BIM Promotes Sustainability

Practitioners are finding paths to green through interoperable software

B.J. Novitski

Construction was about to begin on the restoration and addition for historic Grant School, in Washington, D.C. The contractor had nearly finished the time-consuming coordination of mechanical, electrical, and plumbing trades. Then work ground to a halt. Local legislation had just passed requiring all public buildings to achieve LEED certification. Already underway, Grant School was exempt from the requirement, but the Office of Public Education Facilities Modernization was eager to demonstrate their commitment to green.

Back to the drawing board? Not quite. The so-called "School without Walls" had been designed by Ehrenkrantz Eckstut & Kuhn (EE&K) Architects using "building information modeling" (BIM). So, modifications to the design-upgrading mechanical systems and acoustics to LEED for Schools standards-were relatively straightforward. EE&K principal Sean O'Donnell, AIA, explains that the historic wood-batten ceilings were preserved, but their backing changed from reflective plaster to absorptive ceiling tiles. The project already featured daylighting, reuse of an existing building, and proximity to public transit, earning LEED points. O'Donnell recalls: "The whole team of architects, builders, and an acoustical consultant sat around a table with the LEED checklist to figure out what we'd have to do. After a few weeks, we concluded we could at least get the project certified, and there'd be only a modest impact on schedule and budget. The owner was comfortable with the changes that would fulfill their goals."

Without the flexibility of BIM, the rework would have taken much longer and its cost might have been prohibitive. Now the high school is on track for completion in late 2009. Dwayne Sellars, BIM manager for Turner Construction, was responsible for coordinating the MEP trades. When a quieter acoustical environment called for larger ducts and more transfer grilles, fitting in all the equipment became more difficult. Sellars reports the rework took about six weeks, including the time spent with the architects and completing the coordination. "There would have been a greater time delay had we not had the modeling." Because of such efficiencies, in fact, Turner has begun using models even when the architect doesn't because they reveal conflicts between systems that are often discovered only in the field, resulting in fewer change orders.

An integrated design team works on one building, but each team member sees it through a different lens: architectural, structural, mechanical, or electrical. Illustration by Bryan Christie Design

Building Information Modeling

It's been a half dozen years since "BIM" was adopted as shorthand for the complex merging of computer-aided-design and construction databases. Technical, legal, and cultural barriers remain, and it may be unrealistic to expect a single model to describe an entire building throughout its life. Yet architects, owners, engineers, and builders are reporting benefits of efficiency, cost savings, and, importantly, greener design.

One Market Street Top: Daylighting analysis during an early phase of the renovation of this historic San Francisco building enabled architects HOK and the construction firm DPR to ensure high performance. Springfield Literacy Center Below: A computational fluid dynamics (CFD) model shows wind pressure differential, indicating natural ventilation potential, through a section of Burt Hill�s project in Springfield, Pennsylvania.

 

BIM, in theory, creates a complete digital representation of a building, including physical attributes, geometric form, material descriptions, and thermal and structural behavior. Ideally, the model is the joint creation of all design and construction disciplines. It grows throughout design, informs construction, and continues to serve facility managers during post-occupancy operations. It has been accepted as key to integrated project delivery (IPD) in which the owner/ designer/builder team cooperates in shared risks and rewards. By stressing multidisciplinary cooperation early in design, BIM also provides a framework for sustainable design. "Energy Modeling for Sustainability," [GreenSource, April 2008] described several ways BIM facilitates analytical scrutiny of design ideas. Although they resulted in more sustainable buildings, those examples failed to meet the ideal of a single model that moves fluidly back and forth between architects and engineers, accumulating information as it goes. Architectural design software now has stronger links to sustainability-related analysis software, but "back and forth" is still elusive.

Energy-Efficiency Analysis of Constitution Center, Washington, D.C. (TOP) Firms like SmithGroup are using BIM tools to redesign buildings to be more energy efficient. Using the modeling tool, the firm was able to identify energy savings of 19.6 percent resulting in cost savings of 22.4 percent. BIM User Differences (BOTTOM) Contractors see BIM as having the most benefit to green projects with three in ten reporting a high level of assistance. Two-thirds of architects see BIM as at least moderately helpful. A majority of engineers and owners see BIM as helpful. TOP: Courtesy SmithGroup. BOTTOM: Derived from Data in McGraw-Hill Construction's Smart Market Reports, BIM, 2008, P. 18-19

 

 

One A/E firm that hasn't let that slow them down is Burt Hill. Green permeates the firm's culture, as illustrated in their recent work on the Springfield (Pennsylvania) Literacy Center. The 50,000-square-foot school building was designed to connect students to, and teach them about, the surrounding natural environment. Early in design, the architects had proposed floor-to-ceiling windows in the classrooms, but the engineers, taking the architects' Revit model into Integrated Environmental Solutions (IES) software for analysis, demonstrated that daylight could be optimized and glare minimized if the windows were smaller and fitted with light shelves. The daylighting study was compared to a thermal analysis, also with IES software, to achieve a thermal balance. Engineer Matthew Rooke, who directed the analysis, says: "IES offers an interconnected group of programs that all reference the same building geometry, so the IES suite is itself a BIM system." Because the architects and engineers at Burt Hill work under the same roof, and have been designing green so long, they've become proficient at early, collaborative design decisions. Rooke explains that the architects don't feel constrained by engineering input. "Using these technical tools early on actually opens more doors to the designers. They can look at designs iteratively and try things that may be more cutting-edge." The engineers' review of the light shelves gave the architects confidence to incorporate them into their final design.

