Keeping Cannabis Cool: HVAC needs for growing, processing, and selling marijuana

Compared to a retail shop, for a grow operation “the design criteria and requirements are very different,” says Curtis Holeman, senior sales engineer at Long Building Technologies. “The grow wants to maximize crop and minimize energy use. A retail store is a retail store, but they’re not as stringent as they would be in a grow environment because there’s more to do there.”

Controlled Environment

Odor aside, grow facilities have special air handling needs simply because regulating the climate is vital for healthy marijuana plants.

“You’re growing a tropical plant in an arctic environment,” says Mark Frischkorn, principal mechanical engineer and vice president of RSA Engineering; he’s designed about a dozen grow rooms. “Tropical plants like warm and humid—but not too humid—and surprisingly enough they need cooling almost more than they need heating.”

For the fiscal year ending June 2021, licensed growers in Alaska harvested twenty-one metric tons of cannabis, according to the industry website Leafly.com. The crop—whose wholesale value of $104 million outpaced that of hay, barley, potatoes, and every other agricultural commodity grown in Alaska combined—was raised almost entirely indoors under artificial lights.

Most cannabis in Alaska is produced in grow rooms using controlled environment agriculture (CEA). These are typically sealed rooms with few windows, where artificial light is used for optimal plant growth. CEA allows the grower to maintain the proper light, carbon dioxide, temperature, humidity, water, pH levels, and nutrients to produce year-round crops. Daytime temperature for plants is typically kept somewhere between 70 and 85 degrees. Humidity and airflow are also major considerations, but the precise formula is a matter of opinion among cultivators.

“Indoor grows need robust HVAC systems to keep the plants at the correct temperature and humidity levels for maximum yields,” says Richardson. “Air movement is also a key factor in a successful grow, as it helps regulate temperature by removing hot spots in the room as well as help stem growth with the constant air movement. This will help hold those heavy buds that will come later without having to tie your plants up.”

Marijuana plants need lots of light to grow, and that great amount of light translates into a lot of energy use and a lot of heat, which must be removed without harming the plant, Richardson explains. But because the plants also thrive in a carbon-dioxide-rich environment—and because a high-dollar crop could potentially be subject to theft—growers don’t just throw open windows to let the heat from grow lamps out. Instead, they invest in professionally designed HVAC systems.

“We pour a lot more energy into cooling the building than we would an office building,” says Frischkorn.

Richardson’s advice: “Oversize your air handling units and AC systems. You don’t want to be running your equipment constantly just to maintain your environment; it gets expensive!”

What Plants Crave

Just as HVAC must cope with the heat of the grow lights, the air handling system must take away the water that marijuana plants drink. A dehumidifier removes moisture to prevent mold that could damage the crop or the building itself. As with temperature control, CEA isolates the grow space from outdoor air to keep contaminants out and CO2 in.

Extra carbon dioxide usually comes in bottled form, and grow rooms typically have sensors to check for CO2 levels and to vent the room if the concentration becomes too high. “We don’t do that too much in regular commercial office space,” Frischkorn says. Since workers don’t spend much time in the rooms, CO2 concentrations are higher than they would be if people were constantly in the space, as the plants thrive in that environment.

Additionally, because of those state odor regulations, any air that is vented out must be run through filters to remove the pungent cannabis smell. “Any exhaust air we pull out has to go through a carbon filter so the odor doesn’t go into the neighborhood,” says Frischkorn.

Another consideration for cultivation facilities is the potential for a financially devastating crop failure. As insurance, most growers split the crop into different rooms—at least two, but typically four or five, Frischkorn says—so if something happens in one room (disease, pest, or equipment failure), they can contain it and avoid affecting all the crops. This means more HVAC units. “I have to put in three instead of one because they have three self-contained rooms instead of one,” says Frischkorn. But that’s not unique to the cannabis industry, he adds: “We do that in other businesses up here because of the weather, though, put in multiple systems in case something breaks down.”

Odor is also a concern for marijuana processing locations, according to Frischkorn. To extract cannabis oil, the buds are processed with machines using CO2 or butane as solvents, the same general process to extract any essential oil. Processing workers tend to spend more time inside the building than cultivators, so sensors make sure the CO2 or butane levels are safe. The ventilation system also filters any air dumped outside to scrub out the smell.

“Long [Building Technologies] designs and provides the control systems that are installed for the HVAC systems to ensure the systems are controlled and operate as designed and per specifications,” says Holeman.

Things like thermostats, valves, and sensors that measure pressure and humidity and CO2 and outside air temperature are all controlled by Long Building Technologies systems. “Our control systems… are an integral component to these facilities where they’re growing crops,” Holeman says.

That’s an aspect of the burgeoning cannabis industry that also went unmentioned during the 2014 campaign: that marijuana growers and sellers would pass their prosperity around to mechanical engineers and HVAC installers.

At the time, supporters of legalizing the drug promised tax revenues of up to $10 million or even $15 million; opponents cautioned that the real amount would be a disappointing fraction. In fact, taxes on marijuana added about $24.2 million to the state’s budget in 2020, and sales in Alaska are expected to grow to about $284 million by 2024.