Arie de Gelder, Wageningen UR Horticulture:
Controlling climate using dehumidification
"Growing at higher humidity (> 85% and most preferably above 90%) and increased use of screens are basic elements in The New Cultivation for many crops,” says Arie. “The rose is an exception as high humidity is detrimental to the shelf life. At high air humidity, evaporation will decrease, in particular at night. Depending on the crop it may drop to about 10 grams / (m 2 .hour). During the daytime the evaporation will increase as a result of insulation. For cooling of the crop, the energy balance is the measure with which you can calculate the desired evaporation. The crop must convert the energy of the sun into useful assimilates and drain further through evaporation.”
“At night, moisture removal needs to be set to the desired minimum evaporation level of the crop. That's down from about 25 to 10 g / (m 2 .hour). To test this principle in the Venlow energy greenhouse (the greenhouse in the IDC Greenhouse as energy source sporting a roof with double glazing and controlled ventilation via air handling units), cucumbers were planted on high wire cultivation. This crop lasts until about late June. The challenge for the research is to correlate the moisture drain with the evaporation during the day, so that the greenhouse keeps the high humidity. At higher humidity, the stomata are on average more open than with low humidity and the plants can more easily absorb CO2. This would be beneficial for maximum growth. In the night the moisture drain must be sufficient for minimal evaporation.”
“A second aspect is aiming for a stronger relationship between the 24-hour temperature and the light sum per day. The former is raised with lots of light. An increase in 24-hour temperature of 4 ° C per 1000 Joules irradiation should suffice. The starting point is a temperature of 16 degrees C with no irradiation. At the start of cultivation, we looked for the right balance in a more traditional way during the first few weeks, but now we’ll adapt the climate settings to the desired strategy."
Source: Energiek2020