THE GLASS HOUSE The Eden Project endeavours to both recognise our countrys great past heritage of plant exploration and at the same time look to the future. Helping to define, through research, a world where mankind can live and develop within sustainable parameters. To design the built form of a glasshouse, and to represent these ideals, requires both an understanding of the architectural heritage that made our past botanical achievements possible, and ideas for a more sustainable future.
75 THE EDEN PROJECT GLASS HOUSES WORLD ENVIRONMENTS Andrew Whalley B.Arch AA Dipl AIA RIBA Director Nicholas Grimshaw & Partners THE GENESIS OF EDEN Without plants there would be no life on earth. Plants are unique in their ability to convert the energy of the sun through photosynthesis and supply us with our lifeline support systems. Oxygen - food - fuel - medicines - clothes. Even our use of fossil fuels coal gas and oil are exploiting the results of photosynthesis from millions of years ago. Our increasing understanding of horticultural sciences, exploration of the world and exploitation of plants is inexorably entwined with the development of our civilisation and the potential of mankind. The Earth Intensive farming Sunflowers THE GLASS HOUSE The Eden Project endeavours to both recognise our country's great past heritage of plant exploration and at the same time look to the future. Helping to define, through research, a world where mankind can live and develop within sustainable parameters. To design the built form of a glasshouse, and to represent these ideals, requires both an understanding of the architectural heritage that made our past botanical achievements possible, and ideas for a more sustainable future. As a nation of adventurers we have developed navigational and seafaring skills that have allowed us to explore the globe. The ports of Cornwall were the first landfalls encountered by many returning eighteenth and nineteenth century sea captains, many of whom collected plant specimens on their travels. Captain Cook was well known for his scientific interests and most ships'doctors in particular had great scientific interest in what they saw and collected on their travels. In parallel with the work of such famous botanists as Sir Joseph Banks was the emergence of a new architectural form to house and protect these new and delicate specimens, a built form that could transform the temperate climate of the British Isles into the humid tropics -the Glass House. The first half of the nineteenth century is the period of rapid change during which the demand for more exotic specimens in turn demanded much higher levels of natural light than was provided by masonry buildings with large windows. In 1811 Thomas Knight, head of the Royal Horticultural Society, set out a challenge: " not a single building of this kind has yet been erected in which the greatest possible quantity of space has been obtained and of light and heat admitted - proportionate to the capital expended." Interestingly this statement was almost repeated verbatim by Peter Thoday at our first briefing session on the Eden project. Sir Joseph Paxton is synonymous with the emergence of this new design approach. He introduced industrialised and prefabricated techniques that produced great economies and speed of construction. However it is interesting to note that all of his work including the Great Stove at Chats worth (1841) and indeed the Great Exhibition of 1852 kept to the relatively safe and known technologies of timber construction. A bigger influence on the new architectural form was through the exploitation of new technology. The Great Stove, Timber glazing systems, Chatsworth, 1841 Crystal Palace, 1852 76 In 1816 John Claudius Loudon patented a technique that exploited the malleable qualities of wrought iron, drawing and curving it into a structural glazing sash bar. Immediately he saw that this technology offered possibilities for a new type of Architecture. In his own words: " it may be beautiful without exhibiting any of the orders of Grecian or of Gothic may not therefore glass roofs be rendered expressive of ideas of a higher and more appropriate kind, than those which are suggested by mere sheds or a glazed arcade." Glass during this period was still taxed, and this was applied relative to the size of the panes. Glass was also still an expensive luxury material produced by spinning plates or cutting it out of cylinders. Consequently it was highly desirable to construct these new plant houses with their huge expanses of glass using many small sheets rather than large sheets. Traditional timber glazing bars with small sheets of glass were relatively inefficient in comparison to the slender wrought iron glazing bar; this produced the optimum transparent skin. Loudon developed his system with the contractor W and D Bailey using the glass as part of the structural system. This gave rise to completely new expressions of architectural form. Many of these glass houses were lost during the early part of the twentieth century. Fortunately one example remains to this day at Bicton in Devon. Its very light filigree structure is reminiscent of the delicate structure of a leaf. 6. Bicton Gardens, Devon, J