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Harnessing the sun and the sea

steel design

As the agenda of sustainability tightens its grip, designers have to learn new skills quickly. It is no longer sufficient to think that being 'green' entails low-energy design alone. Sustainable development requires architects and engineers to address the more difficult big picture of ecological design. As perceptions widen and expectations deepen, the challenge moves from energy to water, land utilisation, food production, recycling and waste minimisation. Energy still matters, especially as global warming (the result of burning fossil fuels) will remain the biggest environmental problem into the next century. But a human population of six billion puts stress on all resources, and to focus upon energy alone is to miss the real challenge of our age.

Putting ecological principles into design methodologies allows the elegance of nature to inform designers. After all, nature creates the maximum of richness and beauty with the minimum of resources and the maximum of recycling. Human systems tend to produce the minimum of beauty with the maximum resources and minimum recycling. Somehow society has to bring the two systems - man and nature - into step. The Seawater Greenhouse in Tenerife designed by Light Works is an important example of such harmony.

Interestingly, the Seawater Greenhouse takes water, not energy, as its starting point. It has been argued for some time that water is tomorrow's oil: that water stress is a greater global threat than energy starvation. Water is essential to health, food production and quality of life. By predicating the design of the Seawater Greenhouse on the resource of water, using condensation to create a system of recycling loops driven by sunlight, the design has both internal elegance and external relevance.

Sustainability is the biggest source of innovation in the construction industry at present. Ecological design not only reduces environmental impact, it creates fresh products and skills. Ultimately the green movement will generate a new aesthetic - a fresh concept of beauty. This is the basis for the Light Works design. The Seawater Greenhouse is so closely modelled on the laws of physics and the natural elegance of living systems, that it inevitably challenges orthodox constructs of architectural beauty.

Writing in 1892, L R Lethaby said that by combining 'nature and man ... all will be sweetness, simplicity ... and light'. It has taken a century for such a prediction to actually bear fruit in building. The Seawater Greenhouse is one of the best manifestations to date of the philosophy of organic systems driving built form. There are other examples around, such as the Eden Project in Cornwall designed by Nicholas Grimshaw and Partners and the Planet Earth Galleries at the Earth Centre by Feilden Clegg. But the Seawater Greenhouse differs in one important respect: it is designed for application throughout semi-arid regions in the world where seawater can be distilled to help local communities grow their own crops.

The idea is simple: a structure which uses solar-powered condensation to convert seawater into fresh water. Light Works, under designer Charlie Paton, has developed the Seawater Greenhouse, initially for Tenerife, but with a transferable technology which allows it to be employed anywhere where rainwater stress occurs alongside the sea, in warm to hot regions of the world.

The concept and building have a novel simplicity: greenhouse technologies, the science of evaporative cooling (taken from the car radiator) and the ancient art of de-salination are combined in a single structure. The Seawater Greenhouse produces fresh water and cool air (both essential for horticulture) using as the raw materials seawater and sunshine. The mechanism for the conversion is the building itself - a galvanised steel structure clad in polythene and incorporating cardboard evaporators and aluminium condensers. Cost and transport logistics are key considerations - the lightweight steel frame is both economical to construct and easy to move, the polythene sheeting is cheap and flexible and, like steel and aluminium, can be recycled at the end of its life. Polythene can also be modified to adjust ultraviolet light reflection and infrared absorption to suit local conditions.

The Tenerife greenhouse was prefabricated in the uk by Stratford Joists and erected on site by local contractors. However, the technology throughout is simple and so is appropriate to people's needs in emerging economies. For example, the cardboard evaporators are treated to maximise the crystallisation of calcium carbonate from seawater - a process which mimics the forming of sea shells. The energy sources are sun and wind: solar to drive evaporation and plant growth via photosynthesis. The heated air is trapped in the roof where it is ducted to the seawater evaporator using wind power (or thermal currents). The relatively small electricity requirements are designed to be met in the future by photovoltaic panels and a local windfarm. The overall process is expected to be highly energy efficient: 1 kW of electricity will remove 500 kW of heat, making food production viable in the greenhouse.

The evaporator is a cardboard lattice which is in effect the whole front wall of the building. The evaporator faces the prevailing wind with the seawater trickling down the lattice, cooling and humidifying all the air passing through to the planted area. It works in effect like a car radiator, using its specific conditions to its advantage, an example in this innovative design of technology transfer.

In essence the building collects distilled water in the same way that a plant leaf in the desert attracts dew to its surface. As a result, pure water is created without chemical treatment. The building can produce up to 100 litres per day per m2 of greenhouse, sufficient to irrigate an area up to 20 times that of the greenhouse itself. With agriculture accounting for 67 per cent of all water used globally (and 87 per cent in North Africa) one can imagine the enormous potential of Paton's greenhouse idea.

The pilot building at Grenadilla on Tenerife has confirmed the efficacy of the thermodynamic model. Trials have exceeded expectations in terms of fresh water generated, food produced and acceptance by local farmers. The lesson of this prototype is the importance of ecology in generating both the form of the building and in fashioning its life-support systems. The power of nature is harnessed using low-tech recyclable materials to produce a building which acts like a greenhouse and is shaped like a wind scoop. Without technological posturing or exaggerated engineering, the Seawater Greenhouse quietly points us into the next millennium.

Dr Brian Edwards is Professor of Architecture at the University of Huddersfield and serves on the riba's Sustainable Futures Committee.

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