The project brief was straightforward: Provide 40,000 square meters of energy-efficient office space for Harbin Bank’s new headquarters in Beijing. What wasn’t so clear-cut was the instruction from the bank’s chairman: “Make it the most beautiful building in Beijing.” Of course, beauty can mean different things for different people, but for this project, it meant two things: The 16-story structure had to be aesthetically pleasing, and it had to perform beautifully as well.
The Harbin Bank HQ will be located at the intersection of the third ring-road and the airport expressway in Sanyuanqiao area, just to the north of Beijing’s emerging central business district. The building will accommodate a data center and supporting amenities, including restaurants, cafeteria, retail banking, conferencing facilities clubhouse, and visitor apartments in an area well served by public transportation.
Climate was a big consideration during the design phase. Beijing has unique weather conditions. It’s often overcast, and the city suffers from hazardous air quality conditions. Together, the gray and murky skies make for low visibility and dim light. The city also has long, hot summers and long, cold winters with very short fall and spring seasons. Most of the buildings are always either in cooling mode or heating mode.
For the Harbin building, we knew we needed a transparent exterior wall that could maximize natural daylight and views for the occupants. But this façade would also need to do double duty as a heating and cooling system. And we had to make it look good.
The graceful shape of an ellipse
We decided to develop an approach that would provide as much transparency and daylighting as possible on those year-round overcast days while providing a calibrated approach to the changing seasons and extreme opposing conditions in summer and in winter.
The client chose a split-core elliptical plan orientated on a northeast/southwest axis. The building shape developed into a graceful form in both plan and section. The perimeter is a flat ellipse along the long axis, with a tighter radiused curve on the minor access. To achieve a smooth elegance on the exterior without blowing the budget on premium curved glass we decided that the outer skin should be single glazed. Most of these single-glazed exterior panels along the long axis are flat and fixed into place with a point fixing system throughout the length and height of the envelop. The two bullnosed ends have bespoke curved geometry.
Saving energy with a “thermal duvet”
The inner skin is a standard floor-to-floor double glazed system in a series of 1,200 millimeter flat panels on the longer, shallower curved axis. This inner skin does not follow the full elliptical form. Instead, we created a series of stacked three-story atria to the northeast and southwest ends of the building, which allowed the inner glazing to be formed with the standard 1,200 millimeter insulated glazing module. We applied a low ‘e-coat’ (a painting method that uses electrical current to deposit paint on a surface) to both the outer and inner skin to maximize daylight transmission and reduce the use of artificial light.
Together, the single glazed outer skin and the double-glazed inner skin (both of which are low iron) form an 850 millimeter-wide cavity, which works like a thermal duvet without sacrificing transparency. The air between the inner and outer skins insulates the building year-round. Also, we created and installed a fully-automated mechanized blind system to mitigate solar heat gains and manage glare. The blinds can be fully open, or fully closed, depending on the sun angle and the time of day. In summer, we can ventilate the cavity from top to bottom – allowing the warmer outside air to percolate through the cavity by use of the stack effect. Also, the blind system can block the intense summer sun. Unlike a rectilinear building, the curvilinear building shape means that only those portions of the façade that are exposed to direct solar gain will need the blind system.
On very cold winter days we reverse the process by closing the cavity and retracting the blind system. Beijing experiences very low-angle passive sunlight, so our system allows the building to take advantage of the low-angled sun to heat up the cavity and increase the air temperature inside the building. This innovative heating and cooling system is 50 percent more efficient than the China Energy Code requirements (CEC), and it significantly reduces energy costs for the tenant.
Planning for Beijing’s poor air quality
Another primary reason for developing a year-round “thermal duvet” was in direct response to Beijing’s poor air quality. In the winter months, the air is often so polluted that it’s dangerous to bring outside air into the building for heating or cooling purposes without extreme filtering and ongoing maintenance. This can be problematic for Chinese Facilities Management strategies. By using the cavity as a thermal moderator and by only using 20 percent of the outside air to condition the building, the effect of harmful particulates is minimized.
Keeping the façade clean requires regular maintenance. To make this as easy as possible for the building owner, we designed a cleaning strategy to facilitate access to the panels on both sides of the thermal duvet, so that particulate matter does not build up on the surface to obscure daylight entering the occupied areas. By maximizing natural daylight and energy efficiency, while minimizing harmful particulates year-round, the high-performance building serves as a climate-responsive solution and an elegant example for the city—ensuring that it’s one of the most beautiful buildings in Beijing, both inside and out.
Author: Russell Gilchrist
ARB, RIBA, AIA is a principal/design director in Gensler’s Chicago office and a global leader of Gensler’s Tall Buildings practice. He specializes in high performance, low energy architecture and master planning projects and formerly served on the Advisory Board for the Council for Tall Buildings & Urban Habitat. Contact him at email@example.com.