Cultivating cannabis commercially is a difficult task.

Growers can’t simply toss a few seeds into the soil and expect plants to produce the luscious buds desired by medicinal and recreational users across the nation. The craft requires expertise, experience, and the right equipment. Indoor growing environments demand precise latent and sensible loads that vary depending on where the plants are in the growing stage, the size of the facilities they’re cultivated in, geographical location, and more.

Currently, 29 U.S. states have some form of medicinal or recreational marijuana laws on the books, and Canada will be voting on nationwide legalization in July. As more of these facilities continue to sprout throughout the nation, HVACR contractors are poised to fulfill and maintain the temperature, moisture, and filtration requirements necessary to cultivate this cash crop.


The heating, cooling, and moisture loads necessary to specify and size grow room climate control equipment are expressed as sensible and latent loads.

“These facilities tend to keep their outside envelopes fairly neutral, so the challenge lies in matching the sensible loads of the lighting systems, which are the primary heat sources within these spaces,” said Dave Meadows, director of industry, standards, and technology, Stulz USA. “The good news is that we typically know the types of lights they’re using — whether they’re high-pressure sodium or LED — and we can learn the wattage of those lights. The hard part is getting rid of the moisture.”

The lighting systems of grow rooms create different levels of heat depending on whether they’re on or off. As plants develop, the amount of moisture they release changes. Climate control systems must have the ability to adapt to the challenges of these changing conditions.

“Plants don’t transpire at an even rate,” said Meadows. “They transpire the most when the lights are on, and the light cycle helps determine how fast a plant grows. In the later parts of the life cycle, rapid changes in temperature or humidity could create stress on the plant and potentially impact the yield of the crop.”

Stulz’s CyberONE EC (COS) floor-mounted air conditioners are designed to provide precise temperature and/or humidity control where continuous 24/7 operation is required, such as in a grow facility. The COS is available in 5-, 8-, and 10-ton sizes and is equipped to prevent white mold and mildew, eliminate humidity spikes, prevent pollen contamination, control pests, facilitate CO2 augmentation, and more.

“We have worked closely with our partners in the medical marijuana industry to specifically address all the challenges in a grow facility,” Meadows said. “The COS is robust and designed to operate all year long in a trouble-free manner. The algorithm of our E2 controller controls the temperature of the coil and puts it at the lowest possible temperature above freezing to strip moisture quickly from the space.”


As a plant consumes water, it uses that water to move nutrients through the stems and leaves, and after this is complete, the water is excreted through the plant cells and has to be absorbed in the air around it. In grow rooms and indoor farms, it’s important to surround plant leaves with air that has lower concentrations of water vapor than their internal vapor pressures to establish and maintain the conditions for optimal transpiration rates, said Paul Stewart, director of sales, marketing, and service, Desert-Aire.

“The temperature of the leaves and their internal vapor pressures drive this exchange of gases and the vapor pressures exerted on the leaves by boundary-layer air,” he said. “The process of changing internal liquid water into a gaseous state consumes energy. Vapor pressure differentials, sometimes known in the grow room industry as vapor pressure deficits, drive transpiration and provide the forces for nutrients to be brought from roots to the upper areas of plants. Because the vapor pressures inside of hydrated plants and their stomata is high, water vapor will exit the stomata if the air outside of leaves has lower vapor pressures.”

When restarting the growing process, most growers clone mature plants to start new ones. This process entails cutting the leaves from a mother plant and planting the leaves into the soil. Because these stems lack root systems, they can’t absorb moisture directly from the soil. When nurturing clones, growers tend to implement humidity rates in the 70 to 80 percent range during this stage.

“Growers must maintain a really high moisture content in the clone room because those very small plants can’t transpire enough moisture to maintain the moisture content in the air,” Meadows said. “In those cases, you may see them using ultrasonic or traditional steam humidifiers. The individual temperatures really depend on the grower, as each has his or her own secret sauce as far as what temperatures they’re trying to maintain in the individual rooms.”

Once the plants have roots, they can start pulling water and nutrients from the soil. This is referred to as the vegetative phase. The plants finally round into form during the flowering stage, which tends to last around eight weeks.

“The vegetative phase requires around 70 percent humidity because the root system isn’t completely established,” said Brandon Glancy, channel manager, Anden Humidity Control Systems. “And in the first two to three weeks of the flowering phase, humidity levels are kept in the mid-to-high 60s to help the roots grow stronger. To finish flowering, humidity levels and temperatures are lowered to prevent white powdery mildew, root, and other humidity issues that threaten the plant and its quality.”

During the flowering stage, plants consume a significant amount of moisture. Glancy said poor yield and crop loss is the No. 1 cost to cultivators. The better the environment is balanced, the more protection there is against mold and mildew. With HVAC and humidity control, this happens reliably and organically, so there can be less reliance on chemicals to keep mold and mildew at bay.

“Depending on the strain, some plants will consume as much as a half-gallon of water per plant per day,” Stewart said. “A room with 5,000 plants will require a significant amount of moisture, which will then need to be removed from the air.”

Marijuana facilities require very specific climates at all hours, which creates extreme demands on the HVAC systems that serve these spaces. To accommodate these demands, Anden created the A300, which is specifically designed to cater to indoor agricultural applications.

The A300V1 and A300V3 are 240V and 277V units, respectively, that are designed to adapt to growing room conditions as they change.

