Over the last decade, the legalization of cannabis has managed to break most of the stereotypes and stigmas as ever more growing number of studies discover new medical qualities of the plant’s secondary compounds. A former domain of drug dealers and enthusiasts, cannabis plants have become the darling of the pharmaceutical industry.

Quality cannabis cultivation and cannabinoid compound extraction require high standards of Controlled Environment Agriculture (CEA) with new opportunities for many ancillary businesses, predominately the HVAC sector. Traditional comfort cooling AC systems have proven to be ineffective and inefficient to address the environmental challenges of commercial indoor cannabis cultivation and many HVAC professionals embarked on a quest to develop superior commercial cannabis cooling systems.

However, the majority of HVAC engineers lack the knowledge of biophysics and biochemistry in order to properly evaluate the dynamically changing environment of cultivation, while the majority of cultivators are incapable of relaying this knowledge to the engineers in technical terms. This disconnect still persists in the industry and HVAC professionals must understand the specifics of CEA in order to successfully design the systems.

The State of the Cannabis Industry

Currently, thirty states have some form of legal medical marijuana program and in nine states and in nine states it enjoys a recreational status. The cannabis industry in these nine states alone is worth over $9 billion; a surprising number given legalization was only enacted in 2014.

It is expected that several more states will legalize recreational marijuana in the next several years. The industry is expected to be worth over $21 billion in 2021 as the beverage, food, cosmetics, Big Pharma and many other businesses are aggressively introducing cannabinoid compounds in their products worldwide.

3 Critical Requirements for Healthy Marijuana Plants

Though cannabis is a resilient plant with a broad variety of habitat, only specific environmental conditions allow for expressing full genotype potential of each cultivar. Every single factor of climate control is essential and an inadequately designed climate control system can inhibit growth and development, introduce a conducive to pathogens environment or significantly reduce the beneficial qualities of the plant. Failure to address these issues can jeopardize success of the entire business operation.

The three most important elements for creating an optimal environment in a grow room are airflow, temperature, and humidity.


Effective airflow distribution design is essential for plant growth and development. Experiments have shown that relative growth rate is often maximized at wind speeds below 3.5 ft. s–1. Airflow increased height and stem conductivity, while reducing the strength and rigidity of the stem. An angle with which the wind hits the plants is also important and it has a significant impact on the transpiration rate. A downward direction of the airflow creates a low-pressure eddy on the bottom of a leaf, hence an increase in both cuticular and stomatal transpiration rate regardless of the VPD.

Airflow affects the leaf boundary layer, which is a thin zone of calm air that surrounds each leaf. The thickness of the boundary layer influences how quickly gasses and energy are exchanged between the leaf and the surrounding air. A thick boundary layer can reduce the transfer of heat, CO2 and water vapor from the leaf to the environment.


Leaf temperature is another important factor in the plant’s development. The optimal temperature conditions for cannabis cultivation are between 72F and 85F with night temperatures in general 10F lower. Deviating outside of these parameters for prolonged periods of time significantly inhibits the plant’s development, weakens its immune system and makes it more susceptible to diseases. The sativa family is more tolerable to warmer conditions, while the indica family is better at dealing with cold temperatures.

Setting and maintaining the ideal temperature in correspondence with relative humidity is one of the biggest HVAC design challenges. The environmental conditions are changing with the plant’s maturation cycle, and climate control systems have to be attuned to the plant’s developmental process and have capabilities to maintain a dynamically changing environment.  An oversized HVAC system can create temperature swings and fluctuations, not only affecting the plants directly, but also changing the relative humidity in the grow room. On the other hand, units that are too small will struggle to keep the temperature within the appropriate range.

Supply air temperature usually should not exceed 60F, which places additional constraints on designing a climate control system for indoor cannabis cultivation.


