The Council House 2 (CH2) building

The collaboration between two Australian firms on Melbourne’s new Council House 2 shows off the design possibilities for building-integrated HVAC.

The city of Melbourne intended CH2–the Council House 2 building, which opened in August 2006–to exemplify the best of high-performance, sustainable design as a model to other Australian cities. The 10-story, 135,000-square-foot city office building, which occupies a dense block adjacent to an existing city building in the heart of Melbourne, incorporates a number of radical strategies, like sewer mining for nonpotable water and the use of phase-changing materials in lieu of conventional chillers for cooling water. But it’s the integration of these performance strategies–particularly in the building’s mechanical systems–with the architecture that makes CH2 stand out as a case study, even for less ambitious projects and designers.

Melbourne has long been considered a hotbed of architectural experimentation, a distinction that is waning, much like the diminished visual shock of the landmark Federation Square designed by Lab Architecture Studios that opened in 2002 [record, June 2003, page 109]. This penchant for wackiness is lately being replaced by a more overt expression of sustainable design, such as in Grimshaw Architects’ naturally ventilated Southern Cross rail station [record, May 2007, page 243] and, just as visibly, in CH2, designed as a collaboration between DesignInc’s Melbourne office and Sydney-based engineers Lincolne Scott. It’s as if the designers of the Southern Cross and CH2 projects sought to fuse the city’s past obsession with form-making to a more recent concern: climate change.

The Nature of Architecture

It’s probably safe to say that the average architect doesn’t think much about atmospheric pressure cells, let alone competing cells moving counterclockwise that can completely alter a city’s weather in the course of half an hour. Melbourne architects complain that, due to such atmospheric conditions, the city experiences all four seasons in one day. DesignInc’s Mick Pearce saw opportunities in these circumstances for the design of CH2. Pearce has long adhered to a philosophy of biomimicry, whereby artificial systems–like those in a building–are designed to “mimic” the processes of nature. The biologist Janine Benyus, who Pearce knows well, documented such things in her book Biomimicry: Innovation Inspired by Nature (1997). Pearce implemented the approach with his design for the 1996 Eastgate building in his native Harare, Zimbabwe–a building long-considered a landmark in sustainable design. That naturally ventilated office building relied on basement rock piles as thermal storage for free cooling in a building designed to mimic an African termite mound. “We’re beginning to see a whole new science of biological design,” says Pearce. “It’s much closer to the thinking that goes into a zoo than an office environment.” He connected with the CH2 project through his friend, Rob Adams, who, as Melbourne’s director of city design and urban environment, is largely credited with championing the high-performance design goals of the building. And thanks to Adams’s advocacy, CH2 is the Green Building Council of Australia’s first Six Star office building, which is roughly equivalent to LEED Platinum.

As the sun drifts west, the timber panels slowly close. The phase-change-material tanks in the basement are part of the comprehensive HVAC strategy for the CH2 building. The diagram developed by DesignInc  illustrates how fresh air supplied from the roof circulates from the south side and down through the building before it exhausts through ducts integrated into the north side of the structure. A roof deck provides an up-close view of wind turbines. - Photos © Russell Fortmeyer

With CH2, Pearce and his colleagues at DesignInc sought to implement similar strategies employed at Eastgate, but within the requirements of Australia’s version of a Class A office building. “Our climate analysis showed using thermal mass would work well, but Melbourne’s pressure cells cause an interval of about three days between hot and cold periods,” Pearce says, explaining that rock piles would have needed to be extremely large in order to store heat or cool long enough. “This three-day period is what we exploited with the design. The challenge was to go for serious thermal mass, as well as good thermal storage.” From the street, the three most public facades on CH2 actively convey this environmental message: hydraulically controlled recycled timber shutters on the west side automatically open and close depending on the sun’s position; balconies with planter boxes on the north shield windows; and the south is defined by fresh-air shafts integrated from the roof down, set behind five so-called “shower towers” that act as exposed cooling towers for the mechanical system.

DesignInc had devised a preliminary scheme that called for tearing down an existing building adjacent to CH2’s site, but they scrapped the idea based on the recommendation of the engineers at Lincolne Scott, who were brought in to help rethink the project. Over a three-week charrette in 2003, which included city representatives, architects, and engineers, among other interested parties, the team developed a schematic design incorporating many of the strategies eventually realized in CH2. Ché Wall, managing director of Lincolne Scott and its Advanced Environmental Concepts group, says that “after the charrette, we had 85 percent of the engineering design done.” But he adds that the more riskier items were isolated in the design so they could be replaced by conventional strategies in case they failed to perform as expected.

