Vertical cities and sustainable towers have been possible for some time. Now we just need to make the economics add up
For a quarter of a century now, architects and engineers have known that it is practically possible to build a self-contained vertical city – or to be less grand just a skyscraper – that is broadly carbon-neutral in use. As for the embodied energy of manufacture and construction – consider the vast amounts of energy needed to make and transport steel and glass, for instance – that is a tougher problem, but it can be addressed in various ways, not least the use of green energy, recycled materials and the longevity of the structure. In use, however, the aim is that over the course of a year, say, the building should consume no more energy than it generates, and beyond that become energy-plus, feeding its surplus back into the grid. As a corollary it should be able to collect and/or recycle its own water, and process and reuse its waste – for instance through waste-powered generators. If cruise ships can have these, why not towers?
Net zero as a goal structure can work, but the economics of it are still in progress
If all this seems very obvious, that’s because we’ve had a long time to think about it. It is 25 years since Foster + Partners’ 1989 research project for the Obayashi Corporation, the 840m Millennium Tower. That was conceived as a vertical city of 60,000 in Tokyo Bay, that would be ‘self-sustaining and virtually self-sufficient’. Its exoskeletal tapering needle was also designed to cope with both high winds and earthquakes. The tower’s sustainability credentials were enhanced by its mission to concentrate rapidly-expanding populations into a small footprint, rather than letting them sprawl over valuable food-producing land. Others have proposed vertical farms to address the same problem.
Practically possible, perhaps, but easier to propose than to achieve. However, in the years since Foster flung down that gauntlet, steady progress has been made towards that goal. The steps along the way are significant: on a lesser but still large scale, the designs for the new ‘Scalpel’ tower by KPF on Lime Street in the City of London, close to Foster’s Gherkin and Rogers’ Cheesegrater, has achieved an interim BREEAM ‘Excellent’ certificate, the first to be awarded under the new, stringent, 2014 sustainability standard. For a 400,000 ft2 glass-clad office building rising to 35 floors and 190m above ground, that’s impressive. For the tower’s engineer, Arup, Mel Allwood says the certification ‘demonstrates that energy efficiency can be combined with exemplary indoor environmental quality.’ Including new public space and oriented to reduce southern exposure, the design scored highly in the BREEAM transport, land use and ecology, water, waste and management categories.
SOM’s Pearl River Tower in Guangzhou is nearly 60% more efficient than a conventional tower of the same size
Higher-profile in international terms is SOM’s Pearl River Tower in Guangzhou, China, completed in 2013. At 310m and 71 storeys high, and with a gross area of 214,000m2, this slender tower deploys a range of low-energy initiatives from an aerodynamic double-skin facade incorporating wind turbines to solar panels, a chilled ceiling system, underfloor fresh-air ventilation and good use of daylight through orientation and a relatively narrow plan. However, it is not carbon-neutral – the main reported stumbling block being the state’s reluctance to accept surplus power generated in this way. But it is still nearly 60% more efficient than a conventional tower of the same size, its extra construction cost should be recouped in five years, and it was the springboard for SOM partner Adrian Smith and associate partner Gordon Gill to set up their own eponymous practice. Their FKI Tower in Seoul, South Korea, confirms their commitment to sustainability: its horizontal sawtooth facade uses photovoltaic cells in spandrel panels, angled 30° towards the sun, which double as solar shading to the interior. Generating 780MW a year, the facade thus becomes integral to the energy strategy. Combined with geothermal power, natural ventilation and good daylighting it is the Korean equivalent of LEED Gold standard.
SOM has meanwhile continued its architectural and engineering research into this area. It deploys various technologies – such as the bank of fuel cells designed to generate 4.8MW of combined heat and power for its latest completion, the 1 World Trade Center tower, along with the planned use of electricity generated from Canadian hydro power. There’s been an acknowledged setback: Hurricane Sandy, when it ripped through New York in 2012 with its accompanying floods, destroyed the fuel cells and the building opened without them in operation. But 1 World Trade Center, though massively more efficient than the 1960s Twin Towers it replaces, was never designed with carbon neutrality as a goal, unlike other SOM projects – its research project into a composite timber/concrete skyscraper being a shining example. As SOM New York partner Kenneth Lewis puts it, ‘so much is site-specific’. To cover the possibility of on-site generators failing, he explains, cities like New York need equivalent back-up from the grid – which means that external power generation is not reduced commensurately.
