The cultivation and processing of cannabis for medicinal use requires large amounts of energy due to the requirements of environmental stability during its growth and transformation to guarantee the constancy of the composition of the different cannabinoids. In this way, the final product can be considered as a drug with specific properties.
The energy cost of producing medicinal cannabis becomes, in most cases, the most important cost and the one that will determine whether industrial exploitation is profitable or not.
An efficient design of the facility will increase the direct profitability of the farm and reduce the carbon footprint, providing added value for these products of plant origin.
Most of the actions that allow us to optimise the control and stability of environmental conditions, as well as energy efficiency, involve a higher initial investment. Because this investment is decided and made long before the licence is even granted, it complicates the decision making process for a cost whose return is spread over several years
On the one hand, we have the scenario of the high cost of energy, which leads us to design on the basis of efficiency and savings, and, on the other hand, the uncertainty of the medical cannabis market (volumes, prices, etc.) and its difficulty as a product and process, which makes us be cautious.
It is not possible to speak of an optimal "standard" solution for facility design, as this depends on many factors, and must be developed on a "tailor-made" basis:
For all of the above reasons, in this article we aim to identify the different points that must be analysed in order to implement technical solutions in the installation that will lead to an improvement in energy efficiency.
The result of the analysis should be applied in the calculation of the cost-effectiveness of each individual case, taking into account the possible improvement options proposed.
If there is one thing that is agreed in this sector, it is that any improvement in the stability and security of the growing conditions must be optimal.
The environmental impact of the crop leads to improved yield and product quality and thus to increased profitability.
This is one of the most important conditions as it has a major economic impact. We must look for a good plot, in an area with a climate suitable for the needs of the crop, and sufficient hours of light. In addition, we need to ensure access to quality water and grid electricity, which has a major impact on design, investment and operating costs.
Illumination of the crop can be done by sunlight, artificial light or a combination of both.
Sunlight allows us to save on energy consumption, but in order to be able to use it, we must pay attention to the type of enclosure.
Film-type enclosures provide the highest sunlight transmission, but at the same time less airtightness and insulation for cold areas or nights, so it will be necessary to install black-out screens to help improve thermal insulation.
Other treatments such as polycarbonate or glass improve thermal insulation, reduce solar transmission, but increase inversion.
In locations close to the equator, we will have the best natural light conditions all year round, but as we move away from the equator, if we want to have stability in the light flow, we will have to install support lights, or even lights that can provide the total necessary contribution. In these cases, the lights to be installed should be LED type and dimmable to ensure that we only provide the light necessary to complete the solar system and contain energy consumption.
In opaque enclosure installations (sandwich panel), lighting is provided entirely artificially, and will be constant regardless of the time of year. To control consumption and reduce costs, if we are connected to the electricity grid, an interesting measure is to switch on the lights at night. If we do not have mains electricity, we should install photovoltaic panels and batteries to store energy to enable us to switch on the lights during the day and extend the photoperiod up to 12 hours, or more for vegetative and mother plants.
Due to the need to regulate and control the temperature and humidity of the crop, optimum insulation allows us to reduce energy consumption.
The insulation of roofs and walls may have as a consequence a reduction in the transmission of sunlight and therefore an increase in consumption to ensure illumination, so it will be necessary to study each individual case to find the right balance.
Floor insulation, except in areas with an excellent climate, will always be a good investment. A cement slab, placed on a layer of insulation and vapour barrier (to ensure the durability and quality of the finishes), ensures insulation and thermal inertia for cold nights, and it is precisely in the lower part of the floor (roots) where we want to ensure a slightly higher temperature.
The ability to maintain constant temperature and humidity conditions day and night and throughout the year is another factor in energy consumption. Some locations and technical solutions could be ruled out during the project study due to high humidity or thermal conditions.
The main problem is to combat the humidity generated by the plants. During the diurnal phase, the plant transpires practically all of its water captured by the roots. The most economical way to reduce this indoor humidity is to renew the greenhouse air with drier outside air. Depending on its dryness, there may even be scope for adiabatic cooling, and this is undoubtedly the most efficient way.
