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Hawaii Gateway Energy Center

Credits: ©2009 Green Source/Tristan Roberts

The gateway energy center at the Natural Energy Laboratory of Hawaii commands a view of the Pacific Ocean any Hawaiian vacationer would envy. The 3,600-square-foot center consists of two buildings side by side - a conference and educational center and a smaller administrative space. But what overwhelms the building, appearing like a technological interloper in a natural ecosystem, is a white steel truss system supporting several sets of photovoltaic panels—some of them pointing up into the sky from the roof of the building, some of them shading the project’s front patio entrance and steps from the parking area. Altogether, the 20-kilowatt grid-tied system is currently providing 10 percent more energy than the building needs.


Hawaii Gateway Energy Center

Thermal chimneys emerging from the building’s roofs help power a passive cooling system that reduces energy needs, while a photovoltaic array supplies 110 percent of the energy needs. ©2009 Franzen Photography/GreenSource

Architect Bill Brooks, AIA, of Honolulu-based Ferraro Choi and Associates, intended the design of Hawaii Gateway Energy Center in Kailua-Kona, Hawaii, to catch the eye of passersby. Will Rolston, the Hawaii Gateway manager, reports it’s working. “Visitors come up the stairs with their eyes wide open,” says Rolston, noting that, according to a visitor survey, 70 percent of visitors, many of them passing the building while traveling to or from the island’s main airport, come because they notice the unique structure. “If they are people with energy backgrounds, you can tell it puts them in a place where they think about what is possible.”

In a reversal from the typical effort to reflect heat away from roofs, this building’s curved copper roof is designed as a heat collector. The sun heats air in a plenum under the roof, inducing stack-effect ventilation. The hot air rises out of a set of thermal chimneys, siphoning fresh air into the building at a rate of 12 to 15 air changes per hour through an underfloor plenum. That air enters the building through a small exterior structure that houses coils containing 45°F seawater pumped from 3,000 feet below the ocean’s surface. The coils cool and dehumidify the air. Water that condenses on the coils drips into a collection system and is used to flush toilets and irrigate plants. Despite Hawaii’s hot, humid climate, “the building is pleasant, almost too cool for some people,” says Rolston.

The innovative passive cooling system changed radically over the design process, says engineer Shayne Rolfe of Lincolne Scott, the project’s mechanical, electrical, and plumbing consultants. “We first put together a concept sketch with some preliminary modeling. At that point it was really a square building with a 64-foot-high thermal chimney sticking out the top,” Rolfe says. “Bill came back with the idea of laying it down a little, so that we had an angular chimney.” The engineer embraced the design of multiple chimneys, each three feet in diameter, which, with the angularity, helped improve the system’s functionality. “From then on, it became more of a conventional mechanical design process,” Rolf says.

Although the truss system appears ready-made for the photovoltaic panels it holds, it was originally designed to support long chimneys. When the plenum under the roof became part of the thermal chimney, computer simulations showed the chimneys did not need to protrude far enough to warrant the trusses. Meanwhile, the client had arranged with the local utility to provide the photovoltaic array and the trusses again had a use.

The passive conditioning system was made possible by the availability of cold seawater, offered by the state to the renewable energy campus and adjoining aquaculture facilities for $0.32 per thousand gallons. A pump circulates the seawater as needed through the cooling coils, representing the only moving part and only electricity use in the space-conditioning system. Experience with the facility has shown that in a south wind, which is most common, the thermal chimneys work well. The air exchange rate is too low in a north wind, however. The photovoltaic panels, not originally present in computer modeling, deflect the north wind into the chimneys, counteracting their draw. The designers are working on modifications to resolve this problem. The airflow rate also decreases under cloudy skies, but so does the need for cooling. “You can really notice the building breathing when the sun goes behind clouds,” says Rolfe.