C Loudon Conservatory, Liechtenstein Leaf structure Castle The Palm House at Kew, built in 1848, uses the same technology and is far better known. It, also, demonstrates the value of collaboration, this time between the architect Decimus Burton with the intuitive engineering expertise of Richard Turner. They both answer the challenge from Thomas Knight by harnessing the best of the current technological understanding and generating new architectural solutions that were truly great expressions of the era. Palm House, Kew Palm House. Kew Kibble Palace, Glasgow It is interesting to contrast this to the temperate house designed by Burton ten years later, without the ingenuity of Turner, where a pre ordained architectural form takes over. The development of this very organic exploration of design solutions probably culminates in the soft rolling forms of Kibble Palace, originally constructed in 1865 and later dismantled, shipped and reassembled in Glasgow's botanical gardens. Certainly this building was enormously influential on myself during my time studying at the Mackintosh School of Architecture, and was a very strong influence as we explored solutions for the Eden Project. Paxton's ridge and furrow glazing at Chatsworth with its east west orientation minimised the loss of sunlight due to the reflective nature of glass. At the same time he had developed new mechanised prefabrication techniques that delivered an improvement in construction times and Paddington Station, 1 K Brunei. 1854 77 construction efficiencies. The influence of the Great Exhibition (1852) on I K Brunei's Paddington Station (1854) is well-documented; both were built by Fox Henderson. Undoubtedly the techniques that had been developed for the glass house were transferred and developed for the demands of the latter nineteenth century: the large Railway sheds. This sequential influence took root in our own work when we came to design Waterloo International Terminal . There had in fact been little in the way of ail way architecture since the nineteenth century in the UK. The terminal would symbolise not only a new renaissance of high speed rail travel but also a new permanent connection and gateway to mainland Europe. The roof, although only 10% of the overall building budget, was to be the signature and emblem of this new service. International Terminal, Waterloo Station, 1992 The technical challenge was to design a roof structure and envelope that could deal with the twisting and diminishing geometry of the track alignment. For speed and economy the glazing had to use standard rectilinear sheets of glass. In collaboration with the engineer Anthony Hunt Associates we developed the steel and glass roof that took on the sinuous shape of the tracks below. Aerial view of the International Terminal, Waterloo This is in fact where the line of thought turns full circle. Glass Houses to Railway Halls and back to Glass Houses. It was because of our work at Waterloo that the team were asked to prepare proposals for the Eden Project. Eden International Terminal, Waterloo at night EDEN Our brief was to create a showcase for global biodiversity and human dependence on plants. The structures were to be large enough to allow the exhibition and study of a range of plants on a hitherto unachievable scale. Within the first phase two climate capsules were to be recreated from different world environments (biomes). The humid tropics (rain forest) and the warm temperate (Mediterranean) biomes were to be constructed as enclosures; a third zone, the temperate, was to be in a sheltered external area. It was the team's goal from the outset that the project should both entertain and educate at the same time. The creation of natural habitat zones that have the height and volume to allow plants to grow in a natural way, to their full mature height, has seldom been done; we believed it required fresh thinking. With the humid tropics this required an enclosure that would allow trees to mature and form a canopy at forty metres in height, setting a clear span building height of fifty metres. Botanical science has developed from the nineteenth century encyclopaedic cataloguing of specimens. Now, in the twenty first century, science is exploring our understanding of biodiversity and the importance of genetic grouping and ecosystems. Our goal was to develop an architectural response that was informed by these new demands in the same way that our predecessors had, almost two hundred years ago. Finding the right site for this new botanical garden was critical. The original sites that were considered were the clay workings at Roche. The 'Clay Alps' were mountainous heaps of clay and spoil; apart from the difficult ground conditions they were also highly exposed. The final chosen site was an old clay pit that was coming to the end of its useful life. This hollow in the ground provided the inspiration for our design solutions. 