Air Treatment Requirements for Cannabis - Part 1 of 2

This first article will focus on the different stages of the production of Cannabis from start to finish and the general requirements that are needed. The 2nd section will take a more detailed focus on the air treatment requirements and which solutions are available.

If you have been involved in the HVAC industry for the last few years you will no doubt have noticed the growth of air treatment options for the Cannabis industry. The reasons for this are due to the recent legalization of this plant for both medicinal as well as recreational use, the growth in grow facilities large and small and the potential lucrative profits that result from the harvest and processing of the plants. Air treatment for indoor environments used to grow this plant is very similar for that of any other indoor growing facility (With the exception of mushrooms coming to mind.) with the possible addition of odor control as well as on site drying/curing having possibly unique environmental conditions.

The main requirements for the indoor environment is maintaining the classic balance between too much and too little humidity. The life cycle of a cannabis plant has several distinct stages from start to finish and these will have differing requirements for both temperature and humidity requirements. In most facilities, plants are started as clones which are basically branches from the lower part of female plants that are mature but not yet flowering that have been maintained so as to develop roots. These rooted clones are exact copies of the mother plants and will contain all of the traits of the mother both good and bad. Clones then are selected from mother plants that have desirable characteristics such as sexual stability, potency, flavor and of course hardiness against mold etc.

When the clone cuttings are first taken, they must be stored in conditions that are almost 100% RH as the cuttings do not yet have any root system to draw in moisture so keeping them from drying out is paramount. Light levels also must be kept to a minimum to avoid photo synthesis otherwise the plants will undergo transpiration. This is the evaporation of moisture from the surface of the plant which originated from inside the plant thus increasing moisture losses. Luckily this is a fairly short step in the process but care must still be taken to ensure the right conditions are met, otherwise the rest of the grow will be compromised.

Once the clones have rooted, they are planted in what ever growing medium is chosen and the next 4-6 weeks will involve the growth of the plant in both height and girth. This adds mass and surface area to each plant which increases it's ability to perform photosynthesis to support this growth. The temperature and humidity of the air should be such that it supports this stage and noting that the amount of moisture being introduced to the air from the plants increases due to transpiration as the plants grow in size and surface area. This usually occurs in a room that is set up for this stage (Vegetative) with plants in various stages along the way as this helps even out the amount of moisture being generated and absorbed from the air. Plants in the vegetative stage require longer periods of light for growth with lighting times running from 16-24 hours a day. This results in a higher sensible load for this stage/space which must be accounted for on top of other sources of heat due to seasonal changes, solar loading etc.

Once the plants have achieved the desired size, they will need to undergo a forced flowering stage. This is achieved through the reduction of lighting time to 12 hours on and 12 hours off each day. In nature, the reduction of daylight that occurs in the autumn triggers the plants to begin to flower so that the females can be fertilized by males and produce seeds which will then grow the next year and continue the line. In grow facilities, we replicate this reduction in lighting and the females will begin to flower. The difference is that there are no male plants around so the females will not produce seeds. Generally the mature vegetative plants are removed from this space to the flowering room otherwise the entire space must switch to the 12/12 lighting schedule.

Once the plants are switched to a flowering light schedule, they will spend the next few weeks sprouting new branches and stretching a bit trying to increase the amount of light they receive. After this stage, they will begin to generate the flowers which are the most valuable section of the plant. This will continue for anywhere from another 4-12 weeks depending on the species and variety of plant. It is important to note that the requirements of needed air treatment will change as there will be less sensible heat being generated by the lighting as well as less moisture transpiring from the plants, especially during the last few weeks.

Once the plants have produced mature flowers, they will reach a peak where they will need to be harvested within a short period of time. The plants then are usually cut down, excess leaves trimmed off and the individual branches with flowers cut and placed in a room for drying. At this point, the most critical parameter to maintain is humidity levels as if it is too dry, the plants will dry out before the chlorophyll in the plants can breakdown into glucose and the cannabinoids, which are the active ingredients can transform into the versions that are most effective. If it is too wet, mold will form and ruin the crop. Once initial drying (1-2 weeks) is complete, the dried flowers can be moved to containers for curing for another 1-2 weeks or if the flowers are all from the same crop, they can be left in the same space with the humidity maintained at 60-65% for 1-2 weeks. This is the most critical part of the whole process as if it is not done right, there is no going back to fix it. Over dried or moldy cannabis has little value.

Now that we have outlined the different stages of Cannabis production and the environmental requirements for each, we will look at how we go about achieving these conditions and what is available as far as solutions go to do this.