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The traditional process of energy modeling within our own office typically takes a couple weeks. Using the workflow established with BIM, we can now perform some types of energy analysis in half the time, do twice as many as before, or make energy analysis available to projects that would normally not have the fee to support the endeavor.

In my own practice, to demonstrate the basic use of energy analysis in a building design, the design team compares two design options to understand what the relative energy impact is while also seeing the visual impacts those changes create.

On one project we chose to add a sunshading device to the west facade, but we want to see what the relative energy impact would be with this design change. We created two examples from the same BIM model and simply exported one with the shading device on and the other with it turned off. In addition, we also want some metrics to figure out how improved the performance of one design would be over the other. To do this, we exported the design models to an energy analysis application, leveraging the ability to reuse the model geometry.

The annual energy performance for the building without the sunshade was $46,929. Because we were in an early stage of design and using this as a comparative calculation, we did not rely on the accuracy of that actual number. There are several factors that had not been taken into account during this particular analysis: building use cycle, building loads by equipment, thermal conductivity of the envelope, and so on. What we were studying here was the relative effects of one design pitted against another. This comparison allowed us to qualify the design against the alternative: the building with the sunshade had an annual energy performance was $31,996, or an overall savings of 31 percent.

Daylighting

Streamlining the analysis process also can be extended to daylighting. Using a single model generated with BIM, we can analyze the same location in perspective within multiple applications.

This reduces the time needed to complete the analysis from several weeks to only a day. Working in early stages of design, we can accurately quantify the amount of daylighting in a project and regularly test to see if we've hit certain daylighting design goals.

If the project is pursuing LEED accreditation, these same results can then be used for LEED credits 8.1 and 8.2 by switching from a perspectival view to a plan view. For these LEED credits, it's imperative to demonstrate a minimum lighting level within the building and access to views from all the acceptable spaces. This calculation, formerly very time-consuming, can now be done very quickly.

This also allows us to have better control over how much light we bring in. Depending on the building orientation, we might want to minimize fenestration so we can minimize heat gain. Daylighting tools allow us to optimize our light intake while not overreaching and thereby bringing in too much heat.

By eliminating the necessity to remodel geometry, we have not only improved the speed and accessibility of these types of analytical investigations, but we have also improved the accuracy relative to the current state of the design. We are neither relying on the intuitive sense of the project designer to accurately depict the lighting or energy needs of the project, nor are we relying on a secondary team member to interpret the drawings accurately and remodel the project in an analysis application. The same geometry that represents the current state of the design is being transferred from the design model to analysis almost instantly.

Recycled Materials

BIM by nature is a constantly up-to-date catalog of all the building material information that has been modeled. As we add walls, windows, glazing, or any other element to the model, it is automatically added and tabulated. By leveraging this data, it becomes very easy to quickly calculate the amounts and volumes of these materials in the project. We can extend this to calculating the recycled content of the project as a whole or the content of any individual pieces.

As an example, say we wanted to calculate the volume of fly ash in the building or the quantity of recycled steel. Many BIM applications have the ability to create dynamic schedules. These schedules can be created once in the course of the project and will continually maintain real-time information. In the case of our example, after we create the schedule in the BIM model, we can add building components to the model constructed of concrete (walls, columns, floors, and so on) and the sum of concrete and fly ash in the schedule will dynamically update. This gives the design team an accurate metric for the amount of recycled content in the project. This same type of schedule can then include any other materials in the project with recycled content.

Beyond energy modeling, daylighting, and calculating building materials, there are other sustainable strategies that can be taken advantage of when using BIM. All of these revolve around using the model to calculate areas and quantities of elements in the building design, such as rainwater harvesting (using roof areas in plan to size cisterns) and solar access (calculating orientation and roof area for solar panels).

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Eddy Krygiel, AIA, LEED AP, is a senior project architect at HNTB in Kansas City, Missouri. Krygiel is responsible for implementing BIM at his firm, and consults for other architecture and contracting firms looking to implement BIM in their offices. He teaches BIM to practicing architects and architectural students in the Kansas City area, and has lectured and consulted around the United States on the use of BIM in the construction industry. He coauthored Introducing Revit Architecture 2010: BIM for Beginners and Mastering Autodesk Revit Architecture 2011, along with other books and papers on BIM and sustainability.

This article by Eddy Krygiel is excerpted from Fabricating Architecture: Selected Readings in Digital Design and Manufacturing, edited by Robert Corser, copyright © 2010 (Princeton Architectural Press), with permission of the author. It is adapted from Green BIM: Successful Sustainable Design with Building Information Modeling by Eddy Krygiel and Brad Nies, copyright © 2008 (Sybex).

SUBSCRIPTION SAMPLE The School of Nursing and Student Community Center at the University of Texas Health Science Center at Houston was designed by BNIM Architects with Lake/Flato Architects. Photo: Richard Payne, FAIA/ Courtesy Sybex Extra Large Image SUBSCRIPTION SAMPLE A grid of vertical and horizontal tensile-fabric fins shades the eastern facade of the LEED Gold-certified School of Nursing and Student Community Center. Photo: Richard Payne, FAIA/ Courtesy Sybex Extra Large Image Diagram showing the potential uses of an integrated model (BIM) in sustainable design. Image: Courtesy Sybex Elevation study shows the effect on building shading before and after a slight rotation of the building's plan on the site. Image: Courtesy Sybex Extra Large Image SUBSCRIPTION SAMPLE Plan drawings compare the differences in shadows cast by two versions of a building whose orientations on site vary by six degrees. Image: Courtesy Sybex Extra Large Image An interior rendering with a grid of light levels overlaid. Image: Courtesy Sybex Radiance renderings of daylighting effects. The rendering above was used in achieving the LEED daylighting credit for this project. Image: BNIM/ Courtesy Sybex A graphical comparison of a common model geometry as seen in four energy analysis tools: eQuest, Green Building Studio, Ecotect, and IES VE. Image: Courtesy Sybex   Click on thumbnail images to view full-size pictures.