French fruit vegetable producer Les Serres de Goulaine is building a new 3-hectare Venlo greenhouse. Just like the 4-hectare greenhouse next door, which was built in 2013, the new one is being equipped with the AVS ventilation system from Van Dijk Heating. “We are very happy with AVS,” grower Vincent Olivon says. “It combines effective humidity control with efficient energy usage and a homogeneous greenhouse climate. We no longer get Botrytis, production is higher, and the fruit quality is better.”
Les Serres de Goulaine cultivates tomatoes without artificial light and cucumbers under partial artificial light at two 7-hectare sites. The company is owned by Laurent Bergé and Vincent Olivon. The site near Nantes grows Admiro round tomatoes and Romanello Roma tomatoes, which are harvested loose. Partner Laurent Bergé manages the nursery in the slightly more southerly department of Vendée, where they also grow cucumbers. “We used to grow loose round tomatoes in huge quantities, but now that’s more of a niche product for us. By focusing on quality, we can stand out in the market.”
According to the French grower, humidity control is the key to high-quality, high-yielding tomato cultivation. In the past, Botrytis would sometimes throw a spanner in the works. In his quest to find a solution that would deliver better control of the greenhouse climate, in 2012 Olivon visited various Dutch greenhouse construction companies. “We were very keen to replace one greenhouse, and the Netherlands leads the way in cultivation innovation,” he explains. “Albert Haket of Horconex told us about the Active Ventilation System from Van Dijk Heating, with which they had had a very good experience in a previous project. A meeting with Joek van der Zeeuw was soon arranged.” The owners also looked into semi-closed greenhouses but didn’t see many advantages in them. “Semi-closed greenhouses are mainly designed for efficient temperature control,” the grower says. “In western France, humidity control is the sticking point. So we decided to go for a more or less standard Venlo greenhouse with a single transparent energy screen and AVS air handling units.”
The following year, Horconex replaced the old 4-hectare greenhouse with a new one with 63 AVS units in the external walls. The Active Ventilation System dehumidifies greenhouses in an efficient way. The AVS unit has a mixer valve that sucks in outdoor and/or indoor air and blows it into the greenhouse via a central heating block and a transparent air distribution hose. The relatively dry outdoor air lowers the moisture content of the air inside the greenhouse and the central heating block efficiently raises the air to the desired intake temperature. Thanks to this ingenious process, the air vents and the energy screen can remain closed for much longer, preserving heat and CO2.
According to Olivon, the benefits were immediately evident. “We were able to manage the humidity levels better and more efficiently. In the greenhouse without AVS, we set a minimum pipe temperature of 40-50°C to activate the plants in the morning. This encourages transpiration, which pushes up humidity levels. To counter that, we have to gap the screen and open the vents very early, which costs us heat and CO2. It also causes a cold downdraught under the gaps, which the plants don’t like. The greenhouse with AVS doesn’t have these drawbacks. Also, we haven’t been getting Botrytis there anymore, which we used to get sometimes in the old greenhouse.”
With the old greenhouse making way for a new one with AVS, also being built by Horconex, Olivon hopes to put that behind them for good. He is already looking forward to the improvement in results that lies ahead. “In our first year of growing with the AVS system, production increased from 55 to 70 kg/m2,” he says. “That was our highest production ever, and we have been able to replicate that ever since. The greenhouse allows more light through and enables us to control the humidity better, resulting in an improved and more homogeneous climate. This also means that we can follow a different temperature regime for a higher growth rate. Our energy usage is slightly lower on balance, and because yields have risen, we are growing much more efficiently. So the AVS system will have paid for itself in three to four years. We are hoping to achieve similar results with the greenhouse we are currently replacing.” Another aspect the grower is keen on is the fact that the AVS brings more peace of mind in terms of crop control. It works well and is easy to use, so you don’t have to worry about it. “And it’s not demanding on the maintenance front,” he adds. “We clean the insect-repellent air filters twice a year, and that has already become part of our routine.”