Wednesday, May 22, 2013

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).

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Saturday, May 18, 2013

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.

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Friday, May 17, 2013

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.

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Tuesday, May 14, 2013

Solar heating simulations in Energy3D

We are adding some new features to our Energy3D software that will allow the user to carry out passive solar design of one or multiple buildings (or even an entire city block). These new features will calculate the distribution of solar energy density over an area such as the vertical surface of a wall of a building or the horizontal surface area of open space. The results will be visualized as color heat maps overlaid to the surface. The information in these color maps can be used to help students make decisions when they are searching for optimal passive solar designs.
video
These new analytic tools will be used in our Passive Solar Urban Design Challenge that requires students to design a city block with new buildings that have maximal solar heating in the winter and minimal solar heating in the summer, without severely obstructing solar access of existing buildings in the neighborhood.

These new features are integral parts of the existing heliodon simulator in Energy3D, which allows the user to adjust the sun path. The video in this blog post demonstrates this.

Thursday, May 9, 2013

Energy3D Version 2.0 released

We are proud to release Energy3D version 2.0, available for download from our website. Energy3D is a computer-aided design and fabrication tool for making small model green buildings. This version added new energy assessment features that allow students to evaluate the energy performances of their  designs and investigate the effect of passive solar heating. Currently however, this energy assessment tool is limited to only 12 selected cities around the world.

The next release will feature powerful passive solar heating simulation that can be applied to a wide variety of settings ranging from a single family house to a dense urban area.

Energy3D runs on both Windows and Mac OS X. Java 7 is required. It may also run on Linux (some of our users actually got it to run on Linux), but it has not been thoroughly tested on Linux.