The original plan for CH2 called for a naturally ventilated building, but Wall says once it became clear that the building would need to meet the highest standards for occupant comfort when compared to commercial offices in the local market, they decided against natural ventilation because of noise and air-quality concerns in the busy central business district location. Instead, to maintain 75 degrees Fahrenheit in the building, the designers embraced a combination of passive and active HVAC systems. This meant the floor plate–with a width of nearly 69 feet–was not as narrow as originally proposed (a narrow floor plate assists in cross-ventilation), but it also meant the designers needed to take a more holistic view of how the HVAC systems would be integrated into the structure and architecture.

The Sum of All Parts

The success of that integration is felt every day. Consider an operational profile of the building on a warm day–Melbourne’s temperatures average 80 degrees F in January–as experienced by an occupant sitting at her desk in the open office plan of the sixth floor. The building’s concrete structure, poured with 30 percent fly ash, and its wavy, 7-inch-thick precast-concrete ceiling panels both cool down when windows automatically open from 1 to 6 a.m. to allow in night air. This lowers the office’s temperature 4 to 5 degrees and is directly responsible for a 14 percent energy savings for cooling. The ceiling is wavy for two reasons: first, to increase the surface area of thermal mass, and second, to create cavities used for exhaust air. Wall says they researched laser etching the concrete ceilings to double the surface area, but it proved too expensive (although, analysis showed it would have significantly improved the thermal properties). However, the ceilings are sandblasted, which does increase surface area.

Once the occupants arrive in the morning, air-handling units on the roof kick on and supply filtered, 100 percent outdoor air to cast-concrete ducts running down the building’s south elevation. These ducts tie into the 6-inch, pressurized cavity of the raised floor on each level. “That’s quite tight compared to most access floors,” Wall says, a decision he says was made in order to preserve market-rate floor-to-floor heights of nearly 10 feet. The air, which is treated for humidity depending on the wet-bulb temperature of the outdoor air, enters the space via floor-mounted, user-controlled “twist” diffusers at each workstation. This cool air heats up and rises through the space and, induced by the stack effect, is pulled into slots along the ceiling panels and into cavities where it exhausts into shafts designed into the north elevation. These shafts exhaust through rooftop-mounted wind turbines. Matthew Jessup, a principal at Lincolne Scott, says computational fluid dynamic (CFD) modeling–and, now, postoccupancy studies–illustrate that this combination of night flushing, thermal mass, and mechanically supplied fresh air has been more than enough to keep occupants cool the entire morning and, on milder days, well into the afternoon.

During warm afternoons, however, the building shifts from a passive mode (where outside air is simply moved around) to an active mode that depends on mechanical cooling. The most novel aspect of CH2, in this respect, is the use of radiant panels attached to the underside of the precast-concrete ceiling units. Mechanical engineers like to call this a “chilled beam” or, in some cases, a “chilled ceiling.” Long a solution embraced in Europe, chilled beams have yet to significantly catch on in the U.S. or Australia. For a conventional installation, the beams, which are basically metal tubes, are filled with chilled water supplied by a central chiller. “Using water as a medium for cooling is much more efficient than moving cold air around the building,” says Wall.

At CH2, the beams are supplied with chilled water from two sources: an innovative phase-change-material-based storage tank in the basement and a more conventional rooftop central plant consisting of a gas-fired cogeneration plant. Phase-change materials (PCMs) are natural compounds, generally salt-based liquids, that collect and then release energy. This typically occurs from a liquid to solid state and vice versa. PCMs are basically a more efficient version of ice storage, where engineers have taken advantage of cheap energy at night to make ice, which can then be melted during the day to provide chilled water to a building. And it’s much more efficient when compared to Pearce’s original concept of using rocks for thermal storage.

The chief benefit of PCMs is that they have a significantly higher freezing temperature (around 60 degrees F) than other substances, which means water returning in the loop system via evaporative cooling towers needs to be cooled less than usual. Although HVAC systems using PCMs have been installed in the U.S., they are relatively uncommon anywhere. At CH2, the 30,000 PCMs–they look like baseballs–divided among the basement’s three tanks can be used 80 percent of the year. Otherwise, the chilled beams rely on the rooftop chiller and cooling towers during peak loading conditions in summertime, which is typically the last 2 hours of the work day. The architects supplemented the cooling towers with so-called “shower towers,” which act like public art anchored to the south elevation. The towers are 40-foot-high, 5-foot-diameter vertical shafts of ETFE material with a shower head installed at the top and a glass catchment basin at the bottom. The towers provide chilled water to the mechanical system (cooling it nearly 10 degrees F), while also cooling the air for ground-floor retail spaces. Wall says the towers cool water much more efficiently than the CFD analysis originally indicated. At night they glow like five tubes along the column lines, while water cascades across the glass basins. Pearce likes the way the towers add to the building’s dynamism–the moving wood panels on the west side, the spinning rooftop turbines, and the sway of the plants on the north side–all sustainable signposts meant to engage the city’s residents.