78 The Bodelva china clay pit, St Austell, Cornwall TOPOGRAPHY AND FORM Our starting point was to use the contours of the clay pit as an integral part of the architecture, using the quarry wall as one side of each biome. This had the advantage of creating great spatial drama and a terraced profile as staging for the planting , thus creating drama from day one, even when many of the plants would be relatively immature. A three dimensional model was created on the computer to explore the potential sites for the biomes. This was assessed by looking at both the topography and potential solar orientation. Sun path analyses were used to find the optimum location for each biome. Early concept of 'arch' scheme Early concept sketches Ground model of existing site topography The inevitable protracted funding process gave us time to thoroughly evaluate our proposals. There were the logistical problems of transporting large steel trusses in Cornwall. The quarry was also changing shape as the last of the clay was extracted, effectively meaning that our ground terrain was constantly changing as we tried to complete our proposals. NATURE AND EFFICIENCY There are many influences during any design process. During the development of Eden we often referred to the Science Fiction film from the early seventies entitled 'Silent Running' . This centres around a series of very light weight biomes replicating the earth's principal climate zones, all floating in outer space. The concept of these biomes helped to encourage us in our conviction to explore new and innovative technical solutions for the structure and envelope. At this time we were appraising light weight foil as an alternative to glass and we wanted a solution that would capitalise on the properties of this ultra light weight material, in a similar way as Louden's wrought iron system did for glass. Model of 'arch' scheme Roof of 'arch' scheme « • Our first proposals built upon our work at Waterloo with a series of diminishing primary steel trusses connected to each other with a secondary system, supporting a ridge and furrow glazing system that would have been familiar to Paxton. However at this stage we had established the idea of a free form in plan and section that hugged the contours of the pit. "%rfi*>irr- Image from the film 'Silent Running' 79 3 K^^M^t^S Responsive structural system, Andrew Whalley & Chris McCarthy On a previous project I examined, with the engineer Chris McCarthy, a responsive structural system that could adapt to changing loading conditions. Forces could effectively be moved around the system in the way a body does with bones, muscles and tendons. This skeleton carried an ultra light weight skin formed from a series of pneumatic pillows using layers of transparent foil and spluttered metal coated foil. Again loads could be responded to by varying the pillow's air pressure, resulting in an extremely light weight dynamic enclosure. Ideas that start as theoretical exercises can help develop and inform later projects. Nature has many lessons to teach both architect and engineer; most obviously nature is based on the minimum use of energy and the careful use of resources i.e., efficiency in metabolism. What often appears to be fragile is actually robust as it has an ability to adapt. Radiolaria Honeycomb Microscopic photograph of a fly's eye An excellent example of these efficiencies can be found when examining the one-celled creatures Radiolaria. As they grow through centrifugal force the silica that they are formed from takes the geometric form of the minimum length hexagonal pattern. In just the same way bees build honey combs because they are 'busy bees', trying to achieve the maximum with the minimum effort. Nature seems to continually form hexagonal structures as the most efficient way of absorbing stress. THE EDEN SPHERE We resolved our concerns by finding a simple and direct solution to the geometry. David Kirkland redefined the generation of the biome forms as a series of interconnecting spheres. We took this computer model and intersected it with the terrain model of the clay pit, which in turn defined the final form of each biome. This allowed us to develop a proposal that was independent of the exact quarry profile. It also allowed us to define the surfaces as geodesic shells, that could get the most out of the long span ultra light weight nature of foil pillows. Connecting spheres Sketch of siting Spheres & structure As with the Radiolaria the geodesic shell is formed from hexagons to minimise on tube length to surface area. The size of the hexagonal grid is a proportion of the diameter of the sphere, with the largest dome being subdivided into pillows with a diameter of approximately eleven metres. s ^^mESv' • ft" ' -*WW •0*0 . ,»«••; ^MWW\ Computer-generated image of the first 'geodesic' scheme HOW TO BUILD A SPHERE? Everybody is familiar with the problem of representing the surface of a sphere on a two dimensional plane. An orange skin can not be rolled out flat on a table, and the attempt to represent the surface of the earth on a sheet of paper leads to great distortions as far as the size of the land mass is concerned. However the surface of a sphere can be subdivided into planar triangle-based surfaces similar to a football. The earliest example for the realization of a geodesic sphere is Walter Bauersfelds Zeiss Planetarium in Jena, Germany from 1926. 