Form Follows Performance?

The Bauhaus era mantra of “Form follows function” reflected a philosophy of defining the form of a building around the function of spaces, materials, or systems in that building. Today, building form is increasingly being influenced and even defined by the performance of that building. This is readily seen in designs where occupied areas are opened up to the outdoors, roofs and ceilings are sloped to take advantage of sunlight, and materials are selected based on their ability to protect from, absorb, or reflect weather conditions.

The PBD approach to building design seeks to optimize outcomes so that performance is enhanced by design, not compromised by it. It is an ongoing part of the design process during which building performance is continuously analyzed by assessing the impacts of design changes on things such as energy use, cost, daylighting, thermal comfort, and environmental impact. To do so, it applies industry-based analyses to building-design items such as form and massing, the site where it is located, the materials used, and the make-up of the construction.

The software available to carry out performance-based design also helps design teams to see, in real time, whether the buildings they are designing are on track to meet performance standards or certifications such as LEED, Green Globes, Architecture 2030, or the English BREEAM standard. Most of the available software uses an analysis engine for energy-performance calculations developed for public use by the U.S. Department of Energy known as EnergyPlus. There are also industry-standard engines for daylighting inputs and analysis. The software is streamlined enough that it is very easy to perform numerous analyses quickly and easily such that many different design options can be looked at in a single day, dramatically faster than using traditional separate energy modeling. This software can then be used as the basis to demonstrate compliance with the appropriate performance standard or certification.

Photo courtesy of Sefaira

The SmithGroupJJR has taken the approach of incorporating performance-based design into every project and among every design team member.

Integrating Performance into Design

When fully integrated into a design process, PBD provides better and more accurate awareness of the impact that design decisions have on building performance. At the outset, project teams can establish the appropriate performance goals and prioritize them compared to other project goals. Then analyses can be run on different design schemes or variations in order to compare the different performance results. Depending on the magnitude of difference between schemes or elements, the design team can begin to make informed design decisions about how to maximize performance or where to make adjustments by learning which elements don’t provide enough benefit to pursue. Then more time can be devoted to optimizing the best overall design option that meets all project objectives in the most cost-effective manner. By default, then, this approach makes PBD relevant for every project, not just for those labeled ‘high performing.’

As an example of this “every project” applicability, consider the case of the SmithGroupJJR, which is one of the oldest firms in the country with offices across the United States and in China. Its success with performance-based design comes from a very basic, yet powerful, approach: the firm simply practices it early and often as a normal and natural part of every design process. To be more specific, it has embraced the premise that designers are able to make PBD an integral part of their own workflow. That means performance analysis is no longer the purview of one specialist in the firm, but rather is able to be used and integrated into design by everyone. Don Posson, vice president of the SmithGroupJJR, points out how the firm is doing this: “We start using it in the conceptual and early design stages, where it is led by the architect and assisted by the engineers. As we move into more systems-based analysis, the process becomes led by the engineers and assisted by the architects. That way all of the key decision makers are involved all the way through.” In short, the firm has equipped and empowered its design professionals with the right computer tools to inform their decision-making process while creating a fully integrated, seamless, and effective work flow.

To illustrate how this approach plays out in practice, the firm recently worked on a new construction project consisting of 75,000 square feet of medical office building space located in northern California. Project Architect Jon Riddle and his colleague, Associate Kim Swanson, used PBD to assess this project throughout its progress, thereby enhancing the team’s understanding of the building performance, as well as adding to the firm’s design capabilities and energy-performance portfolio.

Photo courtesy of Sefaira

PBD analyses allow individual strategies to be looked at or a combination of strategies to be considered to determine the best overall solution for a particular building design.

Initially, four unique and fairly well-developed design options had been completed, represented by design massing strategies of 1) an atrium, 2) a courtyard, 3) an interlocking arrangement, and 4) a plaza. Energy and daylighting performance was not a specific project goal per se; however, the team needed to meet rigorous California Title 24 energy code requirements. Riddle used PBD to compare the energy performance of the four options and found them to be fairly close in overall energy use with Energy Use Intensity (EUI) ratings between 41–45 kBTU/square foot/year. It was determined that the atrium design best met the design team’s programmatic performance requirements and aesthetic intent. While its energy use was higher than other options, it was fully acceptable for the project’s goals and code requirements. This basic exercise introduced the team to an important aspect of performance-based design: optimizing performance is relative to the entire scope of design considerations. In other words, a given project may or may not accommodate aggressive performance goals, but every project benefits from well-informed and holistic decision making.

With the best overall basic design selected, Riddle and Swanson then set out to see how they could further improve performance and reduce the EUI. To do so, they used a simple four-step process. First, they analyzed the details of the performance data and observed that while lighting and plug loads were basically fixed due to the building use, the cooling load was a potential area for improvement. They recognized that lowering the cooling load can often decrease the size of the HVAC system, resulting in lower capital costs, lower operating costs, and/or more usable square footage. Second, they sought to identify potential strategies that could be used to achieve the lowered cooling load. The team determined that external loads (e.g. solar gain) would likely be the most fruitful to be explored and managed. Third, they began the process of trying different strategies, recognizing that the successful use of performance-based design is not a purely linear process. Rather, it is more iterative, meaning that it involves some back and forth, even some trial and error based on educated assumptions. They started with the selected design as a baseline and then analyzed one strategy at a time to determine the net improvement (or not) on the cooling load. Each of these analyses then provided quick feedback on where to focus additional design efforts. In this case, the strategies fell into three categories:

• Glazing Ratios: Lowering the glazing ratio helped lower solar gain, and in turn, helped lower cooling capacity.
• Shading Strategies: Adding brise soleil shading improved performance; analysis also showed that north facade shading of any kind was unnecessary, providing a potential capital cost savings.
• Materials: Given the early stage of this project, understanding materials’ effects on performance was key. The team learned that the core structural material and glazing’s solar heat gain coefficient (SHGC) stood to affect cooling capacity.

With a newly gained understanding of design elements that were driving performance, the final step was to present their findings and design recommendations. After reviewing the multiple strategies, the best approach proved to be combining them. This required treating the combination as a separate analysis, since the team recognized that strategies interacting with each other are not always additive (e.g. three separate strategies that save 5 percent each does not mean combining them will save 15 percent).

By taking the design to this next step, Riddle and Swanson showed that even given a fixed massing and siting, performance gains could still be made through glazing ratios, shading, and material selection. Their selected combination of strategies proved to be very effective—the Energy Use Intensity of the building dropped from the original EUI of 45 to an EUI of 35 due in large part to achieving a significant reduction in cooling load. This savings in cooling also translated into a 25 percent reduction in equipment size and a 9 percent projected reduction in annual utility costs. In addition to the project benefits of the effort they led, it also provided valuable internal experience and a case study for their colleagues’ reference, as well as a marketable example to demonstrate the firm’s capabilities to future clients.

Photo courtesy of Sefaira

Lorton Volunteer Fire Station (top) designed by Lemay Erickson Willcox Architects, Reston, VA, and Jefferson Fire Station (bottom) designed by Hughes Group Architects, Sterling, VA, all in collaboration with Brinjac Engineering using performance-based design.