The description of CH2’s mechanical system can make it sound easy to accomplish, but many nuanced considerations and details are required to make it work. For one, Wall says they had to install chilled beams at windows to cut the heat load from sunlight but were able to incorporate the beams into light shelves that could be used to control daylighting. A common concern regarding chilled beams and ceilings is condensation, a topic that raises Wall’s ire. “As an engineer, I find this topic hugely annoying because we only have to maintain indoor humidity between 40 and 60 percent,” he says. “In a museum, you need 45 to 50 percent humidity, so anyone saying you can’t do a chilled beam in this city is saying you can’t design a museum.” Since CH2 isn’t naturally ventilated, the facade was designed to be relatively airtight, helping to prevent condensation problems (the HVAC system also offsets high humidity when the windows open for night purging). All of this is monitored with the building management system through 2,500 probes and control points located throughout the structure. So far, the mechanical system hasn’t had major problems.

By far, the most challenging aspect of the building’s systems has been the unusual sewer-mining plant in the basement. This system draws nearly 12,000 gallons of raw sewage per day from the city’s drains, filters out the physical waste, and then treats the water through a series of high-tech components. Coupled with a rainwater collection system, the mining plant supplies all of CH2’s nonpotable water requirements, including the HVAC system. Eventually, it’s hoped that the plant will feed nonpotable water back to the city for fountains and irrigation, as the system is designed to handle 26,000 gallons per day. “This system uses one-third the energy of a desalinization plant,” Pearce says, in sly reference to political plans afoot for such a plant in the Melbourne area, a region long-plagued by drought.

From Energy to Occupancy

The designers and the client for CH2 all stress that while energy and water savings are worthy goals, the comfort of the occupants is the ultimate reason for the environmental strategies deployed in the building. Pearce says a hallmark of the Australian attitude toward sustainable design in offices is equity–thus, an occupant on the top floor would have a similar environmental quality as one on a lower floor. At CH2, windows narrow toward the upper floors and widen toward the lower, so intense daylight at the higher offices will appear similar to lower floors. To ensure equity, DesignInc and the city are working with the London-based postoccupancy expert Adrian Leaman, with the Usable Buildings Trust, on statistically gauging occupant satisfaction with the work environment in the next several years.

John Williams, a director in DesignInc’s Melbourne office, says the city has invested so much into CH2 in hopes that it could influence the development of subsequent buildings, including housing, that involves city government. The city projected a 4.9 percent increase in effectiveness for the staff of 540 employed in the building, which translates into nearly $1 million in annual savings. Seeing those goals through was always Pearce’s aim. He says he “likes to come to a place, build a building, and stay there afterward to make sure it works.” He adds, “That’s the only way you can find out about your own profession.”

By Russell Fortmeyer (Architectural Record)

Groups advance two sets of high-performance building standards

In the not-too-distant future, there could be two U.S. standards for green buildings. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), in conjunction with two other industry organizations, is developing the Standard for the Design of High-Performance Green Buildings Except Low-Rise Residential Buildings. Meanwhile, the three-year-old, nonprofit Green Building Initiative (GBI) is also working toward establishing its Green Globes rating system for commercial buildings as an official standard. Both organizations are following the protocols of the American National Standards Institute (ANSI) and expect to release fully completed and approved documents by the end of 2008.

The ASHRAE initiative, also known as Standard 189, is being developed with the U.S. Green Building Council (USGBC) and the Illuminating Engineering Society of North America (IESNA), and could ultimately become a prerequisite under the LEED rating system. The organizations recently released a second draft of the standard for public comment. Until April 7, 2008, the document is available at www.ashrae.org/publicreviews.

With 189, ASHRAE and its partners hope to provide a baseline definition of green building in code-enforceable language. The standard is conceived as an appendix to the International Building Code that jurisdictions could adopt “and code officials would understand how to enforce,” explains Kent Peterson, ASHRAE president and a principal of P2S Engineering, based in Long Beach, California. Although many cities and states have incorporated LEED, and to a lesser extent Green Globes, into green-building legislation and executive orders, the rating systems were not originally devised for that purpose. “Jurisdictions have adopted the rating systems, but they are struggling to interpret them,” says Peterson.

In contrast to the code- ready format of 189, the GBI standard would not be written in “mandatory” language. It would establish guidelines for multiple building-performance levels designated by one to four “globes.” According to Vicki Warden, GBI’s vice president of commercial programs and product development, “the standard is not intended to elevate code, but to be an incentive for achieving higher levels of performance.” The group plans to release its first draft for public comment sometime this spring.

Standard 189 will address sites, water use, materials, and indoor air quality, among other issues. It is also part of a set of ASHRAE initiatives aimed at helping teams design more efficient buildings, with the ultimate goal of creating net-zero-energy buildings—those that consume no more energy than they generate on an annual basis. The ASHRAE net-zero initiatives were outlined at the organization’s winter meeting held in New York City in late January. These include a set of Advanced Energy Design Guides, a series of publications tailored to specific building types and providing guidance for achieving 30 percent energy reduction. A set of 50 percent energy reduction guides is due to be published later this year. Eventually, ASHRAE plans to offer a series focused on net-zero buildings.

