Model Behavior: Anticipating Great Design

Cutting-edge projects throughout the Middle East rely on a variety of simulation programs to inform design and predict building performance.

Josephine Minutillo

The Middle East is a land of extremes—economic, climatic, and cultural. When it comes to building construction, it is also a place for superlatives, with projects that are the biggest, the tallest, and the most expensive in the world. Added to that is a growing list of structures that promise to be among the most innovative in terms of design and energy performance. To determine the feasibility of these complex projects—many of which engage natural phenomena created by the wind, sun, and moon—architects are increasingly relying on building simulation programs, utilized both in-house and by consultants who are now being called on during the earliest stages of the design process.

Chicago-based Adrian Smith + Gordon Gill Architecture (AS+GG) and Environmental Systems Design (ESD) used a host of simulation programs to develop the design for their competition-winning Masdar Headquarters in Abu Dhabi’s Masdar City, which is expected to be the world’s first zero-carbon, zero-waste city fully powered by renewable energy. “When we started the competition, we knew that in order to meet Masdar’s goals we needed to have an integrated practice approach, bringing the engineers in at the concept phase,” explains AS+GG partner Robert Forest, AIA.

Eleven imposing, steel-and-glass-enclosed cones define the eight-story building. When completed by the end of 2010, the headquarters will be the world’s first large-scale, mixed-use, positive-energy building, producing more energy than it consumes. Simple building orientation and shading studies were carried out by the architects using Ecotect, a software recently acquired by Autodesk. The three-dimensional architectural model was then transported into eQUEST, a sophisticated building-energy-use analysis tool initially developed as part of DOE-2, which allowed the engineers to optimize the mechanical and electrical systems, as well as the building envelope. According to Forest, “These programs are used to bring up the minutiae of energy performance so we can fine-tune different components of the building.” By taking a section of the exterior wall, for instance, the designers are able to examine facade orientation and overhang size to study heat gain.

The Masdar Headquarters in Masdar City, Abu Dhabi, UAE, will be the world’s first large-scale, mixed-use, positive-energy building (above). The design consists of eleven glass-enclosed wind cones, some of which will have gardens and water features in the courtyards at their base (below).

images courtesy Adrian Smith + Gordon Gill Architecture

In addition to providing structural support for the roof, the staggered cones bring daylight deep inside the 1.5-million-square-foot complex. More important, they cool the interiors by drawing warm air up and out of the building through their tips. Computational fluid dynamics (CFD), which utilizes numerical methods to simulate the interaction of fluids and gases within complex systems, was employed extensively on this project to ensure that the flow of air through these cones produces the greatest cooling effect.

“We looked to traditional Middle Eastern wind towers when designing the cones,” Forest recalls. “At first, we were going on an intuitive reaction that they would work in terms of light and ventilation.” To validate their assumptions, the team used FloVENT, a program that predicts 3D airflow, heat transfer, and contamination distribution in and around buildings. ESD did a simple model of the cones, including the courtyards created at their base, to get an initial understanding of conditions. “By doing such a model, we were able to pinpoint areas of air intake and airflow into the base of the cone,” explains ESD’s Mehdi Jalayerian. “For example, we analyzed the effects of repositioning the intake from the base of the cone to the side. We found that by putting it to the side, air swirls around in the cone and provides more uniform ventilation.” CFD analysis was especially useful given the speed at which the project had to be developed. Follow-up testing was performed in wind-tunnel facilities, wait times for which can run up to a month.

The cone’s design has similarities with traditional Arabic wind towers.

Image courtesy Adrian Smith + Gordon Gill Architecture

In order to ensure that the natural ventilation system functions as planned, CFD software was used to model the building geometry and surrounding wind patterns. Hot winds traveling at high velocities around and over the cone openings create low pressure areas, inducing airflow out of the cones. The cone’s shape captures cool air moving in the opposite direction.

