Basic First Model

Introduction

To demonstrate basic Ventus capability, we will model a simple six-story building for winter and summer conditions. This model features metric (SI) units; Ventus supports both Metric and US Customary Unit systems.

The user should work through this entire example. If you need help, the models are attached as files in Ventus Models.

Problem Geometry

The building has six identical levels that each have two rooms and a stair. Doors provide access between the rooms and to the stair. We will assume leakage through the walls and floors. The floor-to-floor height is 3 m.

Both the geometry of the model, Figure 1, and the flow path areas between each room, Figure 2 will be used to model pressure and flow.

Plan View, Room Names — Figure 1. The geometry of the example problem with zone names.

Plan View, Flow path names — Figure 2. Flow path areas with flow path names at the stairwell. The values in the parentheses are areas to the level below.

For each of the flow paths, the flow elements will use the leakage areas in Table 1.

Table 1. Leakage areas of flow paths.

Path	Element Name	Flow Area (m²)
Single door (closed)	Door-SC	0.0158
Double door (closed)	Door-DC	0.0316
Wall per m²	Wall-per-area	3.50E-04
Floor per m²	Floor-per-area	1.70E-04

Path

Element Name

Flow Area (m²)

Single door (closed)

Door-SC

0.0158

Double door (closed)

Door-DC

0.0316

Wall per m²

Wall-per-area

3.50E-04

Floor per m²

Floor-per-area

1.70E-04

We will assume the winter conditions in Table 2.

Table 2. Temperature conditions

Location	Winter Temperature (°C)	Summer Temperature (°C)
Outdoor	-15	33
Building	22	22
Stairwell	-13	31

Problem Setup using Winter Conditions

Setup a New Model

Define options that are model parameters and save the file:

Open Ventus.
On the Menu Shortcut, click SI to use metric units.
On the View menu, click Edit Snap Grid. Enter 1 and click OK. This sets the grid spacing that we use when drawing the geometry.
Set the default zone temperature. On the Analysis menu, click Simulation Parameters, and on the Environment tab set the Default Zone Temperature to 22. Click OK.
Set ambient temperature. On the Model menu, click Weather and Wind. Click Edit to open the Ambient Temperature dialog. Change the value of the first row to -15. Click OK to close the Ambient Temperature dialog and then click OK to close the Weather and Wind dialog.
On the File menu, click Save and name the file getting started winter.vnts.

Draw the zones

Draw the geometry of Level 0.0 (Level 1):

In the View Toolbar, click Switch to the Top View. If the grid is not displayed, on the View menu, click Show Snap Grid.
In the Model Toolbar, double-click the Add a Rectangular Room tool. Draw Room 2 and the Stair. Press ESC to unselect the tool.
In the Model Toolbar, click the Add a Polygonal Room tool. Draw Room 1 by clicking on the existing corners and then on grid points. After drawing the last unique point, right-click to close the polygon.
Using the Select/Edit Objects tool, select and rename each of the rooms to Room 1, Room 2, and Stair.
Select the Perspective View, click Reset All, and click the 3D Orbit Navigation tool. Spin your model and the view should look as shown in Figure 3.

Define Flow Elements

The flow elements define the types of flow paths we will use in the model. Each flow path will reference a Flow Element. The flow element name and area are given in Table 1

To define flow elements:

Before we create the flow paths we must define the types of flow elements. In the Object tree, double-click Flow Elements. The names of the default Flow Elements indicate the Powerlaw Model and the Type. So the default AREA/Area flow element uses the Leakage Area Data Powerlaw model with the Per Unit Area option.
Select the existing AREA/Item flow element and then click Duplicate. Type the Name Door-SC (a closed single door). The new flow element will be Based On the existing flow element you selected, in this case AREA/Item. Click OK to close the Duplicate Flow Element dialog.
Change the Door-SC flow element Area per Item to 0.0158 m^2. When the leakage is specified Per Item, that defines the total leakage area for that flow element. The remaining default parameters are appropriate. Click Apply.
Repeat for the double-width door Door-DC. Change the Leakage Area to 0.0316. Click the Color box and change the color to magenta. Click Apply.
Select the existing AREA/Area flow element and then click Duplicate. Type the Name Wall. Click OK.
Set the Area per Unit Area to 3.5E-4 m^2/m2. When the leakage is specified Per Unit Area, the total leakage area is calculated by multiplying by the wall area. The other default parameters are appropriate. Click Apply.
Duplicate the AREA/Area element once more and name it Floor. Change the Leakage Area to 1.7E-4 m^2/m2. Click the Color box and change the color to orange. Click Apply.
Select the existing STAIRWELL flow element and then click Duplicate. Type the Name Stair. Click OK.
The Cross-sectional Area is 18 m^2. Assume zero Density of People and Closed Stair Treads. Click Apply.
Click OK to close the Edit Flow Elements dialog.

