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A building that produces all the energy it requires, without sacrifices to its operations or concessions of human comfort, might sound like pie in the sky. But according to the New Buildings Institute (NBI), 160 commercial and institutional buildings in the U.S. are targeting or have achieved net zero energy—meaning that, over the course of a year, they produce at least as much energy from renewable sources as they consume. Although 160 admittedly is a small number, only two years ago the nonprofit institute's count was less than half of that, at 60 buildings. What's more, these aspirations are no longer limited to small demonstration projects: net zero energy buildings (NZEBs) now encompass everything from schools to federal office buildings and laboratories, and many have large, sophisticated programs.

A net zero building will have a vastly reduced energy appetite— a necessity if all of its energy needs are to be met with renewable sources, since its power production capability will generally be limited by the number of photovoltaics (PVs) that will fit on the roof. However, such buildings' achievement is not measured in comparison to some theoretical baseline, as is the practice with green building rating systems like LEED. “We are no longer talking about buildings that are 20 or 30 percent better than code,” says William Maclay, author of the recently published book The New Net Zero and founder of an eponymous architecture firm focused on sustainable design, based in Vermont. An absolute evaluation method has replaced a relative one, he explains: “The new metric is zero.”

Although “net zero” has an inherent clarity, there is still some debate among members of the design and construction community about what exactly constitutes an NZEB. Within the generally agreed upon net zero rubric, a number of variations are possible: all of the renewable energy required for operations could be produced within the building's footprint, or it could be supplied from within the boundaries of its property. Another alternative is that the structure is powered by fossil fuels, such as natural gas, burned on-site, as long as this consumption is offset by renewable energy that the building produces. Depending on who is creating the standards, any one of these examples may or may not qualify as a net zero building.

Only one organization offers a national third-party certification program for NZEBs—the International Living Future Institute (ILFI). It actually requires that buildings be net positive: in order to qualify under the latest version of ILFI's certification system, buildings must generate a small surplus of energy with on-site renewable energy, enough to satisfy 105 percent of the project's energy needs on a net-annual basis. Combustion is not permitted, even with biomass or biogas harvested or captured on a building's surrounding property. The logic behind the restriction is that such on-site resources are available to only a small number of projects, explains Brad Liljequist, technical director of the Living Building Challenge, ILFI's certification program. “We want a vision that can transform the whole economy,” he says.

One of the most ambitious recent buildings aiming for net zero operations is the J. Craig Venter Institute in La Jolla, California. Named after the institute's founder and CEO—one of the first scientists to sequence the human genome—the 45,000-square-foot Spanish cedar–clad building surrounds a central court with wet labs, computational research facilities, and office space, and sits on land leased from the University of California, San Diego, that overlooks the Pacific Ocean. Designed by ZGF and completed last February, Venter has 26,000 square feet of rooftop PVs expected to cover all of its power needs—no small feat, considering that laboratories are notorious energy hogs.

Ted Hyman, ZGF managing partner, explains that the project team gradually chipped away at a typical laboratory's energy use in a design process that is not uncommon for high-performance buildings. The team first applied passive architectural strategies (proper orientation, deep overhangs, and a tight building envelope) and then devised the most energy-efficient building systems possible.

As a final step, Venter's design team took aim at the building's so-called plug and process loads (PPLs)—those loads not related to general lighting, heating or cooling, or other systems that provide comfort to the occupants. They are created by devices like printers and computers and other appliances powered by AC outlets, and by equipment that supports activities such as cooking and refrigeration. Architects and engineers rarely attempt to accurately predict or reduce such consumption, since they typically have little control over these unregulated loads. But in this case, they have actively worked toward reducing PPLs by surveying Venter's existing labs and making recommendations for new equipment and operating practices.

Other projects that have strategies for keeping PPLs in check include PS 62 Richmond, a $70 million pre-K through 5th-grade school under construction on New York's Staten Island. The 69,000-square-foot building, designed by Skidmore, Owings & Merrill (SOM) and slated for completion in the fall of 2015, aspires to be the first net zero school in the Northeast. Bruce Barrett, a vice president at the city's School Construction Authority (SCA), points to the cafeteria, where the team is working closely with the Department of Education's food-service provider to make meal preparation as energy-efficient as possible. Barrett also cites the faculty lounges, which will be equipped with coffee machines and refrigerators, among other amenities, to discourage teachers from bringing their own power-hungry appliances into their classrooms. The view from these lounges into the two-story building's inviting central court should offer extra inducement for teachers to make use of the shared facility, according to the project team.

Naturally, other architectural features as well as building systems will play a crucial role in helping PS 62 reach net zero. For instance, the corridors are ingeniously offset so that the same skylights illuminate the hallways on both the first and second floors. By employing daylight-sharing techniques, such as interior clerestory windows and ceilings contoured to reflect sunlight, the corridor skylights will also help illuminate the classrooms. The school will have many state-of-the-art features, including an ultra-high-performance building envelope, an 80-well geoexchange system, and demand-control ventilation. As its source of renewable energy, about 2,000 PVs will wrap the roof, south-facing elevations, and the canopy over the parking lot. The panels are estimated to generate 662 mWh per year.