One goal of standard 189 is to achieve a 30 percent reduction in energy cost over the 2007 version of building energy standard, ASHRAE/IESNA 90.1. Standard 189 will also contain a requirement that a minimum of 1 percent of peak energy come from renewable sources and is generated on site. With each revision of 189, the energy-efficiency and renewable requirements would become more stringent, “so that we are approaching net-zero energy by 2030,” Peterson says.

By Joann Gonchar, AIA

In Canada, a rammed-earth wall for the ages

The relationship between architecture and nature rarely gets more explicit than with rammed-earth construction. The 18-foot-high western exterior wall of the Nk’Mip Desert Cultural Center in Osoyoos, British Columbia, stretches for 260 feet, making it the longest rammed-earth wall in North America, according to Vancouver-based Hotson Bakker Boniface Haden Architects (HBBH). But the size is downplayed by the ruddy material, much of which was excavated on-site to capture the desert colors of the South Okanagan Valley.

Bruce Haden, a principal at HBBH, says he tried to resist the traditional choice of ersatz regional architecture, like that found in Santa Fe’s fake adobe buildings. “We wanted a building that was simultaneously modern and spoke to the landscape and the contemporary traditions of the Osoyoos Indian Band,” he says. Although the 12,000-square-foot center—used as an exhibition and meeting space by the Osoyoos—disappears behind the earthen wall and under a vegetated roof, these two highly visible sustainable design elements support a comprehensive energy-efficient project that also relies on radiant heating and cooling.

The west-facing, 24-inch-wide rammed-earth wall, bolstered with an internal layer of Styrofoam insulation, performed well enough to resist summertime temperatures that can reach 100 degrees F. The wall consists of local dirt, with organic matter filtered out, combined in a mix of 10 percent concrete and color additives (to get that clean, layered look). Contractors from British Columbia’s Terra Firma Rammed Earth Builders laid down each strip and then mechanically tamped it down to 50 percent of its original height. Haden says it was more labor intensive and expensive than concrete, but his hope is to encourage more rammed-earth architecture in the region by training locals in the construction methods. “If this could become a more generic material, it could foster a modern and regional aesthetic,” Haden says.

By Russell Fortmeyer (Architectural Record)
Photo courtesy Brady Dunlop/HBBH

Learning to Live on Alternative Energy

Three landmark projects show us how to integrate renewable-energy strategies into architecture, without compromising design.

An alternative can only exist when we have a choice. Architects have that choice now when it comes to energy. We can incorporate alternative energy sources, even electricity generation, into our projects, or we can just hook them up to the grid and let someone else worry about it. There are advantages and disadvantages to both, of course, but soon we may reach the point where we have no choice, and then we will need to find ways to successfully integrate alternative energy strategies into our projects. The three case studies that follow—in Chicago, Washington, D.C., and New York—provide some answers.

Near North Apartments, Chicago, 2007

Near North Apartments, a year-old, 96-unit, single-room occupancy in Chicago, was designed by Murphy/Jahn and developed by the nonprofit organization Mercy Housing Lakefront as a model of sustainability. While most of the building’s green technologies, such as a graywater recycling system that flushes toilets and a rainwater cistern for landscape irrigation, are hidden behind the scenes, its most visible ecofriendly feature is also its most experimental: A horizontal-axis wind-turbine system created by Chicagoan Bil Becker forms a lacy crown atop architect Helmut Jahn’s streamlined design.

Becker is a professor of industrial design at the University of Illinois and the founder of Aerotecture. Although he first applied for a patent for the Near North installation’s technology in 2000, his research dates to the 1970s. Becker, an acolyte of Buckminster Fuller, won in 1979 one of the Carter administration’s last research grants devoted to alternative energy.

“Windmills only work out on the farm,” Becker says of his first foray into an urban turbine almost three decades ago. But although capturing urban wind offers the opportunity of producing clean energy within cities, the location of the turbines also entails special limitations. Specifically, if a turbine were to display “runaway” behavior, throw ice, or transfer high vibration or sound loads to interior occupants, its chances of gaining a building permit would be slim.

Four years into his research, Becker realized that traditional propellers were not commensurate with urban needs, and in the following three years, he experimented with helical blades: In wind-tunnel environments, cardboard models of this Savonius rotor did not require much wind speed to start turning. Moreover, “They wouldn’t overspin. They would get in their own way rather than fly faster and faster, because it has a limited amount of lift—about 10 percent lift to 90 percent drag, he says.”

