HVAC For Indoor Grow Facilities
(continually updated, please contact us with any feedback or input. Our sizing cooling/dehumidification analysis webtool can be found at: hvacanalyzer.greenzone-eng.com)
The HVAC system is critical to the success of an indoor grow. Cooling, Dehumidification, and Airflow effect crop quality, quantity, and safety.
In the Cultivation and Dry rooms of indoor grow facilities, temperature and humidity control can be used to help optimize plant growth, improve quality metrics like bud color and density, reduce microbial risk, and dry a product into a shelf stable consumer product.
This page will include the following sections:
Common Temperature and Humidity Targets by Room Type for Indoor Grows
System Options
Technical Notes on Loads and Control
TEMPERATURE AND HUMIDITY REQUIREMENTS BY ROOM TYPE
The types of room covered here are flower, veg, mom, clone, dry and cure/storage.
Flower: These are the rooms where "flower" is grown. Plants are typically in this room around 8-10 weeks (though can vary) corresponding to the length of the flowering cycle of the plant. Plants are brought in from the veg room and usually start at a relatively high temperature and high relative humidity. This might be 80-85F temperature and 65-75% RH. Temperature and humidity may to decrease a bit at night, to maybe 78-80F, and 60-70% RH. Often humidifiers are needed when the lights are on to meet the humidity setpoints. Toward the end of the flower cycle however, lower temperature and humidity is desirable and the plants are transpiring a lot more moisture into the air, requiring a lot more dehumidification. Rooms are often lowered to 72-78F with the lights on, and maybe 68-75F with the lights off, and around 50-55% RH. Without sufficient dehumidification, microbial issues will develop and the room will be a constant struggle.
Veg/Mom/Clone
From am HVAC perspective Veg, Mom, and Clone rooms like to be fairly warm and humid. Clones like it very humid, but they are often grown under domes or in small tents to have a very high localized relative humidity. The greater veg and mom rooms may operate around 80F and 50-70% RH. Some growers will use humidifiers in the veg rooms to maintain high RH.
Dry and Cure/Storage rooms
Typically target conditions for Dry Rooms are 60F/60% RH. The lower temperature is desired to reduce the loss of volatile organic compounds like terpenes which make up the flavor and aroma profile. Dry rooms need sufficient dehumidification to be able to hit reduce the humidity to 60% within a day or two the wet product getting loaded in. Cure and dry flower storage rooms should also be kept cool and dry to continue to maintain product quality.
System Options
HVAC or "HVACD" systems in indoor grows can be categorized in various ways. Sometimes the "D" is added to the acronym "HVAC" to highlight the importance of dedicated dehumidification in these facilities. All Indoor grows require cooling and dehumidification. A small about of heating is generally needed too. If reheat is used for dehumidification, than a lot of heat is needed. Although rooms are typically operated without outside air to avoid blowing away CO2, it is good practice and often required by code to have ventilation (meaning bringing outside air into a room) available on demand and triggered to operate on high CO2.
One way of categorizing types of systems is by how they dehumidify as "integrated" or "decoupled" systems. Decoupled systems use different devices for cooling vs dehumidifying. In a decoupled system any cooling air conditioning unit can work, splits, VRF, packaged RTUs, chilled water fan coils to name a few. Then separate standalone dehumidifiers are used to handle the moisture load.