Hello, I have a question about how building dimensions are handled in the Rhino plugin-specifically, in which direction from the drawn dimensions the thickness of the assembly layers is added (if at all). In the Rhino drawing, a building dimension is represented by a line, but specific assemblies-defined by U-values and actual thicknesses (e.g., a 30 cm thick external wall)-are assigned to it; does this somehow alter the dimensions used for the building calculation? Similarly, a window in the drawing is attached to a plane, but how does the plugin account for the shading effect of the opening if the window’s specific position within the wall’s thickness is unknown?
Hi @andrisv,
This is more of a generic energy simulation question and not specific to the Rhino plugin. Where you draw the exterior wall of a thermal zone can differ. Some energy codes are specific about putting the line inside or outside the exterior wall. I personally think the best place to put your line is right behind the insulation if you have a well-insulated wall. That’s the volume that you would like to cool down and heat up.
If you want the wall thickness to be included in the shading effect, you need to model them as shade geometries. The Rhino plugin has a command that makes this easy. Use PO_AddApertureShade and change the mode to BorderShades.
You will be surprised that unless you have a very thick wall and the window is full inside, the shading effect of the wall thickness on the window will not have a major effect.
I agree with you general suggestion of modeling at the insulation line, @mostapha, particularly for spaces dominated by ventilation loads (eg. hospitals) where having an accurate volume of heated/cooled air is important. But it’s probably also worth highlighting that different simulation engines recommend slightly different geometry modeling practices in order to account for things like window frames and to achieve the most accurate solar calculation. So, for envelope-driven buildings, here is a general rubric for recommendations by simulation engine to get the most accurate solar and conduction calculations:
- EnergyPlus, DOE-2 and all of their interfaces (including Ladybug Tools, OpenStudio, DesignBuilder, and eQuest) - Exterior faces modeled at the outside wall finish; interior faces modeled at the centerline.
- IESVE - Exterior faces modeled at the inside wall finish; interior faces model at the centerline.
- IDA-ICE - Both exterior and interior faces modeled at the inside wall finish.
- TRACE 700 - Never really came up with an official recommendation because the solar calculation is so simplified and does not account for shading. You can probably model the exterior geometry any way that you want and this is good enough. You just need to make sure that interior walls are at the wall centerline so that they’re represented correctly in the gbXML you import to TRACE 700.