WUFI 2D. Calculation Example Step by Step. D. Zirkelbach Th. Schmidt H.M. Künzel M. Kehrer Ch. Bludau - PDF

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WUFI 2D Calculation Example Step by Step D. Zirkelbach Th. Schmidt H.M. Künzel M. Kehrer Ch. Bludau WUFI 2D Short Introduction PREFACE This introduction will show you how to model a building component

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WUFI 2D Calculation Example Step by Step D. Zirkelbach Th. Schmidt H.M. Künzel M. Kehrer Ch. Bludau WUFI 2D Short Introduction PREFACE This introduction will show you how to model a building component in WUFI 2D, how to specify boundary, surface transfer and initial conditions, how to perform the calculation and how to analyse the results. Many useful hints will be given. As an example illustrating each step, we will analyse the hygrothermal behavior of a concrete ceiling supported by a brick wall with exterior insulation. For further information about the various dialogs and commands please consult WUFI 2D s online help. 2 WUFI Manual Contents 1. EXAMPLE CASE - STEP BY STEP... 4 Step 1: Project Notes... 7 Step 2: Geometry of the Component... 8 Step 3: Numerical Grid Step 4: Material Properties Step 5: Initial Conditions Step 6: Boundary Conditions Step 7: Computational Parameters Intermediate Step: Save Project Step 8: Computation Step 9: Analysis of the Results WUFI 2D Short Introduction 1. Example Case - Step by Step This introduction will walk you step-by-step through an example case, demonstrating how to model a building component in WUFI 2D, how to perform the calculation and how to analyse the results. At the beginning of each step, highlighted in green, the procedure will be presented as applying to the example, then a general discussion of the program features will follow. In order to model a new case, to perform the calculation and to analyse the results, please follow these nine steps: 1) You may give the case a name and input some notes concerning the project, the current project variant, the client etc. 2) You must define the geometry of the building component, that is, you build up the component from rectangular elements, using WUFI 2D's graphical component editor. 3) WUFI 2D automatically generates a numerical grid, subdividing the component into small grid elements for the numerical calculation. You may adjust the grid, if needed. 4) You must assign material data to the various elements making up the component. You may take the data from the material database or enter new data. 5) You must specify initial conditions for the component. For each material an initial temperature and an inital moisture content or relative humidity is needed. 6) You must define how the component is exposed to influences from the surroundings. This means assigning heat, vapor and liquid transfer coefficients, specifying inclination and orientation and selecting boundary conditions ( weather data ) for all surface segments of the component. 7) You must specify a start date, the time period covered by the calculation and the time step width. 8) Let the calculation run. 9) Analyse the results. 4 WUFI Manual Example Case Step by step, we will work through the following example case: A freshly cast concrete ceiling is supported by an outer masonry wall with exterior insulation system. The interior surfaces are assumed unfinished. Since no flooring is yet installed, there exists a symmetry axis along the center of the concrete slab. Only one half of the assembly has to be modeled therefore, reducing calculation time. The building component consists of a 20 cm thick concrete ceiling supported by a 24 cm thick honeycomb brick wall. An exterior insulation and finish system (EIFS) composed of mineral wool insulation (10 cm thick) and mineral plaster (1 cm thick) has been applied to the outside of the wall. The initial moisture content of the concrete, due to the mixing water, is assumed to be at free saturation (the equilibrium moisture at 100% RH). 5 WUFI 2D Short Introduction Climate: - Interior climate: Medium moisture load as defined by WTA- Recommendation /E - Exterior climate: weather data from Holzkirchen, facade facing west, rain taken into account Calculation period: 1 year, starting in October The analysis shall consider in particular the temperature distribution in the component and the drying time of the concrete slab. In the following screen shots this icon will be used to denote a mouse click (the finger points at the object to be clicked): 6 WUFI Manual Step 1: Project notes Dialog Project Notes This dialog serves as a memo pad for some administrative project info which can thus be kept together with the project data and the calculation results. All these inputs are optional, they only have an informative character for the user. In the text filed Date you may use the drop-down list to select a different date than the creation date of the project file (the first time it was saved). 