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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