Building Information Modeling and Green Design

PART ONE

When designing the U.S. Federal Courthouse in Seattle, NBBJ and its consultants used computer modeling to analyze air temperature distribution to determine the benefits of displacement ventilation in the courtroom lobby, halfway up the tower (indicated with a green stripe on the drawing).

In a perfect world, energy simulations and design tools would be so well integrated that each time an architect moved a wall, added a window, or changed a lighting specification, the building’s predicted energy performance would be updated and displayed instantly. With that sort of real-time feedback, designers would quickly become skilled at optimizing the energy performance of their designs, and new buildings would be rapidly approaching carbon neutrality. Along the way, other aspects of a building, such as how well it uses daylight, how procuring its material will affect the planet, and even how much it will cost to build, could be similarly tracked and optimized. And all of this would be done while sharing a design seamlessly across disciplines. That world has not yet arrived, and the path to it is strewn with obstacles. But in some settings it is becoming tantalizingly close, thanks to the convergence of data-rich, three-dimensional (3D) design tools, ever-faster computers, and accepted protocols for sharing digital information about buildings across platforms. In spite of the significant investment that designers and contractors have to make to adopt building information modeling (BIM), they are flocking to it because it can reduce errors, streamline costs, and improve the performance of a facility in dozens of ways, not least of which is green performance.

A Brief History of Digital Design

In the early 1980s, technologically savvy architecture firms were replacing their drafting tables and pencils with workstations running computer-aided design (CAD) software. By the end of that decade, firms that hadn’t made that transition were in trouble. Through the 1990s, two-dimensional CAD drawings gave way to tools that could create three-dimensional views of a design, and more advanced tools enabled architects to design directly in three dimensions using virtual models. “Working with a model of a building is actually very natural, because it’s what we architects carry around in our heads anyway,” said Mario Guttman, AIA, vice president and CAD director at HOK. Structural engineers working on complex buildings have been among the early adopters of 3D CAD tools, but architects and other engineers now commonly use these tools as well.

Building information modeling (BIM) adds additional “dimensions” onto those 3D CAD models by attaching information to elements in the virtual building. Early uses of BIM have advanced beyond collision detection to focus on specific functions, such as real-time cost estimating. Autodesk’s Revit, for example, is linked to cost data from RSMeans, so a project’s budget can be tracked as the design evolves. Sophisticated contractors are using tools such as Constructor from Vico Software (recently spun off from Graphisoft) to create cost estimates based on their own cost databases and also to model and optimize construction sequencing.

What is Building Information Modeling?

“BIM is not just software but a methodology of practice,” said Huw Roberts, Bentley Systems’ global marketing director, suggesting that “an architect or engineer would decide to practice BIM and use a bunch of tools to do that.” Adam Rendek, of Anshen + Allen Architects in San Francisco, added, “We are taking advantage of the intelligence that is embedded in the model. That’s what makes BIM different from 3D CAD.” The move towards BIM is driven in part by large building owners, including the U.S. General Services Administration (GSA), which, as of 2007, accepts delivery of designs for major projects only as interoperable models. Owners like GSA have documented the wastefulness of the conventional paper-based building delivery process and are dictating a more integrated approach. A handful of BIM-related organizations and initiatives joined forces under the umbrella of the National Institute of Building Sciences (NIBS) buildingSMART Alliance and, in February 2007, released the first part of a national BIM standard for industry review. Autodesk, the 800-pound gorilla in the CAD software jungle, has incrementally added data-linking capabilities to its flagship Architectural Desktop software package. In 2002, the company made a major commitment to BIM with its acquisition of Revit, a database-driven design software package. Autodesk is now actively seeking to migrate its longtime CAD customers into the Revit product line. Currently there are 200,000 licensed Revit users worldwide—doubled from last year, according to Jay Bhatt, vice president for AEC at Autodesk. Other major players in this market include ArchiCAD from Graphisoft (a Hungarian company acquired in 2006 by the German firm Nemetschek), and the Microstation suite of software tools from Bentley Systems. Bhatt estimates that between 5% and 10% of CAD users worldwide use BIM software from one of these companies.

Streamlining Building-Performance Simulations

The Pearl River Tower designed by SOM for construction in Guangzhou, China, includes integrated wind turbines and photovoltaic panels to offset its energy use. Inset is an Ecotect model showing the amount of solar radiation on the tower’s various surfaces.