Becker proceeded to combine the Savonius rotor with a Darrieus rotor, which looks like an oversize whisk and “can bring you to a high rate of speed and power.” Thanks to their differing starting torques and speeds, the hybrid rotor can generate power in a variety of wind environments. In fact, the Savonius and Darrieus rotors play off one another’s strengths. Comparing the Darrieus to “second gear,” Becker explains, “If I didn’t have the Savonius blades, the Darrieus might not start. It’s like the starter motor in your car. We wouldn’t be driving internal combustion engines if we didn’t have an electric ignition.”

The Near North installation looks remarkably unchanged from Becker’s cardboard models. Becker mounted eight 520H turbines—each one featuring Savonius and Darrieus rotors welded onto a central shaft—on the roof in a horizontal axis. A vertical installation could produce 30 percent more energy, but it would have surpassed local height restrictions.

The turbines produce three-phase AC power from ARE 2,500-watt alternators mounted on each module. Each turbine also includes an Aurora 7200 Wind Interface Unit and an Aurora 3,600-watt inverter, manufactured by Magnetek. The interface converts the AC to variable DC and protects downstream inverters from high voltage surges via a diversion load. The inverter then converts that DC power into building-compatible 208-watt, 60-hertz variable amperage power. The project forgoes batteries, Becker explains, in order to minimize on-site toxicity and maintenance, and to assuage fire fears.

In Near North Apartments’ first months, the Aerotecture installation was producing a paltry 100 kilowatt-hours per module per month, but Becker has slowly improved average production to 300 kilowatt-hours per module per month. Currently, the 520Hs yield approximately 60 percent energy conversion, producing about 10 percent of the building’s power. Becker says his electronics could be optimized even further, although the alternator is proving an obstacle to achieving 80 percent efficiency: Just as the wind interface units were not designed for Savonius rotors, so most alternators are suited for the high rpm of internal combustion engines. Making another comparison to automobiles, Becker describes the disjunction between his rotors and his alternator as “having a car that’s too heavy for its engine. It runs, but it’s going to be sluggish on the hills.” To perfect his invention, Becker continues his search for an alternator suited for lower rpm, or may prototype one himself. David Sokol

Solar Decathlon House, Washington, D.C., 2007

“What we teach here is not just about generating energy in a building, but conserving energy within a building,” says Barbara Gehrung, an assistant professor in the department of architecture at the Technical University in Darmstadt, Germany. Gehrung was one of the faculty advisers on Darmstadt’s winning entry in the third annual Solar Decathlon sponsored by the U.S. Department of Energy in October 2007. The Decathlon program requires university teams to design 800-square-foot prototype houses that rely entirely on solar photovoltaics (PVs) for electricity during the 10-day competition on the National Mall in Washington, D.C.

Darmstadt’s wood post-and-beam house incorporates photovoltaics in three ways: on the roof, on skylights, and on louvered doors. The team used Integrated Simulation Environment Language (INSEL) software, developed in Germany, to analyze the potential energy gains from the sun, as well as to lay out the best orientation for the house’s active photovoltaic systems on the roof. Since the team wanted a flat roof, they realized they were at a disadvantage when compared to other houses with sloped roofs. This led them to incorporate the louvers on the east, west, and south facades.

The roof consists of a 7.8-kilowatt array of 40 photovoltaic modules provided by Sunpower, as well as exterior canopies consisting of 2 kilowatts worth of translucent thin-film photovoltaics provided by Sunways and sandwiched between plates of glass. The canopies cover porches that counted toward the house’s square-footage allotment, but also provided a buffer for ventilation. Schott amorphous silicon photovoltaic cells, generating 2 kilowatts at peak load, clad the louvers, which were designed with automatically actuated controls that would track the sun to increase output throughout the day. Gehrung says these actuators were so difficult to design and install that she doubts the team would use them again.

The PV system feeds four separate electrical bus systems for lighting, mechanical systems, entertainment, and controls. The team could document energy production and consumption, as well as indoor air temperature, humidity, and carbon dioxide values through the controls. They used more software programs, such as the Transient Systems Simulation Program (TRNSYS), for analyzing the reversible heat-pump system and the rooftop solar water heaters that helped the project meet its energy goals.

Although each Decathlon project relies on solar photovoltaics for electricity, Gehrung emphasizes her team’s energy-efficiency strategies as the primary motivation for design. Germany’s “Passivhaus” program, which is similar to the U.S. Environmental Protection Agency’s Energy Star rating program, inspired the team to design for local conditions, which in Washington meant a hot and humid subtropical climate. The 19 Darmstadt team members originally wanted to design an all-glass house. Site analysis (the longer sides of the house would face north and south once installed on the mall) indicated the need for less exposure, in order to minimize heat gain without restricting daylighting opportunities. The east and west facades are solid panels finished on the interior with gypboard embedded with phase-change materials (PCMs) that increase the insulation values while providing thermal mass. In this case, the PCMs are paraffin microcapsules called Micronal, manufactured by BASF. Once the temperature of the house reaches around 74 degrees F, the capsules melt and absorb the energy, helping to cool the non-air-conditioned house. In the evenings, the capsules harden to release stored heat. “Sometimes this worked too well,” says Gehrung. “We had so many visitors and we let them stay in the house too long, so we never had enough time to cool the building the way we wanted.”

