Less than Zero

by David Hill

The Innovation Center in Basalt, Colo., might be a small building, but it has a big story to tell. Located near the tony resort town of Aspen, the 15,610-square-foot two-story structure opened in December 2015 as the headquarters for the Rocky Mountain Institute (RMI), the sustainable-energy nonprofit research group founded by Amory Lovins. Since the early 1980s, Lovins has been championing the virtues and economic benefits of passive-solar design and super-insulation; more recently, RMI helped spearhead a “deep retrofit” of the Empire State Building. So it’s only fitting that the institute, working with Portland, Ore.–based ZGF Architects, designed the Innovation Center to be the highest-performing building in one of North America’s coldest climate zones.

Remarkably, the project, located 6,600 feet above sea level, has no central heating or air conditioning. In winter, when nighttime temperatures regularly dip into the single digits, the building, clad in Colorado sandstone, zinc panels, and untreated juniper wood, stays warm inside largely because of its super-insulated envelope and passive solar features. In the summer, exterior venetian blinds cover the south-facing windows, controlling solar gain; at night, windows automatically open to draw in cooler air. A rooftop solar photovoltaic system generates enough electricity to meet the building’s energy needs—plus enough to charge four electric vehicles.

RMI, which celebrated its 35th anniversary in August, hopes the Innovation Center will inspire other architects, developers, and business owners to design similarly “deep green” office buildings. So how has the experiment fared? Is the project meeting its ambitious energy goals? How long will it take for the extra expense associated with achieving net-zero energy to pay for itself? (At a cost of $13.67 million, the project was no bargain.) For the 30 employees who now occupy the building, is it a comfortable place to work?

To answer these questions, we visited Basalt nearly two years after the center first opened, to discover if the project is indeed living up to its initial hype.

The Design Behind Net-Zero

The first design challenge for ZGF was to create a super tight building envelope. The Innovation Center’s walls are rated R-50; the roof, R-67. Both were built using foam-core structural insulating panels. The juniper on the exterior was chosen for its durability and was harvested from areas in Oregon where the wood has become invasive. Windows are quad pane and include two panels of Alpen Heat Mirror glass and two film layers; the gaps between the panes are filled with krypton gas, and the thermally broken framing is manufactured by Schüco International. Several of the window units did need to be replaced after they were installed because the film layers were wrinkled. It’s unclear whether the flaw was a manufacturer’s defect or occurred as the windows were being transported to the site. But they are now all functioning properly, says Cara Carmichael, a manager in the buildings practice at RMI’s Boulder, Colo., office.

Based on a blower-door test that determined the building’s air leakage—that is, the rate at which the air inside a building is replaced by air from outside—RMI has determined that the Innovation Center is 97 percent more airtight than conventional office buildings. In fact, at the rate of 0.36 air changes per hour, the center is one of the most airtight buildings the institute’s blower-door consultants have ever measured, Carmichael says.

By comparison, the International Energy Conservation Code specifies a limit of 3.0 air changes per hour in a comparable climate zone.

The rest of ZGF's design revolves largely around passive strategies. The building's long and narrow profile-just 52 feet wide in most places-and southern orientation (the south façade overlooks the Roaring Fork River) allow it to be almost entirely daylit, with supplemental illumination from overhead and desktop LED fixtures. Two interior light shelves, one on each floor's south-facing wall, help direct daylight deeper into the building and reduce glare. On the first floor, the architects gained an extra foot of ceiling height by running all the data, mechanical, and electrical systems within a cross-laminated timber (CLT) structure made of salvaged beetle-kill pine. The CLT sequesters carbon and reduces the need for concrete and steel, and the extra ceiling height helps maximize the building's daylighting and natural ventilation.

More than half of the office’s southern façade is made up of windows, which help capture solar heat gain in the winter. In addition, thermal mass—in the form of the building’s thick concrete floors—absorbs heat from the sun, computers, lights, and from the workers themselves, and releases it over time. In the summer, when the temperature indoors reaches 77 F, exterior blinds lower automatically to lessen additional solar gain. Some windows also automatically open to create a cooling “chimney” effect. If the forecast calls for an especially hot day (the control system collects data from the weather station at the airport in Aspen), the building will perform an automated “night flush,” opening some of the windows to cool the building before the employees arrive in the morning.

All of these factors help to maintain the range of inside air temperature that RMI established for the building: 67 F to 82 F. The institute had initially targeted 64 F as the low end, but that proved too ambitious in the winter. Still, the range is wider than in most office buildings, because other factors contribute to the level of personal comfort: the air speed, Colorado’s low humidity, radiant surface temperatures, and how employees bundle up or shed layers depending on the season. “We dress for the climate,” Carmichael says. “In the summer, it’s acceptable to wear short-sleeve shirts. Leave your suit and tie at home. And in the winter, wear a sweater. A lot of it is just common sense.”

On the very coldest winter days, an in-floor electric resistance radiant heating system, which is strategically located under carpeted areas around workstations, helps keep employees comfortable. The open-office plan allows air to circulate without a ducting system in warmer weather—though there is a highly efficient air-to-air heat exchanger and small ventilation ducts that bring in fresh air during colder temperatures.

The building boasts a few innovative features. Experimental battery-operated Hyperchairs, designed by Personal Comfort Systems, feature built-in fans and heating elements (think of a heated car seat) that employees can use to make their workspaces more comfortable. And hidden in the walls and ceilings is a vegetable-based phase-change material, encased in small pouches. The material liquefies on hot afternoons and absorbs excess heat, and then it solidifies at night, releasing the heat when the building is cooler.

But that’s pretty much it for newfangled tech. Almost all of the building’s energy-saving technologies are intentionally off-the-shelf. “We wanted people to look at it and see that net-zero is totally achievable, and it’s not that much more expensive to do,” Carmichael says.