Create the Flow Paths

To define flow paths:

It is easiest to work in the top view, so click Switch to the Top View in the View toolbar. We will turn off snapping to the existing grid to make it easier to place the flow path in any location. In the View menu, unselect Show Snap Grid.
Double-click the Create a Flow Path Between Two Walls tool (the double-click makes the tool stay active for multiple paths).
Select the Element type Wall.
Click and drag to create 11 wall flow paths (the green paths shown below). To make a flow path between zones, click in one zone and drag to the second zone. To make a flow path to ambient, click in the zone and drag outside the zone. The wall area of the flow paths is automatically calculated and used as the multiplier.
Now add the door flow paths. Using the Create a Flow Path Between Two Walls tool, select the Element type Door-SC. For AREA/Item flow elements the multiplier is assumed to be a value of 1.
Add the two single doors, Door-SC (the red paths shown below).
Select the Element type Door-DC and add the double door Door-DC (the magenta path shown below).
Press ESC to leave the Create a Flow Path Between Two Walls tool.
When you are finished, your model should look like Figure 4.

Figure 4. Model after adding flow paths to Level 1

Set Stair Temperature

We set the stair temperature to -13 C, the winter condition defined in the Problem Geometry section.

To set temperature for the Stair zone:

Using the Select/Edit tool, select the Stair zone.
Select the checkbox for Temperature and type -13.

Rename Stair Wall Flow Paths and Verify Wall Areas

In order to make it easier to find the walls that surround the stairs, we will rename the wall flow paths using the names shown in the Problem Geometry section above.

To rename stair flow paths and verify flow area coverage:

Using the Select/Edit tool, click on each of the four wall flow paths surrounding the stair and change their names (StairN, StairS, StairE, StairW).
Also rename the two doors that access the stair (D2 and D3).
Click on each flow path to verify that the areas match expected values.
You can also display the flow area coverage. In the View Toolbar, click the Show Flow Path Coverage tool. This is an easy way to see that all flow paths has been defined.

Figure 5. Display of flow path area coverage.

A short summary of the wall area calculation is useful.
The area calculation is only done when the area is given as Area per Unit Area.
The second wall is projected onto the first wall like in Figure 6. Here the lower flow path was created by dragging from the left to right. The wall of the second zone is projected onto the first wall.

Figure 6. Display of projected areas showing how the second wall is projected onto the first to perform the area calculation.

If the walls are not parallel, the calculated area will depend on the definition of the first and second walls since the projection will be slightly different. Any flow path where the angle between walls is greater than 1 degree will have a warning flag. You can also edit a flow path to manually specify the area you desire; if you select the flow path object, the Leakage Area can be edited in the ribbon.

Copy Level 1 to Level 2

To copy objects, we select them and then use the Copy/Move Objects tool. One easy way to select and copy objects is with the Select/Edit Objects tool; click and drag to select all the objects you want to copy. Another way is to select objects in the Object tree.

To create Level 2 by copying Level 1:

Using the Select/Edit Objects tool, click and drag to select all the zones and flow paths on Level 0.0.
Click the Copy/Move Objects tool. Select Copy Mode and make 1 copy. Type 3 in the Move Z box. Click Copy/Move.
Go to Perspective View and click Reset All. Your model should look like Figure 7.

Figure 7. The model after creating Level 3.0 (Level 2)

Edit Level 2

Often the ground floor (level 1) is different than the higher levels. In this example, there is no double door from the stair to the exterior for any of the levels above the ground level. We will also add flow paths from the active level rooms to the rooms below and add the Stair flow path.

To update the geometry and flow paths for Level 3.0 (Level 2):

Delete the double door from the stair to the exterior.
Double-click the one point flow path tool. Select the Element Floor.
Click on the floors of the two rooms to add flow paths to the rooms below.
Select the Element Stair. Click on the stair zone to add the flow path to the stair below.
Press the ESC key to unselect the tool.
Your model should look like Figure 8.

ventus scrn ventus basics edit level 2 2024 2 — Figure 8. Level 3.0 (Level 2) after deleting the double door and adding floor flow paths

Configure the view

We can configure the rendering to provide some opacity in order for easier viewing and editing.

To configure the view:

In the View toolbar use the Change how geometry is rendered dropdown to select the X-Ray option.
In the Active Level panel of the property editor ribbon, select Show lower level.
In the Object tree, right-click on Level 3.0 and click Set as Active Level.

You now see Level 3.0 and the level below, with a default X-Ray Opacity of 50%. X-Ray Opacity can be configured by navigating to the View menu and clicking Edit X-Ray Opacity

Figure 9. The X-Ray and active level rendering options

Copy Level 2 to Levels 3 through 8

Now we copy Level 2 to Levels 3 to 8.

To create Levels 3-8 by copying Level 2:

In the Level Creation/Sorting Menu, ensure that Ventus is set to Automatically create levels with a default height of 10 ft.
To select and display only Level 2, in the Object tree, right-click Level 3.0 (Level 2) and click Set as Active level. In the ribbon unselect Show lower level.
Using the Select/Edit Objects tool, click and drag to select all the zones and flow paths on Level 3.0.
Click the the Copy/Move Objects tool. Select Copy Mode and make 6 copies. Type 3 in the Move Z box. Click Copy/Move.
Go to the Perspective View and click Reset All.
In the Object tree, right-click Levels and click Show All to display all levels.
Change the Opacity to 20% from the Edit X-ray Opacity option in the View menu.
Your model should look like Figure 10.

