By Art Irwin
In recent years, we have seen dramatic changes in the HVAC world – low mass boilers, radiant floor heating, heat pumps, etc. In our society at large, we are now going through a significant change like the Prohibition days when booze was very limited, and many parts of the country voted on whether to be “wet or dry.”
Cannabis (marijuana) has just become legal. The method of delivery varies from province to province, but millions of dollars are being invested in marijuana growing facilities and this is providing significant opportunities for the mechanical industry.
The indoor advantage
Let’s look at the trend. Marijuana grow operations – “grow-ops” – have gone from outdoor growing to greenhouses to today’s indoor facilities. Growing indoors allows precise control over the environment – and that’s something in which our industry has considerable expertise. Grow operations (grow-ops) must be able to control water temperature, humidity, carbon dioxide levels, light, air quality and nutrients.
It is important to note that medical cannabis is different from recreational cannabis. The active ingredients are different. The amount of active ingredient in cannabis, Tetrahydrocannabinol (THC), has dramatically increased in the last half century. It is not the 1960s weed.
As with most crops, the specific strain of cannabis that is being produced requires a specific grow environment to produce the desired end product. The understanding of the general boundary conditions for indoor cannabis production are being developed as the industry evolves. The environmental conditions change during the grow cycle and can be specific to how the grower wants to develop specific characteristics of the product. The grower may want a characteristic taste or flavour or enhance certain levels of the specific chemical makeup of the product.
The plants start off in a “spring” environment, move to “summer” conditions and then finish in the “fall”. During the growing “seasons”, the temperature, humidity, nutrients, lighting, air quality, etc. all play an integral role in the final product quality and yield.
In general, temperatures in the 60F to 75F (16C to 24C) range are most widely used by growers. The temperature must be monitored and controlled closely to allow the plants to achieve optimal yield.
Probably the most important engineering consideration (and the one that is most poorly executed) is the design of the mechanical systems for control of relative humidity within the grow spaces. Relative humidity should be controlled between 50 and 75 percent depending on the stage of the grow cycle. If the humidity gets too high, mold growth can destroy the entire crop. If it gets too low, it can stress the crop and destroy it.
There are several growing methods including hydroponic, aquaponic, soil based, and other hybrid methods. The goal is to water the roots and leave the foliage dry or leave the aerial parts of the plants dry. Let the plant dry in the air.
Watering operations are critical. Water allows nutrients to enter the plant root system. Roots need to be damp but not wet. The plants need to cool themselves via a process called transpiration which drives the uptake of water and nutrients into the roots and up through the plant.
The plants are basically cycling moisture. Pulling it inwards in the liquid form and releasing it outwards as vapour. It is the vapour form that is of the most concern.
Typically, the incoming water systems are filtered and treated to prevent contamination and disease. Filters are used with reverse osmosis (RO) and UV disinfection. Then fertilizer and nutrients are added in a quantity prescribed by the grower and may change greatly during the grow cycle. Finally, a PH balance is performed prior to delivery to the plants.
Dehumidification and dilution ventilation to control moisture is a big deal in the growing business. Moisture control can be classified into two conditions; lights on and lights off. When the lights are on, the plants are gathering water and requiring humification to maintain environmental set points. When the lights are turned off, the plants immediately begin to release moisture into the grow space and the mechanical systems must respond with dehumidification.
Precise control strategies
We require a very large and complicated system to control differing temperatures and have humidity goals that may be shifting on a timely basis. Controls are required on the mechanical environmental systems, nutrient supply systems, water filtration, lighting, security, and more. Without the aid of automated systems and precise control strategies, the optimal product is not achievable.
Plants grow best in a carbon dioxide rich environment – about 1,500 ppm on average. The ideal situation is to have an airtight grow enclosure, add pure industrial carbon dioxide directly into the air, and couple it with a minimum air change.
Ventilation and indoor air quality are a big deal. These operations need well filtered air. We cannot bring mold spores into the space from the outside, or worse, pollen, or anything else that might contaminate the product. Grow space pressurization is used to enhance the air quality within the grow spaces and minimize the possibility of airborne disease or pathogens causing detrimental effects to the crop yield. This is a similar method used in hospitals and biopharmaceutical facilities to maintain environmentally secure spaces. It utilizes standard and UV filtration to provide outside air to the plant spaces. It also provides some fresh breathing air to the occupants working within the grow spaces.
A sunny environment
Grow-ops have typically used high pressure sodium (HPS) lighting to create an indoor environment that mimics outdoor sunshine. This has provided the right spectrum of light energy to produce the resultant product qualities. Growers have begun to realize that by changing the lighting spectrum during the grow cycle, they can affect the product characteristics.
HPS lighting systems can be expensive to operate and newer light emitting diode (LED) full spectrum lighting systems have been developed to provide a lower energy footprint. Many manufacturers are producing these products and marketing themselves as the best alternative.
Now that marijuana is legal in Canada, grow-ops are becoming big business. The power consumption for grow rooms and grow operations is staggering. A typical grow operation uses 10 to 20 times more energy per square foot as a typical office building. It is not uncommon to see a 3000 kVa electrical entrance installed on a 24,000 square foot (2230 sq.m) grow facility.
In Portland, Oregon, Pacific Power attributes seven power outages during 2015 to indoor grow operations overloading local circuits. It takes about 2,000 kWh to make a pound of product using current indoor growing methods. That’s close to how much electricity an average Canadian household uses in two months.
The recipe for profitability within the cannabis industry is about who can grow the most product for the least cost. Some producers are experimenting with greenhouses and some are looking to move their operations back outside to curb costs.
Most producers who are starting in the industry are developing approximately 20,000 to 40,000 sq. ft. facilities. These “starter” size facilities allow the new entrepreneurs to get a grow operation into production while keeping costs within reason. Once a revenue stream has been established and some history recorded, expansion is inevitable. Some large investors have been building facilities as large as 500,000 sq. ft. (45,452 sq.m) or more.