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Using CFD Simulations to Increase Yields in the Cannabis Industry

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A well-designed facility with contamination levels is essential for successful cannabis growth in a controlled environment. The critical decisions made during the design process of a cannabis facility can affect both the construction and operational costs in the long term. For existing facilities, airflow performance has a major impact on crop yields.  Increasingly, the industry is turning to computational fluid dynamics (CFD) simulations due to its success in better understanding, designing, and optimizing HVAC systems. In this article, we explore how CFD simulation is helping growers to become more efficient, grow better plants, and maximize profits. 

Cannabis cultivation has been a hot topic around the world, with many countries now utilizing marijuana for medical purposes. Our job in this article, is not to explore the political or ethical standpoints taken around cannabis use, but to understand and address this emerging market in the CFD sector, and to highlight the advantages to horticulture, agriculture, and general building design.

In order to maximize output, manufacturers and growers are having to address the somewhat complex HVAC needs of their grow environments. The role played by CFD in the cannabis industry is also transferable to other areas such as the vertical horticulture of vegetables, as engineers contribute valued data in order to find new and innovative ways to produce higher yields with reduced land space. Read more about the role of computational fluid dynamics in HVAC system design

Manufacturers of hydroponic equipment also face a consistent challenge to calculate the HVAC needs presented by the grow environment in which their equipment is placed, and to be able to correctly advise and satisfy their own consumers.

Learn more about CFD & HVAC with one of our engineers

When considering the design of a grow facility, there are many factors to consider. In addition to deciding how many plants are to be grown in the area, and which growing style will be adopted, a successfully designed facility will be;

  • Light-proofed
  • Have adequate and successful ventilation
  • A clean and hygienic space, which mitigates contamination from pests and animals
  • A comfortable working environment for those working in it
  • Tall enough to grow preferred strains and suspend necessary lights and ventilation outlets

VENTILATION

Ventilation is a vital aspect of successful cannabis growth, not only to prevent molds and mildews, but also to reduce and stabilize ambient temperature and ensure the plants benefit from moving air. At the same time, hot air must be removed from the grow room. Successful ventilation reduces heat, controls humidity, and reduces the risk of pathogenic infection or stress to plants.

Designing suitable and successful ventilation has created a number of barriers for many growers, with a trial and error approach often costing money and increasing plant waste. While a hole in a door and well-placed fans may provide some ventilation, a more sophisticated and intrinsic approach is needed to ensure all the plants in the grow room benefit from optimal, consistent conditions. 

The Stack Effect 

    Typically, the fact that warm air rises and cool air sinks works to the advantage of growers, matching the anatomical requirements of the plant. This 'stack effect' is not however appropriate for all buildings, due to the individual temperature and ventilation differences that will vary from building to building. Stack ventilation requires the internal temperature to be higher than the outside temperature, and additional mechanical cooling may still be necessary. Rooms adjoining the warmer part of a building may also experience poor ventilation and undesirable heat gains. It is likely there could also be conflicts between the need for large unrestricted openings between the outside and center of the building, and the need for privacy, security, fire compartmentation, and contamination control.

CFD for Ventilation

    CFD is used to quantitatively predict or optimize the thermal-fluid physical phenomena of ventilation in a grow room, identifying:
          • Simultaneous heat flows (e.g., heat conduction through the building enclosure, heat gains from heated objects indoors, and solar radiation through the building fenestration. 
          • Airflow direction and uniformity
          • Phase changes such as condensation and evaporation of water contents.
          • Chemical reactions.
          • Mechanical movements caused by fans or occupants.

Computational fluid dynamics also:

  • Provides data on air-flow changes within the model.
  • Accurately predicts the performance of proposed ventilation design.
  • Compares system options (i.e. Natural Ventilation systems v. Powered System) for better-informed decision making.
  • Can adjust for seasonal temperature and weather changes.
  • Offers dependable and proven results.

