AIA CBSP Symposium on BIM for Building Envelope Design and Performance

On Oct 26, the AIA Center for Building Science and Performance (CBSP) organized a one-day Symposium in Washington D.C. to explore and further the use of BIM (building information modeling) technology for designing energy efficient and high performing buildings. One of the most significant aspects of BIM is its ability to capture the description of a building in a semantically intelligent format that can be analyzed to study different aspects of its performance, and with the growing emphasis on green buildings, energy analysis certainly ranks as one of the top-ranked criteria that needs to be studied.

The objective of the AIA CBSP Symposium was to explore the current state of BIM vis-à-vis building performance and determine the future potential of BIM in this arena, so that the Center has a better understanding of what kind of research to sponsor going forward. To this end, the CBSP Symposium had a number of presentations and panel discussions featuring representatives from various industry organizations, firms, and vendors including the GSA, SOM, Building Enclosure Council, Lawrence Berkeley National Laboratory, Georgia Institute of Technology, Green Building Studio, and Gehry Technologies. I was also invited to participate in one of the panel discussions. Attendance to the Symposium was by invitation-only to keep it small and focused, encouraging ideas to be generated through audience participation and discussion. This month's issue of "Building the Future" captures the highlights of the presentations and some of the main issues that emerged in the discussions.

Overview of the Main Sessions

The CBSP Symposium featured three main presentations. The first of these was by Calvin Kam, Kevin Powell, and Caroline Clevenger of the GSA (General Services Administration), who described the GSA's BIM initiatives and more specifically how BIM was being used to facilitate energy efficient design. Two projects were presented as case studies: the San Francisco Federal Building, which is currently under construction and will be completed in 2007; and the Salt Lake City Federal Courthouse, which is currently in the schematic design phase. The San Francisco Federal Building had the ambitious objective of using only half of the energy of a typical office building, and to this end, the building was designed with the optimum width for natural lighting and ventilation. The use of BIM on this project provided the platform for early integration of architectural, structural, and MEP designs, and tools such as EnergyPlus and COMIS were used for combined thermal and airflow analysis. The energy simulation was useful in several key energy-conserving design decisions, for example, in determining that night cooling of the building was not needed except on very hot days, and that a chimney would not be very effective, resulting in a savings of $1.5 million. The energy simulation results are being used to design the building's controls, and once the building is completed, its performance will be monitored to see how it compares with the simulated performance. This kind of verification of the accuracy of simulation results is important so that the process can be used with greater confidence and effectiveness in future projects.

The Salt Lake City Federal Courthouse, being in the schematic design stage, has provided the GSA with a good testing ground for the application of BIM in energy efficient design. This is primarily a glass building, making the design and material selection of the shading devices a critical factor in its energy performance. Two different energy modeling approaches are being explored for this process. The first is the traditional energy modeling process, where the model is recreated for input to VisualDOE, a graphical "front end" to DOE-2, the industry standard building energy simulation program. This task is typically performed by energy consultants, who break the design into zones and then assign loads and schedules to the individual zones. The second approach that is being explored is BIM-enabled space-based energy modeling, where a BIM model of the building is exported to the IFC file format for input to the energy simulation application, RIUSKA, which also uses the DOE-2 engine for its calculations. The advantage of the BIM approach is that the model does not have to be recreated by outside consultants, which typically is a very time-consuming and labor-intensive task. Instead, the BIM model can be directly input to RIUSKA by the designers themselves, making certain assumptions about the occupancy loads and schedules, and the analysis results can be used to guide the development of the design. The BIM approach allows greater specificity of input, providing the opportunity to use more detailed assumptions that are better equipped to deal with the variability and uncertainty surrounding building operation. But there are also some limitations in the process, the primary one being that current BIM models do not contain all the information necessary for energy modeling, for example, thermal zoning. Also, the export to IFC causes the loss of some important energy-related information. These limitations needs to be addressed by the BIM software vendors and the IAI (the organization responsible for developing the IFC format) for the BIM energy modeling approach to become more accurate and eventually replace the arduous and inefficient traditional approach.

The second presentation at the CBSP Symposium was by John Kennedy of Green Building Studio, a web-based service that works with a gbXML file exported from various BIM applications including ArchiCAD and Revit, and uses the building information to perform an energy evaluation with established tools such as DOE-2, eQuest, and EnergyPlus. Its "Design Alternatives" feature allows various changes to the building design such as orientation, glazing options, envelope constructions, lighting, and HVAC, to be quickly analyzed to determine which are the most energy-efficient options. It makes certain assumptions about building information that is missing, such as object type, material properties, etc., and when the file is imported back into the BIM authoring application, all this added information also gets transmitted back. Green Building Studio is intended to be used in the early design phases, when most of the key decisions that impact energy are made by the architect, in contrast to the traditional approach where energy analysis is performed by a consultant at the design development or construction document stage, when it is too late to make any major changes to the design. It is also interoperable with TRACE, an HVAC software, allowing architects to work collaboratively with HVAC engineers to design an energy-efficient building.

