Marijuana greenhouses using desiccant dehumidification, an alternative?
After a number of years pondering and specifying desiccant dehumidification in traditional pharmaceutical facilities, we believe that desiccant dehumidification in marijuana greenhouses for medical marijuana should be more favourably considered.
In our very large marijuana greenhouse designs, we have found extremely high air changes are required to achieve cooling and dehumidification. Dehumidification interspersed within the green house can reduce airchanges rates whenever the light intensity is reduced, i.e. light deprivation curtains are activated or at night, typically air change rates are reduced. With fresh no conditioned outside air, relative humidity levels in greenhouses will quickly rise above established specifications. For smaller green houses this is not an issue, however for larger medical marijuana greenhouses without local dispersed dehumidification, the humidity levels quickly rise (indirectly as temperatures fall) and potentially these conditions can cause catastrophic fungal issues in your medical marijuana greenhouse.
During these periods, humidity may be controlled with more traditional refrigeration dehumidifiers which are usually locally interspersed within the greenhouse. These dehumidifiers draw the air from the greenhouse, cool it down to the dewpoint, condensing out the surplus water and then heat the air up again to return return dry air back into the marijuana greenhouse. Unfortunately, this type dehumidifying of air requires a lot of electrical energy, in regions where power costs are incredibly high, the refrigeration has a big impact on the monthly electricity bill.
A desiccant dehumidification system could be a cost effective system for your marijuana alternative as it requires far less electricity and cheaper heat for the regeneration process. Liquid desiccant dehumidifiers are an interesting option as they can be located directly inside the greenhouse and the sites usually have the basic infrastructure i.e. electricity, heat generation and drainage systems already in place.
But what is a desiccant system?
A desiccant system describes a dehumidifier which uses a chemical (desiccant) that absorbs (liquid) or adsorbs water to remove humidity from the air. The moist marijuana greenhouse air passes through the desiccant, gives of the moisture and leaves the desiccant system as dry air. Afterwards, the water absorbed into the desiccant liquid is heated up to purge out the moisture (regeneration) with heat which is usually supplied by a heating hot water system or steam.
A main advantage of a liquid desiccant system is the dehumidification at room temperature and the no need to cool down the air to the dewpoint and the reheat it to greenhouse conditions. Furthermore, the heat from the condensation and regeneration process can be used as an additional heating for the greenhouse or rejected to the ambient environment.
Electrical power consumption and therefore electrical connections are significantly smaller compared to a refrigeration system as there are no compressors required (main power consumers in a refrigeration system.) Finally, most suppliers claim that the brine (sodium chloride or lithium hydride) has a secondary function as cleaning and disinfectant and can reduce bacteria and fungus within the marijuana greenhouse or pharmaceutical clean room.
But what are the drawbacks?
The initial investment in desiccant dehumidification systems are refrigeration dehumidifiers which increases the initial costs. A further cost driver at the beginning can be the heat distribution to the units, (if they are self contained systems). They require a separate heating hot water circuit to provide heat 365 days a year and at a higher temperature level as the common greenhouse heating. If the dehumidification unit is located inside the greenhouse an additional exhaust duct to the outside is required to exhaust the damp, hot regeneration air. Along with the costs the additional pipe and duct work can cause unwanted shading in the marijuana greenhouse.
A desiccant air dehumidification system for a greenhouse can be a good alternative to refrigerant systems to significantly reduce electrical bills and give additional heating during cold periods but comes with a higher initial investment. If a desiccant system is cheaper on the long run usually depends on the ambient and working conditions, initial investment, if there is supply of low-cost heat (i.e. gas) or electricity is particularly expensive.
Further reading – 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.