How to improve air movement in glasshouses
Good air movement in a protected growing environment is an important part of creating an even climate and can help improve crop quality and uniformity. It is important to consider the best way of moving air around your greenhouse or polytunnel based on your crop type and the production system you use, to find the right solution.
Cost and energy needs to be considered. While installing fans may be an expensive upfront cost, pipe heating will have higher energy costs and boilers may need servicing and maintenance. A well-designed fan arrangement will achieve better air movement and a more even climate than pipe heating, and should be less expensive in the long-term.
Why is air movement important?
Air movement helps to keep an even climate, which has several benefits:
- Creates uniform humidity and temperature
- Helps plants to transpire
- Reduces condensation and so lowers the disease risk
- Achieves uniform plant growth with fewer rejects and easier harvesting
- More efficient use of energy
- Creates uniform CO2
How do I know if I need to improve the air movement in my glasshouse?
Measuring air movement can be tricky. Rather than measuring the flow of air, we recommend measuring the evenness of temperature or humidity across the greenhouse or polytunnel.
Use a matrix of sensors to create a picture of the climate in different locations
Create a heat map using different temperature measurements
Consider thermal cameras to measure temperature of fruit, flowers or heads of plants
A target of 1˚C variation is advised vertically and horizontally throughout the greenhouse.
A smoke test could also help you to visualise the flow of air.
How can I create air movement in my glasshouse?
There are a range of traditional and alternative methods that can generate air movement and each has different benefits and disadvantages. It’s important to consider what’s right for your situation and crop.
Pipe heating creates convection currents that help to carry moisture away from the plant, reducing relative humidity. However, this can be expensive, especially if the heat is not required
These fans tend to be mounted above the crop to create a circulation pattern. This can be a good option for a tall crop, but maybe less so for ornamentals and other crops grown at ground level
These fans disperse air in a cone shape, giving a wide range of coverage of about 15 metres diameter at ground level. However, it may mean more fans are required compared with a system based on horizontal fans, but air can be directed exactly where needed.
Air tubes run underneath the crop, with holes allowing air to escape. They tend to have a fan at one end, which can lead to a drop-off in airflow along the tube.
A ducted system consists of a fan at the top, with a long plastic tube directing the air towards the ground. Usually, lower power fans can be used as these vertical ducts mean air is moved a shorter distance. It helps air to penetrate the crop. This could be a good option for bench-grown crops, but could also stimulate too much evaporation and dry out plants.