Introduction: Situated midway between the Forbidden City and Beijing Capital Airport, the Poly International Plaza occupies a highly visible position adjacent to the Capital Airport Expressway, set between a new urban district and the agricultural-industrial sprawl that surrounds Beijing. In contrast to the typical, undifferentiated office space ubiquitous throughout China, this project seeks to reconsider and redefine the human experience within the high-rise typology. The Spatial High-Rise: A long-span diagrid structural strategy is used to create a unique daylight-filled spatial experience for movement and workplace spaces. To address the climatic and air quality challenges particular to Beijing an actuated double-skin envelopes the interior. At the narrow ends of the building the interstitial space expands to create two 29-story atria which pull daylight into the building and harness expansive views towards downtown and the Airport. These atria create opportunities for social interaction and connectivity between floors, through communicating stairs, meeting rooms and balconies. Elevator lobbies open directly toward the atria, providing immediate geographic orientation by way of external views. Diagrid Scaffold: In order to maintain efficient pure axial loads in the elliptical form, structural members are constructed from straight rather than curving segments producing the faceted form. Floor framing loads are transferred to the diagrid at primary diagrid nodes only. Thus, every second floor frames directly into the exoskeleton, while the intervening floors are supported by hangers from the floor immediately above. Active Performative Envelope: The exterior double-skin wall mitigates Beijing's temperature extremes through a system of actuated ventilation slots. In winter, the cavity is sealed forming an additional insulting layer warmed by solar gain, while in summer the slots are opened to relieve the hot air reducing the load on the building’s cooling system. All panels in the glazing system are flat, defining the faceted form consequently reflecting the sky and the ground in unexpected ways. Site Strategy: The tower’s orientation is positioned along a direct axis to the center of Beijing, while it sits adjacent to two smaller buildings the tower acts as a central focus in the landscape. The elliptical geometry of the towers, frees the landscape from the rigid geometry of the adjoining urban fabric, and invites the community into the site by joining the landscape of a new public park to the west to as it flows seamlessly into the site and through to a major open-space to the east. Site walls establish an undulating site topography that define specific spaces in the landscape, which unfold and evolve as one moves through the site. Sustainable Design Intent & Innovation: The design of the Poly International Plaza incorporates the highest levels of Environmentally Sustainable Design (ESD) measures into the project, which are integral to the structure’s overall design objectives. The building itself is LEED® pre-certified and is currently pursuing LEED® Gold certification by incorporating a number of sustainable features, which reduce energy and water consumption while increasing a sense of human well-being. Perhaps, the most notable sustainable feature is integrated into the expression of the tower itself. The exterior wall is comprised of a double skin with a faceted form on the exterior and a vertical window wall on the interior which form an unoccupied cavity. This interstitial space serves as a buffer to Beijing’s harsh climatic swings by holding air in the cavity during the cold winter months—similar to a greenhouse—and venting the cavity through stack ventilation during the hot summer months, allowing cooler air to occupy it. By faceting the outer wall and setting back the inner layer of the double skin, natural horizontal overhangs are created in the cavity, acting as solar shading devices. High sun angles are shaded during the intense summer months while low sun angles are permitted during the cold winter months. The addition of high performance glazing completes the exterior wall system that blends form and function, in order to meet sustainability goals through an integrated approach. Additionally, water use was carefully considered when designing the plumbing systems. The business district has implemented a forward-thinking, district-wide municipal greywater system in which 100% of the water used for flushing is greywater. The project uses water saving fixtures (dual flush toilets, high efficiency urinals, and high efficiency lavatory faucets) which save 48% of potable water over the calculated baseline. Other measures incorporated into the MEP sustainability strategy include: • Full size water side economizers at each chiller plant which pre-cool water being used by the chiller, reducing the energy required to lower the temperature of the chiller water. • Air side heat recovery utilized at outside air handling units, which essentially temper ingoing air so that additional heating or cooling energy is minimized at all times. • Metering and sub-metering are provided for electricity, water, chilled water, and heating water in order to monitor energy usage for energy conservation. • Lighting controls linked to the BMU. By employing a highly sustainable approach into the structural and mechanical configuration of the building, the interdisciplinary project team established places of respite and community within the plaza, protecting those whom occupy the space from Beijing’s cold winters, hot summers, and days of poor exterior air quality. All of these strategies result in a design response that acknowledges the need for increased sustainable performance and responds by not only incorporating efficient mechanical and plumbing systems, but goes further by fully integrating sustainable features into the architecture itself.
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