Phase 1 of thermal model development is putting the geometry together. This is usually done by tracing around 2D CAD drawings. The software can import 2D DWG and DXF files. To trace over a DWG or DXF file you will use the mouse and various tools provided by the 3D Modeller. You can also trace over an image file, such as a BMP, JPG, or GIF. You do not always have to begin from scratch as Tas offers the facility to import gbXML files and transfer building geometry data stored in existing CAD or other building information models. Such files can be created in Revit or you can use some other package. After importing a gbXML file you will be able to further edit the geometry, something which is often necessary at some point.
In the 3D Modeller there are two types of view. Views can be either 2D or 3D but the geometry will always be drawn in on a 2D view. To give you a bit of an overview, you will draw in the perimeter walls of the building and start to partition off the different areas and spaces by adding the internal walls. You can add construction lines to divide up open spaces, which you might want to do when you've got a particularly deep room with a single window on one of the walls and you want to account for a darker zone towards the back of the room. Walls are drawn by clicking the left mouse button while dragging the mouse cursor across the screen to select a point or node at each end of the wall. You will use the architectural plans to guide you.
By drawing walls that are joined together to form closed paths, polygons will be formed which will define the different spaces. Drawing a wall will produce two parallel lines in order to give you an indication of how thick the wall is. The thickness will denote the "width" property of the construction type, which in Tas is called a "building element".
The 3D Modeller provides a facility for assigning building elements to walls, ceilings, and floors so the individual polygons which are formed as the geometry is drawn in can be related to physical building components. As polygons become associated with building elements, the geometry will start to take on the identity of a building. The "sides" or "faces" of the geometry will represent construction types such as a roof, a ground floor, external walls, and so on.
The walls of the building will be given a default height determined by the Floors dialog. This means a 3D building will automatically be produced as the walls are drawn on a 2D view so you won't have to manually extrude the rooms to form a 3D model. You will of course have to open a 3D view to see the building in 3D. Floor and ceiling surfaces are assumed to enclose the spaces which are formed, unless a <null> surface is assigned. You can think of a <null> surface as a non-physical boundary between adjacent spaces. A <null> floor and ceiling can be used to model a double-height space for example.
When you draw in the geometry you must make sure that all of the polygons are planar because walls and other surfaces cannot be modelled as perfectly curved. If you want to draw a circle then you will have to approximate this by faceting line segments to form, say, a 16 sided polygon. You aren't limited to 16 sides but in terms accuracy increasing the number of line segments above 16 to derive a smoother curve isn't usually necessary.
If you do produce a non-planar surface by mistake then the analysis model will give you an error and ask you to correct it. You will have to correct the error before you can export the geometry to a TBD file. All you will need to do is partition the non-planar polygon into planar ones by adding in construction lines.
As part of the geometry input phase you must zone the building. As mentioned, the program has the facility to divide areas with construction lines which are called <null> lines in the software. You can then assign zone names to the various rooms and other spaces within the model. You can zone the geometry according to regulatory requirements where necessary, or you can zone it in order to meet your own modelling objectives, such as investigating the stratification of air (stack effect) within an atrium.
You will also need to add windows and other apertures to the building model before exporting it, although you will not input information about how they will operate until after the geometry has been exported. You can add a variety of fenestration products in the 3D Modeller to model anything from simple daylight harvesting to wind-induced ventilation, including single-sided natural ventilation, cross-ventilation, or vertical ventilation flows. You can draw in products such as windcatchers (or similar) to model a combination of wind-driven natural ventilation and buoyancy.
Whichever method of geometry input you use, the resulting geometry will be exported to the Building Simulator as a building data file (TBD) along with data generated by complex shading calculations.