Solar urban design using Energy3D: Part II

May 18th, 2013 by Charles Xie
Figure 1
The sun is lower in the winter and higher in the summer. How does the sun path affect the solar radiation on the city block in our urban design challenge? Is solar heating different in different seasons? Let's find out using Energy3D's solar simulator. Energy3D has a nice feature that allows us to look at the 3D view exactly from the top. This kind of reduces the 3D problem to a 2D one once you complete your 3D construction and want to do some solar analysis. The 2D view is clearer and the drag-and-drop of buildings is easier.

Figure 2
First, we added a rectangular building to the city block and moved it to four different places -- northwest, northeast, southeast, and southwest -- in the city block and set the month to be January and the location to be Boston, MA (which is where we are close to). Not surprisingly, the solar radiation on the building is the lowest at the southeast location (Figure 1). This is because to the southeast of the block, there are three tall buildings that shadow the southeast part of the block --- you can see in the heat map that the southeast part is deep blue. At the southwest location, the building receives the highest solar energy. The northwest location seconds it with a slightly smaller number.

Figure 3
Next we set the month to be July and repeated the solar simulation.This time, the solar heating on the building at all locations increases (Figure 2). However, the location that receives the lowest solar heating, surprisingly, is not southeast but southwest! The location that receives the highest solar heating is northwest. The reason could be that there is a tall building next to the southwest location that provides a lot of shadow (Figure 3). This shadowing effect seems to be more significant than the shadowing effect from the three tall buildings around the southeast corner.
Figure 4
The conclusion is that the building of this particular shape receives the highest solar energy in the winter and the lowest in the summer at the southwest spot.

Now, what about the orientation of the building? Let's rotate the building 90 degrees and redo the solar analysis in January (Figure 4). The results show that the building receives higher solar energy at all locations. This is because the building has a larger south-facing side in this orientation than in the previous one. The southeast location remains the coldest spot, but the difference between southwest and northwest is less.

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