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Thermochemical Fluids in Greenhouse Farming

Greenhouse in Tunisia

Home > Greenhouse in Tunisia

The second prototype of TheGreefa is located at the research facilities of Partner INRGREF in Tunis. This demonstrator located in the Mediterranean climate focuses on combined Water- and Energy Efficiency.

Description

The governmental research institution is focused on water supply strategies in rural areas of Tunisia. The greenhouse business is an emerging sector of agriculture in the country, especially in the costal zones. However, it is affected by growing draught and intrusion of seawater into the groundwater stocks of coastal land.

A greenhouse with internal water circulation based on evaporation and condensation of water has the potential to make the business more independent. It will allow to reduce the need of fresh water and also potentially allow to continue the use of saline ground water by blending it with the condensate.

Climate control of a closed greenhouse is completely different compared to standard greenhouses. In an open greenhouse, solar radiation is mainly converted to latent heat and is withdrawn as humid and slightly heated air by air exchange with the environment. The main heat transfer is convection. This also means, that all water evaporated by plants is lost to the environment.

In a closed greenhouse, by far most of the heat energy has is released by transmission through the greenhouse cover. By this, the water vapor is kept inside and will be converted back to water by condensation.

To prevent overheating in this situation, the new prototype will be used to test and evaluate the following functions:

• Increase of greenhouse surface for improved heat transfer by adding an air to air heat exchanger cycle.
• Improvement of soil to passively store heat in the ground from day time to night time.
• Active transfer of heat to a day/night heat storage by use of an absorption system with direct heat and thermo-chemical driven latent heat transfer. The thermo-chemical concentrated solution allows the optimisation of latent heat transfer, as phase change between water vapour in the greenhouse air and water can be achieved at higher temperatures and higher total transfer rates.
• Regeneration (re-concentration) of the thermochemical fluid by use of different heat sources (1) heat from the greenhouse and (2) additional heat from external solar collectors

Further potentials of the systems are:

• External heat sources, as residual heat from industrial processes or from concentrated solar power (CSP) can potentially be used for the regeneration process and also contribute to cooling services, as dry cooling is replaced by evaporative cooling in a heat pipe system.
• A closed greenhouse needs CO2 supply but also allows a very efficient use of accumulated CO2 at increased concentration levels, thus improving the photosynthesis of the plants.
• A closed greenhouse allows improved pest control, as no insects can enter. The development of fungus diseases can be controlled by improved methods of air de-humidification.