The shadow pattern

In the elaboration of an energy certificate of a building one of the most cumbersome calculations is the one of the pattern of shades, although it is very simple. To calculate a relatively complex shadow pattern (with non-orthogonal obstacles) the usual method is to make a conical projection on a representative point of the facade to be studied.

Thus, the most appropriate procedure is: first to make an axonometric representation (preferably with some CAD program) of the objects we want to study, defining the vertical edges and the representative point. Then we start with the first step of the measurement process: we measure the angles in plan α (from the north-south axis) and in elevation β (in the plane defined by the triangle that form the representative point and the edge of the volume that of the shadow). We repeat this process as many times as there are edges in the volume that gives us shadow.

Once we have measured all the angles α and β we can tabulate them in the table provided by the CE3X program. The projection of the volumes in the solar path diagram will be drawn automatically. It is a simple process: for each plane a line must be created in the table.

We can also enter in the shadow pattern (if we want to be more rigorous) the exact shadow that projects our own facade (in the drawing below are the two large rectangles left and right), ie define exactly that 180º of sky are visible by the plane of our facade. For example, in our case we have a facade with an azimuth -15º, it is therefore oriented to the South as defined in the Technical Building Code as it is within the -18º deviation, therefore it is facade it will have an opening to the celestial vault of 180º but nevertheless displaced 15º with respect to a facade oriented to azimuth 0º.

The pattern of shadows in energy certification becomes very complicated when there are complicated, unaligned volumes around our building. In this case a possible option is the modeling in Ecotect and the calculation of the orthogonal projection in the calculation option of Sun Path Diagram. In this way we will save ourselves the laborious work of measuring angles.

We model the volumetry in the Ecotect program and once we have the diagram represented we only have to take the angles α and β (the values on the “x” axis and “y” axis respectively) and enter them in the shadow pattern sheet of the CE3X.