In 2000, when Renzo Piano began designing San Francisco's California Academy of Sciences, BIM was not yet in the mainstream. However, by the time consulting engineer Arup conducted simulations, they were using 3D models to produce computational fluid dynamics (CFD) and daylighting studies. According to Michael Wilson, AIA, principal in charge at the San Francisco office of partnering architecture firm Stantec (formerly Chong Partners), the engineer's models were instrumental in informing architectural design. The team was able to fine-tune natural ventilation with operable windows, enhanced by the undulations in the roof. Similarly, daylight penetration simulations helped the architects design appropriate window shades and overhangs. And modeling informed water management on the hilly, vegetated roof. Even after these design developments, the models continued their functional life as illustrations for the architects in educating the owners about the building's behavior. Also, Wilson points out: "These models are important not only for this project, but to help everybody understand how the systems and principles work, so we can take advantage of them on future projects." The building eventually received a LEED-Platinum rating.

Walking the Walk

The major BIM developers are working hard to improve interoperability. Graphisoft, Bentley Systems, and Autodesk market architectural modelers and sibling MEP software, so the design team can work in compatible formats. These systems also export data to specialty analysis software such as IES, EnergyPlus, Ecotect, and Green Building Studio. This interoperability enables architects and engineers to work together earlier, and it helps architects understand the sustainability ramifications of design decisions, making it more likely a high-performing building will result. Still, interoperability is not perfect, and a lingua franca has emerged that further reduces barriers. NavisWorks, now owned by Autodesk, combines 3D data from virtually any format and produces a single model that simultaneously displays the work of all participating disciplines. Within that model, users can "walk through" the spaces in real time and identify potential conflicts between building systems. Importantly, even without access to the more complex design software that creates the model data, subcontractors can visualize how the building systems will go together.

Click on each image for an enlargement.

Constitution Center SmithGroup modeled the mechanical penthouse of the Washington, D.C. Constitution Center to show subcontractors how their tightly packed equipment would fit together. Later photos confirm the reliability of the model. Images courtesy SmithGroup

 

One example of how such coordination aids sustainability is provided by Autodesk itself. A new facility for the software giant has given them an opportunity to "walk the walk" of interoperability. Using IPD, they worked with two architecture firms, Anderson Anderson Architecture and HOK-a longtime national pioneer in both BIM and LEED-and with the construction firm DPR. They converted a 35,000-square-foot building in an historic district of San Francisco into offices and gallery spaces, dubbed "One Market."

The project is expected to receive a LEED-Platinum rating, thanks in part to points earned for reusing the existing structure. Before demolition, the entire space was laser-scanned, and the scan was placed in the model. The designers determined that about 75 percent of the ductwork would be reusable. For this project, model management fell to the builders. BIM engineer Christopher Rippingham received dozens of specialized models in many formats from architects, owner, engineers, and subcontractors, and he combined them in a master model using NavisWorks. The model was exported to Ecotect for lighting and daylighting analysis. And it was used to orient those performing the commissioning.

BIM was an important contributor to the final LEED status, but Rippingham imagines a day when it will do much more. "In Revit you can assign materials," he points out. "In the future, each material might ‘know' how much recycled material it contains so you can track how much recycled material is in the entire project." Similarly, he adds, you could track LEED points and carbon footprint while trying out design alternatives. "The technology is not quite there yet, but I foresee that in the future."

Support Software

That future might not be too far off. Webcor Builders and ClimateEarth, a company that does enterprise carbon accounting, are together developing software that will compute a carbon footprint during a building's design phase. They will add greenhouse-gas-related metrics to existing Vico Estimator databases to dynamically account for direct and indirect sources of emissions. As practitioners discover ways to benefit the environment using BIM-based interoperability, progress is also occurring at the institutional level. In March, a memorandum of understanding was announced that commits the USGBC and sister organizations in Australia and the United Kingdom to "develop common metrics to measure emissions of carbon dioxide equivalents from new houses and buildings." Look for carbon to play a more prominent role in design standards in the near future.