7 WUFI 2D Short Introduction Step 2: Geometry of the Component Example Case Use the graphical interface of this dialog to build up the component from rectangular elements. Each material is drawn as an individual rectangle; more complicated shapes can be composed of several rectangles. In this case, we make use of the symmetry axis passing through the ceiling and only consider one half of the component. We need four rectangles: mineral plaster, insulation, brick masonry and concrete ceiling. While you are drawing, WUFI 2D automatically creates a graphics script (displayed below the drawing area) describing your graphical input. You can edit the script to add elements, to give names to the elements, to refine coordinates, to rotate the component diagram etc. The script describing our example component looks like this: 10.0 mm mm 0.0 mm 0.0 mm (plaster) r stroke mm mm 10.0 mm 0.0 mm (insulation) r stroke mm mm mm mm (brick masonry) r stroke mm mm mm 0.0 mm (concrete ceiling) r stroke 8 WUFI Manual Dialog Geometry Click on the item Geometry in the explorer tree on the left side of the main window to open the dialog panel shown above. The dialog contains the empty drawing area and the script area which already holds a few definitions. Drawing Area Use the drawing area to define the construction in a graphical way. Click into the area with the left mouse button, hold the button down and drag open a rectangle. For each rectangle you draw, a definition line will automatically be added to the script in the script area (see below). In order to add another rectangle, click on a corner of an existing rectangle and drag open a new one. New rectangles are always appended to existing ones. Further functions in the drawing area: Scroll To scroll the diagram in the drawing area, press the CTRL key and the left mouse button, and drag the diagram into a convenient position. 9 WUFI 2D Short Introduction Zoom To zoom into the diagram, press the SHIFT key and the left mouse button, and drag a zoom frame from the top left corner to the bottom right corner of the region to be zoomed. In order to reset the zoomed view, press the SHIFT key and the left mouse button, and drag open a zoom frame of arbitrary size at an arbitrary location, moving from bottom right to top left. Page setup Right-click in the drawing area to open the page setup: Here you can specify the default position of the coordinate origin in x- and y- direction, counted from the lower left corner of the drawing area. Scale defines the default magnification to which the drawing area returns when you zoom out. If the diagram becomes too large to be viewed in its entirety, you may specify a smaller value for the scale. Which value is appropriate depends on your screen resolution. Coordinate Bar When the mouse cursor is within the drawing area, its coordinates are displayed in the coordinate bar. Script Area The script area holds a script which describes the graphic you created in terms of drawing commands. Definitions for mm and cm are already in place, you may add your own definitions in PostScript style. 10 WUFI Manual You can use the script to change the names and the sizes of the rectangles, which is useful for fine-tuning the construction. As soon a you have drawn a rectangle in the drawing area, the corresponding commands appear in the script area. A script line describing a rectangle looks as follows: The first two numbers are the side lengths of the rectangle in x- and y-direction (including their units), followed by two numbers specifying the coordinates of its lower left corner, and the rectangle's name in parentheses. WUFI 2D assigns the names r1, r2 etc. to the rectangles, you may assign a more meaningful name by editing the script. A name must be unique and can only be used for one rectangle. The r stroke terminates each line (the r macro, defined at the beginning of the script, processes the preceding numbers into a complete set of coordinates for the four rectangle corners, and the stroke command draws the rectangle). After a change to the script, press the ENTER key to update the diagram in the drawing area. Press CTRL+ENTER to insert a new line. 11 WUFI 2D Short Introduction Step 3: Numerical Grid Example Case As soon as the dialog panel Grid is opened, WUFI 2D's automatic grid generator creates a numerical grid for the component. For the example case, an automatic grid is sufficient, but we increase the maximum number of grid elements. We set the maximum number of elements to 90 in x-direction and to 60 in y-direction (see screenshot below). Dialog Grid Click on the explorer tree item Grid to open the dialog panel shown above. WUFI 2D displays the construction you defined in the previous step and overlays it with an automatically generated numerical grid. You may use this dialog to finetune the grid if needed. 