With this project there was an intensive focus on the realization of the climate system for the 10 Ha. which was realised in 2013. This system shows great progress in the goal to improve the ‘Next Generation Growing’ principle (Het Nieuwe Telen- HNT).
In the Dutch vegetable growing sector some projects are already known, in which ventilation of the greenhouse does not happen naturally through the vents in the roof of the greenhouse, but where outside air is injected with fans in a mechanical way. With these systems, ventilation of the greenhouse can be better managed and advantages for cultivation and use of energy can be realised.
Also it is possible with this system to keep the greenhouse continuously at an adjustable positive pressure, so the chance on diseases from outside can remain limited. The ventilation with these systems is done via fans and perforated plastic tubes under the gutters.
The project that has been realised at Looije Tomatoes distinguishes itself to other systems by having the outside air intake provided with separately controllable heating elements, which ensure that the outside air is heated before it comes into contact with possible internal air recirculation.
In practice it has been proofed that with prior Next Generation Growing systems severe condensation occurred near the endwalls of the greenhouse as soon as the relative humid air from the greenhouse is mixed with cold air from outside. With Looije Tomatoes this problem has been solved in combination with a focus to achieve the lowest possible electricity use. Admittedly, with mechanical ventilation savings can be made on heating costs as there hardly needs to be heat with a minimum pipe, however, the additional electricity costs can have a great impact on the operating costs.
With the ActivAir design for Looije Tomatoes possibilities have been sought to minimize the air resistances in the overall system. With large ventilation flow rates (as necessary only during summer), the resistance of the heating elements will be switched off through an intelligent system combined with new software. Also there has been strived for high efficiency for fans and electro motors. This has given as a result that for comparable ventilation flow rates with previous projects, only half of the installed electrical power is sufficient.
All ventilators are equipped with electro motors according to the EC technique, in which the turns per minute of the ventilator are adjustable without frequency converter. The outside air inlet is provided with a unique outside air valve and the supply of return air from the greenhouse is adjustable with an independent return air valve. As a result, the flow rate of fresh outside air and return air can be controlled independently. Dehumidification is established by the degree of outside air inlet. Recirculation affects climate influences in the greenhouse.
Per climate group a number of ventilators has been equipped with an air flow rate measurement in order to accurately determine how many cubic meters air are being imported into the greenhouse. With sensors the degree of recirculation and outside air inlet can be determined. It is unique that these measured data are integrated into the control circuit, so the feed forward can be controlled rather accurate at levels of outdoor air and recirculation.
In advance several tests in a model have ensured that a very regular air distribution is provided by distribution tubes. They can be operated at 30% of the full load capacity, without any risk for the distribution.
At these 30% the capacity taken up by the ventilator decreases to only 6% of the full load capacity, which means that under most circumstances there is used very little electrical energy. Also the production of sound is lower with decreased motor capacity.
By smart use of software and control by bus communication it is also possible to have the ventilators switched in cascade based on the capacity demand for dehumidification. So there is modulated and switched in cascade for maximum energy efficiency.
Within the ActivAir design special attention has been paid to the environment concerning light and sound. The objective was to keep light and sound inside the greenhouse as much as possible and still provide a 100% air supply from outside. In order to achieve this, in the air inlet behind the insect nets there have been placed light and sound absorbing panels to ensure that the neighbours will not be troubled.
ConclusionWith the realization of the ActivAir system Looije Tomatoes has contributed to the improvement of concepts for vegetable growing in the context of minimizing crop control, reduce energy consumption and optimizing product quality and production. More information on www.activair.nl
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