Two weeks ago in Portland, Oregon, a new 23-story building added something you don’t usually see in an urban setting: a series of four Skystream wind turbines, with a total capacity of 9.6kW.
There are several reasons why wind turbines are a rarity atop high-rises — beyond the obvious and insidious one: our power infrastructure makes changing from traditional sources of electricity difficult, expensive and, seemingly, unnecessary.
Wind power in an urban setting comes with its own set of challenges.
A natural lack of regular winds forceful enough to generate meaningful amounts of electricity.
Most “wind farms” are located in areas with high, steady winds and use giant turbines. The one on the left is on a floating platform off the UK in the North Sea.
In fact, the trend has been to build larger windmills capable of generating ever more electricity.
In 2006, Technology Review ran an interesting piece about plans for a new turbine with a rotor with a 140 meter diameter.
In an accompanying graphic, the magazine showed a series of existing turbines in relation to the Washington Monument. (The largest turbine was the REpower 5MW behemoth with a diameter of 126 meters.)
Sometimes, however, smaller still is beautiful — and more appropriate.
So some manufactures, like the Flagstaff, AZ, based Skystream, have been building scaled down wind turbine like the ones on top of Twelve|West.
One advantage of the Skystream 3.7 is its lower wind speed requirement. With its 12-foot diameter, the rotor can begin generating electricity with winds blowing at just 8 miles per hour. It reaches peak production (2.4kW) at 29 mph and will continue to operate at winds up to 60 mph. (The Skystream 3.7 is built to withstand gusts of up to 140 mph.)
Wind flow in urban areas is disrupted by other buildings.
Placing the turbines on top of a 23-story building, and then mounting them on 45-foot poles puts the blades at an elevation of 82 meters (270 feet), high enough to escape the distortions of the surrounding built environment.
Still, critics of the project have said that the expense of putting the four turbines into operation outweighs the financial payback delivered in energy savings.
But Robert Packard, a managing partner of the architectural firm ZGF, which occupies the lower four floors of Twelve|West and also designed the building, thinks those critics are missing the point. Packard told the Oregonian newspaper, “[We’re] trying something new. It’s not a gimmick. Not only are we learning, but we can share it with the world, add to the body of knowledge that’s out there.”
Other Green features of Twelve|West
The building is a showcase of green innovation. The information below was provided by ZGF.
Rising 23 stories above Portland, Oregon’s evolving West End neighborhood, Twelve|West is a mixed-use building designed to receive two LEED Platinum Certifications and serve as a laboratory for cutting edge sustainable design. It features street level retail space, four floors of office space for ZGF Architects LLP, 17 floors of “eco-chic,” homes for lease and five levels of below grade parking. The building has an eco-roof, rooftop garden and terrace space, complete fitness studio and a theatre. Four visible wind turbines sit high atop the building representing the first U.S. installation of a wind turbine array on a high-rise. Twelve|West serves as not only an anchor in a rapidly transforming urban neighborhood, but also as a demonstration project to inform future sustainable building design. Twelve|West is on track to achieve two LEED Platinum certifications—one under New Construction and a second under Commercial Interiors for ZGF’s offices.
Because the lower floors of the building are dedicated to commercial activities, all of the building’s apartments rise above the surrounding rooflines, offering unobstructed views in all directions. The 272 Indigo @ Twelve|West apartments, which begin on the 6th floor, offer a mix of studios, one-, two-, and three-bedroom units ranging in size from 541-2125 square feet and include three floors of penthouse homes.
Sustainable materials are used throughout the apartments, including bamboo veneer casework in kitchens and bathrooms, carpet in bedrooms that has 25% recycled content, granite counter tops in kitchen and baths, PVC free window coverings, zero VOC paint, low flow plumbing fixtures and Energy Star appliances. Beyond the high-quality design aesthetic and environmental stewardship of the building, residents can enjoy other amenities including a 21-seat screening room theatre, a workout room and a rooftop amenity room and deck.
