Targeting Net-Zero
The consensus among those who've wrestled with the net-zero challenge is that establishing an approach to the benchmark, like any responsive building design, must be tailored to climate, site conditions, and building type. Success includes a myriad of strategies simultaneously. As Selkowitz puts it: there is no silver bullet for achieving net-zero-only silver buckshot.
Once the commitment is made to design a building that powers itself, a new mindset kicks in. Basically, to reach net-zero affordably, designers must aggressively reduce energy demands and loads, optimize passive strategies, and, if needed, incorporate efficient active mechanical strategies. When the building is tuned to high performance, the design team determines the required amount of renewable energy sources.
NREL engineer Paul Torcellini, PE, co-authored an assessment of commercial buildings in the U.S. to explore how close the country could get to net-zero performance within that sector. The report showed that by using current strategies on existing and projected new projects, it is theoretically possible for 47 percent of the total commercial floor area and 62 percent of buildings to achieve net-zero by 2025.Â
In Practice
The recently completed NREL Research Support Facility demonstrates a multifaceted approach to attaining net-zero energy. The 218,000-square-foot building in Golden, Colorado, gave DOE engineers the opportunity to put several aspects of their research into practice.
The innovation began at the bid phase when the DOE decided to find design-build teams to produce detailed "performance-based design" proposals. The fifty-page RFP required detailed accounting for energy, restricting use to only 25,000 Btu/SF/year. The building needed to perform more than 50 percent better than ASHRAE efficiency standards, and fulfill all four of the definitions for net-zero energy. The winning team of RNL Design and Haselden Construction proposed the only net-zero scheme and convinced the client they could get there within the specified budget.
The recently completed 218,000-square-foot LEED-Platinum National Renewable Energy Lab Research Support Facility in Golden, Colorado, demonstrates a multifaceted approach to attaining net-zero energy. Image: Courtesy NREL |
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With net-zero, it becomes important to incorporate a true integrated-design approach, in which the architect and engineers are at the table developing performance efficiency at the earliest stages of the project. "This effort has to start before the architect puts pen to paper," says Stantec Project Engineer John Andary, PE.
Energy modeling programs are essential tools for the early phases of high-performance design. Stantec used an array of modeling tools such as DOE's eQUEST for energy design and separate programs for windows, daylighting, and 3D heat transfer. But like many aspects of sustainable design, energy-modeling technology is still in the early phases of its development.Â
"The programs that are out there now were developed to help team members make choices about design elements," Andary says. "They weren't intended to be predictive of the actual energy use, because so much of building performance depends on how the building is actually used. That's a variable designers usually don't have control over." Andary says that the issue is important enough that Secretary of Energy Steven Chu has made more accurate predictive modeling software a priority of his agenda.
A mantra for the NREL lab was "invest in the architecture"-make the building elements as efficient as possible, which will pay off in reducing the investment in mechanical systems and renewables. The team generated a set of rigorous assemblies including triple-glazed windows, concrete sandwich panel walls that eliminated thermal bridging, and photochromic glass that dims in response to the sun's intensity on east and west facades. Careful attention to daylighting is especially important in high-performance buildings because of the savings wrought by reducing electric lighting loads. Daylighting and other passive strategies push most net-zero buildings into an elongated form along an east-west axis. The NREL building's massing consists of two narrow bars-a skewed "H" shape allowing good access to sun and ventilation.