12 WUFI Manual Grid Area The grid area shows a graphical display of the component, with the numerical grid superimposed for optical control. You may scroll or zoom using the CTRL or SHIFT key, respectively, as in the dialog Geometry (see above). The numerical solver of WUFI 2D works most reliably if the grid is as fine as possible and if the sizes of two neighbouring grid elements are not different by more than, say, a factor of two. Towards the component boundaries and towards boundaries between different materials the grid should become finer because here steeper temperature and moisture profiles are to be expected which need to be resolved by a sufficient number of grid elements. At adiabatic boundaries, such as symmetry axes, this is not necessary, because here the temperature and moisture profiles tend to remain flat. The grid should try to strike a balance between a high number of grid elements and an acceptable calculation time. Min. and Max. Number of Elements The minimum number of elements is the minimum number of grid elements the grid generator is allowed to allot to a material. You may increase this number if you feel that a thin material in your component should have more grid elements but you do not want to make the whole grid finer. This may be useful if you want the moisture profile across the material to be resolved more finely (e.g. in a moisture-adaptive vapor retarder), or if you want to reduce the effect that the properties of neighboring materials tend to bleed into thin materials because of the averaging WUFI 2D must perform between adjacent grid elements. The maximum number of elements is the number of elements the grid generator has available for distributing across the component. For the fine grid the generator attempts to use the full number of elements, for the medium and coarse grids it uses proportionately less. The minimum and maximum number of elements may be specified separately for the x- and the y-direction. Grid Settings This table displays the properties of the individual grid sections. The sections are numbered serially in x-direction (from left to right) and in y-direction (from bottom 13 WUFI 2D Short Introduction to top). The grid sections always come in pairs, a and b ; the grid is slightly expanding in section a and contracting in section b. Each line of the table describes one of these sections of the grid. The column ID identifies the grid section in question. Width shows the width of the grid section, No. El. gives the number of grid elements contained in the respective grid section. The expansion factor Exp. Fac. determines by which factor two successive grid elements expand or contract. First El. shows the width of the first element in the grid section, and Last El. the width of the last element. Right-click while the mouse is anywhere in the table in order to open a pop-up menu: Here you can select the grid fineness for the x- and the y-direction: Manual: The grid properties can be manually specified by entering the desired number of elements and the expansion factor for each grid section. Coarse, Medium and Fine: A coarse, medium or fine grid will automatically be generated, depending on the minimum and maximum number of grid elements (see above). 14 WUFI Manual Step 4: Material Properties Example Case For the present example, the following material properties are read from the material database and assigned to the different elements of the building component: - Mineral plaster - Mineral wool (heat conductivity: 0,04 W/mK) - Aerated clay brick (density: 600 kg/m³) - Concrete C35/45. Dialog Materials 15 WUFI 2D Short Introduction Click on the explorer tree item Materials to open the dialog panel shown above. It shows the building component as defined previously. Click on one of the retangles to assign the material properties. The material properties in x-direction may be the same as in y-direction (isotropic material), or they may be different (anisotropic material): 1. If no material has yet been assigned to the rectangle, a click with the left mouse button will assign the material specified in the next dialog both to the x- and the y-direction. 2. Otherwise, a click with the left mouse button will assign the material to the x-direction and a click with the right mouse button will assign the material to the y- direction. The list displayed below the construction diagram shows the materials assigned to the construction. Alternatively, you may hover with the mouse above a rectangle to pop up a little window showing the material(s) assigned to this rectangle: The left- or right-click on the rectangle opens the dialog Allocation of properties. Dialog Allocation of Properties This dialog lists the materials that have already been allocated to one of the rectangles. You may re-use materials from the list or add new materials. Initially the list is empty. 16 WUFI Manual Buttons: New: Copy: Edit: Add a new material to the list. WUFI 2D opens the dialog Material Database where you can select the material (see below). Create a copy of the highlighted material in order to edit it or to use an independent copy of the material. Use independent copies if you want to assign different initial conditions (see below) to elements containing the same material. WUFI 2D opens the dialog Material Properties for editing the highlighted material (see below). Unassign: Removes the assigned material from an element (separately for x- and y-direction, see above). Assign: Assigns the material to the rectangular construction element (for x- and/or y-direction, see above). Close: Help: Closes the dialog. Opens the online help for this dialog. Dialog Material Database The dialog Material Database displays the materials contained in the material database and offers them for selection. (If you want to add a new material to the database, use the database editor which you can access via the menu Database Materials.) 