Image courtesy Adrian Smith + Gordon Gill Architecture

Lines in the sand

For The King Abdulaziz Center for Knowledge and Culture in Saudi Arabia, the engineers at Buro Happold are using CFD to study airflow patterns for an entirely different reason. Designed by Snøhetta and expected to open in 2011, the Center will stand atop the oil-rich Dammam Dome as one of the only buildings within the surrounding desert. Commissioned by Saudi Aramco, the world’s largest oil company, Snøhetta’s design calls for five distinct, rock-like structures to house an auditorium, theater, exhibition hall, museum, and archive.

The King Abdulaziz Center for Knowledge and Culture resembles a rock mass in the desert (top). Streamlines generated using Ansys CFX trace the path and speed of particles moving across and around the building. Different colors refer to varying velocity levels, which are greatest at the building’s corners. The white areas represent wells where wind shadows would likely form (below).

Images courtesy Buro Happold

An early design envisions a polished facade (above).

Image courtesy MIR Visuals

Early schemes featured a slick facade meant to evoke the dark, viscous qualities of oil. But unlike structures within urban settings or hilly, wooded areas, the exposed surfaces of this building are subject to destructive winds tossing sand and small stones. “The site is driving this specific set of analyses,” explains Matthew Herman, of Buro Happold’s Computational Simulation & Analysis group. “CFD has been focused primarily on the particulate matter that’s picked up from the surrounding terrain.”

With the use of Ansys CFX, another commercial platform with fluid dynamic codes, Buro Happold is mapping wind patterns to address issues of potential facade damage, as well as pedestrian comfort. Wind shadows—areas of turbulent, but slower wind—abound in denser landscapes. Their absence on such an open site allows winds to maintain greater velocities, reaching their highest speeds at the building’s corners. Design of these surfaces is developing to respond to wind speed concerns. “We were generating data early enough in the design process to influence the makeup of the facade,” says Herman. “While the original facade design consisted entirely of glass, detailing of the surface has changed, and new materials that wouldn’t be affected by the scratching of sand are being considered.”

The landscape design around the building, including a number of sunken courtyards, or wells, is also evolving in response to CFD analysis. The wells—which serve as a metaphor for the region by representing water reserves around which buildings would traditionally sprout—were partly responsible for generating the initial CFD study; the small wind shadows they create would likely cause particulate matter to fall out of the airstream and settle there due to the drop in wind speed. According to Herman, “The concern was that sand would simply pour into those depressions.”

While advances in CFD analysis in recent years have led to very reliable modeling, wind-tunnel testing is typically still employed, partly because it is better able to measure turbulence. But because wind tunnels use scale models, studies of tiny particles such as sand can be inaccurate.

Sun protection factor

Viewed from King Fahad Road, the main axis in Riyadh, Saudi Arabia, the protective enclosure of the Al-Birr Foundation Headquarters tower reveals the spiraling glass volume in the interior carved out by a terracing vertical garden (left). The orientation of the various facades determined the calibration of the enclosure, which controls solar and heat gain and operates as a light shelf diffusing system (below).

Insolation analysis of the tower’s south facade using the building design and environmental analysis tool Ecotect (above). Tower transparency is seen along unfolded elevations (left).

Images courtesy Perkins + Will

ith the Al-Birr Foundation Headquarters in Riyadh, Saudi Arabia, Perkins + Will preferred to do the model-making, both physical and virtual, themselves. Using the building and environmental-analysis program Ecotect, the architects developed an innovative building enclosure for the office tower. By so doing, they were able to integrate sustainability from the start, allowing the building’s aesthetics to emerge in the process.

Like much of the Middle East, Riyadh has a hot, dry climate. The capital is also an old city with few very tall buildings. Perkins + Will’s design for a 28-story structure incorporates both environmental concerns, given the severe heat—average summer temperatures approach 110 degrees Fahrenheit—and historical references—towers symbolize protection, security, and shelter. They also looked to traditional Arabic architectural elements, namely the mashrabiya screen, a window of carved wood latticework that provides privacy and protection from the unforgiving sun.

