You’ve probably encountered HVAC systems. HVAC is an acronym for Heating, Ventilation, Air Conditioning. They’re virtually everywhere: air ducts lacing supermarket and warehouse ceilings, bulky equipment outside or atop office buildings and sports stadiums, or furnaces sitting in the garage or basement of your home. HVAC systems are found commonly in our lives and are there to provide comfortable indoor environmental conditions in the form of temperature and air quality. Studies conducted in office buildings showed that ambient indoor air temperature as well as indoor air quality have significant effects on the productivity and well-being of workers. *
This isn’t true just for people, however. Air quality is also critical for plants. Indoor climate conditions such as temperature, humidity levels, and 02 and CO2 levels are crucial in dictating whether plants will thrive. Growing in enclosed growing facilities means that the grower is responsible for providing the right conditions for plant development.
HVAC systems, which vary drastically in their form, size, capabilities, infrastructure, and prices, provide 3 main functions for a closed growing facility:
- Heating: Higher temperatures in a growing facility may be required depending on external conditions. A heat pump transfers heat from the outside environment inside, utilizing a refrigerant cycle. Many growing facilities are also commonly heated with alternatives where water or air is heated using boilers, furnaces, burners, etc.
- Ventilation: This component circulates the indoor air and replenishes it.
- Air circulation mixes the air in the growing facility, producing more uniform conditions of temperature and humidity within the space. Climate uniformity in cannabis cultivation helps produce a uniform crop. It also prevents humid microclimates, preventing the development of mold and plant diseases. That being said, many HVAC systems often do not provide sufficient circulation to prevent these problems, and may require additional equipment such as fans to do the job well.
- Air exchange exhausts the indoor air to the outside and inputs fresh air from the outside. Depending on the way the system is outfitted, this exchange can provide other unintended consequences including humidity and temperature fluctuations, depending on outdoor conditions. Some growers opt not to ventilate with outside air, allowing for CO2 supplements to be used more efficiently. Different filters can be built into the ventilation system to help remove odors, dust, moisture, airborne bacteria or spores, and more.
- Air Conditioning (Cooling): Facilities often need to be cooled in order to reduce the large amount of heat generated by growing equipment (including grow lights, ballasts, dehumidifiers, and CO2 generators). The air conditioning component of most HVAC systems in a greenhouse utilizes a water chiller which supplies cold water that absorbs heat as it runs throughout the greenhouse. Chillers also have the capacity to produce hot water which makes them versatile options for growing facilities that require both cooling and heating throughout the year. Other cooling alternatives commonly used in cultivation facilities include misting and pad-and-fan systems.
Note from the author: A byproduct of operating the HVAC system is humidity reduction. In our next article we will elaborate on this topic – stay tuned!
The advantage of HVAC systems is that they provide an integrated solution – 3 functions in one system. The system is programmed to a set point and its components are automatically operated. However, HVAC systems can be pricey and involve quite a bit of infrastructure. When designing a growing facility which will utilize an HVAC system, it is important to define the required conditions for successful growth and calculate the size and characteristics of the system which will be able to meet these needs.
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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.