As the number of designers working in BIM grows, so does the opportunity for using those virtual models to do more than just estimate costs. Working in two-dimensional, basic CAD drawings, “you had to do all this heroic behavior to create an environmentally sensitive design,” noted Bhatt. With the advent of BIM, however, “technology is facilitating a much bigger movement around sustainability in the buildings space,” Bhatt added. Vincent Murray, business development manager in the Boston office of simulation software company IES, agrees: “BIM opens up building-performance modeling to the entire building construction community,” he said. Energy modelers use specialized software to create a virtual model of a building. They then subject that model to the building’s anticipated weather and usage patterns to predict its heating and cooling loads and energy use. Until now, setting up an energy model took many hours, even for a relatively simple building, so iterations through various design alternatives were slow and expensive. “Now, since the model is available as a given, representing the actual current state of the design, we can shorten this amount of time dramatically,” said Rendek.

Energy feedback during conceptual design

One of the ironies of energy modeling and other simulations used in the design process is that they tend to require a fairly complete model of the building, which means that by the time the modeling is done, the design is fully developed and only minor changes can be entertained. BIM mitigates this problem to some extent because the integrated 3D design model makes it relatively easy to make changes, even late in the process, by eliminating the need to coordinate changes across multiple drawings. But early-stage simulations from preliminary 3D and BIM models offer the greatest potential benefits. Green Building Studio and (soon) SketchUp are optimized for use in those early stages—specifics on each follow. Green Building Studio. Green Building Studio (GBS) is a pioneer in the field of easy, basic energy simulation from design models. As both a company and a Web-based service of the same name, GBS includes a protocol for translating information from CAD software into the industry-standard DOE-2 energy simulation engine. Because an energy model requires data that isn’t typically defined even in BIM files, much less conventional 3D CAD, GBS fills in the gaps with many default assumptions. “Most of the tools that are moving forward are still engineering tools,” said John Kennedy, president of the company, referring to their intended use for analyses of fully developed designs by trained engineers. He added, “The whole point of this tool is early-stage modeling.” Kennedy has created plug-ins for Autodesk’s Architectural Desktop and ArchiCAD that assist users in defining HVAC zones and validating the BIM model to increase the chances that the energy simulation will provide useful results. This capability is integrated into Revit, so no plug-in is required. The software generates a file in gbXML format (an information exchange protocol developed by GBS) that the software uploads to GBS’s server for analysis. Minutes later, the designer can download the results of the model. GBS allows users five free runs; more runs are available for a nominal fee. GBS recently introduced a “design advisor” service that automatically generates proposed modifications to the design and allows users to experiment with a small number of alternatives. GBS also makes its DOE-2 input file available for download, offering engineers a shortcut for running their own early-stage energy models. Development of the software was funded largely by the California Energy Commission and Pacific Gas & Electric, but for ongoing support GBS is looking to other sources, including manufacturers that appreciate the potential for highly targeted product placement. On that basis, PPG’s SolarBan 70 glazing is one of the design alternatives from which users can choose. GBS has also developed a tool for Owens Corning that identifies what a building would need to implement to qualify for the Energy Policy Act of 2005 tax credit (see EBN Vol. 14, No. 9).

The Georgia State Parks Headquarters in Stockbridge, Georgia, was designed to be environmentally responsible using building information modeling services provided by the independent BIM consultants RCMS Group of Atlanta.

SketchUp and EnergyPlus. While it is a far cry from the full-fledged BIM tools, Google SketchUp offers a 3D modeling interface and the ability to assign characteristics to objects in the design. “A lot of designers prefer SketchUp early on because it’s such a facile tool,” noted Chris Leary, AIA, of KlingStubbins. Most mainstream design tools now have at least some capability to import models from SketchUp and to export simplified models out to it. That capability will soon carry more significance for green projects because by June 2007 the U.S. Department of Energy (DOE) expects to release a SketchUp plug-in for the powerful EnergyPlus modeling engine. DOE intends for EnergyPlus, which was released in version 2.0 in April 2007, to supersede the venerable DOE-2. While EnergyPlus is widely regarded as a more powerful and flexible simulation engine, its use has been limited by its lack of a user-friendly front end. “I could imagine that SketchUp would be a pretty good interface for making an EnergyPlus model,” said Kevin Pratt, director of research at KieranTimberlake. The plug-in, which will be available for both the free and the full versions of SketchUp, will help users define HVAC zones and assign thermal characteristics to elements in their models. It will then export an EnergyPlus input file for a user to run separately—although, according to Drury Crawley, AIA, Technology Development Manager at the U.S. Department of Energy, future versions of the plug-in should be able to run the simulation entirely within SketchUp. Tools like SketchUp are especially useful for early design studies. “A smart team working on sustainable design will start looking at energy models before even designing the building,” noted Guttman, adding, “They may do a lot of analysis on preliminary, pre-architectural models.”