For a German team designing an American house, some things got lost in translation. For example, the team scored low on the hot-water challenge, since the German showerhead limited the temperature to below the American requirement of 104 degrees F. “In the end, our energy-efficiency strategies helped us win,” says Gehrung, who won’t be involved in Darmstadt’s 2009 entry. “And it was a lot of fun.” Russell Fortmeyer

One Bryant Park, New York City, 2008

Though already common in industrial applications, combined heat and power [CHP] technology is rarely used in buildings in the U.S., even though it can provide a more efficient and lower greenhouse-gas-emitting alternative to traditional grid-supplied power. But one project that is a CHP pioneer is under construction in Midtown Manhattan and is headed for completion later this year.

Designed by Cook+Fox Architects, and jointly owned by the its primary tenant, the Bank of America, and the developer, the Durst Organization, the 55-story One Bryant Park will have a 4.6-megawatt CHP system. The designers and owners say that the building will be the first high-rise commercial office tower in the country to use this technology at such a scale. The CHP plant will satisfy about one third of One Bryant Park’s peak power demands and will provide for almost 70 percent of its energy needs on an annual basis.

Also known as cogeneration, CHP involves simultaneous production of electricity and useful thermal energy (typically steam) from a single fuel source (often natural gas). At One Bryant Park, the heat produced by its natural-gas-fired turbines will be used to make steam, which in turn will be used to heat the building and the domestic water supply, and to operate an absorption chiller for cooling.

Relying on CHP for much of its energy needs should significantly reduce the carbon emissions of the tower compared to a conventional office building dependent solely on the grid. Part of these savings are due to its distributed energy strategy. The term “distributed energy” refers to a generation source that is an alternative or enhancement of traditional grid-supplied power, located in close proximity to the building it supplies. Such systems can be more efficient than centralized generation since electricity carried over the grid loses 7 to 8 percent of its power in transmission, according to some estimates. However, retaining this electricity is a relatively minor contributor to the efficiency of CHP, since a much larger portion (about two thirds) of the energy generated at traditional power plants escapes through smokestacks. “By preventing transmission loss, CHP does save something on an overall Btu basis,” says Don Winston, Durst director of technical services. “But it is the heat recovery that really makes the system work,” he says.

About 86 gigawatts of CHP capacity are currently operating in the U.S.; however, the vast majority of these facilities are located at industrial sites rather than in individual buildings, according to Richard Sweetser, president of Exergy Partners, a consulting firm based in Herndon, Virginia. Sources say a number of factors make cogeneration a good choice for industrial applications, including a relatively flat demand for energy over the course of the day and through the various seasons. But in buildings, this demand is generally more variable, creating challenges for making the most of a cogeneration system’s thermal output. “If you are sending steam to the roof, CHP doesn’t make [economic] sense,” says Vinnie Galatro, director of technical services for the Fulcrum Group, commissioning agent for the One Bryant Park project.

The heat produced as a by-product of electrical generation will be used to make steam for heating
the building and the domestic water supply, and to operate an absorption chiller for cooling (above).
A thermal energy storage system (below) will help reduce demand during peak hours.
Diagrams courtesy: Fulcrum Group (top); Doyle Partners for Cook+Fox (bottom).

In order to avoid wasting valuable thermal energy, One Bryant Park includes a thermal storage system that will produce ice at night from excess steam. Then, during peak daytime hours, the ice will be used for cooling, resulting in “a nice and even load profile 24 hours a day,” says Galatro. Other challenges with which the One Bryant Park team had to contend included routing natural gas lines through a densely occupied structure, and the isolation of the CHP equipment for noise and vibration. There were also permitting and regulatory hurdles, though New York City officials are working to reduce such barriers to achieve a goal of 800 megawatts of installed clean distributed energy by 2030.

But impediments aside, CHP proponents say that the technology is an economically and environmentally viable alternative to the construction of additional conventional centralized generation capacity. According to Scott Frank, partner at Jaros Baum & Bolles, the project’s mechanical engineer, “generating electricity on-site and using the waste heat just makes sense.” Joann Gonchar, AIA

By David Sokol, Russell Fortmeyer & Joann Gonchar, AIA

Inside Beijing’s Big Box of Blue Bubbles

A multidisciplinary design team employed an innovative digital process to produce a surprising, highly integrated envelope-and-structure combination.

