Strategies for conserving energy in tomorrow’s buildings have taken center stage in the push to decrease the environmental impact of the built environment. This is understandable given that buildings account for 71 percent of electricity consumption and one-third of the nation’s energy use. While green-building certification programs, such as LEED, a program of the Washington, D.C.-based U.S. Green Building Council, reward reduced energy consumption, they are not design tools that enable detailed evaluations to maximize conservation. New Building Information Modeling software, also known as BIM, allows architects, engineers and building owners to weigh various design options and their effects on energy consumption, daylighting, thermal comfort and more.
GREEN BUILDINGS SAVE ENERGY
The LEED program awards energy-performance points on the basis of predicted energy cost savings compared to a modeled code baseline building. According to a new study by the Vancouver, Wash.-based New Buildings Institute, energy modeling turns out to be a good predictor of average building energy performance for the sample. The study provides a comprehensive view of post-occupancy energy performance of LEED buildings, providing a critical link between intention and outcome for LEED projects. LEED buildings were shown to perform 25 to 30 percent better than the national average; however, green-building advocates long have maintained that much more can be achieved in regards to energy conservation with buildings.
The full study is available for download on USGBC’s Web site, www.usgbc.org. Last year, the USGBC board of directors proposed and USGBC membership overwhelmingly approved a call for all LEED-certified projects to achieve at least two of the possible 10 Optimize Energy Performance points within LEED. The credit was entirely optional previously. This change is expected to improve the energy performance of all LEED-certified buildings by 14 percent for new construction and 7 percent for existing buildings. But what tools are available to help architects achieve greater energy performance? In addition, how do design teams make informed choices about interrelated topics, such as daylighting, glare, thermal comfort and the sizing of mechanical systems?
MODELING FOR FUTURE PERFORMANCE
BIM is a new class of powerful software simulation tools that helps architects, engineers, facilities managers and others better understand the relationships between objects within a building. It is a digital representation of physical and functional characteristics of a facility that portrays the building as a full, 3-D computer model stored as a database rather than as a series of line segments.
According to Charles Eastman, director of the College of Architecture doctorate program at the Georgia Institute of Technology, Atlanta, BIM is the “most massive upheaval of design and construction practices in history.” One of the often-cited benefits of BIM is the identification of design inconsistencies, such as measurements that do not add up or geometric conflicts between HVAC vents and structural components.
Other benefits of BIM include enhanced visualization for clients and ease of fabrication for manufacturers. But perhaps the biggest benefit to using BIM lies with its modeling functionality. With BIM, architects can model various criteria, such as solar, thermal, shading, lighting and airflow, to determine how they will affect building performance. A building’s total energy use and associated carbon footprint can be determined and reduced. Modeling can take place at the early stages of design and continually during more detailed phases. How buildings perform over time will help project owners plan for facility budgets.
SPRINGFIELD LITERACY CENTER
Architecture and engineering consultants Burt Hill, Butler, Pa., used BIM software when designing the new Springfield Literacy Center in Springfield, Pa. The project includes a kindergarten, first grade and outreach literacy center. Although maximizing daylighting was a stated project goal, the physical property had constraints for site orientation, including adjacent trees that necessitated the building take a split form that created deeper classrooms. Burt Hill energy analysts employed BIM software to investigate the potential trade off between achieving the LEED daylighting credit (Indoor Environmental Quality 8.1) and the LEED energy-use credit (Energy and Atmosphere 1 Optimize Energy Performance). Burt Hill architects wondered how different components of the building envelope would affect daylighting and energy performance.
Using BIM, glazing size, type and shape options were analyzed using various wall assemblies and natural- ventilation options. BIM helped determine how big the windows should be, including orientation and location, to achieve the most effective daylight levels. Potential problems also can be identified using BIM. Burt Hill analysts discovered excessive light levels and glare attributable to a bank of floor-to-ceiling windows. A series of alternative designs were modeled before selecting one that removed a section of window at the floor level and inserted smaller windows in another section of wall farther up. Further balancing glare and maximum daylighting, designers used BIM to explore the use and positioning of external shading devices and lightshelves. Lightshelves were added to address a potential glare/overheating issue while glazing was modeled to balance transparency and thermal performance. Given the unique characteristics of the site, achieving the parameters of the LEED daylighting credit had the potential to adversely affect the building’s energy consumption.Using BIM to model various scenarios component by component enabled the project to also meet the LEED energy-use credit. Modeling exterior wall composition, including various insulation values, helped improve the overall energy efficiency while conversely avoiding summertime overheating caused by excessive insulation. Thanks to the modeling capabilities of BIM, architects for the Springfield Literacy Center were able to maximize daylight, conserve energy and meet the project’s occupancy goals. With BIM, design teams can evaluate very dynamic parameters, like daylight, window ventilation, thermal masses, night ventilation, solar heat gain and more. Better understanding the complex interrelationship among these factors helps architects design buildings that can meet the needs of building owners, occupants and facility managers.
JEFF STEPHENS is principal of Oakland, Calif.- based Planet Relations, a public-relations consultancy for Earth-minded businesses. He can be reached at [email protected] or (510) 663-4462.
