Challenges of the Indoor Cannabis Environment

Introduction

We develop all of our systems to provide the tightest controlled environments -- while consuming the least amount of energy.

Plant Requirements

Plants use light energy to convert carbon dioxide and water into plant energy stores through the process of photosynthesis; water and oxygen are released into the environment as a byproduct.  In addition to photosynthesis, another important process to consider in grow facilities is transpiration. 

Transpiration is the process plants use to move water and nutrients through plant tissue to the surrounding periphery.  Vapor pressure differentials, more commonly known in the grow room industry as vapor pressure deficits, drive transpiration and provide the forces for nutrient transfer from roots to the upper areas of plants. Water movement is created by the evaporation deficit of water leaving via microscopic openings in plant surfaces called stomata.  Gases and liquids move from areas of high concentration to low concentration naturally.  Because the vapor pressure inside hydrated plants is high, water vapor will exit the stomata if the outside air has lower vapor pressure. If vapor pressure deficits are not favorable, plants cannot move enough water to supply nutrients or cool properly.  If vapor pressure deficits are too high, plants overly transpire which can lead to nutrient burn.  Over active transpiration also fills the stomata blocking CO2 absorption, thereby slowing photosynthesis and growth.

The key to healthy transpiration rates is to provide consistent environmental conditions.  Air directed at plant leaves is above design dew points so that condensation on leaves does not occur and will not create conditions for mold and fungi growth.

Optimum plant growth occurs when indoor facility design controls space temperatures as well as absolute humidity levels. More importantly, these parameters must be controlled uniformly across and throughout plant canopies.


STANDARD SYSTEM PROBLEMS

The commercial marketplace is in its infancy with most growers adapting their knowledge from small scale and residential operations.  To maintain indoor conditions in those small operations, standard air conditioners and small portable dehumidifiers were used.  When trying to control considerably larger commercial operations using separately controlled standard air conditioners and dehumidifiers you often face these problems:

•   Temperature and relative humidity are constantly fluctuating

•   Oversized air conditioners must be used to remove excess heat introduced into the space by the small portable dehumidifiers

•   In colder climate areas, the air conditioners cannot function when outside temperatures fall below 45F

•   System amperage is higher due to the system lacking reheat energy

Introducing Dewpoint

Relative humidity is a misapplied term. It is often used in place of absolute humidity. The key is the word “relative.”  As the air temperature increases, its total volume increases. Conversely when air temperature decreases its volume decreases. Water, however, is not compressible. Therefore given a specific amount, it will always occupy the same amount of volume.  As moisture-laden air is heated or cooled the air volume changes but the moisture volume does not.

Thus there is a change in relative humidity, without a change in actual water content. The maximum amount of moisture in air is highly dependent on the temperature of the air. Therefore, a change in air temperature will impact the value for the relative humidity even though the total amount of moisture in the air remains the same.

This is important to understand because water condensation occurs at an absolute humidity concentration regardless of its relative humidity. This is known as the constant dewpoint temperature, the key metric in creating vapor pressure deficits for healthy plant growth.

Accelerated Growth Solutions

The phenomenon of relative humidity presents some challenges for conventional dehumidifier control.  Since somewhat small changes in the temperature can impact the relative humidity, monitoring the relative humidity of a space for dehumidification control can cause premature indexing to the dehumidification mode.  Although humidity control is set and read in terms of relative humidity, our systems constantly convert the setpoint and sensor values internally to dewpoints.

Dewpoints also reflect the true operational conditions growers desire. More knowledgeable growers will understand that vapor pressures in the air are the main driving factors in the growth of plants.  Like dewpoints, vapor pressures are not dependent on air temperatures.

Accelerated Growth Solutions systems calculate the desired dewpoints based on temperature and humidity setpoints and then control indoor environments based on these values.  Operation based on dewpoints is one of the main advantages of our systems, providing stability and efficiency.  This is especially important when conditions are changed from photosynthesis periods to dark periods and vice versa.

AGS systems use a unique controller that has a zone-reset function for both temperature and humidity control.  This means that systems are constantly monitoring the difference between the setpoints and the actual grow room conditions.  As differences increase, the calculated supply setpoints of temperatures or dewpoints decrease.  The systems are constantly monitoring 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.

While this is occurring, the operating controllers also modulate the hot gas to the reheat coils. This maintains the temperatures leaving the systems to the current commanded supply air temperature setpoints.  AGS controllers are looking at both temperatures and absolute humidity values.  As a result, our systems can eliminate the wild swings of conventional systems.

Conclusions

AGS systems combine the functions of air conditioners and dehumidifiers.  They have unique refrigeration-based dehumidification systems that allow them to meet the high cooling and dehumidification demands.