Netherlands: Dehumidification of the greenhouse climate

The new cultivation (Het Nieuwe Telen) is focused on five priority areas, which can be executed without making any investment. Application of these priorities is possible in horticultural companies with existing technical equipment.

The five priority areas are: uneven climate, dehumidification, energy loss, isolation, and crop activation. In this second article, in a series of five, Aat Dijkshoorn describes dehumidification in a greenhouse when the screens are closed.

At this time of the year, many Dutch greenhouse growers close the energy screens during the night. Will this lead to an over humid climate in the greenhouse? The level of humidity in the air is the result of supply and the discharge of moister. When the supplied moister is higher than the discharged moister, the absolute level of humidity in the greenhouse rises. The absolute level of humidity can be tracked via a climate computer. It is better to track the absolute humidity level than the relative humidity level. This because the relative humidity level strongly depends on the temperature.

During the night, the crop evaporates, which causes a higher level of humidity in the greenhouse. Evaporation is necessary to supply minerals to the growing parts of the plants. Especially calcium is important, because it can only reach the new cells through water. However, when the evaporation is much higher than requested by the plant, the energy consumption will be unnecessarily high. An evaporator of 10 grams per hour costs 6 watts of heating.