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Thermochemical Fluids in Greenhouse Farming

Solution 3

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Water recovery by evapo-condensation strategies, including sorptive drying and evaporative cooling with saline water

• Use of liquid desiccants for air de-humidification and air cooling in closed greenhouses
• Methods for liquid desiccant regeneration using heat from the greenhouse process as well as external sources like solar- or residual heat
• Methods for heat improved thermal- and thermochemical storage operation
• Methods for improved heat release to the environment with reduced water losses


Optimizing the energy efficiency for greenhouse heating using thermochemical fluids is one of the essential goals within this project. Also, for Mediterranean climate, greenhouse heating playing a big role in the future, as production in winter, when the prices for crops are high, is the most interesting market segment. Keeping the temperatures above ~12°C during 24 hours would allow a constant growth and would clearly improve the production and viability of controlled production in this period.

However, the Mediterranean area is highly affected by water scarcity. Many production areas are facing reductions in the groundwater stock. In this situation, the production may turn towards seawater desalination. Reverse osmosis, the state of art technology in this segment will require energy resources, that are not needed in systems based on rain fed agriculture. Water recovery and desalination technologies based on solar resources can be the alternative. Greenhouses play an important role in this context. Greenhouses contribute to water consumption. However, they can also be regarded as a specific kind of solar collector, in which solar energy is used for saline water evaporation and passive cooling strategies, using the cold of the night hours where it is used for combined water condensation and recycling of water.

Today, the research on irrigation water recovery and integrated desalination within greenhouses, based on evapo-condensation practices is provided only by a small group of enthusiasts. Within this group, a sub division works on the use of thermochemical fluids in open and closed greenhouses. The main purpose is to reduce humidity from air and by this also to reduce the latent energy content as part of a cooling strategy. Heat energy released by the phase change between air humidity and water can be stored within the fluids and stored between daytime and nighttime. In this way, heat from the greenhouse can be provided for the regeneration of the desiccant fluid by evaporating water from the solution back to the air. In this process, cool night time temperatures can be used for a condensation process and allow to produce sweet water. Also cold is stored during night and can be used for cooling processes during the next daytime period.

Water of lower salinity can be blended with condensation water and can be used for irrigation purposes. Water of higher salinity can be used within evaporation pads for additional cooling, while air humidity is recycled by condensation processes.