17 WUFI 2D Short Introduction In order to read a material from the database, 1. Select the respective source and catalog. 2. Select the desired material. 3. Press the Assign button to add the material to the materials list in the dialog Allocation of properties. For each material, the basic material properties are displayed in the colums after the material name. The remaining properties are shown as Hygric Extensions if the option Show optional data is checked. Dialog Material Properties This dialog displays the properties of a material. You can view and edit the properties. If you want to edit the data, you first have to unlock the material by clicking on the padlock icon. Once a material has been unlocked, its name begins with an asterisk (*) to distinguish it from the original material in the database. 18 WUFI Manual 19 WUFI 2D Short Introduction Step 5: Initial Conditions Example Case In our example case, we set the initial water content of the concrete to free saturation (147 kg/m 3 ), and leave the other materials unchanged. Dialog Initial Conditions Click on the explorer tree item Initial Conditions to open the dialog panel shown above. For each material assigned to the component, you can specify the initial temperature and the initial water content or relative humidity. (All elements of the component with the same material will start with the same inital conditions. If you want to specify different initial conditions for elements with the same material, assign copies of the material to them; see the dialog Allocation of Properties above). Since the thermal conditions in a building component usually adapt very quickly to the boundary conditions, it is not necessary in most cases to specify elaborate initial temperatures. Within a few hours, the thermal conditions will usually have become independent of the initial temperatures anyway. The predefined initial temperature of 20 C within the whole component will usually be good enough. If you simulate short-term processes (e.g. laboratory tests), it may be necessary to give more thought to the initial temperatures. 20 WUFI Manual Step 6: Boundary Conditions Example Case The data necessary for defining the boundary conditions in our example are listed in the following table: Ext. climate Int. climate Adiabatic Surface Coefficients Adiabatic/ System Border X Treat as Inner Surface X Heat Transfer Coefficient [W/m 2 K] 17 8 Short-Wave Radiation Absorptivity [-] 0.4 (Bright plaster) Long-Wave Radiation Emissivity [-] 0.9 Rain Water Absorption Factor [-] 0.7 Color in Model Climate File Holzkirchen WTA Azimuth [deg] 90 - Inclination [deg] 90 - For where and how to to enter these boundary conditions see the following sections. 21 WUFI 2D Short Introduction Dialog Surface/Climate Click on the explorer tree item Surface/Climate to open the dialog panel shown above. Here boundary conditions must be specified for each surface segment of the building component. In the example shown here, the exterior facade is exposed to the Holzkirchen weather, including rain. The symmetry axis and the borders where the continuing component has been cut off are treated as adiabatic surfaces (i.e. no heat or moisture can flow across them). Left-click on one of the surface segments to open the dialog Allocation of properties. 22 WUFI Manual Dialog Allocation of Properties This dialog lists the boundary conditions that have already been allocated to one of the surface segments. You may re-use boundary conditions from the list or add new ones. Initially the list is empty. In order to add a new set of boundary conditions click on New. A new list item is added, with a name automatically generated by the program (e.g. If you want to replace the name by something more intelligible (like exterior facade ), double-click on it to change it. In order to edit the boundary conditions themselves, click on the button Edit . The screenshot above shows the building component and the dialog Allocation of properties with the three sets of boundary conditions used in the example (the adiabatic set of boundary conditions has been assigned to the three surface segments marked green in the diagram, the exterior conditions to the red segment and the interior conditions to the two blue segments). Buttons: New: Copy: Adds a new set of boundary conditions to the list. The programm assigns a name describing the surface segment for which you created the list entry. Creates a copy of the highlighted list item. This may be useful if you want to create a set of boundary conditions which differs on
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