Smart Grow Room Designers and Cultivators Understand This One Thing

As we’ve seen in the Colorado market and many others, medical Cannabis prices start out strong, but as the market becomes saturated with new facilities, the price can quickly plummet.

This leaves growers with very little margin for error.

The facilities that survive and thrive will have their grow down to an exact science and understand how to optimally cultivate in the very humid Missouri Cannabis market.

Humidity control and room conditions are some of the most VITAL challenges indoor growers face.


When moisture is not controlled – mold, mildew, and hazardous organisms can flourish, decimating your crop and any chance of making money in the new “Green Rush.”

Today we’re going to lay out the basics everyone should, nay I say need to know when designing a Missouri Cannabis indoor grow room.

High Humidity Will Prevent Your Plant from Properly Transpiring in Missouri

missouri cannabis dead marijuana plant

Cannabis has small holes in the under-sides of the leaves, which are called stomata. As they exhale, oxygen and water molecules in the form of vapor are released by the stomata to the plant tissue and then into the air.

The problem with having higher levels of humidity in grow rooms is that the higher the humidity, the more difficult it is for a molecule of water vapor to evaporate from the plant tissue into the air.

If the humidity level is high and the water vapor is not removed from the plant tissue, the plant can suffocate and end up with dead spots, fungi, and mold. Mold and fungi spread fast, are hard to contain, and can destroy an entire crop (and your profit) in no time.

Lights-off Cycle: The Imminent Danger of Condensation

missouri cannabis grow lighting

Lighting management is vital when growing cannabis. Light cycles are directly related to crop quality and yield, and each stage of the plant growth involve different lighting requirements.

Regardless of what your lighting requirements are, an AC unit needs to be used to control the heat load of the growing room.

When the lights are on, AC systems will run most of the time, removing excessive moisture. But the lights-off cycle can pose more challenges.

That’s because during the lights go off  cycle there is not a heating load to work against, which causes the AC to turn off. When this happens, the moisture removal also stops.

One degree less in temperature represents an increase of about 3% in relative humidity. High humidity will cause the excess water to begin to condensate both on your plants and on the walls of your grow room, ruining the harvest.

There’s only one solution for this problem: a piece of equipment that removes heat or add it back to the space as needed, modulating sensible heat rations during the on and off-light cycles.

Although it’s accurate to say that plants rely on air movement to remove the water vapor from their tissue and that air movement is the solution for high humidity issues, we cannot say that any uncontrolled effort will work.

Inefficient Choices: You Get What You Pay For

missouri cannabis grow dehumidifier

Some indoor farmers try to eliminate the risk of condensation by adding supplemental heat to the lights-off cycle, others choose to keep an exhausting fan running overnight.

A popular yet inefficient way of dealing with high humidity is by introducing one or many portable dehumidifiers into the space.

air quality guide

These portable units operate independently of your building HVAC system and generate excess heat into the grow room while removing humidity – forcing indoor farmers to oversize their air conditioners to remove the extra load. This method creates fluctuating temperature, wastes large amounts of energy and drains your profit margin. These are not recommended for the Missouri Cannabis market.

The secret to preventing the formation and growth of biological contaminants is to manage and control the absolute humidity within the space with a smart HVAC system, where every piece of equipment talks to one another, creating an ideal growing environment.

Attaining the Dewpoint Level and Determining Moisture Load

missouri cannabis dewpoint

What really matters is to find the best way to attain what we call the target moisture or dewpoint level during the lights-on and the lights-off cycle, regardless of the stage of development a plant is in. Dewpoints reflect the true operational conditions growers desire.

The moisture load has 4 components:

1. Transpiration from plants
2. Evaporation from soil
3. Irrigation systems and grow room wetted surfaces
4. Moisture content from ventilation air.

The most direct method of determining the moisture load in a grow room is to calculate the net water usage of plants using the Penman-Monteith formula. In theory, this can be accomplished by measuring the volume of irrigation water added to the grow room minus the volume of water that goes down the drain. The result is the volume of moisture that is transpired or evaporated from the plants and the growing system.

The only downside is this formula generates a reference crop value that estimates the moisture released per day for a large field of a uniform crop, not for indoor grow rooms.

Climate control systems must have the ability to meet the challenges of these changing conditions, but apparently that has been a hurdle for some HVAC manufacturers as well …

… Until Desert-Aire cracked the code.

How Desert Aire Solved the Humidity Challenge

To generate a reference crop value for indoor grow rooms and to make the calculation of sensible and latent loads more practical for the specification of grow room climate control systems, Desert-Aire changed the formula.

The modification uses a shortwave radiation value of 1.53 MJ/m2 each hour during the lights-on period. Also, the soil heat flux was set at zero because it’s assumed that plants are adequately watered in an indoor grow setting. Desert-Aire also considered the following variables:

  • Net radiation of the indoor lighting systems
  • Design air temperatures of grow rooms
  • The velocity of ventilation air at level 3 feet above the plant canopies
  • Vapor pressure differentials

Additional key variables that impact evaporation are the actual crop canopy size at full growth, the space temperature and humidity levels, and the number of hours lighting systems are on.

Once the reference crop value is known, then it needs to be converted into a rate for the crop being grown. Desert-Aire calculates one value for emergent plants to determine the evaporative cooling credit and a second value for the peak moisture release of full-grown plants.

Operation based on dewpoints is one of the main advantages of Desert-Aire and the GrowAire systems because it provides stability and efficiency.

GrowAire Environmental Control Systems

GrowAire systems use a unique controller that has a zone-reset function for both temperature and dewpoint control, meaning that systems are constantly monitoring the difference between the setpoint and the actual control conditions. As differences increase, the calculated supply setpoints of temperatures or dewpoints decrease.

The GrowAire system constantly monitors intake conditions to determine the number of compressor stages required to bring conditions entering the intakes to the calculated supply conditions and to engage the correct number of compressor stages to do so.

Because GrowAire controllers are looking at both temperature and absolute humidity values, they can eliminate the swing of conventional systems.

Desert-Aire’s GrowAire solutions combine the functions of air conditioners and dehumidifiers, helping establish and maintain the conditions for optimal transpiration rates and plant growth without the need to oversize the environmental equipment for the added heat rejection associated with portable dehumidifiers.

Even in lights-off mode, they continue to keep dewpoint control to protect the plants and crops without over-cooling the grow rooms and indoor farms.

The GrowAire product line is configurable to meet your specific indoor farming needs for Missouri Cannabis. The units range from 1 to 60 nominal tons to serve a wide variety of indoor growing spaces. The systems can be designed to fulfill your exact growing conditions from 65 to 85 degrees Fahrenheit at 45 to 75% relative humidity.

air quality guide

Contact Midwest Machinery with your Missouri Cannabis cultivation plans and let us help you select the best humidification system for healthy crops.