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Introduction
The control of the Relative Humidity (RH) in the air must be controlled in a high-tech greenhouse. Indeed, excess level of humidity can cause the development of mold and diseases on plants especially cannabis.
Dehumidification concept
The dehumification system helps to evacuate the condensation excess inside a commercial greenhouse.
There are different solutions to reduce and control the RH :
- Ventilate the greenhouse to drain out the air using passive (sides roll-up, roof vents) or active air extraction using Horizontal Air flow Fans (HAF), exhaust fans… ;
- Heat the greenhouse and ventilate to allow the exit of humid air = efficient if the outside air is drier than inside ;
- Use a dehumidifier units on the ground inside the greenhouse saving energy cost (heat, CO2 %…) – depending of the brand and technology ;
- Installation of a centralized heat pump to capture humid air and blow dry and heated air in the growing area ;
- Desiccant dehumidification system is also a solution more particularly when the energy (electricity) costs are high ;
Dehumidification strategy in a commercial cannabis greenhouse
In a high-tech cannabis greenhouse production adding an artificial dehumidification system can be required. The right greenhouse and equipment will help to increase the yied and quality of the final product.
Indeed, the cannabis plant needs an efficient air recirculation for its development (photosynthesis, flowering, stress reduction…). Cannabis crops grow also best at temperatures between 20 – 30°C during the day / 17-20°C at nigh.
In fact, an unexpected increase of the RH in the growing area can affect the temperatures and create disastrous fungal issues like powdery mildew, botrytis… The best defense is to avoid any water accumulation on the plant tissue.
For these reasons, using a climate control strategy with dehumidification will allow growers to monitor and decrease the RH concentration inside the greenhouse to avoid excessive fluctuations and damaging levels.
Remarks
Passive ventilation (using roll-up, guillotine opening, roof vents…) is the cheapest and easiest solution to implement but has limits more particularly in heated greenhouse during the winter in cold regions. It is also difficult to use this ventilation strategy to drain out the inside humidity when the blackout system (light deprivation) is deployed…
In the tropical regions (Colombia, Malaysia or Vietnam for exemple) the outside air has most of the time a RH concentration higher than 60%. The ventilation strategy must be paired with the use of high and wide greenhouse (=more volume, better chimney effect) and active ventilation to keep an efficient air flow and recycling level (>2 vol/h).
Conclusion
The best thing is to ask your greenhouse manufacturer and climate control experts to select the right model and equipment regarding the project location/orientation, outside conditions, crops, growing system… and your budget.
The relative humidity concenration management in a greenhouse is specific to each project. Dehumidification is an expensive option to purchase and it consumes energy.
Sources:
Analyses des paramètres climatiques, écophysiologiques et énergétiques à l’intérieur d’une serre de production ornementale à double paroi gonflable en présence d’un système à déshumidification (C. Migeon et al.,)
https://www.cannaconnection.com/blog/2245-ideal-temperature-growing
https://www.greenhousegrower.com/technology/three-steps-to-effective-greenhouse-humidity-control/
https://www.pharmout.net/marijuana-greenhouses-desiccant-dehumidification/
