Indoor Gardens: Managing two distinct environments

There are many positives about growing in an indoor, sealed environment. The vast majority of cannabis cultivators rely on this method to maximize output.  Indoor gardens allow cultivators to get multiple harvest per year while reducing exposure to pests, fungus and bacteria.  Further, indoor cultivation eliminates outside conditions as a concern for indoor climate, and ensures a secure operation.

October 27, 2016

There are many positives about growing in an indoor, sealed environment. The vast majority of cannabis cultivators rely on this method to maximize output.  Indoor gardens allow cultivators to get multiple harvest per year while reducing exposure to pests, fungus and bacteria.  Further, indoor cultivation eliminates outside conditions as a concern for indoor climate, and ensures a secure operation.

However, in order to truly get the most from their crop, cultivators must pay strict attention to environmental control. It is up to the cultivator and team to create the perfect ecosystem for their plants, managing everything from lighting to temperature control to humidity levels.

When it comes to climate control, there is no environment quite like an indoor cultivation environment. Comparisons are made to server farms, and there are some parallels there related to heat management, but humidity control is a whole other game. First, the amount of water being transpired by your plants results in dehumidification requirements that have no comparison in other indoor environments (except maybe in indoor, heated Olympic sized swimming pools).  Given the cannabis plant’s sensitivity to humidity, this is an issue that MUST be addressed. To make matters worse, the plant growing cycle means that you are managing not one, but two, distinct environments: daytime (lights on) and nighttime (lights off). These two different environments require a climate control approach that can handle dehumidification needs effectively during both photoperiods.

The good news is there are many options for cooling and environmental control out there. The bad news is that most traditional cooling methods are designed for use in your house or your office and are not equipped to handle the substantial cooling and dehumidification loads present in these facilities. It is critical that cultivators choose an environmental control solution that is designed to address these unique needs.

Check out our breakdown below of what happens when the lights go on and off and how to cover all your bases:

During the day (or when the lights are on)

The lights used in cultivation produce an enormous amount of heat (yes, even your LED’s). For every 1kW of electricity, 3400 BTUs are introduced into the space, regardless of the light source. As you can imagine, that heat load can add up pretty quickly in a commercial sized cultivation facility, which can mean disaster for a crop if it is not managed effectively. If plants are too hot, there are a myriad of issues that can damage, or even destroy, a crop. Take for instance accelerated transpiration which causes plants to process nutrients inefficiently, leading to stunted growth

Almost everyone knows they need to employ a cooling system to keep their plants at a healthy temperature but dehumidification needs are easily overlooked by those less familiar with indoor cultivation. Cooling systems will provide a certain amount of dehumidification as a byproduct of cooling; however, different systems will provide differing amounts of dehumidification (cooling BTU’s that translate to heat removal from the facility are described as sensible capacity and BTU’s that translate to dehumidification are described as latent capacity). Depending on your cooling system and its latent capacity, you may not even need additional dehumidification when the lights are on (but double check that with a Surna expert).

Generally, during lights on, the temperature in the space is warmer, which makes it easier to reach your humidity target for three reasons:

  • Warmer air is less dense and has more capacity to hold moisture.  Therefore, the relative humidity (rH)  is lower in a warmer room than in a colder room even if there is no additional moisture present.
  • Your cooling system is running to help maintain humidity levels
  • Dehumidification equipment is more effective in warmer temperatures (most dehumidifiers are rated at 80 degrees and 60% humidity—as that temperature decreases, so does the output of the dehumidifier)

During the night (or when lights are off)

Nighttime environments are where cultivators struggle the most with relative humidity levels. For the same reason it’s easier to maintain humidity levels during lights on, it’s more difficult when the lights go off.  First, the cultivation area cools down considerably and, second, the cooling system stops running. These two things combined are a recipe for relative humidity spikes and here’s why:

  • When the lights turn off and the temperature inside your facility drops, so too does the dew point temperature, or temperature at which moisture in the air condenses into liquid form. This means that dehumidification equipment becomes less effective, and is not able to condense as much moisture out of the air.
  • When the lights go off, so does your cooling system- say bye to your helpful by-product dehumidification.
  • When the air gets colder, it contracts, and the rH rises: Imagine an 8 oz glass. If it has 4 oz of water in it, it’s at 50% rH.  But if you shrink the glass to 4 oz, then  you’re at 100% rH.  The water volume hasn’t changed but the glass is smaller.  This is the same thing that happens in your grow room.


High humidity levels can spell powdery mildew and bud mold in no time. Therefore, it is critical that cultivators have a plan to manage both environments. The most effective solutions are adding a re-heat to the room and/or adding supplemental dehumidification.

A re-heat is a heating source that allows the cooling system to run when lights are off without overcooling the room. A reheat with more tonnage than your cooling system can cause the cooling system to run and still raise the temperature in the room to daytime levels (which may or may not be desirable depending on your cultivation methods).  But a reheat that is the same tonnage as the cooling system will allow the cooling system to run and dehumidify the space while remaining temperature neutral.  Regardless of how you choose to use a re-heat, you should consider another source of supplemental dehumidification as it’s rare for a cooling system to maintain proper humidity on its own—but a reheat is a great option if you only want to add minimal supplemental dehumidification.  

The other option is to add significant supplemental dehumidification for when the lights go out. This would just be a stand-alone dehumidifier which would run when the lights are off to lower your relative humidity levels. However, it is important to note that any dehumidifier will become less effective the colder your temperatures. This is why considering a re-heat and dehumidifier option together in places where you can expect significant temperature drops at night is typically your best bet.

Regardless of what options you choose, just remember that indoor cultivation is a complicated endeavor with climate control a constantly moving target.  Using an environmental control solution that is not designed with a firm understanding of these unique challenges can mean the difference between fortune and flop.


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