Growing facility climates are constantly monitored, regulated and adjusted. These operations happen in large spaces, meaning large volumes of air, so how is everything optimized everywhere all at once? The answer is air circulation.

Between fans, HVACs, vents, windows and other climate control systems, air moves. In most cases the direction of this movement is not factored in to a grow space design. The majority of grow operations include multiple vents throughout the space, which distribute air, either from an air conditioning system, or from the outside. In addition to vents, most operations use fans, which blow the air from one point to another, but lack dynamic control over the way they move air. This may easily create a cacophony of air currents working unharmoniously and creating varying conditions throughout the 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 the air is constantly treated to be optimal, reducing variability over time (maintaining a constant level throughout the day and throughout the year), most systems do not take into consideration the variability of the conditions across space. This creates a situation in which one area may have, for example, colder or more humid air than another area. This is usually caused by structural leaks of outdoor air which happen at the joints and connections in a greenhouse.

But this doesn’t just differ between far corners of the growing space, it may actually occur among the dense foliage, creating microclimates with different conditions in different areas surrounding the same plant.


Water is constantly being transpired by plants, 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 its place, creating a low VPD (vapor pressure deficit, for more information on VPD check out our blog post “What is VPD?”). Low VPD means that the transfer of water molecules from the leaves to the air is slowed down, in turn, slowing down the entire water cycle, from the soil, through the roots, and to the entire plant. This water transfer is what supplies the nutrients to the plants. So, when the VPD is low, nutrient transfer is slowed as well, causing slower growth. Additionally, slower water transfer directly hurts the plant’s ability to photosynthesize efficiently, further inhibiting growth. Not ideal for an operation which needs to turn a profit.

Every crop has its favorite environment, which allows it to grow faster, larger, healthier and stronger. Just as with temperature and lighting, humidity levels should be kept optimal for the plant, all around, all the time.

It’s not all about physiological disturbances though. A single cold or humid pocket of air may well be a hotbed for disease outbreak. Diseases such as botrytis, known as “bud rot”, develop in these conditions, undoing efforts to maintain low relative humidity levels in order 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.

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In short- microclimates undo all the hard work put into optimizing conditions.


So, how does well planned air circulation work?

DryGair has designed a concept which is built into their dehumidification unit. The concept is based on the principle that closing the growing space and treating the air from the inside allows the grower to maximize growing potential.

The system is located in the center of a closed growing facility (or greenhouse with a thermal screen). Its operation consists of taking in air from the bottom and expelling it from the top, in a 360° radius. The specialized design allows the expelled, dehumidified air, which is dry and slightly hotter, to travel along the ceiling (or screen) throughout the space to all corners, descending as it cools. This concept creates circular air movement which goes through the foliage horizontally and vertically, diffusing the air surrounding the leaves while supplying optimal conditions at all levels.

Greenhouse air circulation

There are several factors influencing the ability to translate air movement and circulation into uniformity, these need to be taken into consideration and integrated into the design of an operation. These factors include the size of the space, both vertically and horizontally, density of plants- both placement and foliage, as well as plant height.


Air circulation has many benefits. First and foremost, it allows an efficient diffusion of microclimates, letting the plant enjoy the conditions it needs. This happens through the creation of homogenous conditions, meaning that similar conditions are maintained throughout the entire space, including inside the dense foliage of the plants.

Creating these uniform conditions is a huge factor in the plant’s wellbeing, both in providing constant optimal conditions throughout the entire growing area, and through the control of disease outbreak. Being on point with this allows the reaping of extra benefits as well, such as the potential to increase crop placement density at lower risk.

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”

this article was originally published on “Growers Network”