“The growing conditions are very much a moving target,” Glancy said. “The A300 was built with components that were designed to modulate the way the dehumidifier works as the environment around it changes."

Having a dehumidifier that adapts allows cultivators to get consistency out of their dehumidification systems.

“A home dehumidifier was meant to run inside your house like an automobile was meant to be driven to work,” said Scott Grefsheim, senior product engineer, Anden. “If you drive your car every day to and from work and maintain it as you’re supposed to, that car is going to last a very long time. If you buy a new car and immediately push the accelerator to the floor and never let up on it, the engine is going to blow in a couple of hours. Cars weren’t meant to be driven like that, and residential dehumidifiers weren’t designed to operate like that, but that’s exactly what is required in the extreme conditions of a grow room, so we created equipment designed to handle this extreme application, and we feel it’s really important that we apply that technology.”

Desert Aire’s GrowAire™ purpose-built systems combine the functions of air conditioners and dehumidifiers into integrated packages. These engineered solutions provide growers with low operating costs and tight temperature and humidity set point control.

GrowAire solutions eliminate the supplemental equipment required with other grow room HVAC equipment approaches, thus lowering energy consumption. An additional, critical benefit is the ability to precisely control the vapor pressure deficits of grow rooms.

“GrowAire allows a grower to create a set point for temperature as well as relative humidity,” Stewart said. “We’re able to compare the actual moisture content in the space to the desired moisture content in the space. We rolled this unit out about three years ago, and the response has been wonderful. We’re doing things with the selection and the evaluation in the space that no one else has done.”

While removing moisture is a primary concern in these facilities, adding moisture is also a consideration when it comes to storing the final product.

“We’re adding a lot of humidification — primarily ultrasonic — in storage areas because growers don’t want to dry out the crop,” said Meadows. “This has an effect similar to a humidor. Places like Denver get really dry in the winter, so growers actually add water to their drying or curing room so the product doesn’t dry too fast.

"It doesn’t sound right, but it’s essential," he continued. "When we first got to Denver, many cultivators were spraying water on the floor and letting it evaporate. We came up with a cleaner solution for them.”


Dave Binz, application engineering manager, Cambridge, said many of these grow facilities are essentially greenhouses being built into concrete buildings.

“Most greenhouses are constructed with some form of transparent or glass walls; however, that is atypical when it comes to marijuana cultivation,” Binz said. “These grow houses are being built into these super tight concrete boxes, which makes it difficult to control humidity and the amount of fresh air being used.”

Enhancing and understanding ventilation and air movement within these facilities is a profit driver in these unique applications.

“Maintaining proper ventilation and having the ability to provide large amounts of ventilation air is something that is not common in other large construction projects,” Binz said. “Making sure you’re putting the proper make-up air technologies in and utilizing high-efficiency air technologies is a much more important part to the overall efficiency and cost to run these facilities.”

One solution lies in Cambridge’s M-Series Direct Gas-fired Make-up Air Heaters. The M-Series heaters include patented Cambridge Low-fire Start Technology and proprietary stainless steel burners that are specifically designed to provide year-round ventilation and tempered make-up air for a wide variety of demanding commercial and industrial retrofits. Units with variable frequency drive (VFD) control are also available to respond to varying air needs to reduce operating costs as well as an optional cooling coil.

“We offer 92 percent efficient direct-fire burners,” Binz said. “The M-Series also has a fairly small pressure drop across the burner, so we actually get very low energy usage.”


Large cultivators are spending hundreds of thousands and, in some cases, millions of dollars on HVAC equipment to properly condition and control their facilities.

“Contractors should certainly look into this, as it’s a very lucrative opportunity for the industry,” said Meadows. “We just did a project in Canada that utilized about $700,000 worth of HVAC equipment. As the rooms continue to get bigger, the a/c equipment becomes more expensive.

“Very few in the growing industry are HVAC-savvy,” he continued. “They need contractors’ expertise. The equipment needs to be sized and maintained, and that is what contractors do. Without proper air conditioning and moisture management, a grow operation simply will not be successful.”

Binz said the potential for contractors is unbelievable.

“In Las Vegas, within three months of it becoming recreational, growers essentially ran out of their inventory to the point where they declared a state of emergency,” he said. “They had created this massive market in very little time and grossly underestimated the demand. The ability to react, build up, and control the climate within growing operations is going to be pivotal from a contracting standpoint.”

Stewart said Desert-Aire has experience with facilities that have installed more than $3 million in HVAC equipment.

“It’s an emerging market, and it makes a lot of sense for contractors to get involved,” he said. “Using the right equipment and creating the proper environments are going to give growers a better outcome. That said, this is the gold rush, and I’m unsure how long this opportunity is going to last, but there are more states that likely will vote to legalize, and there is also an indoor food market that is looming as well.”

Glancy said the major players need to work together to reap the greatest reward.

“We want to get cultivators and contractors as connected as possible because, the two together ... they can do amazing things in this industry,” he said. “The more they work together and the more HVAC gets involved, the better the environment and the better the yield.

“This market is moving at an amazingly rapid pace,” continued Glancy. “Even the smallest of facilities have hundreds of thousands of dollars of equipment. It’s an unbelievable opportunity for HVACR contractors of any size or scale.

Publication date: 4/23/2018

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