Between fans, HVACs, vents, windows, and other climate control systems, air moves. In most cases, the direction of airflow is not factored into the design of a grow space. Instead, the air moves somewhat randomly based on the placement of multiple vents throughout the space, air conditioning units, and fans, which blow the air from one point to another. Many of these airflow designs lack dynamic control over the way they circulate air, and can easily create a cacophony of air currents working constructively or destructively and can create varying conditions throughout the grow space.
The ability to harness all these currents, to know where they come from and where they go, adds great value to an already knowledgeable grower. While most air systems treat the air to be optimal and reduce variation over time, these systems do not consider the growing space itself, and how conditions vary across that space.
This creates a situation in which one area of your structure may have colder or more humid air than another area. This can be caused by any number of things, including structural leaks of air, temperature differences between indoor and outdoor air, differing rates of airflow, and more.
But these problems don’t just exist at the far corners of the growing space. They may actually occur among the dense foliage of your plants, which create microclimates with different conditions surrounding the plant.
Why is Air Circulation Important?
Plants constantly transpire water, creating a small area surrounding the leaves which is cooler and more humid than the rest of the space, this is known as a boundary layer.
Without sufficient air movement, this layer stays in place, creating a low VPD (See our article on VPD here: "VPD For Cannabis Cultivation"). Low VPD means that the transfer of water molecules from the leaves to the air slows, and in turn, the entire water cycle slows. When water transfer slows, so does nutrient transfer. So, when the VPD is low, nutrient transfer is slowed as well, causing slower growth. Slower water transfer also hurts the plant's ability to photosynthesize efficiently, further inhibiting growth.
It's not all about physiological disturbances though. A single cold or humid pocket of air may well be a hotbed for disease outbreak (or pathogenesis). Diseases such as botrytis, known as "bud rot", develop in these conditions, undoing efforts to combat its appearance. Once bud rot appears on even one plant, spores are produced and carried through the air, potentially infecting the entire operation.
In short, microclimates can undo all the hard work you and your team put into optimizing conditions and preventing diseases.
How Good Air Circulation Works
We’ve designed a concept which we built into our dehumidification unit. This concept is based on the principle that closing the growing space to the outside and treating the air from the inside allows growers maximum growing potential.
The system is placed in the center of a closed growing facility (or greenhouse with a thermal screen). It operates by taking in air from the bottom and expelling it from the top, in a 360° radius. The design allows the expelled, dehumidified air to travel along the ceiling (or thermal screen) throughout the space to all corners, descending as it cools. This concept creates circular air movement which spreads through the foliage horizontally and vertically, diffusing the air surrounding the leaves while supplying optimal conditions at all levels.
The Benefits to Good Air Circulation
Good air circulation has many benefits that all begin with how good airflow efficiently dissipates microclimates. This creates homogenized conditions that the plant needs, including inside the dense foliage of the plants.
These uniform conditions not only provide optimal temperatures and humidities, but also control and prevent disease outbreak. Being on point with airflow provides extra benefits as well, such as the potential to increase crop density at lower levels of risk.
According to Dr. Avraham Arbel, Head of the Department of Growth, Production & Environmental Engineering at the Agricultural Research Organization, Israel: "Circulation is the glue which binds all efforts to maintain uniform climate conditions to maximize crop yield and quality. When it is not integrated into the entire operation design scheme, growers experience fluctuations in all aspects, from the conditions themselves to the end product."
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- Want to get in touch with DryGair? They can be reached via the following methods:
- Want to read related articles by DryGair? Check these out:
- Ask DryGair: An eMail-In Question and Answer Series
- Ask DryGair: Humidity 101
- Ask DryGair: Ventilation vs. Dehumidification
- Temperature Management in Cannabis Cultivation
- HVAC Systems
- Is an HVAC unit enough for humidity?
- Using Climate Control to Prevent Disease
- Dehumidification - It's All About the Dew Point
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About the Authors
DryGair’s writers include a team of experienced engineers, agronomists, and economists. They specialize in climate control in closed growing facilities and practical solutions for effective climate management.