The humidity of a cannabis grow room plays a large part in how plants function. It can affect the growth and final yield as well as having implications in the spread of disease, mold, and mildew. Through an understanding of exactly what plants need and how to make sure they have it, the cannabis will be of the utmost quality and consistency.
The reason it is so important to plants is because it will affect the rate at which they transpire. During transpiration plants release water vapor into the air, the water levels inside and outside the plant will try to level out to equilibrium. This means that if humidity is low, plants will rapidly transpire as water is drawn out into the air, reducing the amount of water within the plant and potentially having detrimental effects when water levels become too low. If humidity is high, then plants will transpire at a much slower rate and have a lesser potential for loss. It should be noted that as an essential part of its functioning cannabis plants will always transpire because they have a “humidity” rating of nearly 100%.
Plants transpire for a number of very important reasons. It is done for temperature control, it is how plants cool themselves and regulate their own temperature. It is also how the cannabis plants move minerals and nutrients about, as water leaves the plant it draws more up from the roots, allowing for the absorption of nutrients from the soil. Finally, it is how cannabis plants get the carbon dioxide they need out of the air – Plants open their stomata to let water vapor out, and in the process carbon dioxide gets in.
If the humidity is too low, then cannabis plants are going to do a lot of transpiring and it will play havoc with their transpiration systems. They will lose a lot of water and begin to exhibit the damage usually caused by dryness – stunted new leaves, shriveling old leaves and dying flowers. If the transpiration is too high, it can also cause nutrient overload, plants take in more nutrients than the plant can use, the leaves will begin to show yellow or burnt tips, which is the result of nutrient burn in addition to excessive use of nutrients and water.
High humidity has its own risks. In a grow room with excessive humidity and poor air circulation/distribution plants are susceptible to fungal disease, mold, mildew, bud rot, and root rot.
Temperature and humidity need to be correct, which means heat and moisture need to be both added to or subtracted from the room at different times and seasons.
| Controlling Humidity|
When it comes to HVAC in cultivation facilities, so far, everyone has missed the mark. The problem in the cultivation industry is that everyone that has designed an environmental (HVAC) solution has done it with a “comfort cooling” mindset. That is, they are using equipment designed specifically to maintaining psychrometric conditions within the “Comfort Zone” as per ASHRAE STD. 55, basically supplying saturated air at 55°Fdb coming off a 40°F Coil. This can achieve a 42%RH at 80°F and will require reheat. 
Then, because it can’t handle the latent load when the sensible load (the lights) goes off. So, they add dehumidifiers in the space, which are also operating with a 40°F coil and reheat from the condenser. The whole thing is Crazy!! They are applying equipment and processes that are common to HVAC for hospitals and office buildings rather than looking at it as an industrial process.
Clearly, it is very energy intensive and it is not working. They run sophisticated comfort cooling systems and then add stand-alone dehumidifiers scattered throughout the facility. This is ludicrous! First, they refrigerate the air to condense out the moisture, then they reheat it to get back up to an acceptable temperature. In a hospital where the desired condition is 74°Fdb and 50% RH that is fine, even with 100% outside air at 95°Fdb/78°Fwb. This process, in a 20,000 SF Flower room would use 5,995,044 BTU/Hr. to do 3,493,843 BTU/Hr. of actual work; almost double.
Nobody really knows what the ideal temperature and humidity for cannabis cultivation are because nobody is controlling it with any kind of accuracy or consistency. If I hadn’t applied for a license I never would have thought of, or even about, a solution to the multiple issues plaguing the industry until someone hired me to do so.
Approaching it as an industrial process rather than an office building opens up a myriad of possibilities. The solution is simple and solves four of the biggest problems facing the cannabis industry; energy use, environmental control, contamination and water conservation. Treating it as an industrial process directly addressing the Psychrometrics will provide exact control of Temperature and Humidity within 1-degree Fahrenheit & 2-grains of moisture using roughly half the energy. There is no new technology involved, I have merely applied, tried and true HVAC technologies that are common to pharmaceutical and microchip industries and applied them with a different point of view; hence, every component of the design is still “off the shelf”; just a different shelf.
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Following is an “Envelope” calculation used for illustration. There are many more components involved and the numbers get better with the details. This small example will remove 500kW from the Utility Electric Grid.
|A Better Way|
There is a better way to save energy and it is being overlooked. Cultivators need to get their heads out of their Buds and hire someone that knows what they are doing. They will mitigate crop lose, have precise control and save money every day! Hence, controlling temperature and humidity will also control water and nutrient consumption. Growers should care about the Psychrometric conditions because it impacts yield quality, overall plant vigor, nutrient & water utilization. Using fewer nutrients, less water and energy improves the bottom line. One thing worth noting for both indoor and greenhouse grows is that outside conditions will affect your indoor environment. It’s not “the old cement factory” every site is unique and requires an engineer to look at the desired range of conditions and the micro-climate of the location to properly design an appropriate solution.
For more information on a better way to save energy, please contact Bryan Sherman with Innovative Energy Solutions. Bryan can be reached via email bls@ies-company.com or phone 516-767-0525.