It isn't unusual for projects to take several years to reach net zero performance. In the summer of 2010, a design-build team that included architecture firm RNL, Haselden Construction, and Stantec's mechanical engineers completed the first 220,000-square-foot phase of a Research Support Facility at the National Renewable Energy Laboratory (NREL) in Golden, Colorado. Just over a year later, the same team finished a 138,000-square-foot expansion. But only in April 2014 did NREL document the first complete year of net zero operations for the office complex, which has PVs on the roofs of its three wings as well as over two parking lots, and relies on a number of readily available energy-efficiency technologies combined in unusual ways. Reaching net zero is an ongoing process, explains Shanti Pless, an NREL senior research engineer. “It requires robust commissioning, metering, and tenant engagement, and then recommissioning,” he says.

One building in the process of working toward its net zero goal is the Wayne N. Aspinall Federal Building and U.S. Courthouse in Grand Junction, Colorado. The project team of architecture-and-engineering firm Westlake Reed Leskosky and design-builder Beck Group proposed the target as part of its $15 million renovation of the nearly century-old Renaissance Revival structure, even though the objective was considerably more ambitious than the one set by the client, the General Service Administration (GSA), for LEED Silver certification and a 30 percent reduction in energy use when compared to the energy standard ASHRAE 90.1. Achieving net zero is likely to make Aspinall the first such building on the National Register for Historic Places.

In addition to restoring historic details and finishes, the firms' overhaul of the 42,000- square-foot structure, completed in early 2013, includes variable refrigerant flow heating and cooling tied to a 32-well geothermal system, dedicated outdoor air with heat recovery, and new fluorescent and LED lighting with wireless controls. The combined effect of these and other strategies was to cut Aspinall's energy use intensity (EUI)—that is, energy use as a function of a building's size—approximately in half. It went from 42.6 KBtu per square foot per year prior to the renovation to 21.2 afterward, without counting the contribution of the 123-kW PV array on the roof.

Although the reduction is impressive, it is not quite sufficient to achieve net zero. For the 12-month period ending in August 2014, the building ran at a net EUI of 7.1, according to Roger Chang, Westlake Reed Leskosky's director of engineering. He points to a number of problems identified during an ongoing measurement and verification period, including diminished power production caused by dust accumulating on the PVs during dry conditions and ice forming on the panels during severe winter weather; higher than expected nighttime plug loads; and incorrect thermostat settings. To remedy the situation, settings and controls have been adjusted and the GSA has instituted an incentive program to encourage occupants to reduce their energy use. The plan now, Chang says, is to monitor the building closely over the next two or three years before installing additional PVs over a nearby parking lot if necessary.

Such teething pains, common with recently completed projects—both renovations and new construction—can easily derail net zero efforts. This was almost the case at the new 50,000- square-foot headquarters EHDD designed for the David and Lucile Packard Foundation, in Los Altos, California, which opened in 2012. During a particularly severe cold snap a few months after the nonprofit moved in, two of Packard's air-source heat pumps failed. For about two months, the building's fans and its two functioning heat pumps were kept running almost continuously, driving energy use way up, says Eric Soladay, a managing principal at Integral Group, the project's mechanical engineer. Even so, the headquarters consumed less electricity in its first year of operation than its 285 kW of rooftop PVs produced, owing to several tightly coordinated energy-conserving features like long and narrow floor plates that help maximize daylighting, an extremely thermally efficient exterior envelope, and a sophisticated building management system. In September 2013, Packard earned ILFI's net zero certification, making it the largest building to earn this distinction so far. “Usually the first year is considered training and the second year is when we start the verification process,” says Soladay. “Doing it in one year was a push.”

The biggest challenge remaining, experts say, is bringing the costs associated with ultra-energy-efficient construction down. But they also say the necessary technologies are becoming more readily available, more reliable, and less expensive. For example, according to ZGF's Hyman, chilled beams were considered exotic when he started working on Venter seven years ago, but now the heating and cooling devices are “practically ubiquitous.”

Barrett, meanwhile, points to rapid improvements in LED lighting. As a result, PS 62 will rely almost exclusively on LEDs, even though tried-and-true fluorescent lighting was specified in the 2012 bid set. Because designers anticipated that LEDs would be a viable alternative by the time the school neared completion, the contract stated that the owner would provide final direction on lighting fixtures at a specific point in construction. A similar arrangement for the solar panels will allow the school to benefit from the latest developments in PV technology.

Peter Rumsey, a San Francisco Bay Area mechanical engineer who has been involved in at least 15 net zero projects, including Packard and Venter, predicts that costs will fall enough to spur a wave of net zero construction in the next five to 10 years. He sees particular promise in the retrofit market, especially of one- and two-story buildings, where the ratio of roof area to occupied area is advantageous for achieving net zero. “The vast majority of buildings in the U.S. are two stories or less,” he points out. “There is tremendous potential.”

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