Marijuana Cultivation Environmental Controls - HVAC
Marijuana grow rooms are designed in one of two basic ways- open systems and closed systems. Open systems have historically been the most common type, but that has changed in recent years. Open systems are set up to exchange the air in each plant room about every 10 minutes, keeping the environment fresh and breezy. They have a few downsides, however. For one, any heating or cooling that is added gets wasted by exhaust fans that almost immediately expel it. For marijuana growers who want to save electricity, this is an obvious and significant waste of energy, but it does do the job well in certain climates. Waste can be mitigated by routing the cold air just above the canopies so it drops down directly over the plants before being evacuated. In concert with that, exhaust fans are mounted at the tops of the rooms to remove hot air that has risen up. For odor control, carbon filters are usually attached to the exhaust fans. They collect particulate matter and, as long as they are periodically replaced, troublesome odors should not be detectable by humans outside the building.
Filtered intake fans are always a good idea. MERV and HEPA filters remove mold and mildew spores from the air and also keep insects from entering through vents. Just take care not to get filters that are too fine because they will slow down the intake fans too much. This can also happen when the filters aren't getting cleaned regularly. Since powdery mildew and botrytis are such world-wide scourges for cannabis cultivators, investing in good air filtration is highly advised. In the realm of high-tech cannabis cultivation, computer server data center technology is being utilized to maintain temperature and humidity within very narrow ranges.
Closed systems are those that have no air intake or exhaust and compensate for the lack of freshness by using Co2 injection. Plants primarily use oxygen when lights are off and Co2 when lights are on. The room will retain all the added AC and heating with a closed system, while also better containing odors, and will need Co2 supplementation to make up for the loss from plant intake. This method is more common in hot climates where fresh air intake does not help to cool the site, but they are increasingly becoming standard in other climates as well because of the odor control and energy savings that come along with them.
This approach has the upside of saving power on temperature control, but it can have a few downsides too. For one, you might need added dehumidification since marijuana plants release quite a lot of moisture as they grow. For another, Co2 supplementation has its own set of special needs when it comes to temperature, humidity, and nutrient balance.
Monitoring Co2 levels is necessary, whether you are supplementing Co2 in an open system or using a closed system. Human exposure to high levels can be fatal (over 100,000 ppm for 30 minutes). Licensed marijuana grow operations are required to have automated monitoring and exhaust systems in place to both warn workers of dangerous levels and mechanically solve the problem by evacuating the air when levels exceed healthy ranges. Fire departments will have some say over the requirements for signage and automation that must come along with Co2 usage.
Fire departments also regulate fumigation substances and methods. Marijuana grows often need to treat plants for various pests with fumigators, and worker safety is the most immediate concern in this case. I recommend having pest treatment rooms rather than treating the entire plant area. If plants are on rolling modules, each module can be rolled into the treatment room for fogging or atomizing with whatever pesticides and fungicides might need to be applied. This saves labor, materials, and protects workers from the residues that can build up on surfaces in the cultivation area.