Rhino model setup

The standalone application uses a construction table for layered assemblies. KOALA for Rhino calculates three-dimensional heat transfer using geometry and material assignments in a Rhino document.

The Rhino plugin supports junctions with geometric or material variations in three dimensions, including corners, structural penetrations and window installations. Model the materials and boundary environments as volumes on assigned layers.

Start from an example

Open Library… → Examples for complete bridge and window-in-wall setups, or download 3DTestCase_Balcony.3dm, the balcony model shown in the interface screenshots. Assignments and study settings belong to the Rhino document.

Modeling for Koala

Geometry: Closed polysurfaces, extrusions, surfaces and meshes are all accepted. Each object is meshed and tested as a closed volume, so make sure solids are watertight.
One layer per material: Koala works with Rhino layers. Every object on a layer gets that layer's material or boundary condition.
Boundary volumes: Interior and exterior climates are modeled as volumes too (for example a thin block of "room air" against the inner face). Wherever a material touches a boundary volume, a surface film with that boundary's surface resistance is applied. Material faces that touch nothing are adiabatic.
Grid alignment: Faces that are parallel to the world X, Y or Z planes become exact grid planes (see The Mesh). Sloped or curved faces are approximated by the grid in a staircase fashion.
Units: The panel follows the document units, including feet and inches. Changing the model units keeps the physical cell size; your standalone unit preference is not affected.

Layer Editor and Voxelization

The layer editor is used to assign materials and boundary conditions to the geometric volumes in your document. Double-click a layer, or right-click and choose Assign Material/Boundary…, to pick from the libraries; Clear Assignment excludes the layer from the simulation. During voxelization, layer priority determines the material assigned to overlapping volumes.

Layer priority: Layers higher in the list take precedence over lower layers. Drag layers to change their order. Intersecting volumes can therefore be assigned without Boolean subtraction. For example, place a metal-fastener layer above the insulation layer so that cells within the fasteners are assigned to metal.

Boundary conditions have a Zone (Interior or Exterior). The U-value sums the heat flow through all interior boundaries, so you can use several interior boundaries with different surface resistances in one model (for example Rsi = 0.13 m²K/W on the wall field and 0.20 m²K/W in a corner). The console reports the U-value, reference area and applied Rsi/Rse values for comparison with calculations using equivalent boundary conditions.

Mesh Settings and Running a Simulation

The toolbar under the layer list holds the mesh settings. They are saved with the Rhino document.

Cell: The maximum cell size, in document units. Cells next to thin parts are smaller; this is the size they grow to in thick parts.
Auto: Uses the recommended cell size for the geometry (a tenth of its characteristic thickness, at most 10 mm). Recommended for most models.
Verify: Runs the mesh independence check after every simulation: the model is solved again at half the cell size and the two U-values are compared (ISO 10211: less than 1 % difference). The refined run can have up to 8× the cells.
Cell estimate: The grey number next to the settings shows roughly how many cells a manual cell size will produce, so you can avoid accidentally huge runs.

Click Simulate to voxelize and solve. A progress bar appears with a Cancel button next to it, so long runs can be stopped at any time. Progress, timings, the U-value and any warnings are written to the console above the button.

Viewing and Exporting Results

Once a simulation has finished, the results area at the bottom of the panel shows the solution as a slice in the Rhino viewport:

Geometry / Thermal / Flux / RH: Switch between the voxelized materials, the temperature field, heat flux and relative humidity.
Plane and slider: Choose the slice orientation (XY, XZ or YZ) and move through the model cell by cell. The 3D toggle shows or hides the slice in the viewport. Results are kept per document, so switching between open files shows the right result.
Bake Slice: Adds the current slice, with its legend, to the Rhino document.
Bake Points: Bakes the cell centres as point clouds on a KoalaResult layer with Material, Temperature, Flux and Vapor sublayers, for further processing in Rhino or Grasshopper.
Export Slice Drawing: Opens a plot preview of the current slice where you can adjust the legend and save it as an image for reports.
Legend Settings: Fixes the minimum and maximum of each result legend, so several slices or models can be compared on one scale.
Ψ/χ Calculator: Turns the 3D result into linear (Ψ) or point (χ) thermal bridge coefficients. See Psi (Ψ) & Chi (χ) Workflows.
IDF Export: Exports an EnergyPlus construction that matches the 3D result (see below).
Save / Load .kvox: Stores a finished simulation in a file and loads it again later without re-running it.

For result storage, report preparation and EnergyPlus export, see Results and reporting.