Last month we examined the functions of HVAC systems: heating, ventilation, and air conditioning (cooling). Today, we’d like to look at another important effect of HVAC systems: humidity reduction. Plants are constantly transpiring – water is being pumped by the plant from the roots and out through leaves and upper plant parts, transporting nutrients and facilitating growth processes. Relative humidity levels play a key role in the prevention of cannabis diseases such as botrytis and powdery mildew. These diseases thrive in humid environments and can cause severe damage to yields and quality.
The typical ways an HVAC system can reduce humidity are as follows:
- Heating: Hot air can hold more water vapor than cold air. This means that as ambient temperature rises from a heating unit, relative humidity decreases, even though the overall moisture content of the air remains the same. For example, if a growing facility has 90% relative humidity at 65⁰F and is then heated to 70⁰F, the relative humidity would decrease to around 75%, even though the water vapor has not left the facility.
- Ventilation: When indoor air is exhausted out of the growing facility, humidity in the air is expelled as well. In this way, humidity can be reduced by being released to the outside environment. It is important to note, however, that outdoor air replacing the exhausted air may enter the facility at different levels of temperature and humidity, ultimately causing the indoor climate to fluctuate. Sometimes, the outdoor conditions will not allow for ventilation to be effective at dehumidifying your facility at all.
- Air Conditioning (Cooling): While the air conditioning is operating, surfaces in the system are chilled to significantly lower temperatures than the ambient air. As warmer air comes in contact with these cool surfaces, the air temperature drops drastically and can hold less water vapor. Below a certain temperature, called the dew point, the water vapor will condense out of the air into liquid form, effectively distilling water out of the air. This works for the same reason that condensation forms on the outside of a cold beer glass.
You should be aware what your facility’s requirement for dehumidification is; often times an HVAC system is insufficient for humidity regulation around growing plants, and more dehumidification tools will likely need to be implemented in order to reach optimal levels.
At DryGair, we set up our systems to work jointly with HVAC systems in order to dehumidify and control the climate inside the growing room. During lights-on times – when plants evapotranspire a significant quantity of water, humidity is regulated by the DryGair concept, factoring in the humidity reduction capabilities that HVAC contributes. During lights-off times, usually DryGair operates individually and provides optimal humidity levels.
If you’re a grower, you should look for the right combination of effectiveness, efficiency, and costs to control the climate optimally in their growing facility. Learn more at our website, or reach out to us below.
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Canna Cribs Podcast Episode 8: Jarret Ricci from Next Big CropFebruary 2, 2021
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About the Authors
DryGair’s writers include a team of experienced engineers, agronomists, and economists. They specialize in climate control in closed growing facilities and practical solutions for effective climate management.