80 Later, Richard Buckminster Fuller carried out substantial research into geodesic spheres and their underlying geometry. The problem has always remained the same. How can the surface of a sphere be subdivided into a number of building elements that: • can be easily constructed with available construction methods • are ideally selfsimilar in order to reduce the number of different components • preserve the structural integrity of the overall structure THE GEOMETRY OF THE ICOSAHEDRON APPLIED AT EDEN Like earlier predecessors our geodesic domes are based on the geometry of the icosahedron, an element with 12 corners and 20 surfaces. Circles drawn through two adjacent comers of the icosahedron result in 'Great Circles', because all corners of the icosahedron are positioned on the surface of a sphere. These Great Circles intersect in such a way that 5 warped triangular and selfsimilar surfaces are generated around each comer of the icosahedron. Because each comer of the icosahedron is surrounded by 5 triangular zones the element directly on the comer is a pentagon. The subdivision of the sphere's surface into triangular zones with equal side lengths is the key to finding a construction method that applies selfsimilar sticks and varying nodes to form the structural 'net'. The triangular base zones described above can be further subdivided into triangular elements at a selected frequency. The body formed with planar triangles approaches the spherical shape more and more the smaller the subdividing triangular elements. At Eden we have omitted triangles in such a way that the zones between the pentagons are filled with hexagons very similar to the surface of a football. Unfortunately these hexagons are not planar in a geodesic sphere based on an icosahedron. This was obviously a problem keeping in mind that the hexagons are the basis of our cladding panels. Developing our ideas futher with Mero GmbH a solution arose. This was to apply a recently developed theory by the Russian scientist Pavlov who managed to work out a geodesic sphere with hexagons that are planar and the geometry still based on the icosahedron. THE HEX TRI HEX GRID The resulting net of hexagons alone could have formed the envelope for the Eden biomes. However the stick diameters for the individual elements would have been around 500mm. It was felt that by introducing a second, inner layer, of structure the member sizes could be reduced substantially leading to a far more economic structure with a more light weight appearance. The inner layer consists of triangles below the node points of the outer layer which circumscribe hexagons themselves. The connection between the two layers is established with diagonals which connect the node points of both layers. We call the resulting geometry a 'hex-tri-hex' grid. Although on first appearances this is a very ordered geometric solution there is a complication in resolving the interconnection of the spheres as each has a different diameter and sub divisional grid. Again a solution can be found in nature. A dragonfly's wing is constructed from a series of very light weight skins with a hexagonal cell structures. These are connected to the body by a series of primary sub dividing elements. When the cell system meets the primary system it simply connects in a perpendicular relationship. Exactly the same can be seen with soap bubbles. If they are approximately the same size they take on a hexagonal geometry. If you sub divide them then again they join the subdivision at right angles. Nature does not have formalist architectural hang ups! Dragonfly wings Soap bubbles As we developed the geometry the computer was invaluable not just as a number cruncher but as a way of exploring the spatial forms that the combination of differing diameter interconnecting spheres and the pit topography created. We undertook a series of computer studies that culminated with a series of 'fly through' animations. Still from 'fly-through' animation in the Humid Tropics Biome 81 ENVELOPE The skin of the biomes utilises Ethyltetraflouroethylene foil, ETFE. It was selected as its performance was far better than glass in both horticultural and energy terms. It allows a far greater range of daylight to pass through in particular the Ultra Violet part of the light spectrum. Its light transmittance quality is further enhanced by its long span characteristics: the largest pillows at Eden span eleven metres without any secondary structural system. Consequently there are very few light-blocking structural members. Efficacy Transmission (relatival L ultraviolet tuv> -L visible light (VIS) 0.00001 +^—•—, , i ~ ! 1—i 1—• i i——i—i—i—. 