It might seem like an obvious choice of design parti: A facility built to host the swimming and diving events for the 2008 Summer Olympics in Beijing should be all about water. But realizing such a concept in bricks and mortar is far from straightforward, and more challenging still if the designers intend to create more than a container, but hope to capture the “spirit” of water. “We wanted the building to dematerialize, to change moods, to react to changes in the environment around it,” says Min Wang, a design principal with China Construction Design International (CCDI), a state-run design institute that worked on the project.

But despite the difficulty of realizing such an abstract goal, the National Swimming Center’s international and multidisciplinary design team, composed of the Australian architecture firm PTW, engineers from the Sydney office of Arup, and a group from CCDI, managed to pull it off. They created a building that not only embodies some of the elusive characteristics of water, but one that tightly integrates skin, structure, and the performance requirements of an Olympic-level sports venue [for more on the project, see page 100].

Naturally, the designers didn’t use bricks and mortar for the $100 million, boxlike structure known as the Water Cube. The consortium, which was awarded the project through a competition in mid-2003, chose steel and a space-age plastic, ethylene tetrafluoroethylene (ETFE). The material, a cousin of Teflon, which the team used to create translucent pillows for the building’s cladding, is strong and resistant to degradation from ultraviolet light and air pollution. By electing to envelop the building in it, the design team could treat the Swimming Center as an insulated greenhouse, capturing the energy from the sun for heating and lighting. ETFE was more appropriate for such a use than glass, the design team reasoned, because of better acoustic and insulating properties, and it is lightweight, which eliminated the need for a secondary structure to support the skin.

In order to create a building structure and ETFE enclosure with the desired references to liquid, the team members explored the geometry of soap bubbles, studying the work of Irish physicists Denis Weaire and Robert Phelan. In 1993, the pair proposed a solution to the so-called Kelvin problem (named after late 19th-century British mathematician William Thomson Kelvin) that asks how to divide space into an equal number of cells with the least surface area between them. Weaire and Phelan’s “foam” is made up of a combination of polyhedra with either 14 or 12 faces. Despite its regularity, the honeycomblike structure was well suited to the team’s goals because “when viewed at an arbitrary angle, it appears totally random and organic,” says Tristram Carfrae, leader of the group of engineers from Arup.

Although Weaire and Phelan’s foam forms the basis of the structure, there is only one spot in the building where their “pure” geometry is clearly recognizable—the second-floor Bubble Bar. Here, a collection of ETFE-clad polyhedra encloses a room where visitors can sip champagne.

Elsewhere in the building, the underlying geometry is hard to discern because of the team’s form-finding process. In order to develop a building structure from the theoretical foam structure, the designers from CCDI wrote a script that would allow them to assemble an infinite array of the Weaire-Phelan units, rotate it in three dimensions, and then slice the packed cells to create a box 584 feet square in plan and 102 feet tall. They then removed three interior volumes for halls devoted to swimming and diving competitions, the pool for water polo, and the leisure center. From the foam left behind after this virtual cutting and deconstruction process, they created a space frame by replacing the edges of the polyhedra with steel tubes that meet at spherical nodes. They decided to encapsulate the space frame in 4,000 bubblelike, air-filled ETFE pillows to create a vented cavity 12 feet wide within the walls and one that is 25 feet deep within the roof, protecting the steel structure from the corrosive humidity of the pool environment.

The result is a seemingly irregular, but in actuality a rigorous and buildable structure -and-building -envelope combination appropriate for earthquake-prone Beijing. The on-site welded space frame, with column-free spans of up to 396 feet, is highly efficient, nonlinear, nondirectional, and remarkably stable. The ETFE cladding, which weighs just 1 percent of an equivalent glass panel, contributes to the building’s seismic performance, since it helps reduce the gravity and lateral loads that the structure would be subject to during a temblor, explains Carfrae.

The ETFE cavity wall and roof also provide thermal efficiency. The double skin is designed to capture solar energy to heat the swimming pools and the building and light the interior spaces. The building collects 20 percent of the solar energy that lands on it, equivalent to covering the 340,000-square-foot roof with photovoltaics, according to Arup. The firm estimates that the Water Cube saves 30 percent of the energy typically devoted to lighting and half of the energy that would be required to heat a well-detailed and well-insulated metal-clad box.

The Water Cube relies on the thermal mass provided by the pool water and surrounding concrete to retain heat during the day and release it at night. The double skin allows the venting of excess heat in the summer but permits its containment during the winter, when solar gain is most beneficial. The concept was realized almost unchanged from the design team’s original competition entry scheme.

One of the few features of the envelope implemented differently in the built Water Cube is the solar control strategy. The team originally imagined the inner ETFE cladding as an operable and variable surface, providing the facility’s managers with the ability to turn shading on or off, depending on the desire to admit sunlight and control glare within the Water Cube’s various spaces. But in the end, the designers opted for a fixed aluminized frit pattern that blocks between 10 to 95 percent of visible light. The frit is most dense on areas of building skin that enclose areas where direct sun is least desirable and glare would be most distracting. For example, the roof over the competition pool admits only 5 percent of visible daylight due to strict broadcast-industry lighting-control requirements.

