Greenhouses with few vents call for adapted climate control
Blowing in large amounts of air from below ensures that on sunny days the greenhouse air at the top is, on average, 3°C warmer than at the bottom. In a traditional greenhouse, the vertical temperature differences are much smaller. The result is that the tomato plants grow much more generative than usual. The production is good, but the leaf is clearly smaller during the summer.
Ways of countering this phenomenon have proved tricky or expensive. That is why recently, both companies added the ability to moisten the air from outside.
Preliminary results appear positive. This suggests that not the vertical temperature gradient, but the vertical evaporation gradient has the most influence on the growth of the crop. Whether this is so, remains to be seen in the coming months. The energy-saving potential of these greenhouses is in the controlled dehumidification and in the lower utilization of the lamp heat. These potential savings do not differ from greenhouses that can blow in only 5 m3 per m2 per hour. At night, dehumidification usually only takes 2 to 10 m3 per m2 per hour.
However, the maximum ventilation capacity of these greenhouses is 70 to 80 m³ per m² per hour. That means that at night but a small fraction of the installed ventilation capacity is required. The fans however should run at least 30% of their capacity. Admixture of greenhouse air is a possibility, but costs more electricity and causes unnecessary air movement under the crop. By using only a small number of hoses at the same time, creates more accurate control and also improves the climate at the bottom of the greenhouse.
Source: Kas als Energiebron