The purpose of a greenhouse is to provide a controlled environment that promotes the optimal growth of high-value crops such as salad tomatoes, cucumbers, peppers, or flowers. With optimal conditions the output per unit area can be increased by a factor of 10 to 20 times that of growing plants outside. Saltwater-cooled greenhouses provide suitable growing conditions that enable year-round cultivation of high-value vegetable crops even in desert conditions that can be very hot but also cool and humid, particularly at night and in the winter. They provide the climate and crop control typical of very high productivity commercial greenhouses, while avoiding the high environmental and economic costs of traditional cooling methods.
By using seawater to provide evaporative cooling and humidification, the crops’ water requirements are minimized and yields maximized with a minimal carbon footprint. The basic principle is that the incoming air is conditioned through pads and pushed with fans into the growing environment using inflatable ducts under the crops. This ensures that the air is well distributed through the greenhouse. The greenhouse is therefore under positive pressure to prevent untreated air entering the space. The air is pushed out through openings at high level.
When it is hot outside incoming air is pulled over evaporative pads that have salt water running over them. The hot air is cooled by evaporation to produce cool and humid conditions in the greenhouse.
When it is cool and humid outside the greenhouse can be heated in a conventional way using heating pipes on the ground. In addition the air is can be passed over the pads with concentrated bitterns that will absorb the moisture in the air and warm it, instead of using heat through the rails.
The bitterns comprises mostly of MgCl that is the faction of seawater that comes after the NaCl has been removed. It is dried in ponds during the day using sunlight to heat the solution and drive of the water vapor to dry the solution.
The double roof can be used as a way of both providing heating and desalination the seawater. Waste heat from other processes in the SFP system can be used to evaporate water and create hot humid air that is circulated around the roof cavity. As it cools the moisture condenses to create fresh water and providing heat at night to the greenhouse. In this way we are able to produce enough water for production of crops.
The most water-efficient cultivation and irrigation methods will be used in order to maximize the benefits of hard-won water resources in the SFP system. Hydroponic growing methods, standard in the commercial greenhouse industry, will be utilized, which reduce water requirements by up to 50% compared to soil-based methods. A fertigation (fertilization + irrigation) system will deliver each plant with exactly the water and nutrients it needs, tailored to its stage of growth. The high-humidity environment of the greenhouse will improve water performance even further by significantly reducing the thermal and water stress on the plants. In effect, the evaporatively cooled greenhouse shifts the cooling mechanism by which plants regulate their temperature outside the plant and into the greenhouse infrastructure. Overall water requirements for evaporative cooling are not reduced – but, because the cooling takes place outside the plant, seawater can be used instead of precious freshwater. Under these conditions, the plant is allowed to devote its internal resources to growth more fully, leading to higher yields and water efficiencies.