While Green Building Studio also provides a means to link a BIM model to an energy analysis program like the RIUSKA approach being explored by the GSA, it is significantly different since it does not rely on the IFC format for making the link but works instead with gbXML that was specifically developed to exchange energy-related information. According to Kennedy, the IFC model is not a thermal model and needs significant work before it can be analyzed, making the RIUSKA approach actually longer than the traditional VisualDOE approach. Another area of caution in the use of BIM models for energy analysis is the "correctness" of the model. Current BIM tools do not check for model integrity, correctness, or completeness (see my repeated emphasis on this aspect in my recent reviews of Revit Building, ArchiCAD, and Bentley Architecture), and the "garbage in, garbage out" adage is true for all analysis applications. Green Building Studio tackles this issue by warning the user of issues with the model before it is exported to the gbXML format for energy analysis, so that they can be fixed. Other issues with current BIM tools from an energy analysis perspective are that they lack a "building" object and have a poor implementation of space objects. The BIM software vendors need to work on resolving these issues, otherwise they will continue to hamper the ability of BIM to provide full support for energy analysis and simulation. In the meantime, Green Building Studio is working on a Design Advisor to accompany the web-based analysis service, which can provide guidelines on the proper creation of the BIM model, fill in missing information, as well as provide guidance on how to reduce energy use. It is also starting to include links to actual manufacturers' products so that designer can evaluate how specific building products perform in the context of an actual design.

The third main presentation at the Symposium was by Malcolm Davies of Gehry Technologies, and was more focused on the topic of BIM rather than on energy efficiency per se. Gehry Technologies is a spin-off company from Frank Gehry's architecture firm that was established to disseminate his CATIA-enabled design and construction methodologies to the rest of the world (see the AECbytes article, "Technology at Work at Gehry Partners: A Case Study"). Gehry Technologies has developed a high-end CATIA-based BIM and construction management software called Digital Project for architects as well as other members of the planning, design, construction, and operations and maintenance team. Gehry Technologies also provides consulting services on the implementation of Digital Project, and one of the interesting facts that Davies revealed about the company in his presentation was that 80% of its revenues come from its consulting business. One example of its consulting work is for Swire Properties of Hong Kong for its next big development, One Island East, a 70 story office building now under construction. Gehry Technologies became the "BIM consultant" for this project and used Digital Project to create the virtual 3D model prior to construction, discovering close to 2000 clashes leading to a cost savings of close to $13 million. The contractor is updating the virtual model as the building is being constructed, so that the model can be used for operations and maintenance once the construction is completed. Swire Properties plans to use this methodology on all its projects going forward. While the model was used to do some cladding studies in this project, the focus of BIM was primarily on clash detection, automated quantity extraction, and construction scheduling rather than on energy analysis. It was not clear from the presentation, what capacity, if any at all, Digital Project has for facilitating energy analysis and simulation.

Other Presentations and Discussions

In addition to the three main presentations, the CBSP Symposium included two panel discussions and a number of breakout sessions to discuss the issues that came up during the presentations as well as offer additional perspectives on the application of BIM to energy performance. Chuck Eastman of the Georgia Institute of Technology talked about the importance of being able to create custom parametric objects in BIM applications that can capture real-world behavior and fabrication information, which would enable more accurate predictions of the building's performance. Richard Keleher, an independent energy consultant who is also a member of the Building Enclosure Council, stressed the importance of making design decisions early about daylighting and provided an overview of the leading daylighting analysis tools including Ecotect, DesignBuilder, and IES VE. Steve Hagan of the GSA spoke in his capacity as the 2006 Chair of the AIA TAP Committee and described TAP's various BIM initiatives, including the BIM Awards. While the recent BIM Awards did have an "Analysis or Simulation" category, he revealed that building performance would be an important criterion for the BIM awards going forward.

In another panel discussion, Paul Seletsky of SOM described SOM's long-standing use of digital design processes, starting with their own internal BIM product called AES that was developed and used several years ago. While that product was a little too early for its times and is no longer being used, SOM is continuing with its BIM implementation, now using commercial software including the Revit platform as well as Digital Project for more complex projects, such as the Lotte Tower in Seoul, Korea, which at 112 stories ranks as the second tallest building in the world. SOM is putting several BIM and related technologies, including analysis and simulation tools, to work on this project.

