Marijuana Greenhouse

Cannabis Greenhouses using Desiccant Dehumidification

After a number of years pondering and specifying desiccant dehumidification methods in traditional pharmaceutical facilities, we believe that desiccant dehumidification in cannabis greenhouses should be more favourably considered.

In our previous experiences designing large marijuana greenhouses, we have found that extremely high air changes are required to achieve the desired cooling and dehumidification levels. Exposure to fresh, unconditioned, outside air can cause relative humidity levels in greenhouses to spike above the desired specifications. For smaller greenhouses this is not an issue, however, for larger medical marijuana greenhouses that lack evenly dispersed dehumidification, the sudden increase in humidity caused by falling temperatures could potentially cause catastrophic fungal issues in your medical cannabis greenhouse.

If dehumidification is more evenly distributed within the greenhouse, it can reduce the rate of air changes required whenever the light intensity is reduced (e.g. during deployment of light deprivation curtains or during the night). Traditionally, humidity has often been controlled by refrigeration dehumidifiers interspersed within the greenhouse to provide more control over localised pockets of the greenhouse environment). These dehumidifiers draw the air from the greenhouse, cool it down to the dewpoint, condense out the surplus water, and then heat the air up to return dry air back into the cannabis greenhouse. Unfortunately, this type of dehumidification requires a lot of electrical energy, and in Australia, where power costs are incredibly high, the use of these systems has a big impact on the electric bill.  

All factors considered, a desiccant dehumidification system could be a far more cost effective system for dehumidification of marijuana greenhouses as it requires far less electricity (only requiring heat for the regeneration process). Liquid desiccant dehumidifiers are an interesting option as they can be located directly inside the greenhouse and utilise pre-existing infrastructure (i.e. electricity, heat and drainage systems).

But what is a desiccant system?  

A desiccant system utilises a chemical (desiccant) to absorb liquid (e.g. water) to reduce the humidity in the surrounding environment. In this scenario, the humid marijuana greenhouse air would pass through the desiccant, give off moisture, and leave the desiccant system as dry air. After use, the water absorbed by the desiccant is heated to purge out the moisture (thus regenerating the system) by using heat from the pre-existing heating system.  

A main advantages of a liquid desiccant systems are as follows:

  • the ability to dehumidify an environment at the current room temperature with no need to first cool down the air to dewpoint.
  • the ability to reuse the heat from the regeneration process as additional heating for the greenhouse or easily ejected into the ambient environment.
  • less electrical power consumption due to smaller and fewer electrical connections – no compressors required (the main power consumers in a refrigeration system.)
  • the brine in the system (sodium chloride or lithium hydride) has a secondary function for cleaning and can act as a disinfectant to reduce the bacteria and fungus within the cannabis greenhouse or pharmaceutical clean rooms. 

But what are the drawbacks?

The initial investment in desiccant dehumidification systems can increase the initial cost. A further cost driver at the beginning can be the heat distribution to the units. If they are self contained systems, they will require a separate hot water heating circuit to provide heat 365 days a year at a higher temperature level compared to the common greenhouse heating. If the dehumidification unit is located inside the greenhouse, an additional exhaust duct to the outside will be required to exhaust the hot and humid regeneration air. Another disadvantage is that the additional pipe and ductwork required could cause unwanted shading in the cannabis greenhouse. 

Final Thoughts

A desiccant air dehumidification system for a greenhouse can be a good alternative to more traditional refrigerant systems. They can significantly reduce electrical bills and give additional heating during cold periods, however, will come with a higher initial investment. Whether a desiccant system is cheaper in the long run will depends on the routine ambient and working conditions, but will make a big impact in locations where the supply of low-cost heat (i.e. gas) or electricity is particularly expensive.  

Further reading – case study

Case study:

Several years ago PharmOut Mechanical Engineers modelled and designed a liquid desiccant system and wrote a White Paper on the economics of Liquid Desiccant Systems, which could provide further information alternative call to speak to one of our consultant, or a supplier of these systems.


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