Taking all these things into consideration, Perkins + Will developed a perforated enclosure of lightweight, precast concrete that acts as a sunscreen. With the help of Ecotect’s insolation analysis—which measures solar radiation energy received on a given surface area in a given time—the architects were able to precisely calibrate elevations in response to changing sun angles, leaving a significant level of opacity on the southern elevation where there is the highest heat gain. The northern elevations are predominately transparent, allowing unobstructed views back to the city from the vertical terrace gardens and spiraling glass volume on the interior of the building. “Ecotect allowed us to bring analysis into the design process early on,” says Perkins + Will design principal Robert Goodwin, AIA. “That is a huge benefit of the program.” Situated on a corner along King Fahad Road, the city’s main axis, the building will be illuminated internally at night so that the arrangement of variously sized apertures result in a dazzling pattern of light; an inversion of the solar-regulating function of the tower enclosure during the day.

Moonlighting

The lighting design for the Sheikh Rashid bin Saeed Crossing in Dubai, UAE, will allow the bridge’s nighttime lit appearance to subtly respond to the five distinct phases of the moon during the monthly lunar cycle: full moon, three-quarter moon (gibbous), half moon, crescent moon, and new moon. AWA Lighting Designers used the lighting analysis software program AGi32 to simulate the moon phases over the bridge.

Image courtesy AWA Lighting Designers

Simply put, as the moon gets brighter, so does the bridge. To achieve that basic concept, however, AWA developed a complex mathematical algorithm to calculate the quantities of light reflected from the surface of the two arches. The fact that they were dealing not with straight lines or regular arches confounded the issue even further since they had to modulate the lighting across the length and height of the bridge.

Another challenge was to establish a system for controlling the fluctuations of light levels throughout the predictable 291⁄2-day lunar cycle. Since maintenance-friendly, energy-efficient light sources are not dimmable, gradations of light would have to be achieved by way of a complex switching system involving multiple layers of light.

In mirroring the lunar cycle, AWA developed a separate lighting scene for each phase of the moon’s illumination, including the full, gibbous, half, crescent, and new moons. “To get a certain amount of uniformity, we had to design the lighting for all five settings,” Wadhwa explains. “Each setting has a different zone of light on it, so when we do the calculations and simulations, we have to do it for all five zones.” On the brightest night (full moon), all five zones are switched on. The front and inside elevations—the most prominent feature of the lighting design—are lit by fixtures located on 61⁄2-foot-long outriggers.

The new moon phase is not represented by complete darkness, but instead emits a subtle glow suggestive of the dim light that is reflected by the moon during a total lunar eclipse. For two days, observers will see this glow, which results from gentle reflection of the light used to illuminate the bridge cables. The lighting of the arches returns with the appearance of the crescent moon, the most significant phase of the moon for followers of Islam. After this point, the arches’ light alternately accumulates and dissipates in sync with the rest of the moon’s phases. Reflections of the illuminated arch in the water beneath the bridge “complete the circle” of the full moon’s profile.

“Painting a pretty picture is one thing,” Wadhwa says. “Being able to deliver it is really what the simulation software is about.” Starting with extensive Excel spreadsheets that measured items such as the distance a beam of light travels, AWA then used AGi32—a lighting-analysis program for lighting calculations and renderings of electric lighting and daylighting systems—to confirm their projected algorithmic calculations. “After we entered our calculations into the program, we found that we had accurately specified 95 percent of the lighting. We then had to go back and tweak the other 5 percent, much of it through trial and error.”

All of these projects represent designs in progress. The architect’s job is to integrate the information provided by these simulation programs into their design. “That’s when the input from these types of analytical programs is truly successful,” says Buro Happold’s Herman. “Ideally, you’d never know that changes to the design had ever happened. Everything about the finished structure would simply look like it was always meant to be there.”

The roadway is lit at the center by light poles.

Image courtesy AWA Lighting Designers

Originally published in the December 2008 issue of Architectural Record

http://continuingeducation.construction.com/article_print.php?L=5&C=471

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