H2020 TheGreefa Project: Thermochemical fluids in greenhouse crops.

Humidity Solution Provides Energy Efficiency for Greenhouses A new technique for dehumidifying and heating greenhouses could help achieve significant energy savings and offer potential for other end-use applications, such as gyms. Greenhouse agriculture allows growers to grow crops in optimal conditions, maximizing heat and sunlight to extend normal growing seasons.

While this process offers numerous benefits, farmers still face difficulties in achieving energy efficiency. One major challenge, for example, is ventilation: the natural transpiration of plants generates humidity. “Many greenhouses open their windows to reduce this humidity,” explains Serena Danesi, coordinator of TheGreefa project at the Zurich University of Applied Sciences in Switzerland. “However, this entails a loss of heat and water. A lot of energy is required to compensate for losses caused by ventilation.” Absorbing moisture from the air TheGreefa’s goal was to develop a system that would reduce energy costs by recovering heat and water from the air while maintaining optimal conditions in the greenhouse. Key to this was the pilot testing of a magnesium chloride-based saline solution. This solution absorbs moisture from the air caused by plant transpiration, and the absorption process releases heat.

The system works on the same principle as a simple salt-based household humidifier placed in the basement. “However, there comes a point when the solution absorbs too much moisture and becomes diluted,” Danesi adds. “To regenerate it, simply heat it gently. This can be done outside the greenhouse at any time. What remains is the concentrate, which can be reused.” This circular process requires low-temperature energy to operate—energy that would otherwise go unused. In addition to solar energy, another option, Danesi notes, could be recycling the heat generated by an energy-intensive activity, such as a data center. Reducing thermal energy losses.

The saline solution system was tested in greenhouses in Switzerland and Tunisia. The necessary equipment is relatively simple: a scrubber or plastic column, along with pump and fan components. "Here in Switzerland, we managed to operate our automated demonstration plant for a year," says Danesi. "We demonstrated that it eliminates the need for outside ventilation. As a result, thermal energy losses were reduced. In addition, thermal energy is released during the absorption process, which can be used to heat the greenhouse." Another advantage of this system, according to Danesi, is that the saline solution can be regenerated with low-temperature heat and stored.

This means it can be separated from daily greenhouse operations and used only when necessary. Swimming pools, drying processes, and historic buildings Danesi and his team hope their innovation will help the European greenhouse agriculture sector achieve significant energy efficiency. The absorption process, which produces dry air, has also been applied to dried products such as herbs and fruits. "Greenhouses were the ideal test case for this technology due to the humidity in the air," notes Danesi. "Other possible uses could include gyms, swimming pools, and historic buildings, where the air is also very humid and needs to be dehumidified." The various applications mentioned above can also be integrated into innovative district energy networks.

The team is seeking industrial partners to scale the technology and raise market awareness. "The technology itself isn't complex," says Danesi. "However, you need to understand how the system works. This is the main challenge in bringing it to market."