The Seawater Greenhouse generates fresh water, grows crops in the desert

An innovative project that turns the normal function of greenhouses upside down has been garnering environmental awards. The Seawater Greenhouse uses seawater to cool and humidify the air that ventilates the greenhouse and sunlight to distil fresh water from seawater, enabling year round cultivation of high value crops that would otherwise be difficult or impossible to grow in hot, arid regions. Greenhouses were built in 1992 on the Canary Island of Tenerife, and in 2000 on Al-Aryam Island in Abu Dhabi in the United Arab Emirates. The quality and quantity of crop production has been excellent in both cases, and the greenhouse has supplied more water than was needed for irrigation.

By combining natural processes, simple construction techniques and mathematical computer modelling, the Seawater Greenhouse thus offers a sustainable low-cost solution to the problem of providing water for agriculture in arid, coastal regions and a sustainable approach to desalinization.

The UK project won a Tech Museum 2006 Environment Award, the global annual Institute of Engineering and Technology (IET) award for Sustainability in 2006, and won second place in the prestigious St. Andrews Prize for the Environment in 2007.

The greenhouses are built of timber on a galvanised steel frame with polythene cladding, pipework and cardboard evaporators. All material are available locally, at low cost, and can be completely recycled. Air entering the greenhouse is cooled and humidified by an evaporator which provides good climatic conditions for crop growing. As the air leaves the growing area, it passes through a second evaporator which has hot seawater flowing over it heated from the greenhouse roof canopy. Fresh water condenses out of this hot and steamy air stream when it is cooled by water circulated through a condenser. The volume of fresh water is determined by air temperature, relative humidity, solar radiation, and the airflow rate.

Choosing the project as one of three finalists from 265 entries in the 2007 contest, the St. Andrews Prize for the Environment noted that this technology provides pure distilled water and food which could benefit more than 80 countries with arid regions near the sea, as well as areas of the world that face drought, salt infected soil, high temperatures and increasing shortages of groundwater.

The technology also inspired a dramatic 2005 design by Grimshaw Architects for a proposed redevelopment of the Las Palmas waterfront, in Grand Canaria, that would include a 3km promenade, botanic garden, and Water Theatre. The island’s two unique geographic features - steep beaches which bring the deep ocean's cold water near to the shore so it can be siphoned off for air conditioning, and a steady wind direction that can be harnessed to produce fresh water - could create the world's first harbourside development that is entirely cooled and irrigated by natural means.

Grimshaw’s architects believe biomimetic principles can be taken further, to generate new income as well as reduce running costs and resource use. They have designed a completely carbon neutral indoor botanical garden that could be built on an existing landfill site. For most of the year, the hothouse would be heated by solar heating through a glazed roof; in winter, additional heating would come from the landfill biomass. Biodegradable waste, deposited in large vertical composting units flanking the building, would generate heat for the indoor garden, and could earn as much as £7m ($14m) a year by substituting for a landfill site - and the compost could be sold for agricultural use.

This story was compiled from information on the Seawater Greenhouse website, the St. Andrews Prize website, the Tech Museum Awards website , a fascinating story entitled Borrowing from nature that appeared in The Economist’s Technology Quarterly Sept. 6, 2007, and the website of Grimshaw Architects.

 


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