"Saving energy will be much easier with dehumidification"

In Meterik in Limburg, a pilot project is underway, initiated by Grodan and Signify, using Philips LEDs in collaboration with various partners. The goal is to save at least 40% on heat input in year-round tomato cultivation. Ridder, as one of the partners, is responsible for controlling all aspects of the greenhouse. In the first year, the target was more than achieved. But can semi-practical conditions be translated directly into real-life applications? "Very easily," says crop team leader Bram Rongen. "The only remaining barrier is the investment in dehumidification."

"In the past, using screens in tomato cultivation was almost sacrilegious," says Joost Veenman, Strategic Product Manager for Climate & Water at Ridder. "But we achieved our goal by pushing screen use to the extreme. However, with two screens closed and LED lighting, moisture buildup is inevitable. That's why Maurice Ammerlaan's Air & Energy system is essential for this project."

At the Botany research center, a 260-square-meter greenhouse has been set up for the three-year study into energy saving. The aim is to achieve year-round cultivation of tomatoes while exploring ways to reduce heating requirements. Two screens have been installed in the research compartment, one against light emission and one for energy saving. An additional, non-standard feature is a dehumidification cabinet using an air-to-air heat exchanger—an efficient method for dehumidifying the greenhouse environment.

'As long as you have the right techniques'
Reducing energy consumption in cultivation by half may sound ambitious—and it is—but Bram Rongen was not surprised. "We've seen it work before," he said. "In a similar study with cucumbers last year, we demonstrated that it's achievable, provided you have the right technology. Dehumidification makes all the difference. It allows you to control the climate with greater precision and use dehumidification as a tool to reach specific temperature and humidity targets. This level of control is entirely achievable."

Holistic approach
Ridder's climate computer controls the entire complex: the lighting, the irrigation, the climate, the air exchanger, and the screens. Sensors contribute to active plant management. 'A holistic approach', Joost calls it. Beforehand, the cultivation strategy for climate and water, chosen by the partners in the trial, was tested in a simulation. 'It will be a kind of autonomous cultivation. What could be easier than keeping the screen closed all the time? Normally, as a grower, you are looking at whether it should be opened, or should it be closed. The temperature and other things from outside have no influence. That makes the regulation very flat, you have the same conditions every day. What Bram set up, he got.'

Challenges
With the achievement of the energy target and an average light use efficiency of over 4.0 g/Mol for a truss cherry tomato yield of 0.63 kilograms per square meter per week, the first year concluded positively. However, there were 'challenges', says Bram. When screens remain permanently closed, bumblebees lose their sense of orientation without sunlight. "It works well enough in a 260-square-meter greenhouse, but on a 20-hectare farm? I know that lighting manufacturers are working on solutions to address this issue."

Higher brix and fruit weight
In the second year, the Brix level and fruit weight of the BASF-Nunhems Vitalion variety are expected to improve. Bram explains, "We accelerated crop growth so much that we ended up with too many fruits, causing the plant load to become too heavy with the chosen stem density. At that point, the plant struggles to maintain fruit weight. The lower Brix levels observed during certain weeks are likely also tied to this plant load. However, these factors weren't an issue in the first year, where our primary goal was to demonstrate that production could be achieved with lower energy input—and we succeeded. This season, we're focusing on optimizing the plant load to enhance quality further."

A certain stubbornness on the part of the grower
There's little standing in the way of applying the trial's principles in practice. Bram explains, "The biggest hurdle is the investment in dehumidification. But if gas prices continue to rise and you want year-round production in the Netherlands, dehumidification becomes nearly essential." And what about the grower's mindset? "Yes, there's a certain resistance among growers. I sit on a few advisory committees, and you often hear things like screens open, windows open, moisture out, active crop—those are familiar terms. Growers are accustomed to this approach; it's how they've always done it. But when they see the potential savings, that barrier may fade. Dehumidification also stimulates activity at the base of the crop, offering a wide range of control options."

New types of screen fabric from Ridder
The bar is set even higher this season, partly due to the addition of two new types of screen fabrics from Ridder. Bram explains, "To save even more energy, we'll be adjusting lighting levels at different times of the day. If electricity prices are high, we'll use less lighting. I'm confident we can achieve even better results— adjusting becomes much easier this way." Joost agrees: "In theory, energy savings could reach up to 70%. But for growers, there are various reasons to hesitate, like the need to invest in dehumidification, LEDs, and screens. However, with 2030 in mind, we need to move in this direction." Season two is underway.