‘Net zero as a goal structure can work, but the economics of it are still in progress,’ says SOM New York’s technical architecture director Nick Holt, pointing out that in 10 states of the USA there is parity in energy costs between solar and fossil fuels – but that this depends at the moment on tax incentives. As for a building generating its own power, rather than relying on green-energy sources from outside – that again comes down very much to location, some having many more natural advantages in terms of solar exposure and prevailing winds, for instance, than others.
Other energy sources are available, if you’re lucky. In Jakarta, Indonesia, SOM is now getting very close to the Holy Grail with the 500m Pertamina Energy Tower, an exemplar project for the state electricity generating company. ‘This one could be net energy positive,’ says Holt. ‘There’s a full-blown geothermal system that actually produces more energy than the site requires – a super-tall skyscraper and two other buildings. But that’s unique – it’s a volcanic archipelago that it’s being built on. We have superheated ground a couple of hundred feet down that we can take advantage of – that normally wouldn’t be available to you.’
Size matters – not just in terms of buildings but in the practices producing them. SOM is famously a multi-disciplinary global powerhouse of design, with enviable and very necessary research capability. Kenneth Lewis concludes: ‘We’re a global practice and we’re looking at this issue very carefully – both as a practice and as our commitment to the 2030 Challenge.’
The 2030 Challenge, an independent initiative adopted by the American Institute of Architects, is tough: to get to Net Zero in building design by 2030, with a sliding scale of energy efficiency operating in the intervening years. It’s ambitious – there’s 15 years to go. Achievable? 2030 will bring us to the 40th anniversary of Foster’s Millennium Tower project which arguably set the ball rolling. The RIBA is meanwhile pressing the UK government to accelerate its phasing-in of carbon neutrality in buildings, and condemns backsliding. We know it can and must be done. The only question is – by when?
ELEVATORS GIVE CARBON REDUCTION A LIFT
Skyscraper typology has always relied on developing lift technology to progress, so it’s no surprise to learn that the latest super tall buildings are pushing the envelope for lift design – or the cables at least. ‘Once you go above 300m, cable weight alone exceeds that of the lift and its occupants,’ says Arup director Julian Olley. ‘Steel’s capacity to support its own weight diminishes too. At 1km, the cable can support nothing more than its own weight and lifts of 600-800m need multiple heavy cables.’ This has driven carbon fibre technology, with firm KONE launching its own carbon fibre ‘ultrarope’ last year, pushing for it here on KPF’s Scalpel tower at London’s Lime St. ‘For tall buildings it has real advantages – it’s much stronger and lighter, creating energy efficiencies.’ And it doesn’t cost much more to specify either; as Olley points out, the main outlay at these heights is not the mechanisms, but their installation.
The jury’s out, it seems, on the other lift technologies that might, on the face of it, yield carbon savings. This is because the need to save energy has to be offset against convenience for the user. Thus double decker cars are great for people movement, but not for energy reasons, as you might be moving 20 tonnes of equipment to get a 65kg human from one floor to another. Likewise, there’s a big debate raging on the efficiencies of ‘destination control’. ‘The emphasis here is on minimum stops, so you could end up with four different people getting four different lifts, which doesn’t optimise energy use’ says Olley. Twin cab shafts, where two cars share the same shaft, can increase movement efficiencies and so save energy. Regenerative drives, generating energy from the braking mechanisms of high speed lifts, are now standard practice in Europe but are yet to gain widespread adoption state side.
In fact, Olley explains, the biggest savings are generally to be realised in the simplest ways. ‘Lifts do nothing for a considerable part of the day, so closing down banks of lifts, switching off lights and conditioning systems can have a real impact on energy consumption,’ he explains. There’s also using your feet, says Olley. ‘We have conducted anecdotal research which suggests that if a stair is placed in an obvious, accessible position between floors, 90% of people will use it rather than the lift to travel a single floor,’ which should influence multi-floor office fit-outs. As a result, he concludes, Arup, for example, is looking at the KT Building in Seoul for RPBW, which has lifts that stop every other floor, asking users (apart from the mobility challenged with an override) to take a flight down if necessary, to get to their destination. This reduces the number of lifts and energy consumed.
Of course, if energy saving energy is not your bag, then the sky’s the limit. Mitsubishi is now building the fastest lifts in the world, travelling at 18m/s for the 121-storey Shanghai Tower opening next year. And 2016 will see the 530m tall Guangzhou CTF Finance Centre opening with lifts travelling at 20m/s. The issue then becomes the performance of the brakes to stop them.