A crucial part of active climate control in horticultural greenhouses is the correct circulation or ventilation and fan choice, based on your specific situation. So, what types of ventilation are there for greenhouses? We cover the different methods in this article.
Horizontal circulation of air
As soon as the leaf temperature falls below the air temperature, condensation takes place, creating an ideal environment for moisture-associated diseases such as Botrytis, mildew and Mycosphaerella. With horizontal circulation, air movement is started between the crop and the screen. Horizontal ventilation ensures a more uniform temperature in the greenhouse and can reduce the development of leaf diseases. The moving air removes moisture from the foliage of the crop, resulting in a drier microclimate.
Vertical circulation of air
With vertical circulation, air is sucked in from below and spread over the crop like a blanket. The air mainly passes through the crop, creating a uniform temperature and humidity. Local vertical air movement achieves, among other things, (Wageningen University, July 2012, P.A. van Weel, J.O. Voogt):
- That no temperature differences caused by cooling along the screen or by heating via lamps, as a result of air flows along the greenhouse cover over large distances
- That the air movement penetrates better into rising crops
- That the air movement actually provides an active microclimate around the plant
- That an even movement is created over a larger surface
- That heat from the sun or from lamps is effectively transported downwards
- That movement without pressure build-up means that much less energy is required for a certain air displacement in m3/m2/hr.
- That any local disruptions have much less influence on the rest of the greenhouse
- That due to a suitable distribution with sufficient overlap between the fans, in addition to a vertical temperature equalisation, there is also a small horizontal equalisation
With parallel ventilation, the fans hang side by side in the greenhouse. From the centre aisle, the air above the plants is blown to the side of the greenhouse. The air collides with the side wall and bends downwards. At the root level, the air then flows back to the aisle. This creates a large loop. Usually this system is used with high crops where the fans blow through the crop. This method is rarely used today.
Series ventilation is the most common and is often used for low planting. With this system, the fans are placed in extension of each other throughout the greenhouse like a loop. One fan takes over the air flow from the other unit and moves it further. This creates good air circulation above the crop.
When choosing the type of fans used in horticultural greenhouses it is important to consider the following:
- The durability and reliability of the fans
- The resistance to high temperatures and moisture
- The suitability for intensive use