A vast amount of data associated with design projects is neither numeric nor geometric, but verbal communication in the form of reports, e-mail, specifications, and so on. A popular software system that organizes such project information is Newforma. During design review and construction administration, it streamlines work processes, tracking design decisions, potentially reducing errors and omissions. The newest edition, released in February 2009, facilitates the labor-intensive LEED documentation and tracks materials for certification. It also assists in documenting local product sourcing and project commissioning and manages the interactive communications among disciplines during IPD.

For specifiers, there is the new GreenFormat, a Construction Specifications Institute (CSI) format that organizes and displays the properties of products that affect sustainability. It does not certify greenness but instead relies on manufacturers' reports on those properties. A long list of characteristics includes third-party certification, chemical content, green practices of the manufacturer, life span of the product, and whether the material is reused, rapidly renewable, or includes recycled content. GreenFormat was begun by the CSI Sustainable Facilities Task Team and its ongoing development is supported by manufacturers, specifiers, environmental consultants, BuildingGreen LLC, and McGraw-Hill Construction's (publisher of GreenSource) Sweets.

Some manufacturers are taking their own initiatives. One example is a recent enhancement to USG Design Studio software, which helps architects design and specify USG products. The latest version includes a LEED reporting tool that creates a report of possible credits for the selected products.

Informing Construction and Operations

The connections between BIM and LEED can be found throughout design and engineering. But sometimes BIM comes into play only after construction has begun. This was the case for the renovation of the Washington, D.C. Constitution Center, designed by SmithGroup and currently under construction by the James G. Davis Construction Corporation. Subcontractors became nervous about installing their equipment in the tightly packed 90,000-square-foot penthouse, so the owner commissioned the architect to model the space. The 3D representation demonstrated that everything would indeed fit-and uncovered a few possible conflicts-giving the subcontractors the confidence to proceed. Making the penthouse taller to accommodate the equipment was not an option "without an act of Congress," says SmithGroup's David Varner, AIA, in reference to the capital city's strict limits on building heights. The model had to show how the equipment could be layered; it was organized so closely that some would become inaccessible after other equipment was installed. Varner recalls: "We have ductwork 4 to 6 feet wide and 3 feet tall, and it's covering up a lot of conduit. We had to show how all that got structured, where the pull boxes go, for instance, and how it could all get suspended without being overly redundant." The process also contributed to the greenness of the building, which is expected to receive a LEED-Silver rating. Varner explains: "Modeling the penthouse has made us more confident that our design intent will be preserved and not compromised in some unforeseen way."

California Academy of Sciences Top: A CFD analysis by Arup displays the temperature distribution due to natural ventilation in this San Francisco project, designed by Renzo Piano and Stantec. Below: Air speeds are mapped in the domed rainforest exhibition. Images courtesy ARUP

BIM came to the rescue several years after construction, when the Pittsburgh Convention Center was not performing as well as predicted by architect/engineer Burt Hill. Engineer Rooke explains that it had been designed as a high-performance building, but the owners weren't seeing the expected energy savings. He says: "Using a detailed energy simulation normalized to actual energy usage, I was able to pinpoint some areas that either hadn't been thought of in the design or weren't being operated as intended. After we fixed those, the energy performance of the building improved. This is the tip of the iceberg of how BIM can carry energy information through the life of the building and help owners operate their buildings effectively."

That's been the experience of facilities manager and CAD Manager Clyne Curtis, at Brigham Young University in Provo, Utah. He is in the process of converting their AutoCAD databases into Revit models. In the past, he needed to maintain redundant files for each building: one to show the architectural drawing and another for the polylines used in area calculations. Revit models include both forms of representation, so changes only need to be entered once, reducing the chance of errors. The Revit models contribute to the ongoing energy conservation on campus in several ways. With data exported to Green Building Studio, heat loss and gain can be easily calculated for individual rooms allowing managers to fine-tune the equipment for efficiency and appropriately size air supply and return lines. In this dry climate, concrete surfaces can serve as thermal mass, so the energy analysis, Curtis explains, informs changes to flooring or ceiling materials that can improve comfort in each room.

Although the technology has a long way to go before BIM fulfills all its promises to promote sustainability, pockets of success abound. James Barrett, Turner's national manager of Virtual Construction Technologies, claims that BIM itself is green and worthy of LEED points. First, he argues, BIM results in a huge reduction of paperwork. Also, because subcontractors can reliably predict the amount of material they'll need in the field, they do not need to over-order, which traditionally leads to waste. Barrett asks: "If LEED gives points for recycling waste, why not for avoiding waste?"

The perfect ideal of BIM may not be attainable, but pieces of it are definitely coming together. Projects-and the environment-are benefiting from more cohesive teamwork and a greater degree of interoperability among software systems. Architects are receiving better, earlier energy-related analysis; engineers are providing more focused expertise during design; builders are reducing waste in construction; and facility managers are increasing the efficiency of their operations. And many of those experiencing the benefits of technology and teamwork have visions of still more capabilities and benefits in the future.