The water engine

It was raining in the desert. Squashed into a clapped-out old bus, its windows shut tight against the deluge, Charlie Paton was being bounced along a rutted road heading towards the foothills of the Atlas mountains in Morocco. Outside the bus, in spite of the rain, it was unbearably hot. But inside, despite the desert's heat, Paton was amazed to find the windows streaming with condensation. It set him thinking: why was this occurring inside a bus in the desert and, more importantly, could this phenomenon have practical applications?

Paton is a director of research and development consultancy Light Works. Back in his London office, he spoke to Philip Davis, a physicist colleague, who shed light on his observation. Davis explained that condensation had occurred because two things had happened.

First, the air inside the bus was hot and steamy from the passengers and their wet clothes. Second, rain falling on the roof and windows of the bus kept its bodywork at a constant low temperature. Condensation was occurring because the bodywork was cooling the air below the dew point of the air inside the bus, so water vapour in contact with the bodywork turns into water. "It is the same phenomenon that causes condensation to form on a glass of cold larger on a hot summer's day," say Paton.

That was 10 years ago, and since then, Paton has been busy. He has succeeded in using the condensation principle he first observed in Morocco to design a greenhouse for arid coastal regions. This greenhouse can produce fresh water for irrigation directly from sea water. And, by the same process that produces water for the crops, the greenhouse creates a cool and humid environment in which to grow them. The result is a bumper harvest where, otherwise, none would be possible.

The principle behind the building is that pure water is evaporated from sea water. The greenhouse is designed to maximise the amount of that evaporation by adding as much moisture as possible to the air inside. This moisture is condensed on a cold surface to produce distilled water for irrigation.

The costs of producing water this way are minimal – most of the energy for the process is freely available from the sun and the wind. Electrical power is needed to pump sea water into the greenhouse, but this can be sourced from photovoltaic panels where grid power is absent.

In 1994, Paton built a prototype of the greenhouse on Tenerife in the Canary Islands.

This prototype was initially part-funded by the European Commission. Funding dried up part way through construction, however, after the powers that be became concerned that the greenhouses would flood the European Union with cheap fruit and vegetables from North Africa. The project went ahead anyway, and Paton was able to ratify the theory behind his design. In fact, the experiment proved highly successful, with crops grown in the prototype producing much higher yields than expected – and in a shorter growing period. His greenhouse won the Corus-sponsored Design Sense award in 1999.

This year, the first full-scale greenhouse has just been completed for the government of the United Arab Emirates. The building has been designed to minimise construction costs, as it consists of a light steel structure covered in polythene. This allowed most of the construction work to be sourced locally.

Paton is now looking for other applications for his design. "It is," he explains proudly, "suitable for producing pure water from sea water for any application where waste heat is available." At the moment he is looking into the possibility of using waste heat from air-conditioning systems or manufacturing processes, and it is even being considered as a way of irrigating plants at Tenerife airport.