BIM and Analysis for Sustainable Design (1-2-3 Revit Tutorial)9 Apr, 2007 By: AIA ,Rick Rundell
Linking BIM and building analysis software offers greater opportunities for green design.
Not that long ago, most building professionals would have classified sustainable design merely as an interesting idea. But awareness of climate change and other environmental issues has catapulted it to center stage. The international movement toward sustainability has created a flood of new green building regulations and initiatives around the globe and sustainable design practices -- once considered niche -- are now widespread.
Quality sustainable design requires an understanding of how a building will perform after it's built, which in turn requires computer-based simulation software for rigorous building analysis. The advent of BIM (building information modeling) offers even greater opportunities for building analysis by pairing the analysis software and BIM for the seamless assessment of building performance.
This month, I begin a two-part series exploring how BIM supports analysis for sustainable design, punctuated by Autodesk's recent announcement that it's partnering with Integrated Environmental Solutions (IES) to further enhance the Revit software platform to support green design.
Green Design Revisited
One of my earliest "1-2-3 Revit" columns outlined how Revit could be used in conjunction with the Green Building Studio Web service for sustainable design. At that time, approximately 180 million square feet of LEED-registered projects were in the pipeline, per the USGBC (U.S. Green Building Council). Currently the USGBC estimates 750 million square feet of LEED-registered space: a 4x increase in just two years (1). Statistics like this one underscore the acceptance of green design and sound a hopeful note in the discord of climate change news.
Governments around the globe are implementing new building regulations that mandate sustainable design. According to Dr. Don McLean, CEO of IES, "Countries that represent almost three-quarters of the world's GDP require performance assessment tools for either code compliance or building rating purposes." McLean explains that countries or regions such as the European Union, Australia and California, which represent almost a one-quarter of the world's GDP, already require performance assessment to comply with building regulations. Additionally, countries that represent more than one-half of the world's GDP (such as the United States, India and China) have or are adopting voluntary building rating systems such as LEED.
But compliance with the performance-based criteria of these programs can be difficult to assess by traditional methods. McLean explains, "It's fairly easy to design good performing buildings -- ones that will consume more than 50% less energy. However, there's a severe lack of understanding and experience of low energy design in today's building design community." For decades, simulation software tools have been available to assist the design of energy-efficient buildings. Unfortunately these tools were difficult to use and thus limited to specialists, so most designers relied on simple hand-calculation methods to assess building performance.
The integration of the Revit BIM and the building performance analysis tools from IES targets these challenges and provides an easy way for architects and engineers to examine the implications of alternative design strategies, helping them achieve higher operational efficiency and building performance.
This integration also underscores the advantages of a computable BIM, a model that contains the necessary level of detail and reliability for performance analysis that can be done directly by designers for their own baseline energy analysis.
Linking BIM and Building Performance Analysis
Established in 1994, IES is headquartered in Glasgow, Scotland. Its software is the first commercially available system for the integrated analysis of a building's performance, generating detailed data for a range of analyses such as thermal simulation, load calculations, daylight assessment and solar studies.
The company's software, called IES <Virtual Environment>, or the <VE> for short, is relatively new to North America but is widely used in other areas of the world, with several thousand users in more than 500 commercial sites throughout the world and many more users in academia. Representative customers include Skidmore Owings & Merrill, Stantec, Arup and even Wal-Mart (a customer of IES's own consulting group).
The integration between the Revit platform and the <VE> features a link between the Revit BIM and the IES analysis software. There's no need to recreate the building geometry, because users can pass the BIM room geometry and data directly to the <VE> and with one mouse click run a variety of analyses without specialized skills, separate analysis packages or separate models for each analysis.
This tight integration allows Revit users to quickly and easily analyze alternative green designs. Thermal and daylighting studies that would have taken weeks (if they were done at all) can be done in minutes, and the results are output in a HTML report. The quality and speed of the technical feedback enables firms to use building analysis tools for sustainable design rather than just equipment sizing. More importantly, these tools can be used in the very earliest stages of the design process to help monitor and guide a design rather than waiting until the end of the design process and using building analysis for just validation when design changes at that point are difficult and costly to accommodate.
The integration manifests itself within both Revit and the <VE>. Revit MEP, developed for mechanical, electrical and plumbing engineers and designers, has a native functionality for heating and cooling load analysis that uses established IES methodology. In the <VE> you can use the new Sustainability Toolkit to perform thermal assessments and daylighting calculations.
The Sustainability Toolkit is an analysis package within the <VE>, unique to the Revit platform, that lets architects conduct a variety of analyses: ASHRAE load calculations, dynamic thermal analysis and daylighting assessment -- and produce a LEED daylighting credit report, all based on the Revit Building model. As mentioned above, the integration features a link between Revit BIM and the IES analysis software, so there's no need to recreate the building geometry for analysis. The analysis is launched with a single icon, and the feedback is a simple HTML report.
This analysis package allows architects to receive quick feedback on their design; feedback such as how much energy the building will use, what are the anticipated CO2 emissions and if the building will pass LEED daylighting requirements. By giving architects the ability to quickly and easily assess their design for building performance, they can make better informed building-design decisions to iterate on a greener design.
The Sustainability Toolkit lets designers conduct a variety of analyses all based on Revit BIM.
The toolkit has two kinds of thermal assessments, the first of which is an ASHRAE steady-state load calculation that determines how much energy the building will consume during peak heating and cooling situations. This type of analysis can be used to size and spec mechanical systems, but it can also be used very early in conceptual design, perhaps during design charrettes (sessions to study the design often used early in the building design process), to gain quick insight into a building's carbon footprint. For example, an architect may investigate a dozen or so forms early in the design process, using any number of criteria to select which options to pursue -- one of which could be building performance. He or she can run this ASHRAE load calculation to get a baseline and then modify the design (such as replacing a brick wall with a curtain wall or selecting improved glazing performance for the windows) and then rerun the analysis to see how the changes affect energy consumption. With easy energy calculations such as these, analysis becomes a routine part of the design process and allows architects to factor environmental performance into early design decisions.
The second thermal assessment is a more rigorous analysis that uses advanced dynamic thermal simulation to evaluate a building's performance over time. Because it provides a more comprehensive analysis, it's typically a requirement for green certification. But the time required to run this type of analysis may be 10 to 20 times greater than the steady-state ASHRAE method, so it's better suited for detailed design. For example, it may be used to evaluate subtle design differences such as varying the angle of the brise soleil or changing the building occupancy schedules.
The Sustainability Toolkit's ASHRAE load calculation gives quick insight into a building's overall energy performance.
The Sustainability Toolkit also contains point-to-point daylighting simulation for evaluating how natural light can be used to illuminate the interior of a building design. Effective daylighting design can reduce the electrical lighting load and subsequent energy loads of a building, so it's an important aspect to sustainable design. The integration of the <VE> daylighting tools and the Revit building model allows designers to evaluate daylight levels from within their design environment as a routine part of the design process just like the thermal assessment mentioned earlier. The results can be displayed in both graphic and tabular forms or in a format required for LEED submittal, which eases the certification process.
The Sustainability Toolkit performs daylighting analysis with results displayed in a graphic form (inset) or in a format required for LEED submittal.
The link between the Revit platform and the IES <VE> helps the building industry meet the demands for sustainable design and increases the value of BIM. Next month, I'll drill down into the new functionality within Revit MEP for heating- and cooling-load analysis, which uses the IES ApacheLoads analysis module. I'll also profile two firms currently using the integration to give a clearer picture of the role BIM can play in analyzing a building design for sustainability.
(1) Figures from USGBC's PowerPoint presentation "Introduction to LEED and Green Building," available online.