Proper Airflow in Controlled Environment Agriculture

Dave Donohoe, Airflow Engineer – Ag Fan Systems by Breeza Industrial

The perfect fan system is simple to describe but elusive to most growers. When perfected, the fan system evenly mixes temperatures and humidity while providing proper air velocity inside all areas of the crop.

As I travel the country visiting different facilities, I get to see many approaches to airflow in controlled environments. Most facilities place significant effort into their systems in an attempt to achieve perfect airflow. Approaches vary greatly but one common theme is apparent in all but a few facilities. Despite growers best attempts, most still aren’t satisfied because they fall short of their desired results.

When asked how growers selected their fans and placement, I’ve received a broad range of responses. Some very experienced growers simply scaled up from the smaller grows they managed early in their career. While rooms are empty, their approach seems sound. Once the room is full of plants, airflow problems become obvious. Stagnant air is apparent in many areas of the crop and broad temperature and humidity differences are observed as the wall mounted fans fail to evenly mix the room’s air.

The inside of a scaled grow facility with wall mounted fans

Scaled Grow with oscillating wall fans – Dave Donohoe 2021

Some growers used a math-based greenhouse air flow calculator provided by reputable agricultural publications. The simple formula often referenced is length x width x 2 = CFM required to move the air mass. These approaches make complete sense, and provide decent results, if the grower’s only goal is to balance temperatures above very short crops. If this approach is used with crops over a few inches tall, canopy drag short circuits the airflow and the systems quickly lose effectiveness as plants grow taller.

High growing crops inside a greenhouse

Dense plant growth short circuits greenhouse air circulation in traditional math-based approaches – Dave Donohoe 2021

Greenhouse circulation fan placement can be incredibly tricky

Some growers I visited took a trial-and-error approach and made educated guesses based on things they had seen or heard. They are the growers who seem to put the most effort in. They continually try to find better ways to achieve proper airflow. Some of these growers achieve good, but not great, performance. It is common in these facilities to see 2 to 4 different styles of fans being used in unison. While some of these rooms end up close to achieving their desired results, they typically fail to meet all parameters and they waste a massive amount of energy as fans work against each other.

Multiple fan set up for air flow

Three different greenhouse circulation fans being used in an attempt to achieve good airflow. This grower was committed to finding a solution and eventually achieved perfect airflow with Ag Fan Systems – Dave Donohoe 2021

Ag Fan Systems designs and manufactures the solution

How air moves through a room dramatically changes as plants progress through their growth stages. Some crops create more challenges than others. For instance, tomatoes, hemp, and other crops that reach tall heights, change drag factors drastically through their growth cycle. What worked when the room was empty, or when plants were short, will no longer work as well once plants grow.

Air will be short circuited in many areas of the room causing vast temperature and humidity differences, as well as inconsistent plant growth in some areas of the crop. The only way a fan system can deliver good results through all stages is if it can deliver different airflow volumes as drag factors increase. With the proper system, growers can adjust airflow as necessary to account for the additional drag. Ag Fan Systems is the solution because it allows growers the ability to adjust airflow as needed throughout crop life cycles. However, our system will only work properly when fans are placed in the right locations.

Fan placement needs to be carefully considered in each room.

All fans should be arranged so they work together to maintain air mass momentum. Location of air returns, and other airflow generating devices need to be considered. For instance, you never want fans blowing air directly into an air return. Air should be completely mixed prior to passively entering the air returns. If other airflow generating equipment exists in a room, fans should be arranged to not go against the flow of the other devices. Spacing of fans is dictated by available space between the crop and ceiling, and the growers’ desires for actual airflow velocity.
For best results, fans should be placed based on airflow mapping that accounts for high and low pressure predictions, ceiling height, projected canopy height, and desired airflow inside the crop at each stage of growth.

Diagram of airflow inside a growing facility

This greenhouse air circulation diagram illustrates a basic fan layout in a 60×60 room. The 3 south-facing fans are set to a slightly higher velocity to balance the airflow moved north by the 6 outside fans. For every high pressure created, a low pressure opposite pulls the air to the next set of fans allowing momentum to continue.

Ag Fan Systems by Breeza Industrial can drastically simplify the airflow mapping process for growers. Growers simply need to provide room length, width, height, table height if applicable, projected canopy height, and return air vent locations if applicable. With this information, computer airflow mapping software is used to generate a precise fan layout.

Proper fan layouts for buildings

The two layouts above are example layouts used for informational purposes only. To achieve perfect airflow, it is critical to have layouts generated for each unique room. Ag Fan Systems provides this service, free of charge, for all customers. Growers should remember, these layouts are specifically designed for the Ag Fan System variable speed fans. Use of other styles of fans in the locations recommended is not advised as they can result in poor airflow, and potentially lead to crop damage.