Grow Operation (Grow Op) Cooling & Dehumidification

 By Michael Haughey

March 8, 2104

Cooling for indoor Grow Ops involves more than simply adding up the lighting watts and converting that into cooling tons.  Plants release a surprising amount of moisture into the air (by transpiration, plus evaporation from the soil), and this has to be accommodated as latent load in the air conditioning equipment.  The result when using standard air conditioning equipment for dehumidification will often be over-cooling or insufficient dehumidification.  Adding in-room dehumidifiers can help, however they normally reject the heat from the process back into the room, which the air conditioning equipment needs to remove.  While this does provide a form of “reheat”, it also uses a lot of expensive energy (electricity).  Other methods are available that while costing a little more up front, will save considerable energy cost in the long run.

In Colorado, there is also the need to correct the design for altitude.  There is no one factor to make this correction, therefore consultation with an local engineer who has experience with high altitude design is strongly recommended.

Indoor Grow Ops can accelerate the plant growth by mimicking the natural diurnal solar cycles and then by accelerating them.  This is done by changing the length of the day and night cycles and the lighting intensity.  While details of the plant growing cycles are beyond the scope of this article, there are cooling implications.  A primary concern is that the cooling load will not be at the peak for a good part of the year.  If the cooling equipment cannot operate at lower sensible capacity, the over-cooling issues can be aggravated.  This brings up the subject of controls.

Manual controls using primarily thermostats will work fine if you have the time and trained staff to make the necessary adjustments and coordinate them with the lighting level adjustments.

The next upgrade will be to use programmable thermostats.  Programmable thermostats can have multiple time periods during the day and night.  A different temperature can be set for “occupied” and “unoccupied” periods.

Programmable controls systems commonly called “god systems” or “grow room controllers” are used by some grow ops to control just about everything from lighting levels and temperatures to ventilation, soil pH, and irrigation and more.  Most of these are limited to a specifc number of items that can be controlled by one controller.  Many work by controlling outlets on the controller into which various equipment can be plugged and then put on a schedule.

Direct Digital Control Systems (DDC Systems) are widely used in the building industry not only to control the HVAC systems, but also lighting, security, alarms systems, and more.  DDC Systems make an excellent choice for a larger Grow Op, especially one with more than one room on different schedules.  Some engineers have extensive experience writing the control sequence for the HVAC system and can assist in integrating that with the other grow room equipment controls.

So much effort is put into finding a location for the Grow Op that meets all the legal requirements that an important consideration in the suitability of an existing facility may easily be overlooked.  Since plant growth emits such a large volume of moisture year-round, it is important to consider whether the building construction is suitable.  In Colorado we can normally count on the low relative humidity of outdoor air in the winter to help mitigate moisture problems in walls, roofs, and ceilings.  This may not be the case in a Grow Op.  In a Grow Op, not only is there a large amount of moisture generated in the building, but outdoor air ventilation is kept to a minimum for a couple reasons.  One is to retain as much CO2 as possible, especially when CO2 is injected into the grow rooms to increase growth rates.  Another is to minimize the odors in the neighborhoods.  The added moisture in a low-ventilation environment can result in condensation within walls, roofs, and ceilings.  The result of that can be water damage and/or mold.  Thus an evaluation of the moisture control features of the building construction should be part of the location selection criteria.  For this evaluation retaining the services of both an engineer and an architect with experience in the area of building construction moisture control is recommended.