Energy Lab at Hawaii Preparatory Academy
Stellar Student: A little more than a year after opening, a laboratory dedicated to the study of renewable energy is performing even better than the ambitious goals set by its project team.
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If any location offers ideal conditions for a net-zero, fully climate-responsive building, it's the site of the Hawaii Preparatory Academy's new Energy Lab. The $4.5 million, 6,000-square-foot facility, designed by Boston-based Flansburgh Architects, provides space for the study and development of renewable technologies, and sits at one corner of the private K-12 institution's upper-school campus in Kamuela, at the foot of the Kohala Mountains. With the exception of almost too-strong winds from the north, it offers excellent “resources” in terms of sun, precipitation, and relative humidity, says Ana Serra, an associate in the New York office of Buro Happold, the project's sustainability consultant.
The Energy Lab received a LEED for Schools Platinum rating in October, and in late April achieved full Living Building Challenge certification—only the third such project to do so. The “Challenge,” a program developed by the Cascadia Green Building Council and widely regarded as the most demanding green building certification system, requires that energy needs be satisfied on-site from renewable sources and that all of its water come from precipitation or from a closed-loop system. The program also prohibits the use of the potentially toxic substances on its “red list,” many of which are commonplace in construction materials. In addition, it places limits on the distance from which products can be shipped in order to reach a building site. In all, 20 “imperatives,” or prerequisites, must be met for a project to be designated as “living.” Bill Wiecking, the Energy Lab's director, compares the difficulty of Living Building certification with going to the moon. But LEED certification, with its Silver, Gold, and Platinum plaques, “is more like winning the Olympics,” he says.
To make the most of the site's natural assets and satisfy the project's goals, the team developed a scheme made up of three long and narrow volumes that step down with the landscape and open to views to the south. These volumes echo the materials and structural systems of buildings elsewhere on campus: They have walls of boards and battens and poured-in-place concrete and roofs supported by wood decking spanning glue-laminated beams. The uppermost barlike element has a double-pitched roof canted so that it nearly touches the ground and deflects the strong wind from the north. The two lower volumes are sheltered under gently sloping shed roofs with deep overhangs that shield the interiors from heat gain.
In addition to providing shelter from the elements, the roofs also provide surfaces for energy production and rainwater collection. The two shed roofs incorporate 27 kW of generating capacity, with three types of photovoltaics (PV), including a 4 kW array of bifacial panels (a type of PV in which the back face generates electricity from ambient light reflected off surrounding surfaces). The precipitation that falls on the roofs feeds a 10,000-gallon storage tank that provides water for hand washing, toilet flushing, janitorial needs, and irrigation.
Spatially, the building is organized to support what Flansburgh president David Croteau calls “project-based learning.” The first zone is divided into rooms where students develop ideas in small teams, while the two more open, lower parts of the lab house workstations and a workshop. Here they refine their concepts with computer simulation tools and build physical mockups. Several decks provide space for outdoor instruction and prototype testing.
Various types of analyses, including computational fluid dynamics, helped the project team optimize the design for natural ventilation. The resulting configuration has a series of openings controlled by the building management system (BMS) with louvers tucked under the low-level overhang at the building's north edge that let in fresh air. High-level louvers and clerestory windows allow spent air to escape via the stack effect, a phenomenon assisted by the pressure differential created when the mountainside winds waft over the roof.
The energy-conservation and -generation strategies have proved so effective that in the first year of operation, the building consumed only a little more than half of the power predicted by the design team's model, and exported 25,285 kWh of electricity produced by the PVs to the campus grid (about 60 percent of the power generated). Exhaust fans, intended to augment the natural ventilation scheme, have so far not been needed. And a backup split air-conditioning system, included in the building primarily to keep sensitive lab equipment cool in extreme conditions, has also never been used.
Several factors account for the building's even-better-than-expected performance. The most important is a difference between the microclimates at the building site and at Hilo Airport—the location where the U.S. Department of Energy (DOE) collected the historical weather data used in the simulations. Although the airport is the closest site with such information, it is situated at 38 feet above sea level and on the coast, while the Hawaii Prep campus, about 60 miles away, is at a much higher elevation and further inland. Now that the energy lab has been open and collecting data from its own rooftop weather station for more than a year, it is clear that the actual conditions at the site are much more favorable for natural ventilation than the DOE data indicates.
Wiecking's vigilance also plays a significant role in the lab's efficiency. The BMS, which he designed, depends on about 600 sensors distributed throughout the building that monitor everything from CO2 levels, temperature, and humidity to power generation and consumption. It automates the operations of many of the building's systems and gives Wiecking real-time information about such factors as energy generation and use. It even allows him to identify specific equipment that has been left on mistakenly, such as a printer or the UV lamps that students use for experiments.
Although these controls are extremely sophisticated, they were hardly the most effort-intensive part of the project, according to the team. Instead, the task presenting the biggest challenge was finding materials from within the Living Building program's allowed transportation radius that were free of prohibited substances. “We must have rewritten the specs three times,” says Chris Brown, Flansburgh project architect. One illustration of the difficulty surrounding materials selection is the acoustic panels needed to satisfy LEED for Schools requirements. The only off-the-shelf panels from nearby suppliers contained formaldehyde or flame retardant. So, to solve the problem, the contractors built their own from locally available wood, recycled cotton core material, and hemp canvas.
Given all the effort involved in meeting the requirements for both Living Building and LEED certification, it is somewhat surprising that the architects like to point out that the Energy Lab, at least at a quick glance, doesn't seem overtly green. “It doesn't scream ‘sustainable building,' ” says Croteau. “It is just real architecture, appropriate to its climate and its context.”