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Thermochemical Fluids in Greenhouse Farming

Solution 1

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Humidity control, heating and cooling in one system through a single process

• Use of thermochemical fluids TCF (aqueous solution with MgCl2 ) for air de-humidification and air heating in closed greenhouses.
• Injection of the conditioned air directly to the crop’s areas.
• Energy saving due to the reduction of heat losses to the ambient and due to the recovery of the latent heat from the humid air.
• Combination to evaporative effect for a more effective cooling during the warm/hot periods.

Description

The reduction of the energy consumption and at the same time the increase of the use of renewable energy in the greenhouse farming is one of the main objectives of TheGreefa.

Greenhouse vegetable production in the Central and Northern EU countries is characterized by a very intensive direct energy input and differs significantly from the production system in the Southern EU countries. In Central and Northern Europe, the direct energy input is predominant accounting for over 99% of the total energy input using for heating, ventilation and air circulation.

Principles
The reduction of the energy required for heating is reached in TheGreefa recirculating the air inside the greenhouse avoiding the exchange with the external air. At the same time, the latent heat of the humid air is reconverted in sensible heat used for heating scope.

In TheGreefa, greenhouse is not necessary to regulate the humidity opening the windows: the TCF removes the excess of humidity produced by the transpiration of the plants, the thermal energy losses can strongly be reduced. At the same time, the water vapour of the air (humidity) is condensed during the absorption process released useful heat.

Beside the absorption process, TheGreefa investigates and tests different air distribution systems with the scope to provide the greenhouses with treated air only around the crops. This solution allows to save energy, because it is not necessary anymore to treat the air of the entire greenhouse to reach the conditions required by the crops, but only the air above the crops.

During the warm summer days, the humidity is still removed by the TCF inside the same system. The dried air passes then through a wet surface and is cooled down due to the evaporative effect.

Main components
Absorber
The main component of the air conditioning system is a plastic scrubber (absorber), where the air and the TCF flow counter-flow. The absorber is filled by random packings which increase the contact surface and time between the air and the TCF allowing the absorption process. The air humidity is controlled by setting the TCF concentration, while the air temperature by setting the TCF temperature.

Desorber
The desorber has the same construction of the absorber, but it is used to regenerate the TCF, e.g. to increase the salt solution concentration in the TCF. The evaporated water leaving the TCF is released to the atmosphere.

Seasonal storages
The great advantages of TheGreefa are the storages. The renewable energy used for the regeneration of the TCF can be stored in form of the concentrated for long time and transported over long distance without degradation in its properties. The storage shall be corrosion resistant, for example plastic, otherwise they do not require any specific design.

Air injection
Different solution for the air injection systems have been tested:
• Injection below the tables in case the crops are growing on tables (design 1),
• lateral injection with cover above the crops (design 2),
• air injection through the crops (design 3).