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Frequently Asked Questions

This page lists frequently asked questions and answers for quick reference. It is quite new so feel free to address your questions to

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Content: >> Climate settings
>> Material properties
>> General simulation settings
>> Miscellaneous

Climate settings

Assigning moisture or heat sources

If moisture or heat sources shall be assigned the units have to be taken into account necessarily. In DELPHIN, the unit for eg moisture sources is dependent on time AND volume: kg/m³s (or kg/m³h). Therefore, the known output parameters are to convert.
Example: In a two-dimensional construction, an area of 0.25 m height and 1 m width shall be burdened for 10 days (=240 h) with 0.5 kg/m² in total. To find out the dimensions of an area mark it, in the bottom left of the construction window the dimensions are shown. Except when otherwise agreed, the extension in z-direction is 1 m. The volume burdened with moisture measures 0.25 m³, the area 1 m². In DELPHIN >> Conditions >> Field has to be declared:

0.5 kg/m² / (0.25 m * 240 h) = 0,00833 kg/m³h
for a time period of 10 days.

NOTE: In DELPHIN single elements can reach water contents over saturation which can lead to relative humidities above 100%. This may slow down the simulation.

Generate or change decline and orientation of walls and roofs

The boundary conditions short- and longwave radiation as well as rain are dependent on decline and orientation of the surface. These properties can be chosen at >> Wall data.

To generate or change such properties go to DELPHIN >> Edit >> Wall definitions. There the geographical orientation, decline and geographical longitude can be defined. The value at Wall area currently is not used. A '0' is sufficient here.

Change or generate climatic data

Climatic data included in DELPHIN are located in the folder DB_climate_data, e.g. in

C:\Program Files (x86)\IBK\Delphin 5.9
Open the file to be changed or the climate component you want to generate with a text editor or tabulation program. During import into a tabulation program watch that dots are recognized as decimal separators (in Excel’s text-conversion assistant: step 3 at Others). Now, change the values or insert complete new values and save the file. Again watch that decimal separators are dots not commas (eventually rework with ‘Find and replace - Ctrl+H ’ in a text editor). At tabulation programs the files can be saved as text file (format tapstop separated *.txt).

Afterwards, rename the format from .txt to .ccd and import it to DELPHIN (Conditions >> Climate >> New >> Course: Data points). Let it display in DELPHIN to check whether the climatic data files are readable. The format of climatic data files are explained in the DELPHIN Help at Appendix >> Climate data file formats.

WTA model to consider leakages

This simple model in >> Conditions >> Field considers that e.g. in wood constructions impermeability coatings made of foils in reality are not dense due to different reasons. Through leakages room air rather flows into the construction convectively. The basics are explained in WTA-leaflet 6-2 (12-2014).

Above all the model is used with insulation systems with vapour barriers and fibre-type insulation materials. Three values have to be indicated: q_50 - if A/V ratio ca. 1 the value from the blower-door measurement can be used. Air Space height - height of coherent air layer in the building; different floors are not coherent only if they are separated e.g. by airtight doors. Pressure difference mech. - additional mechanical pressure difference caused by air conditioning.

This field condition is assigned to the outer 10 to 20 mm of an insulation layer and depending on the sealing and outer structure to more outer layers as well. At >> Outputs >> Format/Types an output format can be defined and assigned, which records the additional amount of moisture created by this fiel condition.

Material properties

Moisture dependent vapour barriers

How the moisture dependent vapour diffusion of moisture adaptive vapour barriers can be adapted to specific products?
Import the vapour barrier into the dpj-project file (right-click on material >> Import material into project) and save the project. Open the *.dpj file with an external editor by pressing key F2. Do not use the Microsoft Editor which often creates problems, use another free editor software. In the editor scroll to the vapour barrier. The numbers below [MOISTTRANS] and FUNCTION = My(Phi) describe the vapour diffusion resistance factor µ(My), dependent on the humidity (Phi) and for a thickness of 1mm! Adapt the numbers, best change the material name and save the *.dpj file. Returning to DELPHIN you will be asked whether the changed project shall be loaded. Confirm with ‘Yes’.

HINT: You can define a moisture dependant vapour diffusion for any material if you enter the above key words [MOISTTRANS] (add word-wrap!) FUNCTION = My(Phi) and input in the following line the humidity (not with unit [%]) and in the next line the µ-value. If existing, delete the line FUNCTION = lgKv(Ol) and the two following lines with numbers. Otherwise the vapour transport would be defined twice.

Adapt material properties

Material properties can be adapted easily in DELPHIN. Changed materials are saved into the project file because materials are not to be changed within the data base. Only if name or colour are changed the material will not be saved into the project file.
Choose a material from the data base that is as similar as possible to the one that is requested. Open the material with a double-click. Choose the value you want to change in the list on the left hand side. After EVERY single change the button Modify material has to be clicked otherwise only the last change will be taken into account. If the initial or final value of a material property is changed that is represented by a function, e.g. the liquid water conductivity, the whole function will be scaled down or up.