Below is a view of airflow streamlines throughout ventilation equipment in a plant. It visualizes airflow uniformity and where velocities exceed proper thresholds. 

case4_stream_7.png

For those who are offering HVAC design services, the visual outputs can be used to market engineering design services to prospective clients. They can also be used to pin point problems and recommend solutions within a cultivation domain. 

TEMPERATURE

Another key factor in the design of a grow room is the indoor climate - notably temperature, humidity, and CO2. The ideal temperature of a grow room is between 65 and 80°F (18 to 26°C), and the climate in a specific country or region will also play a role in the temperature and humidity of a grow area. 

Where one area of the United States may struggle to maintain humidity, another area could find themselves battling to reduce humidity.

Engineers have typically used climate management tools including humidifiers, dehumidifiers, humidistats, thermometers, fans, CO2 drips and generators, and light timers to successfully maintain a consistent environment. This equipment is expensive to purchase and run, and as cannabis plants are so sensitive to atmospheric changes, it is essential each piece of equipment is placed correctly. Poor temperatures can easily result in the 'drying out' of plants, and too many humidifiers can present a contamination risk to plants due to their ability to harbor pathogenic microbes - a potentially catastrophic result for growers. CFD simulation enables growers to identify where to best place any building or hydroponics equipment for best effect.

Cut planes can be extracted from simulation results from any X,Y,Z axis to show you the distribution of airflow velocity, temperature, or pressure. Solid objects can be modelled using a conjugate heat transfer model to account for objects adsorbing heat (or providing heat if they're heat sources). At a certain airflow pressure, cannabis plants can go into shock, which can inhibit growth. Optimizing uniform temperature and airflow without compromising plant growth is an important consideration. 

case4_velocity_slice_b.png

Temperature Stratification

    Having knowledge of temperature stratification in an indoor environment or grow room can lead to more efficient control and performance of displacement ventilation, ultimately reducing the need for air conditioning equipment and maintaining a healthier indoor environment for cannabis to grow. This is applicable right across the horticultural, agricultural, and even medical sectors.
    Accurate and reliable CFD simulation of temperature stratification in an indoor environment (such as a grow room) is required for the design and evaluation of displacement ventilation in buildings. By better understanding this, cannabis growers can create the best environment for growth, maximizing output and overall profits.
    In a study by Gilani, Montazeri, and Blocken et al., a detailed assessment of 3D steady RANS CFD simulations for the prediction of temperature stratification in a room was carried out. This study was based on sensitivity analysis and validation with full-scale measurements of indoor air temperature. 
                  Their study confirmed that the steady RANS CFD simulation has the capability of demonstrating the key features of temperature stratification in an indoor environment. The report showed a satisfactory agreement between the CFD simulation and the experiment, and reported the grid sensitivity analysis to show a higher sensitivity to the computational grid resolution in the lower part of the room. In relation to the turbulence models, the SST k- model showed more reliable results when compared with other turbulence models.
Temperature (Thermal) Advantage
                Computational fluid dynamics clearly illustrates temperature changes throughout the building and offers detailed information about a buildings thermal behavior enabling the possibility if taking action or making improvements to create an optimum solution.

CONTAMINATION & POLLUTANTS

Computational fluid dynamics plays a key role in preventing cross contamination in cannabis facilities. Mildew, botrytis and bud mold (along with many other infestations) can spoil a yield and cause huge financial losses. While a facility may be able to control contamination from some sources i.e. staff, many pollutants can occur via airflow. Understanding this airflow, through CFD simulation, can be hugely beneficial.

Hospital clean rooms have a similar need to control pollutants and contamination, so comparisons can be made in their HVAC system approach. In the case of clean rooms, hospitals have traditionally regarded the "solution to pollution as dilution". While this recognizes the importance of airflow in addressing cross contamination, it also has the problem of potentially blowing contaminants all over the clean room and patient (or in this case, the cannabis plants themselves) in an attempt to ventilate the area.