In any case, as outdoor environmental conditions cannot be assured, we should consider the need for dehumidification and cooling installations to combat the humidity generated by the plants, as well as the internal (lights) and external thermal load. Energy efficiency will depend on having a good control system in place in order to be able to reduce operating costs when external conditions are favourable.
At night, in cold areas, it is important:
In order to increase crop result it is common practice to increase the CO2 concentration above ambient during the day, but this practice has a cost and a carbon footprint that needs to be analysed to ensure cost-effectiveness.
Working with higher CO 2 rates implies the need to maintain the perfect balance with the nutrient supply and the amount of light, otherwise we will not obtain the desired result, but will suffer from higher costs and even lower quality of the final product.
Increasing the CO2 rate while we have high fresh air inputs is not cost-effective, so it is only recommended for indoor or airtight wintering.
In large farms, where there is a combustion process to generate energy or hot water, the flue gases could be used to increase the carbon dioxide concentration by means of a filtering, storage and cooling system.
A concrete slab, laid on a layer of insulation and vapour barrier (to ensure the durability and quality of the quality of the finish), ensures insulation and thermal inertia for cold nights.
The processes of air conditioning, dehumidification and drying imply the need to install cooling and heating equipment. Our proposal is to opt for centralised production systems because, although the economic investment is higher, they provide us with the following advantages:
For the distribution of this heat and cold, the use of circuits is recommended of hot and cold water. In this type of installation, the use of variable flow distribution circuits is highly recommended due to the large differences in cooling and heating requirements between day and night, or between the different seasons of the year.
Any generation process that harnesses solar energy, co-generation, adiabatic or evaporative cooling, bio-gases, etc. will be applicable and welcome.
The quality and quantity of accessible water is one of the decisive factors in the choice of water supply.
Location, but it will not always be the most decisive one.
Efficiency solutions in these rooms are standard in air conditioning systems, here we will give some guidelines to apply them to the particularities of cannabis processing.
It is important to differentiate the different zones according to their environmental and work scheduling needs.
A humidity-controlled environment is only necessary in rooms where the product is already dry, and exposed to the environment (dry trimming, curing and packaging).
In the areas where the material is in wet form (leaf removal, green trimming), the temperature will be lower, so it is an interesting option to have a separate air conditioning unit for these areas.
Within the same installation, we find that most of the rooms will work in one or two shifts and until the operation is at full capacity for many days, some rooms will be unoccupied while others, such as the drying tunnels, will work 24/24 hours, so it is important that the air-conditioners can be segmented, switched off or made to work at reduced temperatures and flow rates.
The same will apply to localised extractions (dust, vapours, etc.). t is very interesting that they can be switched on and off independently, as the number of hours of use is relatively low.
Adapt the filtration level (F9... H14) to the renewals in order to have the ISO 8 particle level quality. An over-specification in the design has high operating costs.
Water is a resource that needs to be managed well. Good quality water (low conductivity) can be used with a simple pre-treatment, whereas poor quality water will require reverse osmosis treatment, with associated operating costs, water rejection consumption and investment.
The quality and quantity of available water is one of the decisive factors for the choice of location, but it will not always be the most decisive, so here are some items to take into account:
Technical solutions for energy efficiency are existing and known. Perhaps the difficulty within medical cannabis lies in the evaluation, due to a lack of data, of the impact on the quantity and quality of the product of using a more controlled and precise environment (greater energy expenditure), compared to one with wider margins.
Based on our experience, we believe that one should start with a robust design to ensure quality and, once stable operation has started, monitor and test to allow us to gather data to improve efficiency through future expansions or investments.
This continuous monitoring and analysis must be planned and carried out by expert staff focused on achieving these energy efficiency and cost-effectiveness objectives.
Author:
Eudald Bogatell
Project Engineer at VALTRIA