GRIFA Thermochemical Fluid System for Greenhouse Climate Control

The GRIFA system is a thermochemical fluid-based technology for humidity and temperature control in greenhouses, using hygroscopic salt solutions like magnesium chloride and sodium hydroxide. It dehumidifies and heats greenhouses by absorbing moisture and releasing latent heat, reducing reliance on external heating. The system operates in two phases: absorption inside the greenhouse and regeneration outside using low-grade heat sources such as solar thermal panels or waste heat. In a 600 m² greenhouse near Zurich, orchids are grown on tables. Energy savings exceed 50% when regeneration energy is excluded and around 35% when included. The system uses a counterflow absorber with random packing made of corrosion-resistant polypropylene or PVC, operates under slightly negative pressure, and recirculates the thermochemical fluid (TCF) via pumps and heat exchangers. Concentration and temperature are monitored to control humidity and air temperature. Regeneration occurs in a desorber, where diluted TCF is heated to release water vapor, which is vented. The process is batch-based, with storage for concentrated and diluted TCF separated to prevent mixing—requiring about 175 litres per m² of greenhouse area. A separate TCF system using sodium hydroxide is used for food drying, which is more hygroscopic than magnesium chloride. CO2-induced carbonate precipitation is minimised by recirculating air in a closed loop. A staged concentration approach improves efficiency and reduces storage needs. The technology enables full decoupling of thermal energy use from drying, allowing renewable or waste heat to be used. Specific energy consumption is lower than conventional compression dehumidifiers, especially when regeneration uses otherwise wasted heat. Developed and tested at the Zurich University of Applied Sciences, led by Serena Danesi, with support from the Cordy project and Horizon Europe-funded initiatives. The system offers significant energy efficiency and sustainability benefits in agricultural applications.