in the construction is then highlighted in dark color.

5. Notes

If several initial conditions are assigned to the same area, only the last assigned condition is used.

If the moisture content of the condition is outside the permissible range, e.g., greater than the saturation moisture (ThetaEff), the solver will issue an error message when the simulation starts and the simulation will not start.

To specify moisture distributions, you currently still have to create and assign many individual initial conditions.