The greatest challenge for designing climate control for cultivation facilities is controlling relative humidity and keeping the VPD within the range of 0.5 kPa – 1.5 kPa. As the plants grow, the transpiration rate increases and the excess moisture must be effectively removed from the space. This poses significant challenges to traditional HVAC systems since the latent load can be as much as 1,000 Btuh per each 10 sf of grow space. To make it more challenging, late flowering phases require grow conditions with dew point temperatures in the high 30’s or low 40’s, which critically reduces dehumidification capabilities of vapor compression technology.

While the exact humidity needs of the plants will vary depending on the strain being grown, here is a general guide:

  • Clone stage needs 70-80% humidity
  • Vegetative stage needs 50-70% humidity
  • Flowering stage needs 50-60% humidity
  • Final weeks of flowering is below 50% humidity

Cannabis Plant

Typical Grow Room Setup

The goals of commercial cultivation facilities are to increase the biomass production while reducing the cultivation time and energy consumption. The kernel factors in achieving these goals are lighting system, climate control system, cultivation method and integrated pest management (IPM).


As we learned from Biology 101, plants need energy of the sun to drive photosynthesis and fix sugar. Solar radiation generates a full spectrum of wavelength from 250nm to over 2500nm, but only a narrow spectrum from UVA (380nm) to far red (750nm) produces photosynthetically active photons. Until recently, commercial cultivation facilities have employed mostly inefficient HPS lighting, but the recent advances in LED technology allowed cultivators to have better control of the grow process. New facilities are being furnished with multi-tier vertical rack systems with LED lighting cultivation technology that can guide plants’ development by modulating light spectrum while saving real estate and reducing the energy of the operations.


Floor mounted horizontal fans and oscillating ventilators still dominate the market, however innovative stratifying fan technology and fabric duct distribution schemes are rapidly gaining popularity. Ample ventilation is important for many factors, including preventing fungus related diseases and keeping adequate CO2 circulation.

HVAC system

Commercial indoor cannabis cultivation facilities benefit from 100% airflow recirculation to prevent contamination, reduce odor dissipation and to have a superior control of the environment throughout the year (CO2 purging system must be present). HVAC cultivation systems must be designed not only to control temperature and humidity but also mitigate the odor and treat the airflow with bi-polar ionization, ozone generators or UV.

Special Environmental Considerations

In addition to managing the conditions within the grow room, growers also need to consider the conditions outside that have an impact indoors. Here are few variables that are often overlooked:

Building design and outside environment may also affect conditions in a grow room if the building is not properly insulated. If not taken into account, yearly and daily temperature fluctuations in many regions can reduce the capacity of the HVAC system and cause adverse effects on indoor climate.

Outdoor humidity levels fluctuate with the seasons. The ambient moisture content can affect the humidity level in a grow room if it draws ambient air instead of a 100% re-circulation typical to a controlled environment room.

Odor mitigation is an integral element of cannabis cultivation operations. The odor is produced by tangenes, the plants’ oil compounds. As a number of grow facilities increases, the odor has drawn complaints since it has often dissipated into the environment, causing air quality issues. As operations migrate into urban areas, the odors commonly cause a public nuisance.

Employing Smart HVAC Technology

The field of HVAC technology for indoor cultivation has been evolving over the last few years and adapting the innovations from Data Centers Cooling. Advanced climate systems for indoor farming utilize such technologies as adiabatic cooling, water and air-side economizers, heat pipes and desiccant dehumidification. Smart HVAC technology helps cultivators achieve the best results, while reducing energy consumption, shrinking labor cost and mitigating human errors.

Advantages of Air2O cultivation line:

  • Up to 70% reduction in energy consumption
  • Enhanced humidity and temperature control
  • Low acquisition cost
  • Superior airflow distribution
  • Custom-built systems to fit design criteria
  • Advanced climate control software

Designing HVAC systems for commercial cultivation has many challenges, but it also presents opportunities for professionals to show their expertise, take advantage of the newest technology, and fulfill the client’s needs.

Air2O is the global leader in cutting-edge evaporative coolers and hybrid HVAC systems.

Contact us today for help with your next commercial cannabis cooling project!