Though much of the building’s heating needs are satisfied through passive means, some spaces within the Water Cube do require mechanical cooling, setting up a challenge for designers. In the competition pool area, “it was tricky to keep the swimmers warm and wet and the spectators cool and dry,” says Carfrae. In order to cope with the differing requirements of the building’s various types of occupants, the engineers relied on the displacement ventilation principle, supplying cool air through an underseat supply system, conditioning only the zones occupied by spectators.

Digitally driven

The Water Cube’s structure is the outcome of applying sophisticated analysis and optimization software that Arup’s engineers created in-house specifically for this project. The program helped the designers examine the space frame under various loading scenarios to determine the size, shape, weight, and other properties for each of the 22,000 steel tubes. These characteristics were automatically recorded in a database and a 3D model, which in turn were used to produce the construction documents.

Team members say that the process of digital form finding, analysis, and documentation employed to produce the Water Cube was cutting edge for a building designed largely in late 2003 and completed earlier this year. “There is a lot of talk about autogenerated architecture, but this was one of the first projects where such a process was realized,” says Chris Bosse, a former project architect at PTW and now head of the Laboratory of Visionary Architecture (LAVA), in Sydney.

Because of the high degree of automation that the parametric process afforded, the team could generate a complete set of new construction documents in less than a week following a major change in the Water Cube’s configuration, according to Carfrae. But speed was not the only advantage. The process also ensured accuracy. Prior to construction, the team issued the 3D model, traditional 2D drawings, and the database to the contractor. They did not worry about potential conflicts between the various media (or resulting construction errors) since “it was all the same information conveyed in different ways,” he says.

Fabrication of the ETFE pillows depended heavily on the digital information. The digital files controlled operation of the foil-cutting equipment, the same way CAD files run a plotter. This step in the fabrication process was not completely automated, however. The data did require some manipulation, especially to address areas of the building skin where the bubble shapes are interrupted, such as those around corners and openings. “There was still a large human factor involved,” says Edward Peck, director of design and development for Vector Foiltec. The international company, headquartered in Germany, partnered with a Chinese curtain-wall manufacturer to engineer, fabricate, and install the ETFE cushions.

Most of the cladding cushions are composed of three layers of of 0.008-inch-thick ETFE foil. But those located in areas of high wind loads, particularly corners, have two or three more. These extra layers provide “load sharing”—they help the building skin withstand the additional pressure and suction exerted on those spots, since making the foils thicker was not an option, says Stefan Lehnert, Vector Foiltec managing partner. At thicknesses greater than 0.01 inches, the material becomes too brittle, he explains.

To create the rounded pillow surfaces, Vector Foiltec cut 5-foot-wide sheets of ETFE into shapes that resemble sections of a banana peel. The company then assembled the pieces into larger sheets, some as wide as 30 feet, via heat welding. The pattern for each of the 4,000 cushions is unique, even though there are only 15 pillow types in the walls and seven in the roof. Since none of the pillows have exactly the same orientation, and since the design team required that the heat-weld seams run continuously from one pillow to another, from the roofline to the ground, the result is that no two cushions are alike, explains Lehnert.

After assembling the foils, workers transported the cushions to the site and attached the ETFE layers into aluminum extrusions that secure the pillows to the space frame. They then inflated the pillows with 18 radial ventilators permanently installed in the building. Because the pillows will gradually lose air, the building management system constantly monitors the pillows and signals the ventilators to supply filtered and dehumidified air when the pressure falls below a desired level.

Collecting and conserving

Appropriately, some of the building’s most innovative features are its systems for handling water. Unlike most swimming pools, which send filter backwash water to the municipal wastewater systems, the Water Cube collects such gray water for treatment and returns it to the pool. The system substitutes rainwater collected from the roof for the small amount of gray water lost in the treatment process. The strategy lessens the burden of the building on Beijing’s wastewater infrastructure and makes it less dependent on the city’s already constrained fresh-water supply. “The idea was to make it as self-sufficient as possible,” says Carfrae.

To visitors, the gray-water-recycling and rainwater-harvesting systems will be invisible. For them, the bubbles (and the Olympic competitors) will steal the show, especially at night, when the Water Cube becomes a glowing blue box with the help of LEDs integrated into the pillow frames. During the day, it is sometimes soft and playful, or cold and hard-edged, depending on the weather and the angle of the sun. This ability of the building to transform is perfectly in keeping with the design team’s goals: “Water has no fixed image,” says Wang. “It can be still, it can reflect the sky, or it can have big waves.”

By Joann Gonchar, AIA