Hygroscopic dehumidification is a way to avoid heat losses when ventilating to avoid high humidity in a greenhouse. The method results in an energy saving of 30 % in cultivations without supplementary lighting.
Wageningen UR Greenhouse Horticulture examines the potential of hygroscopic dehumidification in cooperation with Lans (a large tomato grower) and several suppliers of horticultural equipment. The aim of this research is to develop an energy saving method for drying greenhouse air. This replaces the common method of opening windows, keeping the heat inside the greenhouse. In this way it is possible to achieve significant energy savings without compromising the growing conditions for the crop.
Hygroscopic dehumidification is a way to dry the greenhouse air with the use of a very salty fluid. The fluid ‘sucks’ moisture from the air because of its hygroscopic properties. By bringing this hygroscopic solution in contact with the greenhouse air, moisture is taken from the air thus making the climate in the greenhouse dryer. Apart from drying the air, the air is heated as well. This is caused by the latent heat of vaporisation which is released when moisture is absorbed in the salty fluid. As a result, the greenhouse air is being both dried as well as heated, without losing energy to the outside air because of ventilation.
After drying the greenhouse air, the moisture from the air is absorbed in the hygroscopic fluid. As the salt concentration decreases, the excess water should be separated from the fluid; a process called regeneration. In the regeneration system, the water is evaporated from the fluid, which requires energy. It is therefore important to design the regeneration in an energy efficient way. To this end, a number of systems are industrially available, like vacuum evaporators and multi stage flash evaporators.From this first study we found that the principle of hygroscopic dehumidification works well. An energy saving of approximately 30% in cultivations without supplementary lighting is possible. In the coming year, the research will most probably be continued to demonstrate the potential energy savings in practice.