To reduce solar penetration in this hot climate, the project team oriented the energy center on an east-west axis. Daylighting provides all of the building’s lighting needs during business hours, with overhangs blocking direct sunlight. Occupancy and daylight sensors control the lights, which never come on during daytime, according to Rolston. Located on the barren landscape of Hawaii’s pahoehoe lava, the building does not disturb the site beyond its footprint. For irrigation of native plantings, the project again uses the thermal energy of the cold seawater. The plants are watered with vapor that has condensed on cold-seawater pipes running over the ground like a drip irrigation system but with water dripping off of the pipes instead of out of them.

A project with this many innovations could only result from a fully integrated design process. The client wanted an environmentally responsible building, with a request for proposals that emphasized sustainability. “We had a team that was purposefully constructed to be highly motivated to do something sustainable,” says Brooks. Even without experience on green projects, a contractor based on the island beat several off-island contractors for the job. “They became totally invested in the idea that they were one of the first contractors in the state working on a sustainable project,” says Brooks. About the engineering firm, Lincolne Scott, Brooks adds, “They came from a mind-set of ‘Let’s go for it; let’s do something different.’”

Completing the project on its $3 million budget was a challenge, in part due to construction costs. “It’s a contractor’s market on the island,” says Brooks, noting the limited pool of contractors and the need to import building products. The team found most LEED credits were applicable to the project, making LEED Platinum achievable, but the building performed poorly in the materials-and-resources category. “To use local materials [which can earn LEED credits], you’re restricted to a few selections, which normally boil down to concrete,” says Brooks. “Everything else is imported.”

Despite the building’s exemplary energy performance, the project faced an obstacle attaining LEED Platinum in energy use. “LEED calculation doesn’t account for passive ventilation systems that work like mechanical systems,” says Brooks. Since the building has no mechanical cooling system, LEED compared it with buildings with no cooling systems at all, which negated the energy savings achieved by its passive system. The project achieved the maximum number of energy points possible by leaning on its renewable energy generation, Brooks notes. According to the energy analysis performed by Lincolne Scott, the building performs 54 percent better than an ASHRAE 1999-90.1 base case using a conventional cooling system.

The building was commissioned by Environmental Economics, although, says Brooks, “there was not that much to commission since our building is designed to move air without moving parts.” The commissioning called for some corrections with daylight sensors and lighting, and the process also resulted in refinements to the rate of flow and pressure in the on-site seawater pump, resulting in significant energy savings. “The whole idea was to circulate only enough seawater to allow proper cooling,” says Brooks, and the team is still refining that balance. “We think [pumping energy] can still go down 10 percent to 15 percent,” he notes.

The center won an AIA/COTE Top 10 award for 2007. Speaking for the jury, Traci Rose Rider said, “We were impressed by the way they blended active and passive technologies. It’s really using all of earth’s devices, then dramatizing that with this visible structure.”

With the center fully booked with educational sessions, the attention garnered by its architecture has also brought attention to the need for renewable power in Hawaii. Even passing aircraft seem to change course to get a better look at the building, says Rolston, noting “Sitting out there on the lava, it’s an interesting thing to see.”

Additional project information from Architecture 2030:
Kailua-Kona, HI United States
Architect/Engineer: Ferraro Choi And Associates, Ltd.
Owner: Natural Energy Laboratory of Hawaii Authority
Building Type: Governmental
Year Built: 2005
Size (SF): 3,600
Cost/SF: $593.00 per square foot
LEED Level: Platinum
Renewable Systems: PV
% Load Met by Renewables: 100
Energy Use Intensity (EUI): 43.1 (Total); 20 (Non-Renewable)
HVAC: Natural Ventilation, sea water cooling for slab and air
Lighting: Daylighting
Envelope: Shading, thermal mass, well insulated
Controls: Energy Highlights: The building was designed with an onsite, photovoltaic array. When the building was constructed, this provided about 50% of the total energy needed to run the seawater pumps, lights, and other electrical equipment. A pump adjustment, in 2006, allows the photovoltaic system to now provide all of the energy needed on site. The building is designed to consume about 20% of the energy that would be required by a comparable building designed in minimal compliance with ASHRAE 90.1-1999.


Hawaii Gateway Energy Center Case Study (USA)

Ferraro Choi Architects (Hawaii, USA)