Dehumidification Capacity for Indoor Grow Room HVAC

dehumidification chart for cannabis grow rooms and vertical farming

Dehumidification Capacity within Changing Grow Room Conditions

When I ask growers what temperature and humidity they want to operate their indoor grow rooms at, I’m expecting the answer to be a single operating point consisting of two numbers — one for temp and one for humidity. Perhaps something like 72⁰F at 50% Relative Humidity (RH). What I have come to understand is that growers need the flexibility to use their environmental control system across a wide range of temp and humidity, for example between 70⁰F and 78⁰F with humidity between 40% and 60% RH. This makes equipment selection challenging.

Whether you are using gPods, our all-in-one temp, humidity and CO2 control system or a one-off dehumidifier, the ability to remove pints of water from the air in your grow room is dependent on the temp and humidity in the space. The dehumidification capacity increases as temp & humidity rises and decreases as temp & humidity falls. This sounds simple, but things get more complicated when both temp & humidity are changing at the same time.

To be informed buyers, growers must understand the dehumidification capability of their gPods at all the temp & humidity conditions they may want to maintain and at different watering volumes they want to use.

Indoor Grow Room Dehumidification Capacity
at a Single Point

The orange circle on Chart One is the amount of dehumidification required by the grow room at 81⁰F/50% RH, at a watering rate of ½ gallon per plant per day. The green circle is the dehumidification capability of the gPod at 81⁰F/50% RH. If the green circle is the same size or larger than the orange circle, the gPod selected will maintain the intended 81⁰F/50% RH. As you can see the gPod selected will do the job at that operating point.

Said another way, the orange circle is what you need from your gPods. The green circle is what you can get from your gPod(s). If you can get more than you need at a given temperature and humidity you can achieve those set points. If you have less than you need at a set point, the gPod(s) you are considering won’t hold your room at your desired temperature and humidity.

As the temperature and humidity in the room changes, the dehumidification that you can get from the gPod changes significantly. But the amount of dehumidification that the space needs changes by a much smaller amount. The size of the orange circle only changes significantly if the watering rate per day is changed.

Indoor Grow Room Dehumidification Capacity
at Multiple Points

Chart Two shows how the green circles (what you can get) get smaller as the temperature and humidity set points in the grow room are reduced. The size of orange dot (what you need) doesn’t change much because we assume the same watering rate at all conditions. As you can see, there are only four combinations of temperature and humidity at which the gPod will hold the set point for both temperature and humidity.

Now that the growers have this information, they can make an informed decision. There are several options to consider.

  1. Is the daily watering used to size your gPods accurate, or is it a guess? A watering rate of 0.50 gallon of water per plant per day requires twice as many gPods (or one gPod twice as large) as a watering rate of 0.25 gallons/plant/day. Using the wrong watering rate can double the cost of your gPods.
  2. How much run-off do you have when you water? The runoff should be deducted from the watering rate since runoff goes down the drain and is not going to transpire through the leaves of your plants.
  3. Transpiration rates depend on the vapor pressure deficit (VPD) between the leaf and the room. Can the VPD requirements be met using higher temperature and humidity settings than planned? The higher your temperature and humidity settings the fewer gPods you need.
  4. Ideal VPD targets may be higher for plants in the flowering stage than in the vegetative stage. If this is the case in your grow, you may be able to use smaller gPod(s) in the flower rooms?
  5. If it’s important to operate at lower temperature & humidity points, what is the impact on the budget? The options are to:
    1. Buy a larger gPod
    2. Buy more gPods
    3. Do both

Be skeptical of any supplier that is incapable of or unwilling to have conversations with you to this depth of detail. You must live with your climate control equipment decision for years once it has been made. Having this type of conversation with a knowledgeable equipment supplier allows you to match the needs of your grow to your available budget and gives you a clear understanding of what to expect as you change temperature, humidity, and watering rates in your grow.

Learn more about the gPod system.

Download the gPod datasheet.

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