Humidity solution delivers greenhouse energy efficiency
Greenhouse farming enables producers to grow crops in optimal conditions, by maximising heat and sunlight to extent normal growing seasons. Though this process offers numerous benefits, farmers still face difficulties when it comes to achieving energy efficiencies. A major challenge for example is ventilation: the natural transpiration of the plants causes humidity. “Many greenhouses open windows to reduce this humidity,” explains TheGreefa project coordinator Serena Danesi from Zurich University of Applied Sciences in Switzerland. “This however means losing heat and water. A lot of energy is required to balance the losses caused by ventilation.”
Absorbing humidity from air
The goal TheGreefa sought was to develop a system that reduces energy costs by recovering heat and water from the air, while maintaining optimal conditions in the greenhouse. Central to this was the piloting of a magnesium chloride-based salt solution. The solution absorbs humidity in the air caused by the transpiration of plants, and the absorption process releases heat. The system works on the same principle as a simple salt-based house humidifier that one might place in the cellar. “At a certain point however, the solution absorbs too much humidity and becomes diluted,” adds Danesi. “To regenerate, the solution simply needs to be gently heated. This can take place outside the greenhouse, and at any time. What you are left with is the concentrate, which can be reused.” This circular process requires energy at low temperature to run – this is energy that might otherwise not be used. Beside solar energy, another option notes Danesi might be to recycle the heat generated by an energy-intensive activity, such as a data centre.
Reducing thermal energy losses
The salt solution system was trialled in greenhouses in Switzerland and Tunisia. The equipment required is relatively simple: a plastic scrubber or column, along with pump and fan components. “Here in Switzerland, we managed to run our automated demonstration plant for a year,” says Danesi. “We showed that it removes the need for outdoor ventilation. As a result, thermal energy losses were reduced. Furthermore, thermal energy is released during the absorption process, and this can be used to heat the greenhouse.” Another advantage of this system, says Danesi, is that the salt solution can be regenerated with low-temperature heat and stored. This means that it can be separated from day-to-day greenhouse operations, and only used when needed.
Swimming pools, drying processes and historical buildings
Danesi and her team hope that their innovation will help Europe’s greenhouse farming sector to achieve significant energy efficiencies. The absorption process, which produces dry air, was also applied to dry goods such as herbs and fruits. “Greenhouses were the ideal test case for this technology because of the humid air,” notes Danesi. “Other possible users though could include fitness centres, swimming pools and historic buildings, where the air is also very humid, and there is a need to dehumidify.” The different applications mentioned above can also be integrated together in innovative district energy networks.The team is looking for industrial partners to scale up the technology and to create market awareness. “The technology itself is not complex,” says Danesi. “There is a need though to understand how the system runs. This is the major challenge to bringing this to market.”
Keywords
TheGreefa, humidity, greenhouse, energy efficiency, thermal, farming
