what is the preferred methodology for modeling ground reflectance in HB+? if I need to define a geometry that represents the “ground”, how far beyond the footprint of the building being analyzed does the ground geometry need to extend on all sides to accurately take into account the reflectance? Is there a pre-loaded set of materials that includes typical reflectance values for different exterior site conditions (grass, asphalt, concrete, etc.)?
I have not come across any specific standard that mentions how far the ground plane shall be modelled. I believe you should use your best judgement here.
The standard reflectance value for ground is 10%. I believe that is for ground soil. Most ground finishes such as pavers or asphalt have reflectance value higher than that. One way to account for reflectance values for
is to take a good picture of the same or use a reference image. Get the RGB values in a tool like Photoshop. Then you can use Radiance Material by color component. That will give you average reflectance.