The amenity room has full height glass windows on three sides which protect residents from the elements but provide sweeping view of Portland. The room is anchored by a stone wrapped fireplace on one side and a kitchen on another, plus a large community dining table and living room furniture that can be rearranged easily or stored to allow the room to be utilized for dinner parties, catered receptions, meetings, yoga classes, etc. The amenity room has sliding glass doors that open to an adjacent roof deck that has two fire pits and two built-in gas barbeques. The 6,000 SF roof features several other outdoor, yet protected seating environments which allow multiple groups to enjoy the space at the same time.
The design team made the bold decision to incorporate building-integrated wind turbines into the design of Twelve|West, a process that led not only to the mounting of four wind turbines on the tower’s roof but more importantly, to a body of research that will help advance the application of building-integrated wind power and provide a roadmap for others.
The elevation of the turbines, rising 270’ above ground, places them well above the major turbulence caused by the irregularities in the built environment below. But to determine the best location, the team took into account urban topography, weather data and seasonable variability of wind directions and then built a large scale physical model of the building to test in the wind tunnel. This in-depth analysis and testing allowed them to determine the best location on the roof for the wind turbines to capture smooth, ambient wind flow from two dominant wind directions.
The 12’ diameter horizontal axis turbines from Southwest Windpower feature a passive yaw or rotation system that orients the turbine blades to the wind and the downwind blade design eliminates the need for a tail or other orienting device. The turbine has undergone extensive testing at the National Wind Technology Center in Colorado and has been approved by all major certification programs.
The turbine array is predicted to generate roughly 10,000 Kwh per year. Recognizing the ground-breaking rigor of investigation into this untested application, local and state agencies agreed to fund the entire system’s cost through renewable energy grants.
Modeling predicts that energy efficiency strategies utilized in the building will reduce consumption of energy by more than 44% and exceed the 2030 Challenge benchmarks for this project type. Some of the efficiency measures include: thermal mass; daylighting and occupancy sensors; low-flow fixtures for reduced domestic hot water demand; high-efficiency equipment; heat recovery; fan-assisted night flush of the office floors; chilled beams and under floor air distribution in the office floors; and CO2 sensors for ventilation demand control in large volume spaces.
Located within Portland’s urban core, the project takes advantage of existing public transportation infrastructure (bus, light rail, and streetcar) and nearby walking and biking opportunities, the latter of which is supported with on-site bicycle storage for residents and office workers, and locker and shower facilities within the ZGF office space. Moreover, the existing site transformed a surface parking lot and a low-rise commercial building into a site with vastly improved stormwater attenuation and habitat potential.
Water efficiency is achieved through a combination of conservation and stormwater reuse. The building has a 50,000 gallon storage tank in the underground garage, part of which is dedicated to fire suppression, with the remaining 22,000 gallons devoted to reuse in irrigation and toilet flushing. This system, which gathers and filters runoff from the rooftops as well as condensation from the mechanical system, is projected to reuse 286,225 gallons annually, utilizing 59% of the rainfall to the tower’s roof surface. As a result, 100% of the green roof’s irrigation needs, and 90% of the office’s flushing demands, will be met by the volume of non-potable water collected from the building.
The roof of the building features a 6,000 SF terrace and eco-roof, the latter of which serves to both mitigate stormwater and reduce the building’s heat island effect as well as provide a green amenity for the building’s residents. To that end, the roof features plants of various shape, color and size, including an array of plants with varying leaf types and colors that evolve with each season. A mix of evergreen and deciduous plants plus seasonal flowering bulbs and grasses add to the changing display, and well-placed deciduous trees help frame some of the views to the east and west.
Indoor Environment and Comfort
Office ventilation, cooling and heating is mostly achieved through a combination of an Underfloor Air Distribution System (UFAD) and natural ventilation through operable windows. The UFAD system delivers air directly to the occupied zone near the floor at more moderate temperatures and velocities than a conventional ventilation system, using less energy and providing better occupant comfort. The system also provides individual control of air flow via adjustable diffusers at each workstation.
On particularly hot days passive chilled beams will add cooling capacity to keep the office space comfortable. Passive chilled beams are perforated metal panels mounted near the ceiling and chilled with cold water tubing. As air in the office space is warmed by the sun, people, and equipment it will rise toward the ceiling, be cooled by the chilled beams, and fall once again to the floor to keep inhabitants cool. Passive chilled beams save energy over conventional systems by moving heat with water instead of air, and by moving air without the use of fan energy.