Unique Conditions 

It's important to understand that each of the phases in a cultivation facility has different demands and different purposes, said David Sandelman, chief technology officer and co-founder of Cannatrol. For example, the grow process requires controlling variables such as the vapor-pressure deficit (VPD), while the post-harvest process requires tight vapor pressure control. 

“Traditional comfort cooling equipment typically attempts to control sensible heat and relative humidity, and to produce premium quality cannabis, a consistent, repeatable environment is critical,” said Sandelman. “Instability in environmental conditions can destroy the quality of the finished product, robbing it of the valuable volatiles that cannabis is grown for.” 

Sean McCarthy, general manager of Anden, added, “Cultivators desire very tight control of their environment in very challenging conditions. The changing of both sensible and latent loads throughout a grow cycle is much more demanding than a single set point application. The HVAC system needs to be able to perform across the range of conditions.” 

Cannabis cultivation facilities are also unique due to the exceptionally high value of their end product, which justifies the strict level of environmental control not typically seen in large-scale agriculture, said Chip Seidel, head of business development at Desert Aire.  

“There's some marijuana that's grown outdoors or in greenhouses that might be $200 a pound, and then there is the very highest end of the market for specific strains that are useful for anti-seizures or for really targeted medical conditions, and they could be several thousand dollars a pound.” 

Whichever strain the cultivator is growing requires nutrients that are optimized for that specific cultivar, said Seidel. This includes CO₂ levels, light intensity, temperature, and relative humidity, each tailored to the specific strain being grown. This tight environmental control results in higher yields and better-quality cannabis, which can command significantly higher prices. 

“As these cultivators mature and the industry becomes more sophisticated, there is an increasing willingness to invest on the front end in the right equipment to be able to deliver those very, very tight set points, when it comes to temperature and relative humidity,” said Seidel. “Almost all the innovations in this space have been focused around achieving a tighter level of control and also energy efficiency.” 

Innovative HVAC 

To that end, Desert Aire has engineered a line of HVAC equipment that is specifically designed for indoor agriculture. As Seidel explained, grow facilities often use standard rooftop units, which are designed for comfort cooling and mainly control temperature, not humidity. If the facility ends up being too humid, the common fix is to add dehumidifiers, which convert moisture into heat, prompting the air conditioner to turn back on and remove that heat. 

“Our all-in-one GrowAire system does the moisture removal and cooling together in one process to deliver air that is the perfect temperature and relative humidity,” he said. “It uses about 30% less energy, and the units are specifically designed for indoor agriculture. They look like a regular rooftop unit, but everything inside is all set up with more beefy components that are tailored for the indoor grow environment.” 

HARVEST READY: This indoor cannabis flower room is nearly ready for harvest (Courtesy of Desert Aire)

GrowAire units are primarily designed for the flower rooms in grow facilities (see sidebar), and according to Seidel, the systems use a cold coil to cool and remove moisture from the air. If the air is overcooled, a second coil reheats it to the desired temperature, using waste heat that would otherwise be exhausted. “This method is much more efficient than traditional systems that dump all the heat outside and then use new energy to reheat the air.” 

VT Dry & Cure technologies from Cannatrol are designed for the post-harvest stage, which includes drying, curing, and storage. According to Sandelman, their Vaportrol technology is independent from existing HVAC systems and allows precise control of dry bulb (sensible) and dew point (latent) variables in the controlled space. 

“Our technology is unlike any other available system that has existing sensible and latent ratios,” he said. “Cannatrol systems give the user precision control of vapor pressure, which is an integral part of achieving success. By providing a consistent vapor pressure, we also eliminate the continual cycling of HVAC units and dehumidifiers typically found in post-harvest operations, thereby reducing energy consumption.” 

Cannatrol systems are also beneficial for odor control, as they are sealed and do not utilize active air exchange with the outside environment, said Sandelman.  

“Additionally, our technology preserves trichome integrity (the part of the plant where much of the volatiles are produced and stored). We have done extensive independent lab testing that demonstrates our system's superiority in reducing trichome damage, which in turn, reduces off-gassing of terpenes.” 

Anden offers variable-speed dehumidification systems that reduce the need for defrosting in lower temperature and relative humidity conditions, said McCarthy. These systems help maintain tight environmental control while also saving money for growers. 

“Reducing energy consumption is at the forefront of everyone’s mind in this industry,” he said. “True operational savings is what we’re striving for versus simply a higher energy factor at a single condition. Matching performance to demand can accomplish that.” 

In order to match performance to demand, contractors need to understand the sensible and latent loads across the entire grow cycle, said McCarthy.  

“This is determined by the plant type, watering schedule, and temperature and relative humidity targets in all stages of growing. This isn’t known many times during the construction of a facility, which can make sizing a challenge.”  

Looking ahead, McCarthy expects to see more connected HVAC products in cannabis grow facilities. “Making products more connected will help growers have better control of the variables that affect their indoor environment and deliver better results.”