Set the building orientation

Model axes relationship to compass points/ cardinal orientations

Set the building orientation to ensure that solar and wind conditions will be treated properly by the simulation engine. When drawing the building geometry using a graphic modeling interface, it is often convenient to align the geometry with the drawing/CAD interface's X, Y, and Z axes so that right angles can "snap" to the axes. The X axis typically corresponds to the East/West cardinal orientations on a compass, the Y axis typically corresponds to the North/South orientations, and the Z axis typically corresponds to the elevation of the building (consult your software program's documentation to verify).

Building true north orientation rotated by 10 degrees. This image is generated from the OpenStudio Sketchup plugin. Entering a value of 10 in the "North Axis" input rotates the true North orientation counterclockwise by 10 degrees as indicated by the orange line.

However, since buildings do not always align perfectly with the cardinal orientations, many BEM software programs provide the ability to adjust the orientation of the building to reflect the true orientation. This is typically done by specifying an angle of rotation of "true north" compared to the Y axis in the modeling interface. BEM software interfaces may specify this input as "Azimuth angle, " "North axis angle," or other terminology. An input here will treat the building model as being rotated by that angle when the simulation is run (although it will not be rotated in the drawing interface itself to allow for ease of editing while still aligned with the axes. Consult your modeling software's documentation for guidance on how these inputs rotate the model in the simulation to make sure you understand if the rotation is clockwise or counterclockwise.