1—i 1 r—i—i—"-^H O 250 300 3B0400 500 600 TOO nm 780 Wavelength = . • i». Light transmission of ETFE/glass compared (information from Dyneon GmbH) The pillows are up to two metres deep and are formed from three layers of ETFE foil. The two air cavities are pressure equalised by means of a small connecting aperture but in terms of thermal transmittance they are effectively separate. The complex geometry of the pillows - hexagonal on plan and double-segment-shaped in section - makes U-value calculation by conventional methods impossible. Much of the cavity space is large enough for significant convection currents to be set up. A combination of theoretical analysis (computational fluid dynamics / finite element analysis) and empirical testing (by means of hot-box experiment) determined that the U- value was approximately 2.7W/m2K. Therefore, in spite of the material being 200 microns thick or less for each layer, it performs better thermally than double glazing. As with glass it would be possible to apply low emissivity coatings to one or more of the ETFE layers to achieve even better performance. Our goal was also to create a solution that embodied Eden's environmental ethos. The embodied energy is substantially better than a glass solution. In material terms it uses less than 1 % of the volume of material that would have been used in a double glazed solution. This, coupled with a proportionate reduction in supporting framework, again substantially reduces transportation impact and costs. The material is very light to erect so again there is a reduction of site equipment. Most importantly it can be recycled. This desire to optimise on the properties of foil, i.e. large span pillows, has meant a great deal of research and testing. Single-chord & bowstring Hexagon with ETFE cladding geodesic Our original design was for a single chord hexagonal grid geodesic form with a secondary bow string cable stay support. The geometry and pillow sizes were informed through discussions with the two principal foil supplying companies. A whole series of solutions were then developed and considered including timber/ glue-lam and aluminium for the geodesic structure. The eventual winning contractor was Mero GmbH who offered a combined structure and envelope package. As the two are intrinsically linked this was a significant advantage. Their experience with this type of structure brought considerable benefits to production and assembly. Their preferred material was steel and by adopting a double chord system the tubes could be kept below 200mm despite the fact that the span was 100 metres. Mero's sub contractor for the envelope was another German company, Foiltec GmbH, and over a period of nine months we have developed and tested the pillow solutions. Initially the size for the biggest pillow was based on intuition - a feeling for what the largest achievable span was likely to be. There were incentives on all sides to design as large a hexagon as possible: • the larger the hexagons were, the lighter the steel would be and thus the cheaper the overall building. • bigger hexagons also meant more light and, because the frames are relatively less insulative than the pillows, better thermal performance. A hexagon side length of 5.5m, equating to a diameter of 11 m, was set as the target. This resulted in pillow sizes of over 75 square metres. The first stage was to establish the wind loads that needed to be accommodated. A scale model of the biomes and a few square kilometres of the surrounding terrain were built and tested in a wind tunnel. This was followed by full-scale tests to establish the behaviour of the ETFE under dynamic biaxial loading at varying temperatures, the strength of the welds (ETFE is manufactured in 1200mm wide strips) and the strength of the connection to the extruded aluminium frames. Parallel to the empirical testing, computational non-linear analysis was carried out based on the material's physical characteristics (established by Instrom testing). By comparing the results of the empirical and theoretical analysis a clear picture was built up of how the overall system behaved under the design loads. 82 Testing an ETFE foil pillow in Bremen, Germany It emerged that the 3-layer cushions were not robust enough to construct hexagons with a 5.5m edge length! The first solution that was attempted was to install reinforcing cables over the pillow to reduce the effective span of the ETFE. While this was workable in principle there were a number of disadvantages: it was a relatively expensive solution, and was likely to cause chafing between the steel cables and the ETFE. Significantly increasing the thickness of any individual layer was not feasible because it resulted in embrittlement: to work effectively the ETFE needs to maintain elasticity. In one of many round-table discussions a solution emerged to use a double layer of foil for the externalsurface (the part subjected to the most onerous suction loads). The two layers would work together to share the load. A second series of tests was then carried out which established that the proposal would work with a margin of comfort. Test pillow in Bremen, Germany ENVIRONMENTAL SYSTEMS Greenhouse design has frequently suffered from the environmental control systems, both from a successful operational aspect and from the visual impact of the system itself. Very early on, with Peter Thoday, the horticultural consultant for Eden, we established the plants' environmental requirements for each biome. Within this context we defined the design parameters with Ove Arup. We did not want to have any sun-shading devices on the envelope and we aimed for the minimum of any mechanical devices or plant within the biomes. In principle this was achieved by using the form of the biomes for warm air reservoirs; the curved biome form would assist the natural convection currents created with air jets. 