Greenhouse effect

At Kew Gardens science and art go hand in hand. Recognised by the United Nations as a world heritage site both for its work in preserving plant species and for its remarkable landscaping and buildings, Kew is also home to two remarkable examples of Victorian glass technology: the palm house and the temperate house. So when the Royal Botanical Gardens decided to commission its first new greenhouse for 19 years, it was vital that it embodied the best in both architecture and engineering. In the case of the Alpine House, that engineering had to include an air-conditioning system that would keep the cold-loving plants bathed in a constant draught of cool air -and it had to do this while consuming the minimum amount of electricity. To achieve this, architect Wilkinson Eyre called in Patrick Bellew, director of environmental building services company Atelier Ten. Founded by Bellew and fellow engineer Steve Marshall in 1990, Atelier Ten specialises in exploiting the properties of materials and forms to maintain buildings at comfortable conditions for their occupants - whether they are people or plants -using little or no electricity. ‘The Alpine House was an extraordinarily collaborative undertaking with the architects,’ Bellew commented. The air cooling is provided by a ‘labyrinth’ of concrete passages built into the foundations of the greenhouse. These passages draw in the air, and the thermal mass of the concrete draws in heat. The cooled air is channelled to the top of the planting beds, where it cascades down through nozzles, which prevents the plants from growing leggy. Compared with conventional cooling systems, relying on air-conditioning and refrigeration, power consumption is cut by up to 90 percent. However, Bellew said, it was only Wilkinson Eyre’s familiarity with techniques such as this and willingness to use environmental technologies that allowed this development. ‘If the architect hadn’t allowed the conversation to happen at that time, and just said he wanted to make an air-conditioned box with frozen trays to keep the alpine plants in, then we would never have had that debate,’ he said. As it happens, the labyrinth was the ideal way to support the tall, narrow curving glazed arch of the greenhouse. ‘The engineer used both levels of the labyrinth as his structural stiffeners - a box is much stiffer than a slab, and the labyrinth gave him the top and bottom surfaces of a stiff box that helps resist all the loads. So we formed this concrete box which is making the structure work, doing something to help control the environment, and all in a simple way.’ Bellew is in tune with architects. ‘I think it goes back to my training in some ways,’ he said. Educated at Bath University in the 1980s, Bellew came under the wing of Edmund ‘Ted’ Happold. This visionary architectural engineer was involved in the design of the innovative Pompidou Centre in Paris, whose services are outside the building to free up space inside for its modern art collection. ‘Ted ran a joint course with architects, structural engineers and building service engineers, and very much stressed commonality of purpose and vision — how you aspire to a common vision for a project,’ he said. After graduating Bellew worked for Happold for several years until starting up Atelier Ten with Marshall. Since then the firm has completed a number of high-profile projects to reduce the energy footprint of buildings. These have included the arts and media centre at Federation Square in Melbourne, which is cooled by a labyrinth similar to the Alpine House, but much larger; the library at Leicester University, which uses large thermal storage blocks in the ceiling and is heated by the body warmth of the students and the heat given off by the computers; and the Singapore Opera House, whose distinctive spiky coat is formed by thousands of ‘scales’ that shade the interior from the heat of the tropical sun. Bellew is modest about his place in these projects. ‘What we design in a building is basically the heating system and a fan. In terms of the engineering, it’s quite simple. But it’s the analysis of the problems to take out the engineering, to make the engineering weightless, that we do. That requires collaboration in a way that perhaps other engineering disciplines don’t.’ Computer simulations are an important part of this analysis. ‘We use multizone thermal models which look at the relationships between adjacent zones,’ explained Bellew. ‘We use quite advanced heat transfer models which are for the most part purchased in.’ These systems help to design the components of a cooling system, which might include labyrinths, thermal storage blocks in ceilings and floors, and earth-based systems where long underground ducts convey excess heat out of the buildings into the ground during the summer months, and pump heat from the earth into the building during the winter. These systems are powered by low-energy fans, often run through solar cells or wind turbines, which are controlled using inputs from temperature and humidity sensors throughout the building. ‘The controls are the most difficult things to specify and design, and the most critical part is the algorithm, the decision-making process that looks at the inputs and decides what action to take,’ Bellew said. ‘Our biggest problem is getting people smart enough to write the algorithms. The industry is set up to work a certain way, and if you don’t - and we don’t - you’re off the map.’ Convincing clients to work off the map is an important part of Bellew’s work, and not all of them are as easy to convince as Wilkinson Eyre. Bellew finds that comparing the systems to the way termites dig tunnels and use the mass of earth in their huge mounds to maintain the temperatures in the living and nursery chambers inside is highly persuasive. ‘Biomimicry is something I’ve been using in teaching for 15 years,’ he explained. ‘It immediately evokes in people the response that if it’s that simple, why can’t we do it? There’s a very, very simple mental process that makes us feel humbled by a small animal that does things by intuition.’ Sometimes the biomimicry can rear its head in unexpected ways, though. When devising the glass exterior of the Singapore Opera House, Atelier Ten used its own shading system. The basic design was two long, rounded glazed areas made up of around 10,000 glass panels, each of which had to be shaded to limit the amount of sunlight that could enter the building. The solution the team devised was a series of kite-shaped trapezoidal panels with two edges fixed to the glazing bars and the point projecting above the glazed surface. ‘We had to find a way to develop a computer model to pick that point in space and optimise the orientation of it.’ When completed, the building posed a remarkable resemblance to a durian - a large, spiky tropical fruit native to southeast Asia which smells so pungent that it is banned on Singapore’s public transport system. ‘There were titters when we unveiled it,’ Bellew said. ‘Everyone said, “It looks like a durian!” And we said, “What’s a durian?”’ These sorts of communication issues are rare. But Bellew is adamant that communication is increasingly important in projects where architecture meets engineering; and such projects are becoming much more common. ‘What we lost in the conjunction of architecture and engineering in the 20th century was the instinct for what works and what doesn’t work,’ he said. ‘In our world for engineers just to be engineers, and architects just to be architects, doesn’t really work that well. In many types of engineering, structural or mechanical integrity is all that matters, and looks come a poor second; but for us there are so many more variables to work with, physical things like light and sound. What’s important for engineers is to understand that three- dimensional space.’