Next Generation Growing (NGG) is all about energy-efficient cultivation and achieving optimal production at the same time. Control of the moisture in the greenhouse climate plays hereby a key role. "With more knowledge of physics and plant physiology, a grower knows how and where moisture is being discharged," says Aat Dijkshoorn of LTO Glaskracht Nederland and project manager of the ‘Kas als Energiebron’ project (Greenhouse as source of energy).

Growing in balance
NGG is growing in balance. In addition to an assimilation balance of the plant, where it concerns the sugar levels, there is also a moisture balance from the greenhouse. Hereby, controlling (removing) moisture in the greenhouse climate is approached in a different way. "If the moisture content is too high, we look where that moisture supply comes from," says Dijkshoorn at the WaterEvent. "For example, it was not known how much plants evaporate at night."

Climate equality and air movement
With NGG, there are still several things to keep an eye on. For example, climate equality has not improved. For example, by shielding crop lighting, due to the environmental regulations, there are large temperature differences in the greenhouse. The project leader: "These differences also occur because screen cloths are sometimes like a sieve. "In addition, growers also open the windows slightly, which does not contribute to equality."

Another point is the extra air movement to cause a minimum evaporation. This is done instead of using minimum pipe temperature to stimulate evaporation. By using the minimum pipe temperature less, energy will be saved.

Prevention of radiation
In order to encourage evaporation at the head of the crop, the energy screen can be used against radiation. "If you expose the leaves to a lot of radiance, at a given moment they may not be able to provide energy for evaporation. With a closed screen cloth, that radiation can be curbed in the head of the crop, so that the head temperature and evaporation can be controlled. The promotion of evaporation leads to a healthier crop, but sometimes growers just want to cool down," according to Dijkshoorn.

Limiting ventilation
During sunny weather in the afternoon, reducing the ventilation can help to keep moisture and CO2 inside the greenhouse. With a higher moisture content, the leaf stomata will remain open, making it easier for them to absorb CO2. "In addition, the solar energy that comes into the greenhouse is easier to discharge with humid air. In order to discharge heat, the windows do not have to be wide open."

With a closed screen cloth at night, a grower can approach the limits in terms of moisture content. With closed screens that are moisture permeable, the moisture above the screen can then be discharged by opening the roof windows.

Functions of water
Water in the plant is needed for the transport of minerals and sugars. Evaporation of water from the leaf cools the plant down. This can also be achieved by atomizing water, with the advantage that the windows can be (more) closed and thereby keeping the CO2 in the greenhouse.

Evaporation of water requires a lot of energy (2,500 kJ/l). It is therefore wise to limit evaporation as much as possible. The project leader: "Therefore, do avoid standing water in open cultivation-gutters, puddles in the greenhouse and rising moisture from the soil, which enters the greenhouse through a moisture-permeable ground cloth. That water is also a nutritional base for fungi."

The NGG project focuses on further energy savings by additional insulation and by reducing water evaporation as much as possible.

Source: Glastuinbouw Waterproof (Harry Stijger)