Solar urban design using Energy3D: Part IV

In Part I, II, and III, we mainly explored the possible layouts of buildings in the city block and their solar energy outputs in different seasons. In those cases, the solar radiation on a new construction is mostly affected by other new constructions and existing buildings in the neighborhood. We haven't explored the effect of the shape of a building. The shape of a building is what makes architecture matter, but it also has solar implications. In this blog post, we will explore these implications.

Figure 1: Compare solar heating of three different shapes in two seasons.

Let's start with a square-shaped tall building and make two variations. The first one is a U-shaped building and the second is a T-shaped one. In both variations, the base areas and the heights are identical to those of the original square-shaped building. Let's save these buildings into separate files and don't put them into the city block. We just want to study the solar performance of each individual building before we put them in a city.

The U-shaped building has a larger surface area than the square-shaped and the T-shaped ones (which have an identical surface area). Having a larger surface means that the building can potentially receive more solar radiation. But the two wings of the U-shaped building also obstruct sunlight. So does the U-shaped building get more or less energy? It would have been very difficult to tell without running some solar simulations, which tell us that this particular U-shaped building gets more solar energy than the square-shaped one both in the winter and in the summer.

In comparison, the T-shaped building gets the least amount of solar energy in both seasons. This is not surprising because its surface is not larger than the square-shaped one but its shape obstructs sunlight to its western part in the morning and to its eastern part in the afternoon, resulting in a reduction of solar heating.

Links:

• Part I
• Part II
• Part III

Solar urban design using Energy3D: Part III

Figure 1

In Part I and II, we discussed how solar simulations in Energy3D can be used to decide where to erect a new building in a city block surrounded by existing buildings. Now, what about putting multiple buildings in the block? The optimization problem becomes more complex because students will have to deal with more variables while searching for an optimal solution.

Figure 2

Suppose students have to decide the locations of two new constructions A and B that have identical shapes. Now they have six options to layout
the two new constructions. Figure 1 shows the results of the solar simulations for all these six layouts in the winter. Placing the buildings in the northeast and northwest parts (the first in the first row of Figure 1) seems to be the best solution for receiving solar heating in the winter. This is not surprising because this layout creates large south-facing areas for both buildings that will get a lot of solar energy in the winter and there are not shadowed very much by the surrounding buildings.

Switch the season to the summer.  Figure 2 shows the results of the solar simulations for all these six layouts in July. Placing the buildings in the southeast and southwest parts (the first in the second row of Figure 2) seems to be the best solution for avoiding solar heating in the summer.

To make a trade-off between winter heating and summer cooling, it seems the southeast and southwest locations are the optimal solution: In the winter the solar heating on the two buildings is the second best (which is not much lower than the highest) and in the summer the solar heating on them is the lowest (which is much lower than the contender).

Links:

• Part I
• Part II
• Part IV

Solar urban design using Energy3D: Part II

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.

Links:

• Part I
• Part III 
• Part IV

Solar urban design using Energy3D: Part I

Figure 1

In sustainable architecture, passive solar design refers to searching for optimal strategies to maximize solar heating on a building in the winter and minimize solar heating in the summer in order to reduce heating and cooling costs of the building. A passive solar design challenge is a typical optimization problem that requires many steps of engineering design to solve, such as testing ideas, analyzing data, considering constraints, and making trade-offs.

Figure 2

For urban design, site layout has a big impact on passive solar heating in buildings as neighboring tall buildings can block low winter sun. Energy3D’s solar simulator can compute, visualize, and analyze solar radiation in obstructed situations commonly encountered in dense urban areas.

The solar urban design project we have developed challenges students to use Energy3D to construct a square city block surrounded by a number of existing buildings of different heights, with the goals to maximize solar access for new constructions and minimize obstruction of sunlight to existing buildings. The existing buildings, which cannot be modified by students, serve as constraints for the design challenge. This design challenge is an authentic engineering problem as it requires students to consider solar radiation as it varies over seasons and apply these math and science concepts to solve open-ended problems using a supporting analytic tool. This distinguishes it from common computer drafting activities in which students draw structures whose functions cannot or will not be verified or tested.

Figure 3

Energy3D can generate solar radiation heat maps on the walls of buildings and the ground (Figures 1 and 2). These heat maps show the cumulative heat of solar radiation on a surface over a certain period (a day or a month). They are calculated by summing up the solar energy projected onto each unit area of the surface while the sun moves cyclically in its path at the given location. The total solar heating result (in kWh), summing from all the unit areas of all the walls, is shown on top of each building. This number will go up and down as students move or reshape the building. This calculated result is more accurate than shadow and shading, which only reflects instantaneous solar heating at a particular moment.

The horizontal radiation heat map can be used to identify the hot and cold areas of the empty city block. With this heat map, students can find out where the new constructions should be in order to have maximal solar heating in the winter. Once they put in a new building, they can move the building around within the construction site to experiment how much solar energy the building will gain. As an example, Figure 3 shows that a rectangular high-rise building will receive the highest amount of solar radiation in January if it is placed at the southwestern part of the square and it will receive the lowest amount of solar radiation if it is placed at the southeastern part.

Such an analytic tool provides data for students to make their design decisions, creating plenty of opportunities of inquiry in design processes.

Links:

• Part II 
• Part III 
• Part IV