'Traditional' calculation methods were used early in the design process to establish the number of air-handling units needed to supply the large volumes of heated air required. Similarly the strategy for ventilating the Biome enclosures was established, involving a combination of opening glass louvres at low level, with hinged panels at the top of each dome to exhaust hot air. As the design progressed, Ove Arup & Partners undertook a number of more detailed studies to refine the environmental systems. In particular a Dynamic Thermal Model was used to calculate the thermal conditions within the Biomes for typical days in selected months. This study then provided the data to allow a detailed study of air movement within the Biomes using Computational Fluid Dynamics (CFD). CFD analysis was carried out for the Humid Tropics and Warm Temperate Biomes during Winter and Summer conditions. These studies produced predictions of environmental conditions in terms of air temperatures and velocities; the results broadly followed the conclusions of the initial calculations. Critically, however, the CFD model allowed us to assess the effects of removing, or relocating, some of the air-handling units. This proved important as the terrain around the Biomes makes access to some areas difficult both for initial installation and subsequent maintenance of the mechanical plant. Consequently we were able to fine-tune the mechanical systems, omitting a number of air-handling units and relocating others to areas of easier terrain, whilst maintaining the required environmental conditions within the Biomes. One interesting result of the CFD study relates to the effect of air movement on the plants within the Biomes. In normal greenhouse conditions plants tend to grow with relatively weak stems due to the lack of wind. We have discovered that air speeds within the Eden Biomes will tend to strengthen the plants; ripples of air movement recreating natural conditions to produce specimens as close as possible to their counterparts in nature. THE GARDEN Throughout the project we have continued the same philosophy towards sustainability, challenging the way we have previously considered designing buildings. The visitor centre is a prime example. Again it is built into the topography of the pit with part of the building sunk into the terrain with a grass roof. To keep the embodied 83 energy of the building to a minimum we have used materials from the site in the form of gabion walls using site rocks. Soil from the pit has been used to construct rammed earth walls and much of the cladding utilises light and economic cedar wood shingles. The Visitor Centre A very similar approach can be found in the "Biome Link", the connection and entrance building for the two biomes. The Biome Link responds in plan form to the same rhythm of interlocking spheres exhibited by the geodesic structures that it connects. Dining and exhibition areas are bounded by the sweeping perimeter of the front glazed wall, and separated from back-of-house facilities such as kitchens, toilets, offices and "plant holding areas" by a continuously curving double-height earth-rendered wall. Access from the external gardens into the building is via an elevated walkway, which passes over the external terrace then penetrates the glazing where it splits, taking visitors at high level either to the Humid Tropics or the Warm Temperate biome. jtxjjSw The Biome Link The perimeter glazed wall achieves solar control by the use of external cedar louvre screens. These allow views directly in and out of the building, whilst shielding the internal public areas from strong direct sunlight. They also lend a layering to the facade that helps to break down the boundary between internal and external spaces.The Biome Link has a turf roof that curves to align with the adjacent geodesic structures. It slopes down at each comer of the building where the surrounding ground slopes up to meet it, so that the overall effect is of a "saddle" of ground covering the Link. The roof structure is an array of steel bowstring trusses. These vary in shape to accommodate the profile of the curved roof as it transforms from the Humid Tropics arch geometry to the Warm Temperate arch geometry. This self effacing approach hopefully puts the aspirations of the Eden project before any preconceived architectural metaphors. We hope that in the same way as the technology of wrought iron brought about a revolution in the design of the glass house at the start of the nineteenth century, the technologies adopted at Eden will be part of a major step in the development of greenhouse architecture at the beginning of the twenty-first century. Model of the Humid Tropics Biome We have been inspired by the elegance and economy of design of airships, more than any other type of constructed form they have to explore maximum efficiencies. Perhaps this can be best summarised by the weight of the biomes. The humid tropics biome weighs approximately 450,000kg; this is actually less than the weight of the air that the envelope encloses. Fortunately it is firmly bolted down to the ground! Luftschiffbau Zeppelin airship 129 Hindenburg, 1936 84 Dome A, Humid Tropics Biome, February 2000