Airflow Mapping: What Is It? | Where to order Skittles Moonrock online

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Question: We have had some issues with powdery mildew (PM) in our mid-size grow. I learned that PM can be often attributed to poor airflow, so I’m trying to figure out the solution. Can you explain what airflow mapping is? And how can we “map” airflow to optimize for plant health?

And related to that, what can you tell me about the use of evaporative cooling pads in relation to airflow–in what situations can they be helpful?

Answer: There are many questions here. Let’s start with the first and simplest one. Airflow mapping is the process of measuring, visualizing, and analyzing how air moves through a cannabis grow space. Ideally, airflow mapping is performed prior to the construction of a greenhouse or indoor cultivation environment, but it can be done post-construction or as an ongoing practice to monitor crop health and diagnose issues.

In days past, farmers would set off colored smoke bombs in front of the incoming ventilation system and watch the dispersion and direction of the smoke toward the ventilation exhaust. This offered a very basic and inexpensive visual airflow map.

Modern technologies such as hotwire anemometers are now more commonly used for accurate airflow measurement, while infrared thermometers with adjustable emissivity can be used for proper leaf surface temperature readings.

In the facility planning phase, digital airflow modeling techniques such as computational fluid dynamics (CFD) are utilized to model the influence of different facility design parameters, including room layout, plant height, crop spacing, plant count, cultivation stage, and transpiration rates, on airflow.

These computer-based methods help predict how air behaves under different conditions without having to perform physical experiments. They often use complex algorithms, making them difficult to build in-house without the right expertise. Thankfully, several companies offer airflow mapping services in the cannabis space. A non-exhaustive list is offered in the box below.

Why Airflow Matters

As you mentioned in your question, airflow plays a role in managing PM–or rather, it aids in managing the optimal conditions to avoid PM.

Airflow is a critical factor in plant growth–it delivers CO₂ to plants to utilized for photosynthesis, and it facilitates gas and heat exchange to freely enable plants to photosynthesize and transpire. Proper airflow also encourages the plant to develop thicker cell walls, which in turn improves resistance to pests and diseases, enhances water retention, and supports better nutrient transport, all leading to overall healthier growth.

Conversely, poor airflow can cause issues such as hot spots (where pockets of hot, humid air sit over a given area in your grow room) and uneven growth (e.g., plants further away from a CO₂ source may not receive the needed supplementation), and it can also bring ideal conditions for mold and diseases to proliferate. Excessive airflow can also cause nutrient toxicities by increasing transpiration rates, causing cannabis plants to absorb more water and nutrients than needed.

To begin optimizing airflow, we need to understand the differences among airflow, air velocity, and air exchange rates.

Airflow describes the movement of air from one environment to another and is measured in cubic feet per minute (CFM). The optimal airflow range for vegetative and flowering crops is 200 to 300 CFM. Just as important is achieving a consistent airflow distribution throughout the cultivation environment. Many growers leverage cross-ventilation fans or openings that move air from one side of the room to the other.

Also consider that heat rises, so another way to generate cross-ventilation is by having air enter at the lowest point and exit at the highest point.

Air velocity, or airspeed, describes the speed air moves from one place to another, measured in feet per minute (FPM) or meters per second (M/S). Most growers utilize an airspeed between 0.35 and 1.0 M/S (80 and 200 FPM). Flowering plants typically prefer a velocity in the middle range to achieve good evapotranspiration as well as nutrient delivery. That said, all environments and cultivars are different and will have slightly different airspeed requirements.

Air exchange rate (AER), or air turnover rate (ATR), is the number of times a total volume of air inside an environment is removed and replaced with new air in a given amount of time (usually hourly). Greenhouses typically target 50 to 60 air exchanges per hour when peak summertime cooling is required. When dehumidifying the space at night or during the winter, when the goal is to achieve proper air exchange yet limit any need for heating and avoid any environmental fluctuation that occurs as a consequence of over-ventilating, growers should utilize a much lower AER. What that target is will be different for each environment–California has a different climate than Denver, and Nevada has a different climate than Massachusetts.

Indoor facilities that recirculate air usually target 15 to 30 air exchanges per hour, depending on plant density and plant numbers, as well as their height. Higher density and maturity will typically require higher AERs.

Air Delivery Methods

Once you’ve mapped out your airflow and determined airflow, air velocity, and air exchange rate targets, you can determine how to reach those goals.

Air can be brought into a grow environment in multiple ways, including via air conditioning, whereupon ducts move conditioned air from an HVAC unit to a given space(s).

Greenhouses usually employ exhaust fans on an end wall that pulls air through filtered inlets at the opposite end of the greenhouse as a fresh air intake. In hot climates, some greenhouses utilize evaporative cooling pads (which you inquired about) at the fresh air intake end of the greenhouse. These forms of cooling are best utilized in dry and semi-dry climates, as they can sometimes impart unwanted moisture in an environment that already has a propensity to be excessively moist. Evaporative pads work by passing water over the pads which evaporates by the air passing through the pads, thus cooling the air.

In indoor production facilities (as well as in some greenhouses), horizontal airflow (HAF) fans are utilized for air circulation and directing preferred airflow, while vertical airflow (VAF) fans destratify the air and help redirect it into the canopy.

So, to answer the question regarding airflow mapping and PM: Airflow mapping alone will not address your PM issue, as PM is a result of a variety of interconnected factors. However, by optimizing your environment via airflow mapping, you can control the adverse conditions that contribute to the continued proliferation of your PM problem.

Kenneth Morrow is an author, consultant and owner of Trichome Technologies. Facebook: TrichomeTechnologies Instagram: Trichome Technologies Email: k.trichometechnologies@gmail.com.

About this column: Cannabis industry expert Kenneth Morrow regularly fields questions in response to his “Tomorrow in Cannabis” column in emails and direct messages. Now, Cannabis Business Times is giving people an opportunity to ask questions and get them answered in an open forum. What questions do you have for Ken? Please send all questions to Noelle Skodzinski, noelle@transpiremedia.net, and your inquiry may be the foundation of the next article.