by Kelson Redding
Indoor cannabis grow facilities present a unique climate control challenge. High quality cannabis production has very specific temperature, humidity, and ventilation requirements. In addition, the required mix of heating, ventilation, air conditioning (cooling), and dehumidification, HVAC for short, is one of the top two energy consumers in this industry along with lighting. Until now, HVAC requirements have been largely addressed through a built-up system of residential grade mini-split heat pumps with separate ventilation and dehumidification equipment. The residential systems were well suited for the economic, security, and process needs of the formerly illicit facilities but will not scale as the industry, and producer scale, grow into their new potential. In addition, it’s likely that the current energy consumption will not be acceptable as the market becomes more competitive and profit margins are threatened.
Traditional commercial HVAC systems bring in outdoor air to economize and save cooling energy when a demand for cooling exists and the ambient temperature is less than the desired supply air temperature. This would be a great solution for cannabis production; however, this solution is not acceptable for two reasons. Indoor growers do not want to introduce outdoor air into their controlled environment because it can bring pests, disease, mold, and other crop dooming contaminants. Furthermore, they keep elevated levels of CO2 in the garden environment and the addition of outdoor air would hinder this practice. Cool outdoor air can still be used to effectively reduce HVAC energy by about 50% by ducting it directly through sealed light fixtures and then out of the space. This solution allows the cool outdoor air to be used without threat of introducing contaminants into the controlled environment. The latest lighting fixture technology addresses bulb cooling and maintenance concerns with a two chamber design. The fixture is separated into two chambers, the lower chamber houses the bulb and reflector while the cooling air is ducted through a sealed upper chamber effectively removing heat without cooling the bulb or dirtying the glass.
There are some promising existing HVAC technologies that are reliable, scalable, and have been found to meet the process demands. So called three-coil systems from firms such as Desert Aire were originally designed for the HVAC requirements of indoor pool facilities. These systems are designed to provide heating and cooling along with dehumidification and water recovery in a single system. This system design is promising because evapotranspiration within the facilities results in substantial demand for dehumidification. When facility cooling loads are large enough to allow for investment in heavy industrial equipment more traditional energy efficiency measures such as water cooled chillers and water side economization become viable. Another approach being considered are Variable Refrigerant Flow Systems, or VRF. VRF systems allow for the heat to be transferred between zones within a facility and have good part load efficiency due to the utilization of inverter driven compressors.
One of the first barriers to change will simply be that growers trust current approaches to yield the desired results. They have been ingenuitive in evolving their approaches over time; however, they were evolved to fit a broader set of needs than just environmental process control. Now, as the size of recreational and medical production operations grow and operational costs becomes more important, growers will need to investigate new approaches. A second and more challenging barrier is the large initial capital investment industrial grade HVAC equipment requires. This challenge is typically intensified when considering energy efficient equipment options because as the efficiency of equipment increases so too does its initial cost. If growers plan to be competitive over the long term however, the operational cost of equipment must be considered when making capital investment decisions. Fortunately, many utility providers have efficiency incentive programs like Energy Trust of Oregon that can provide no cost technical assistance and incentive funding to help producers invest in energy efficient equipment from the start. These programs exist in order to suppress the need to build new energy infrastructure and generation facilities by helping industrial, commercial, agricultural, and residential customers reduce their energy consumption.