Moisture-dependent heat conductivity

It is possible to define a moisture dependent heat conductivity for any material in DELPHIN, e.g. with absolute values of water content. Import the material into the dpj-project file (right-click on material >> Import material into project) and save the project. Open the .dpj file with key F2 (regarding the editor consider the remarks ahead). Scroll to the material and there you may have to replace the numbers at [HEATTRANS]. Example:

        FUNCTION = lambda(Ol)
          0     0.1     0.21
          0.6   0.8     0.88 

In the above example the thermal conductivity of the dry material is 0.6 W/mK. At porosity (0.21 m3/m3), the thermal conductivity is 0.88 W/mK. The function must begin with the pair of values lambda_dry and 0. It must end with the THETA_EFF value.

Using an own sorption isotherm

If scaling up or down of the sorption isotherm is not sufficient an own sorption isotherm can be entered. To change material properties all properties of this material have to be stored in the project file. Right-click on the matrial, choose Import material into project and save the project. Now open the project file in an editor with F2. The Windows editor is not very useful for this task, other editors (such as PSPad, Notepad++ etc.) ease the work a lot. Afterwards the porosity (THETA_POR) und effective saturation (THETA_EFF) should be corrected.
The section after [MOISTURE_STORAGE] contains the moisture sorption isotherm. Delete all data till [MOISTURE_TRANSPORT]. Now type in FUNCTION = Theta_l(RH). DELPHIN subsequently awaits the water content in dependency ot the relative humidity (unit: -). In the next line type in the relative humidtiy starting with 0, ending with 1 and separated by spaces or tabs. In the connecting line follows the corresponding water content (unit: m3/m3) starting with 0, ending with the water content at effective saturation. DELPHIN calculates quicker if you enter afterwards the inverse function, meaning FUNCTION = RH(Theta_l) followed by interchanged lines for relative humidtiy and water content.

General simulation settings

Slow simulation speed

There are many reasons for slow simulation speed, some are explained at DELPHIN 5 Help >> Modeling >> Numerical solution >> Fixing numerical problems. Especially at the beginning of 2D simulations the first time steps can take quite a long time. If the simulation speed does not accelerate within some hours (simulation time) you may try these approaches:

  • with the current solver the number of discretized elements should not exceed 10.000.
  • it should be avoided to assign boundary conditions associated with moisture on moisture dense materials, e. g. humidity or rain on steel or glass.
  • some materials are identified, e.g. PE-Foil, that provoke low simulation speed due to their material functions. Try to replace these with similar materials or by changing the sorption isotherm. Subsequently, these materials will be replaced in higher Delphin versions.
  • at >> Simulation >> Solver settings: Relative tolerance the precision of the results can be changed. Reasonable values are between 0,0001 and 1E-8. A lower precision does not always lead to quicker simulations.
  • at >> Simulation >> Solver settings >> Advanced settings [1]: Max. method order instead of the predefined value 5 as well 2 or 1 can be used.

The last two suggestions one can change during the simulation. Just cancel the simulation, change the simulation settings and proceed at the same point in time with Continue simulation.

Consideration of air flow

DELPHIN 5 is able to calculate laminar air flow. Therefore, the following requirements have to be fulfilled:

  • activate at Simulation >> Modelling/Simulation settings >> Include air flow model. „Include buoancy effect” should NOT be activated currently.
  • a reasonable Update interval is between 5 and 30 minutes, by no means '0'.
  • air not only can flow through air but material pores. Therefore, 1. the flag AIRTIGHT hast to be deactivated at correspondent materials, 2. the air permeability has to be defined as KG =   xx s; KG means air permeability, xx the value, s is the unit seconds. This should be done in the dpj-file with an editor.
  • define with >> Conditions >> Climate >> “New” >> Type: Gas (air) pressure constant air pressures or courses (from a file).
  • define with >> Conditions >> Boundary >> “New” >> Type: Air pressure air pressure boundary conditions and assign them.


Windows error message api-ms-win-crt-runtime-l1-1-0.dll

With the first start of DELPHIN it might happen, that this error message appears: " [...] api-ms-win-crt-runtime-l1-1-0.dll is missing". In this case Windows-Update KB2999226 is missing. It can be downloaded e.g. from here.

Set an useful editor to work with .dpj-files

Using the predefined MS Editor creates a lot of problems and is not user-friendly. Therefore download an alternative editor and install it. Then set the path in DELPHIN to this new editor with >> File >> Preferences >> External tools. In the top field choose the .exe file of the new editor.

Installation on Apple

If DELPHIN shall be run on an Apple device within a virtual system such as Parallels please make sure that DELPIN is both downloaded and installed within this virtual system. Otherwise DELPHIN might no work.


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