China is leading the new wave of mega-tall towers, but locating services such as lifts and cooling towers within these slender giants has required some serious lateral (and vertical) thinking.

The Home of Super-Tall

If America was the birthplace of the skyscraper, China is undoubtedly the home of the super-tall tower. The Council for Tall Buildings and Urban Habitats defines a tower as ‘super-tall’ when it tops 300m. So far, 97 have been completed around the world and 36 are in China. Of the 41 super-tall towers under construction, 27 are in China too. By 2020, it will be home to 14 of the tallest 20 buildings in the world.

Vincent Tse has a front-row seat for China’s extraordinary high-rise boom, as managing director of building systems for WSP | Parsons Brinckerhoff in the China region. Of the CTBUH’s projection of the world’s 20 tallest buildings in 2020, his team has worked on 11, providing full building systems design consultancy on six and partial consultancy on a further five.

Prestige Competition among World Leading Cities

He sees the era of the ‘mega-tall’ building of 500-600m fast approaching. “It’s mainly due to the competition among all major world cities – Seoul, Jeddah, Dubai, New York, Kuala Lumpur, Beijing, Shanghai, Shenzhen, Taipei, Bangkok, Jakarta… Every one of them wants to be number one of some kind, so that the whole world remembers their landmark towers. That’s why developers and city planners are building mega-tall.”

Complex Mixed-Use Towers

But buildings are not only getting taller, they are also becoming more complex. With architects and developers seeking to stand out, ‘iconic’ shapes are the norm – no two buildings are the same. And while 90% of high-rise buildings were single-use offices before 2000, now 80% of the mega-tall towers under construction are multi-use, combining commercial space with luxury hotels, service apartments, retail and leisure spaces.

This is partly for technical reasons, says Tse, and partly commercial. “All towers will change shape as they get higher to minimize the impact of the wind. The floorplates will be smaller in the upper floors, so most mega-tall towers will have hotels, CEO offices and observation decks at the top. Or there will be apartments in the middle of the tower rather than just offices, to give a higher cash return. Having multiple building functions also gives the buildings life day and night. A pure office tower has no life at night or at the weekend.”

Pumping Water Up Hundreds of Meters Into the Sky

For the services engineer, however, this makes buildings much more complicated. They must overcome not only the gargantuan pressures involved in pumping water up the best part of a kilometre into the sky or the combined resistance of hundreds of metres of electrical wiring, but also serve the potentially conflicting needs of different user groups, while fitting all the kit into the smallest possible space.

“As buildings get higher and higher, with mixed-use, it’s like a jigsaw to fit everything within the core,” says Tse. “The majority of buildings have more than 100 storeys and there might be seven different components.” What’s more, advances on one project can only ever serve as inspiration for the next one: solutions can never be replicated. “If you try to copy, you will make a mistake.”

Space Constraints

Tianjin CTF Financial Centre will be 530m tall, with retail and parking space in the podium and 100 storeys of offices, service apartments, a hotel and club all stacked on top, providing a total floor area of 350,000m2 . The problem is that the space is not necessarily where the services engineer would like it to be.

“The most difficult thing when designing the services for tall buildings is always the shape,” says Tse.

“This is a very slender tower and by the time you reach the top, the whole building shrinks like a bowling pin. At the top levels, the floorplate is very small and the core is only around 19m2.” The smaller floors lend themselves to hotel accommodation rather than offices, but how to fit the hotel lobby – and its considerable vertical transportation requirements – at the point where the core is at its thinnest?

The solution was to put the hotel at the top, but with the hotel lobby below the service apartments, keeping the core as compact as possible. It is shaped like two square tubes, one inside the other. The inner part of the core contains all the building systems, local lift shafts and the fire escape stairs, and runs the full height of the building. The outer part of the core contains the shuttle elevators: “The big core stops when you get to the hotel lobby, and by the time you get to the hotel floors, everything’s in the small core, which is tiny,” explains Tse.

Achieving 6-Star Level of Service at Extreme Heights

A challenge for all mixed-use towers is how to reconcile demand for some functions to remain separate while others are shared. For example, the hotel at the CBD Z6 Sino-Ocean Centre needed separate lift capacity for its guests, but had to connect directly to the communal service elevator too. The hotel also required a separate chiller plant, while the hotel operator imposes even greater requirements on building systems. Achieving a 6-star level of service at such a great height meant overcoming extremely high hydraulic pressures – achieved by splitting water systems into several zones. “At the top, the walls incline at an angle of 4° so the floorplate shrinks every floor,” says Leung. “All the pipework around the guest rooms needed to be inclined. There’s no typical floor.”

“We Don’t Want People to Think That the Building is on Fire“

Tall buildings are often designed to maximize the potential of tight sites, which leaves little space for essential infrastructure. Their iconic nature also means this must be hidden away. On Beijing’s 528m China Zun Tower, now under construction, the location of the cooling tower gave the engineers a major headache. The building is on a tight site, it does not have a podium and the top is a sealed garden, so the only option was to locate it within the building itself. But a mega-tall tower must also be careful not to attract the wrong sort of attention: “In Beijing, the outdoor temperature in winter will be well below -10°, and if people see the plume from the cooling towers, they will think the building’s on fire,” says Tse. “So we have designed and developed a plumeless cooling tower instead by using the ice storage system, so that in the daytime, we will not need to operate the chiller or cooling tower.”

The Question of Sustainability

There’s one more complicating factor: building systems engineers are on the frontline of improving environmental performance of buildings and reducing their energy and water use. This can no longer be ignored on projects – partly to mitigate climate change, but also to futureproof buildings against energy price rises, increasing temperatures and demand from global occupiers for ‘green’ buildings.

Maintaining Environmental Comfort

Maintaining a comfortable internal environment is not easy in a glass tower, especially where it’s not possible to open the windows. In temperate climates, outside air can be used for low-energy night-cooling. But in a humid tropical climate – in Singapore, for example – allowing wet indoor air to enter at night would result in an indoor rainstorm when the air-conditioning comes back on the next morning, as the liquid in the air condenses on the cooler surfaces.

“Opening louvres to ventilate a building may work in New York, but not in warm, humid climates such as Singapore, Guangzhou or Taipei,” says Tse. “If you shut off the air-conditioning and open the windows at 7pm, when you come back the next day, I guarantee everything will be wet.”

Techniques for Achieving LEED

Instead, the first step is create a highly thermally efficient building façade to manage energy gain and optimize daylighting, and design innovative building systems to optimize energy consumption inside the building, such as variable speed pumping and fan systems. Power can be regenerated from elevator systems, and grid supplies supplemented with renewable wind and solar energy. “With all of these techniques, it is possible to achieve LEED accreditation,” says Tse.

But the most sustainable feature of a high-rise design is adaptability. “The Empire State Building is 84 years old, and when it was designed there was no chilled water, no air-conditioning, no sprinkler systems, no IT,” he points out. “So we need to design buildings that are very flexible. We have to ensure that the space provision for building systems will be sufficient for future changes.”