Run the Simulation

To run the simulation:

On the Analysis menu, click Run Simulation. If successful, the final line in the Run Simulation dialog will be DONE!
Click OK to close the Run Simulation dialog.

Process Results

We can now process the results. There are several options.

Graphical Display of Results

The graphical display shows lines representing the pressure difference (magenta) and the flow rate (green) at each flow path.

To view pressure differences:

In the View toolbar, select Show Results.
In the Object tree, right-click on Flow Paths and click Hide.
Your model displays arrows showing the pressure difference and flow as shown in Figure 11.

Figure 11. Results display of pressure difference and flow.

You can select a flow path to see the pressure difference and flow rate displayed in the ribbon, as in Figure 12. These match the CONTAM-W model results.

.The stair flow on the north side of the top stairwell has been selected. — Figure 12. The stair flow on the north side of the top stairwell has been selected.

Tabular Display of Results

We can also filter and display the flow path data using a tabular display built into Ventus.

To show a table of flow path data for the North Stair:

On the right of the screen, click Path Data. The Results panel displays all results for the simulation.
To filter to just the north flow paths, in the search box type StairN. The search is case-sensitive. See Figure 13.

Figure 13. Display of path data filtered to StairN.

You can now use this data and make a graph of the results using external software. We will plot the flow rates of the north stair flow paths as a function of Z location to visualize stack effect.

Figure 14. Spreadsheet plot of flow data.

Work with Results File

We can save a file of tabulated results for zones and flow paths. To create this data, Ventus uses a combination of the simread executable provided by CONTAM and internal Ventus linking of names to flow paths. The names give us a way to use a spreadsheet to display only the flow paths that are connected to the stair. This description uses Excel.

To work with the results data using spreadsheet software:

In the Object tree, under Results double-click Link-Path Flows. This will open a tab in your browser.
Copy all the data in the browser page (press CTRL A to select all, then CTRL C to copy).
Paste the data into Excel (press CTRL and V to paste in empty Excel sheet).
This data is comma separated. To convert to columns, click column A, on the Data tab, click Text to Columns, select Delimited, and click Next.
In the Convert Text Wizard, click Comma and then click Finish. The values will now be displayed in columns.
To filter to see only connected to the stair, click PathName and then click Filter. Select the PathName dropdown. In the search enter stair, and click OK.
Now only flow paths that include "stair" in their name are displayed.
Use the SUBTOTAL function to work with only the filtered data. Figure 18 shows how to find the maximum pressure difference for only the stair flow paths.

Converting text to columns part one. — Figure 15. Converting text to columns part one

Converting text to columns part two. — Figure 16. Converting text to columns part two

Figure 18. Use SUBTOTAL function to find the max pressure difference of the flow paths connected to the stair

Instructions for Summer Conditions

In Ventus, from the getting started winter model, save the file for a separate run.

To save another version:

On the File menu, click Save As and name the file getting started summer.
In the Object tree, right-click Results and click Delete.

Change the weather

Set the ambient temperature. On the Model menu, click Weather and Wind. Edit the default Ambient Temperature to 33 °C.
Click OK to close the Ambient Temperature dialog and then click OK to close the Weather and Wind dialog.

Ventus has a warning system built in to avoid stale (out of date) data display. When you make changes to the model data without re-running the program, caution icons appear on the Results folder(s) in the Object tree.

Change the Stair Temperatures to 31 °C

We select all the zones for which we want to specify summer temperatures.

To change the stair temperatures:

Click on the Top View.
Using the Select tool, click and drag a small rectangle in the stairwell. Do not select any flow paths. See Figure 19.
Return to the Perspective View, and you should see all zones in the stair selected.
In the ribbon, click to check Temperature and enter the value 31 C.

Run the Simulation

Notice that the naming of the Results data folders in the Object tree has changed to reflect the getting started summer conditions. The data is also free of any stale results warnings.

Process Results

We can now process the results.

To show pressure differences:

In the Object tree, right-click on Flow Paths and click Hide.
In the Object tree, select Levels and set the Opacity to 20%.
Your model displays arrows showing the pressure difference and flow. Note how the flows in the summer conditions, Figure 20, have reversed relative to winter results.

In Figure 21 are the flow results at the top of the stairs. These match the CONTAM-W model results.

Figure 21. Results for the top exterior flow path of the stairs.

The summer data can be combined with earlier results to create Figure 22.

Figure 22. Spreadsheet plot of winter and summer flow data.

Conclusion

This model provided step-by-step guidance to create your first basic model and simulate two seasonal conditions.

To continue learning Ventus, visit the Ventus tutorial list and choose your next topic. Please contact support@thunderheadeng.com with any questions or feedback regarding our products or documentation.

Ventus Models

You can download a zip file of the example Ventus and CONTAM models for Winter and Summer scenarios.

Getting Started Basics.zip