Michigan Cannabis Grow-Op Increases Yields with HVAC System Retrofit

Like most North American cannabis industry grow-ops, Kalkaska, Michigan-based Real Leaf Solutions (RLS) is still refining its growing methods, but the two-year-old company may have finally found a state-of-the-art HVAC design that will help it reach optimum yields in the near future.

Tom Beller, co-owner and COO, RLS, believes his latest HVAC retrofit for two 1,500-square-foot flowering rooms is a major step toward optimum harvest goals. It consists of fabric duct supplied by 6- and 8-ton variable refrigerant flow (VRF) systems — a combination he’ll use when doubling the operation this year from 12,000 to 24,000 square feet. Beller’s confidence is backed by his last harvest's 20% yield improvement, which he attributes partially to the new HVAC design.

Beller’s HVAC retrofit design team was headed by mechanical contractor, Marc Burnette, president, Superior Heating and Cooling (SHC) in Traverse City, Michigan; Brad Bonnville, regional sales manager at fabric duct manufacturer FabricAir; the Fujitsu VRF team at Johnstone Supply, Traverse City; and Jeromy LaRock, outside sales, West Michigan, at manufacturer representative, Major Lozuaway.

Prior RLS HVAC challenges revolved around getting airflow to the plants and their soilless peat/coca mix at the right velocity, uniformity, temperature, and relative humidity (RH). The fabric duct solution incorporates a linear orifice array at the 4 and 8 o’clock positions on each 20-inch diameter. The Combi 70 fabric also disperses approximately 12% of the airflow through the duct’s permeable surface to prevent condensation. The factory-engineered permeability and linear dispersion results in a uniform 2,500-cfm air distribution per duct run that helps plants thrive.

Meanwhile, each flowering room’s four ceiling-hung V-II Airstage Fujitsu evaporator units, supplied by two outdoor heat pump condensers, can maintain Beller’s preferred 77°F and 56% RH within a tight ±1 tolerance. SHC’s Burnette set up each room to provide cooling/dehumidification and heating from any of the four evaporators simultaneously, if needed. The design is invaluable when latent and sensible heat load shifts during light/dark room cycles create environmental changes unsurmountable by conventional HVAC air-handling equipment. Beller said the VRF stabilizes and pinpoints temperature/RH settings without adding portable dehumidification or humidification equipment that other grow-ops depend on.

Finding the Best HVAC Combination

When opened in February 2019 as one of the first recreational and medical marijuana grow-ops certified and licensed by Michigan’s Marijuana Regulatory Agency (MRA), the staff at RLS struggled to maintain optimum growing conditions, resulting in yields they knew could be improved upon. The all-metal building’s flowering rooms were supplied with conventional DX split systems. The ceiling-hung air handlers’ metal spiral ductwork with registers every 10 feet created drafts, hot spots, and air stratification that affected yields. The new HVAC environment not only raises yields, but the enhanced air comfort is also increasing staff productivity.

“It [the flowering room with the fabric duct/VRF system] is a totally different environment; you get a very strange sensation when entering compared to the other rooms,” said Tyler Pickard, RLS’s lead cultivator, who, upon entering the first time, immediately gathered his cultivation team to experience the air comfort difference.

RSL will save energy costs as well because fabric duct’s more uniform air distribution was proven more efficient than metal duct/register systems, according to a study conducted by the Iowa State University’s mechanical engineering department. Improved air dispersion leads to narrow temperature room gradients, decreased HVAC run times, and reduced energy consumption.

Furthermore, metal duct is prone to condensation formation in humid environments. Metal duct’s galvanization process contains toxic silver oxides that drip into the soil with condensation, get absorbed by the plants, and ultimately infiltrate the cannabis user. State governments regularly check for heavy metals and can mandate a failed cannabis harvest’s destruction.

“Using antimicrobial fabric duct is an advantage for us, because Michigan’s MRA has the strictest heavy metal and mold test standards in the U.S.,” said Beller.

Maintaining Sanitary Environments

RLS cleans every flowering room after every harvest. Disassembling and commercially laundering the fabric duct, which requires less than a half-day for one employee, is also part of the disinfection process even though the fabric is antimicrobial.

“Cleaning metal duct is difficult in place,” Beller said. “Taking them down would require the added costs of a contractor with the correct equipment. Laundering the fabric duct just makes for a more sterile environment.”

Other disinfection efforts include the air handlers’ 100% return air bipolar ionization modules manufactured by AtmosAir Solutions, which floods the rooms with positive- and negative-charged ions. The ions disinfect and electrically attach to airborne contaminants, thereby making them large enough for entrapment in the air handlers’ MERV-8 media filters.

Fabric duct’s lighter weight and installation ease enabled SHC’s two-person crew to install five 35- to 38-foot-long duct runs in less than three days and without heavy-duty lifting equipment or removing the facility’s dozens of 1,000-watt, double-ended, mixed-spectrum, high-pressure sodium light fixtures. Each run is suspended on a PVC-coated metal cable hung 2 feet below the 14-foot-high ceilings. Metal duct would most likely have required more time, a larger installation crew, and interfered with post-cleaning fast-track planting.

RLS’s future plans include doubling its space by spring 2021, installing more efficient lighting with variable spectrums, and retrofitting the current third and fourth flowering rooms with fabric duct and VRF.