The benefit of vertical-axis wind turbines, such as those in Chicago's Greenway Self Park (above), is that they make use of breezes coming from any direction, and at a variety of speeds. By chamfering the parking garage corner where the 12 turbines are, HOK increased the turbines' exposure to Second City winds.

The benefit of vertical-axis wind turbines, such as those in Chicago's Greenway Self Park (above), is that they make use of breezes coming from any direction, and at a variety of speeds. By chamfering the parking garage corner where the 12 turbines are, HOK increased the turbines' exposure to Second City winds.

Credit: Courtesy HOK

Project: Greenway Self Park
Architect: HOK
Location: Chicago

Despite their high-tech appearances and promise of free energy, building-integrated wind turbines have been criticized as ineffective, noisy, and incompatible with cities’ unpredictable wind patterns. One recent project that may prove more successful in matching wind energy with architecture is the Greenway Self Park, a partially self-powered, 11-story parking garage in downtown Chicago designed by HOK. The building’s dozen vertical-axis wind turbines, which are stacked in two double-helical columns along the southwest corner, have a specific, finite objective: Generate enough power to cover the cost of lighting the building exterior at night, including the elegant turbine system itself.

The design makes intelligent use of passive as well as active technologies for harnessing natural energy flows. Ventilation, for example, is accomplished without a mechanical plant because the garage’s porous skin—a tapestry of vertical cast-glass planks spaced at varying widths and overlaps—is at least 20 percent open on every level, meeting local code requirements. The client, Friedman Properties, saved several hundred thousand dollars on air handlers and ducts, according to HOK, and will also see savings on monthly utility costs. Interior light fixtures are conventionally powered, but shut off automatically in response to ambient daylight.

The 12 self-starting, lightweight aluminum S594 turbines, manufactured by Helix Wind, were selected for the relatively low wind velocity (11.1 mph) at which they start producing usable electricity, explains Todd Halamka, director of design for HOK’s Chicago office. Vertical-axis turbines can exploit wind from any direction at a wide range of velocities, a strong bonus for harnessing the fickle breezes of urban microenvironments. The more familiar horizontal-axis turbines—which resemble propellers—produce energy more efficiently, but they take up more space and are harder to integrate architecturally.

Each turbine rotates independently and is capable of producing up to 4.5kW of power. The Greenway Self Park’s two-way power meter allows the garage to give and take, redirecting electricity back to the Chicago utility grid whenever there is more energy produced than consumed. Although the turbines became fully operational last May, it will take two to three more years before their energy-performance data can be meaningfully assessed, Halamka says.

As is always the case with prefabricated or off-the-shelf components, the architect’s handling and presentation of these elements in context are integral to the project’s public character. HOK does well to give the turbines a prominent yet well-ordered presence by positioning them as two continuous vertical stacks against a chamfered corner facing the intersection of West Kinzie and North Clarke streets. The chamfer not only increases the turbines’ wind exposure, it also enables them to visually anchor and define the corner. Each modular unit, measuring 16 feet high and 4 feet in diameter, is clipped in to a dedicated support column, or “spine tube,” which transfers the turbine’s weight to the garage’s precast concrete structure. Uplights are mounted to the inside surface of the exposed façade beams. In this dynamic “hot corner,” as Halamka calls it, the turbines rotate like a “kinetic sculpture” in front of a bright-yellow glass backdrop.

Because the most efficient layout of parking spaces in a rectangular structure means no spaces in garage corners, the chamfer causes no loss of usable square footage. Similarly, the Greenway Self Park’s other three corners are put to work, containing stairs, elevators, and electrical hardware and transferring rainwater harvested from the building’s green roof down to street-level trees. And in a final nod to sustainability, the garage is also equipped with a dozen charging stations for electric cars.