A recent case study saw Huntair, an Oregon-based engineering company, borrow an idea from the semiconductor and drug industries — to use laminar airflow directed down and away from the critical area. While this case was referring to a hospital clean room and an operating table, the approach can easily be applied to a cannabis grow room and its plants. Laminar flow is uniform in direction and velocity and directs particles and contaminants along a predictable path. If airflow is turbulent, contaminants float undirected, eliminating the ability for planners to predict where they will land. In the study, Huntair had several goals including ensuring the airflow remained laminar despite interacting with lights and ceiling-mounted equipment - a similarity shared in grow rooms. In addition, they wanted any air flowing over surgical staff to be carried away from the operating table and toward the air returns and vents. To achieve this, Huntair used CFD simulation to visualize and better understand the complex interactions that affect airflow. In this case, the CFD simulation showed that industry-standard diffusers set up several different airflows each interfering with each other or creating gaps in coverage, leading to turbulence and re circulation. As a result, appropriate steps could be taken to improve the flow of air in the room, and minimize contamination.

By having such an understanding of a building's airflow, individual issues can be addressed and contamination risk can be reduced, while still maintaining a satisfactory level of ventilation, promoting ideal conditions for plants and maximizing output and profits.

The key advantages provided to the cannabis industry by CFD, are:

(1) Less expensive when compared to physical modeling, although some physical modeling may be required.

(2) May sometimes predict some potential design flaws so that they can be remedied before the facility is constructed. 

(3) May quickly explore possible opportunity for improved performance.

(4) Can model a variety of options for both planned and operating designs so that the most economical solutions can be pursued with a high degree of confidence in their validity. 

 

CONCLUSION

Computational fluid dynamic simulations are extremely helpful in understanding complex HVAC scenarios, and give information needed to identify problem areas that potentially impact productivity and yield. The results provided through simulation include:

  • 3D flow pattern and temperature maps
  • Identification of stagnation (velocity) zones and hot spots
  • Suggestions on how to improve the airflow conditions in the cultivation facility

From such an output, one can extract 2D slides of the domain, 3D streamlines, quantitative data tables, and 2D and 3D animations. This information can be used to adjust ventillation position, temperatures, and velocities, and used to help mitigate cross contamination from other zones. It can also be used to model dynamics in extraction rooms (alcohol vapor ventillation). 

CFD enables growers to prepare a virtual HVAC design testing environment representing a particular facility over a specified period of time or during a number of scenarios. CFD is traditionally a cost-prohibitive or time-prohibitive tool, however with advances in simulation technology, the cost per simulation has reduced dramatically (See about EXN/Aero below), making this a new powerful tool to help growers improve their performance and reduce risks. 

 

References:
      Blackmore, B. (2017, June) Guidelines for accurate cleanroom CFD modeling. Retrieved from www.//electroiq.com/blog/2006/05/guidelines-for-accurate-cleanroom-cfd-modeling/
    Gilani, Montazeri, and Blocken et al. (2013). CFD simulation of temperature stratification for a building space: Validation and sensitivity analysis.
        Wilcox, A. (2017, May) 8 steps to building the perfect grow room. Retrieved from www.herb.co/2017/05/04/indoor-grow-room/
    Yan Chen (2015). How to correctly use CFD as a tool for ventilation design?
About EXN/Aero:
        Our general purpose, cost-effective CFD, cloud solver reduces simulation times by up to 20x, and the platform includes a meshing tool, the solver, and a post-processing tool, as well as plenty of storage for your files. If you're in the cannabis industry - or have any HVAC simulation requirements - why not try a free demo of our on-demand software today? We also offer a discovery project program where we will conduct the simulation for you to demonstrate how CFD can impact your operations or designs. 
Learn more about CFD & HVAC with one of our engineers
2017-12-14 | Categories: CFD, simulations, HPC

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