Anyone have a crazy uncle whose bizarre tales make family gatherings almost worthwhile? I do. And one of the tales he’s spun on repeat for years focuses on how, with a few shovelfuls of soil and a handful of seeds, he grew the most bombastic weed ever cultivated in the 1960s. 

Over the last 60 years, the views and beliefs of the masses have evolved exponentially. Marijuana no longer needs to be grown in secret nor does it need to be hidden in the back corner of your sock drawer. In 2021, marijuana is big business. According to Cannabis Business Plan, the overall legal cannabis market in the U.S. is expected to reach $35 billion by 2025 — and that number may be on the low end, considering voters in five states favored the legalization of marijuana in some form or fashion last year. As of January 2021, only 15 states still fully outlaw marijuana within their borders.

Oh, how things have changed! 


Meticulous Design

Despite the boasts of my uncle, growing marijuana is difficult — especially in commercial settings. All factors of these facilities, including the airflow, temperature, moisture levels, lighting loads, and more, must be meticulously controlled and tracked to ensure the desired products or flowers are efficiently and adequately produced.

The operation of these facilities requires much more effort than flipping a light switch off and on. Load calculations for the lights, conduction, ventilation, infiltration, heating, and more must be adequately designed, set, and scheduled. 

Evapotranspiration — the process by which water is transferred from the land to the atmosphere by evaporation from the soil and other surfaces and by transpiration from plants — is the building block to crop production. Therefore, CO₂ enrichment must be managed to allow the plants to build their fruit and flowers. An HVAC system's design will have a direct impact on this process. 

Managing the vapor pressure deficit (VPD), defined as the difference (deficit) between the amount of moisture in the air and how much moisture the air can hold when it is saturated, is crucial. Once air becomes saturated, water will condense out to form clouds, dew, or films of water over leaves. Too much water increases the threat of mold and mildew, while too little water leads to an unhealthy plant. And, perhaps most importantly for a mechanical engineer, a high VPD strains the HVAC equipment. To ensure the operation remains functional, redundancy must be considered. 

Many crops, especially marijuana, need to be grown in different environments at different stages. Clones require high temperature and humidity levels to encourage root growth. After the roots are established, they're moved into a warmer, more humid room to imitate a vegetative climate, which encourages photosynthesis. The flowering process requires more light, perhaps on a different spectrum, with a more extreme temperature and humidity delta between day and night. Additionally, male and female plants must be separated to ensure the flowering process is properly completed. 

As you can see here, the cultivation process is convoluted. The articles in this "Smarter Engineering" supplement are designed to pique your interest. If you're interested in connecting with any of the authors, reach out to me and I'll do my best to facilitate a conversation. 

As entrepreneurs seek to profit on this budding market, ensure your firm is ready, willing, and available to fulfill these requests. Construction crews are breaking ground on grow facilities nationwide on a daily basis. Capitalize on this cash crop by demonstrating how your expertise can provide them the best growing environment for their indoor agricultural applications.