London-based Seawater Greenhouse has developed a specially designed greenhouse for arid environments that acts as a humidifier through a combination of seawater, cardboard and air.
Charlie Paton, founder of Seawater Green, told The Engineer: ‘If it’s too hot, too dry, too windy, and too sunny then a plant’s stomata closes up to prevent water loss and photosynthesis doesn’t happen.
‘However, if the temperatures are extremely high then plants can still survive on the condition that they have high humidity.’
In use, seawater is evaporated at the front of the greenhouse to create cool humid conditions inside.
The greenhouse has a porous wall at each end that contains a rigid cardboard lattice. Seawater is poured over the cardboard lattice, which temporarily retains the moisture before releasing it into the greenhouse due to hot prevailing winds that blow through the wall. The evaporated seawater then cools the temperature within the greenhouse and creates humidity. Salt and other minerals collect in the base of the wall where they can be harvested and sold.
‘Seawater is taken from a saline groundwater well. It’s better to do that than use a pipe from the sea because this way it’s already filtered and comes up very clean,’ explained Paton.
The relatively cool air is then drawn through the greenhouse by fans. The company says that as the air leaves the growing area, it passes through the second evaporator over which seawater is flowing. This seawater has been heated by the sun in a network of pipes above the growing area, making the air hotter and more humid. It then meets vertical pipes containing cool seawater. When the hot humid air meets the cool surfaces, fresh water condenses as water droplets that run down to the base where they can be collected.
Paton, who has trialled units in Tenerife, Abu Dhabi, Oman and Australia, said up to one tonne of water can be generated per day through this process, which can be used to irrigate the crops. Excess water can be used on crops outside the greenhouse.
He added that Seawater Greenhouse can cut water consumption in greenhouses in arid regions by 75–90 per cent.
According to the UN, 1.2 billion people, or almost one-fifth of the world’s population live in areas where water is scarce and there are an additional 500 million people approaching this situation.