Greenhouse horticulture is aiming for a fossil-free future by 2040, which will make CO2 a lot scarcer and more expensive. This increases the need to use available CO2 more efficiently, especially in spring, summer and autumn when ventilation is frequent. This is because CO2 concentration in greenhouses is influenced by ventilation, dosage and crop uptake. Dennis Medema shares a study on Kas als Energiebron on techniques to increase ventilation rates to save CO2.
Achieving a concentration of 380 ppm without CO2 dosing requires a ventilation rate of 16-26/hour, depending on light intensity. With CO2 dosing of 30 kg/ha/hour, lower ventilation multiples can suffice. With a dosage of 60 kg/ha/hour, CO2 concentration in the greenhouse always remains above 380 ppm.
In average weather, a natural ventilation rate of ~10/hour can be achieved if the vents are fully open. However, a natural ventilation rate of ~5/hour is more common. Thus, to increase this further, additional techniques will have to be used. However, the question is whether these techniques are available and whether it is profitable to invest in such techniques. Therefore, discussions took place with various parties to clarify the above questions.
These discussions showed that ventilation multiples of 7-10/hour should be technically feasible. By using this technique, in combination with natural ventilation, a ventilation rate of 12-15/hour should be feasible. PlantLighting's calculations showed that such ventilation multiples are not sufficient to eliminate the need to dose CO2. A dosage of 30kg/ha/hour is still needed to maintain a CO2 concentration of 380 ppm in the greenhouse.
Since CO2 dosing will still be needed despite the deployment of technology, the question is whether it is profitable to invest in technology or whether it is better to be economical and efficient with CO2 dosing. A trial showed that a dosage of 8 kg CO2/m² per year was sufficient for cucumber production at 400 ppm. Since investing in technology to increase the ventilation rate costs ~€50.00/m2 (extending the Air&Energy system), even at high CO2 prices, it is economically more advantageous to dose to 380-400 ppm. In addition, growers can accept production losses in summer due to lower dosing given low product prices.
This consultancy was conducted by Botany and funded and coordinated by Kas als Energiebron, an innovation program of LVVN and Glastuinbouw Nederland. It was made possible in part by Kennis in je Kas (KijK).
Read the final report here
Source: Greenhouse as a source of energy