The cannabis industry has two main cultivation methods. The first one is the indoor method – growing cannabis plants in a completely closed structure, fully isolated from the environment. This way the sunlight does not reach the plant, leading to a massive use of energy for lighting. The second method is the outdoor method. This way the cultivation is done outside, utilizing the sunlight, but leaving the crops without protection.

There is a third option for cannabis, which is greenhouse cultivation, an isolated structure that allows the sunlight to reach the plants.
As the legalization of marijuana spreads throughout the United States, more growers invest in indoor cannabis cultivation. In this industrialized method, growers use a large amount of energy to produce greater yields through the intense management of pests, diseases and process control. The idea is to isolate the plant from the natural environment and create an optimal climate for cannabis growing in a closed structure in order to try to increase the yield per sq. ft.. This energy intensive method may contribute to a large carbon footprint.

Indoor cannabis cultivation is highly energy intensive

Examples for high-intensity energy uses are heating and cooling –maintaining the ideal temperature in the system and generating carbon dioxide by burning fossil fuel to boost plant growth, traditional ventilation, and dehumidification system – removing water vapor to avoid mold formation and lighting.

As a result of high energy usage, indoor cannabis production has a large carbon footprint. In average US climate conditions, the carbon footprint of one kg indoor cannabis produced is 4600 kg CO2. One single cannabis cigarette represents 1.5 kg CO2 emissions, equivalent to 25 hours of 100 watt light bulb average emissions.

The majority of CO2 emissions come from 3 main categories: humidity treatment, air conditioning and lighting. Focusing on the first two categories, wasteful traditional dehumidification methods and air conditioning constitute 27% and 25% accordingly of total emissions. Air conditioning, including space heaters, and CO2 injection to increase foliage require 1681 kWh per kg yield, emitting 1120 kg of CO2 per kg of yield, based on average U.S carbon burdens of 0.666 kg per kWh. Dehumidification using traditional methods (including air ventilation) requires 1848 kWh per kg yield, emitting 1230 kg of CO2 per kg of yield.

Greenhouse cannabis has a smaller carbon footprint

Although indoor cultivation is a common method to grow cannabis, it is not sustainable. On the one hand, it allows growing larger amounts of cannabis per sq. ft., but on the other hand it does not utilize the advantage of the sun and outside climate. The greenhouse method combines the advantages of the indoor and outdoor – the energy from the sun with better air circulation.

Either way, both methods create isolated air system from the external air and as a consequence, require high efficient dehumidifiers to remove extra water from the air. The humidity forces the grower to open the greenhouse. In some cases, not only the water goes out but also the carbon dioxide injected into the growing facility. The high density of the cannabis flowers prevents water vapor escape to air and thus causing diseases like grey mold (botrytis) and mildew. A suitable dehumidifier should generate airflow on the leafs and flowers to avoid this problem.

Scaling cannabis cultivation

Many of the common methods today in the cannabis industry were originally developed for small-scale growing facilities. When increasing the growing scale to commercial (like many growers do), the technology and growing methods must be adapted accordingly. The commonly used dehumidifiers in small-scale growing facilities are not designed according to the plants’ evapotranspiration loads. DryGair solution treats the humid air separately from the temperature and is used as a complementary tool for humidity problems.

DryGair Energies offers several solutions for air dehumidification in greenhouses and commercial indoor production. Our solution provides humidity control, while improving energy efficiency and creating uniformity and homogeneous conditions in greenhouses and warehouses. DryGair’s units were designed to answer the plants’ needs. One unit can cover 300-1400 m2 (3,000-14,000 ft2) of cannabis cultivation, and removes 45L/h (12G/h) at the design conditions (18oC and 80% relative humidity). DryGair saves 50%-80% of the energy consumption compared to other solutions thus prevents at least 920 kg of CO2 emissions per kg yield in warehouse indoor production. The energy saving in greenhouses is achieved through  low electricity consumption, saving energy for heating and for CO2 production because the greenhouse can stay completely closed. Additionally, DryGair may be used to achieve a slight raise in temperatures.

For more greenhouse energy saving methods check out 6 Tips to Increase Energy Efficiency

Finally, cannabis growers face many challenges, the increasing competition requires more advanced techniques and technologies that reduce the initial investment and operation costs, while reducing the carbon footprint.

This article is based on Evan Mills’ “The Carbon Footprint of Indoor Cannabis Production“, April 2012.