Air Movement

Why it's Important:
1. Facilitates gas exchange
2. Mitigates mold growth
3. Increases weight of leafy greens
​
Air flow and air movement is important for facilitating gas exchange between your plants and enviornment.  Air movement helps to deliver carbon dioxide to the leaves, while transporting away water vapor produced by evapotranspiration.  In this capacity, air movement enhances photosynthesis and nutrient delivery within your plant.  Because air movement transports moisture away from the plant, it also helps to prevent growth of certain pathogens, such as molds and bacteria. 

Air movement also helps to build up the cellular structure within the vegetative structures of your plant, including the leaves and stems. Therefore, it is important to move air across the plants at the right speed: If you are primarily selling the weight of leafy greens, higher air velocity will bulk them up.  But if you are primarily selling fruit weight of tomatoes or cucumbers, then you only want enough vegetative structure to support your plant, without comprising the reproductive yield or quality of your crop. 

Therefore, the desired air speed (or velocity) across the plants will depend on what type of plant you are growing. In general, the desired range of air speed is  0.3-0.5 m/s (60-100 fpm). 

How It's Achieved:
1. Fans
2. Wind and Buoyancy
3. Air ducts

In a greenhouse, air movement is achieved both through the ventilation process (with mechanical fans or natural ventilation), as well as the use of horizontal air flow (HAF) fans.  HAF fans are typically hung from the greenhouse structure (eg. trusses) and configured to blow air in a circular pattern around the greenhouse and above the top of the plants.  These fans provide air circulation to create a more uniform environment, and help to break up the stagnant layer of air that would otherwise build up at the top of the plants. Duct socks may also be installed beneath grow benches or above the crop to deliver air from a central heating and/or cooling system. 

In a vertical farm, air movement is more challenging because the racks themselves obstruct airflow and also due to the chimney effect, causing the top grow racks to be warmer than the bottom racks.  Many growers opt to attach small computer fans (or similar) to the racks to blow air directly over the racks.  Air ducts can also be designed to deliver air uniformly and consistently over the racks without the need for many, small pieces of equipment.