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Thermochemical fluids in greenhouse farming

Periodic Reporting for period 1 - TheGreefa (Thermochemical fluids in greenhouse farming)

Reporting period: 2020-10-01 to 2022-03-31

This project is aimed at a new technology for heating, cooling, air humidity control and water recovery in greenhouses as well as for drying of agricultural goods using thermo-chemical conversion principles based on the use of salt solutions (TCF). The common effect in all applications is the hygroscopic property of TCF, allowing an uptake of water vapor from air thus releasing sensible heat involved in the phase change.

The technology allows
- the use of unexplored potentials of solar- and residual heat at farm level
- the conversion and storage of the heat in form of thermochemical potential without thermal losses, also for long time (seasonal storages)
- the use of this potential through re-conversion into heat for heating, cooling and humidity control.
- a circular economy for water: watering of crops, transpiration of crops, absorption through thermochemical fluids, evaporation, condensation, watering
- an effectiveness for capital and operative costs

The greenhouses are assuming more and more importance. In the developed countries a high quality of life concerns especially the diet, which must be fresh, healthy and varied. Long transport routes are often necessary. The transport of fresh fruit and vegetables causes high CO2 emissions. The poor regions with adverse conditions for cultures cannot afford the import of food. For both cases, the greenhouses with dryer and water recovery, operating with renewable energy, will be representing a right solution.

Thermochemical applications in agriculture have the potential to significantly reduce the energy consumption in greenhouse climate control as well as in crop drying and will provide an alternative to energy intensive water desalination in arid regions.

The overall objective of the project is to demonstrate the technology and prepare a path to the market.
Within two different demonstrators the technology is tested, further developed and disseminated (objective 1). Development of improved knowledge on modelling of the involved processes and the development of control strategies provide a bright insight into the novel approach (objective 2). Economic and environmental assessments will improve the economic and environmental potential of the technology by reducing costs and increasing energy efficiency (objective 3) and will allow to develop strategies to bring the technology to market as well as appropriate policies (objective 4).
The activities in the first period of the project were aimed to develop the concept for the demonstrators and begin the installations, to prepare the basis for the assessment activities through the market analysis.

The control philosophy for the demonstrator in the continental climate regions has been implemented: it allows to automatically control the temperature and humidity in a big greenhouse. It can switch from heating to cooling mode in order to manage the intermediate seasons and manage more systems simultaneously.
TCF are used for heat and humidity removal from a closed greenhouse, aimed to provide water recovery and CO2 enrichment. Therefore, a system is installed to remove sensible and latent heat form the indoor volume. This is achieved by increasing the overall surface of the greenhouse., by qualifying the soil for better heat uptake and by a set of absorber devices. Demonstrated in the Tunis greenhouse during night, water is released from the storage to the greenhouse using the thermal energy from the storage itself and from stored heat in the soil while achieving condensed water yields on greenhouse surface. Irrigation water evaporated in the greenhouse during daytime is recycled during nighttime by collecting the condensate.
The technology has been tested for food drying applications. The MgCl2 used for air conditioning scope is not suitable for the drying. The NaOH solution has been successful tested. A high quality of the dried food was achieved (project funded by the Swiss Federal Office for Energy, project Sonitro).

Market research has been performed: competition and potential positioning on the market. This preliminary study enhances that its alternatives are quite unique since all other competitors of the high-tech greenhouse sector propose isolated solutions whereas TheGreefa is an all-in-one technological package. The project deals with pre (greenhouse) and post harvesting technologies, such as water recovery or drying process.
Based on the market study, three cases have been selected for modelling, simulation and potential evaluation combined to three different crops.

To broaden the reach of the project's target groups, it is advisable to establish cooperation with other projects, which allows for the exchange of knowledge and broader networking.
TheGreeFa has started to collaborate with five projects funded by the EU and established the Alliance for Renewable Energy in Agriculture and Zero Fossil Energy (AREA ZERO). The projects within the alliance developed common dissemination materials and events.
Innovations:

- Use of TCF for air conditioning in greenhouses: air de-humidification can be provided by absorption processes with increase of the indoor air temperature. Turning aerification is replaced by closed air circulation. A further application allows to remove heat during daytime weather with re-direction of the heat during night or during colder periods of a day.

- Closed greenhouse climate control for water recovery and production with highly elevated CO2 concentration: irrigation water is evaporated by the vegetation and related water vapor is taken up by the TCF releasing heat. Water and heat can be stored together. Condensed water can be collected from the inner side of the greenhouse roof, while using the cool of the night to drive the phase change back to water and by releasing heat to the environment. The greenhouse operates in closed mode, with elevated CO2 for increased photosynthetic activity.

- Drying process at low temperature for food: the air is dried by the TCF but is not necessarily heated, as heat could harm the vegetables and affect their quality.

- Use of thermo-chemical fluids in a district network: Greenhouses or dryers based on absorption processes are not necessarily stand-alone applications. The TCF can be transported in district network. This allows shifting energy potentials in space, time and provides seasonal storage for smart energy systems.

The potential impacts are:

Energy savings:
• Reduction of energy consumption in air conditioning for greenhouses.
• Competitiveness of the food producers and food safety in times of growing energy prices.
• Less energy demand for food transport, if more food is produced locally.
• Higher productivity, e.g. reduced energy and water per kg of food.
• Increase the use of low temperature heat, which otherwise will be lost.

Water savings
• Reduction of water demand up to 80% compared
• Reduction of saline groundwater, the condensed water can be used to dilute the salinity content of water externally provided.
• Use of impure water, like pre-treated greywater from cities for irrigation and conversion to clean and hygiene condensation water

Reduction of pesticides
• Reduction of the use of fungicides thanks humidity control
• Less insects due to closed greenhouse
• High safety of labor conditions, no use of pesticide
Demonstrator in the greenhouse in Switzerland