Other participants in the panel discussions included Jerry Laiserin of The LaiserinLetter, who made the important point that it is optimization rather than simulation that should be the end goal of the application of BIM to building design and construction. Simulation is just the means to the end—if simulation is done but the results are not used to improve the design, it is simply a wasted effort. Other perspectives came from Vladamir Bazjanac of the Lawrence Berkeley National Laboratory, who warned that there are no simple solutions to complicated problems like those of designing energy-efficient buildings; and Brad Workman of Bentley Systems, who emphasized Bentley's support of interoperability and commitment to open standards such as the IFC and gave a brief overview of GenerativeComponents, a sophisticated modeling application that allows multiple design variations to be easily explored for a project simply by changing one of the controlling parameters.

While most of my own writing and consulting work is currently in the general area of AEC technology rather than on energy efficient design or energy analysis tools, I have some experience in this field from earlier work that was based on my knowledge of computer programming and my interest in the potential of computing to design better performing buildings. As part of my "M.Phil. in Environmental Design" degree at the University of Cambridge, UK, I developed a prototype application that could generate all possible window configurations in a room which met specified daylighting criteria. Subsequently, for my Ph.D. work at UC Berkeley, I developed a prototype building model that intelligently captured spatial and structural information, which could output, as proof of concept, a building file in the DOE-2 format for energy analysis. During this time, I came across a lot of research on energy-efficient design being done at universities, and it is still surprising to me to find how little of it has been integrated with the mainstream design tools used by architects and engineers. In my brief presentation at the CBSP Symposium, I highlighted the need to have closer interaction and synergy between university research and commercial software development so that they both can build upon each other's innovations. We also need more analysis tools that can help us optimize multiple aspects of a building's performance rather than a single aspect, as well as "generative" or "rule-based" tools similar to my window tool prototype that capture expert knowledge and rules about energy-efficient design and can help architects make critical design decisions such as building orientation, amount of glazing, window placement in a room, and so on. Also, for energy analysis to really become an integral part of design, we will need to eventually bring the analysis right into the BIM applications rather than rely on file exchange with another application via a neutral file format.

Analysis and Conclusions

The AIA CBSP Symposium was a very significant event, as it was the first to focus exclusively on how the growing adoption of BIM can be used to facilitate the design of energy efficient and high performing buildings. The link between BIM and building performance is significant, with the potential for both to boost each other. BIM makes it much easier to simulate a building's performance and use the analysis results to redesign the building for better performance. And with the growing importance of sustainable design across the world, BIM's ability to provide support for it will, in turn, speed up the implementation of BIM. As John Kennedy of Green Building Studio pointed out in his presentation, buildings are the primary emitters of greenhouse gases, even more than the transportation and industrial sectors, and across the world, new regulations are being or will soon be put in place for mandating high-performance buildings. For example, the AIA has set a goal of 50% reduction in the use of fossil fuel by 2010, while ASHRAE is looking at systems to get from 50% reduction to net-zero. In the European Union, all houses will soon need energy certification. It would be very difficult to achieve these goals without the intelligent support of BIM technology. It is great to see the GSA taking the lead in exploring how BIM can be used for more complete and accurate energy estimates earlier in the design process, improved life-cycle costing analysis, and increased opportunities for measurement and verification during building occupation. It will be publishing its findings and recommendations in a series of GSA BIM Guides, the first drafts of which were just published online at http://www.gsa.gov/bim.

At the same time, a lot of work still remains to be done if the vision of integrated design and analysis is to become a reality. BIM vendors need to first work on guaranteeing the completeness and integrity of the models that are authored by their applications. Otherwise, so much time will need to be spent "fixing" the models that the process will become just as tedious as the traditional process of re-entering the building data manually into analysis tools, and analysis will continue to remain a dispensable, after-the-fact exercise rather than an integral part of the design process. Also, the vendors need to work on closely integrating the analysis tools into their BIM applications, rather than just rely on the IFC file format to make the link. We also need closer cooperation between BIM vendors, the developers of analysis tools, as well as professional organizations like the US Green Building Council and the AIA CBSP, so that there's a collective understanding of what needs to be developed. Aspects such as LEED compliance and certification should eventually be working right off BIM models rather than by manual checking and data entry into forms.

And last but not the least, we need to hear more from architects who are successfully using BIM to design high-performing buildings at more Symposiums like this one.

About the Author

Lachmi Khemlani is founder and editor of AECbytes. She has a Ph.D. in Architecture from UC Berkeley, specializing in intelligent building modeling, and consults and writes on AEC technology. She can be reached at lachmi@aecbytes.com.

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