Olympic velodrome one of the most energy efficient buildings
Thanks to its unique shape and beautifully architected curves, the Velodrome has become a favourite in the Olympic village. We investigate the challenges overcome in building one of the most efficient buildings in the history of the games.
As one of the more aesthetically striking constructions to grace the Olympic Park, the Velodrome created a discernible buzz in the architectural world from its inception. The sleek feat of architectural innovation, which began its advanced design stage in 2007, has provoked the usual tongue-in-cheek comparisons: a soup bowl; a riding saddle; a Pringle. The previous four Olympics took differing approaches to the design of their velodromes, but all of them now sit in various stages of dilapidation. With this in mind, London’s main priority was longevity with organisations working on the Velodrome dubbing the Olympic Games a ‘housewarming party’ when measured against the proposed legacy of the village.
In the process of redevelopment for the Olympics, an existing east London cycle circuit called the East Way was demolished. To counter negative perception of the new venue Mike Taylor, senior partner at winning bidders Hopkins Architects Partnership, reached out to the legacy target end-user first. He spoke to local cyclists to determine what they expected from a replacement cycling venue, meaning the resulting design is much more open than initially intended. A panoramic glass ‘ring’ of windows provides transparency, opening up the Velodrome and generating a direct visual connection between indoor and outdoor cyclists and spectators.
Chris Wise, of Expedition Engineering, argues that the now famous bowl-shape of the Velodrome is a piece of good design, but not as costly as people may believe. “We wanted to work with a minimum amount of material, minimum money with minimum damage to environment.” says Wise. “A flat roof is actually very heavy, so when it is curved it becomes half the weight. Two curves, as with the Velodrome, is one quarter of the weight and materials of a traditional flat roof, making it much cheaper and lighter.”
The design marries the efficient natural forms of a spider’s web with the natural geometry of the track. The long stiffness of the bowl and curvature of the 13,000m2 roof balance the structure, preventing it from buckling. Unlike most stadiums, which have a large structure on the top, the Velodrome peaks in a minimal, sharp point; to create this sharpness the building is angled at 42° at its steepest point and 12° at its lowest.
The roof is constructed using a cable system that can carry 20 times its own weight, a system modelled on a venue that featured in the Munich Olympics. “This is a very efficient way of using material, which is why people think it’s a green building,” says Wise.
“It was originally costed on the basis that it would be a steel-tube roof rather than cables, but we ended up using 14km of 36mm steel cable. The way the cables were laid was very innovative; they were laid flat on the seating area of the bowl and pulled out from edges, meaning there was no need for scaffolding.”
Gustavo Brunelli of BDSP Partnership, a UK-based engineering consultancy, won the bid to become the senior environmental consultant for the Velodrome. The building has since been rated the most energy efficient venue on the Olympic park, operating at 32 per cent below Building Regulation Part L, no mean feat considering the complicated needs of those who would be using it. “We wanted to make the building very efficient in its own right so we didn’t have to rely so much on the systems of the park,” says Brunelli. “But we only had control over a very small aspect of the building. As designers of the structure we had no control over the energy centre, so we had to concentrate mostly on energy reduction.”
However, reducing energy in a venue with such specific environmental design criteria from both its athletes and its spectators was not easy. The optimum competing environment for cyclists is a hot and humid one at 28°C, with a minimum level of 24°C, evenly distributed. This atmosphere creates minimal air movement, allowing cyclists to move through the ‘thinner’ air at a higher speed. The 6,000 spectators on the other hand are unlikely to opt for stifling temperatures of 28°C during the summer months, preferring a more temperate 18-26°C, with good levels of air movement for comfort.
Owing to the layout of the Velodrome track, the engineering issues were not only with reducing energy, heating and ventilation levels, but also with science. The 7km track sits in the bowl-like base of the venue, where optimum levels of heat must stay at a higher level, whilst the spectator seats rise up around the track demanding significantly lower temperature criteria. BDSP had to design a heating and ventilation control system that would in effect overcome the laws of science and prevent the hot air from rising, and combining the two without causing excessive air movement.
To compound the issue, architects and engineers alike had to consider the legacy of each individual building. Whilst athletes would be using the Velodrome at optimum competing levels for the two weeks of the Olympics, and a subsequent 20 days every year after, the public would be using it consistently for 345 days per year, reinforcing the mantra that the Velodrome was not just for the Olympics, but for life.
“This was the challenge of the design,” says Brunelli. “We ultimately had to cope with both conflicting requirements. Televised events for example require a minimum of 2,000 lights, whereas spectators only need 300, and they will be using the stadium far more. So we wanted to make the process very lean, very simple, and we started with natural ventilation. In this climate a velodrome does not really need artificial cooling, so we thought it would be a good idea to take advantage of natural ventilation during the mid-season and summer.”
Owing to the sleekness of the building, it was important the ventilation was integrated in a way that would not spoil the aesthetics, and as result the ventilation ducts are cut seamlessly into the base of the bowl’s façade. “We worked very closely with the architect in relation to fluid dynamics to find out how we could get the natural ventilation of the building to work at an optimum.”
BSDP and Hopkins Architect Partnership used computer modelling to determine the internal atmosphere within the proposed building in 12 different internal wind configurations, and aerodynamics and pressure effects of the building were a heavy influence on the eventual positioning of the ventilation ducts. The bikes are fragile structures, meaning athletes wanted the least amount of air movement possible on the track. At the highest level of the Velodrome only the façade is used to drive the air in and out of the building, which is made possible due to the shape of the structure, featuring higher outlets and the lower inlets at the edges and the base of the bowl.
But one of the most prominent technical struggles experienced by BDSP was heating the structure to a competing level of 28°C during the trickier winter months. Their answer was to design a compact building with high levels of insulation. “The Pringle-shaped roof was designed to wrap around the track and make it as compact as possible so that there is less air to heat, as unlike a gym we could not rely on radiant heat.”
The mechanical heating system, employed in the winter, uses an almost identical principle to the summertime natural ventilation system. Heat is pumped into the building on very short duct-runs in the same top-level position outlets as the summertime natural ventilation; these short runs mean pressure loss is minimal, making the whole system more efficient with less heat loss. Underfloor heating is also installed on the track centre and on the mid-concourse above the first tier of spectator seating.
So how does the heating and ventilation system work? Bruneilli exlpains: “We did a lot of simulation to [work out] how we would mix the two air temperatures up and initially had a lot of crazy ideas as to how we were going to store and release the heat. In the end, what we did was use the upper tier as a natural ventilation plenum, so the air can come in through the heating slots and out under the seats, and then back out through the top. We also have additional glazed louvers on the concourse to provide extra ventilation. Boost jet-nozzles mix the air ventilation as quickly as possible.”
All the mechanical ventilation equipment is squeezed into the cavity behind the upper tier of seating, meaning this cavity doubles up as natural and mechanical ventilation and a plant room. It is thanks to its unique shape and beautifully architected curves that the Velodrome is one of the most efficient buildings in the Olympic village in regards to use of space, with a small and compact footprint. *
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