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Optimizing HVAC Systems in Cannabis Cultivation

If you’re growing cannabis indoors, odds are you’re going to require some assistance from your HVAC system. However, if you’re growing commercially in a state or country that has passed legalization or medical marijuana legislation like Oregon or Colorado, you’re likely looking to maximize your energy efficiency to get the highest crop yield per square foot.

Whatever the size of your setup, HVAC (heating, ventilation and air conditioning) plays a notoriously instrumental role in maintaining your indoor climate, whether that means using cooling systems to help beat soaring summer temperatures or heating the place up a bit to avoid sub-zero freezes.

HVAC systems come in all shapes, sizes, and configurations, meaning there are limitless possibilities for maintaining the perfect climate in your indoor grow room. Many growers choose to fully automate their HVAC system with various control systems meant to monitor and control environmental conditions.

With so many options, it can be tough to know where to start when it comes to picking out the proper equipment for the job. We’re here to help you decide just what choices you can make to help you optimize your HVAC equipment for peak control and efficiency.

The Purpose of HVAC in a Cannabis Grow Room

If there’s one thing that seasoned growers in the cannabis industry know, it’s that lights produce heat – lots of heat – and when you’re growing a decent-sized crop of marijuana, you’re going to need lots of light. Thus, without a proper air conditioning system, you can fully expect your grow facility to sizzle like the inside of an oven, leading to fried, crispy plants that won’t be good for anything at all. That’s where the role of HVAC comes in.

Or let’s say your growing environment is situated high in the mountains, where temperatures never even come close to the “Mediterranean” climate that marijuana plants love. Sure, your many grow lights may offset the cold temperatures a bit, but it may never be enough to bring the temperatures up into the 20-30℃ range that plants find optimal. But, again, that’s where the role of HVAC comes in.

Your HVAC system will, by and large, be the main component in maintaining steady environmental conditions. In many cases, such as when a timer malfunctions or a fan stops working, HVAC systems can prove the last line of defence against inevitable disaster.

HVAC systems play a role in many aspects of your grow, including:

  • Temperature control
  • Humidity control (humidification and dehumidification)
  • Airflow and circulation
  • Air filtration/Odour abatement

On the downside, HVAC systems are also responsible for a large portion of the energy consumption (and thus energy costs) within a grow facility. Therefore, it’s imperative, especially for commercial growers, to factor their HVAC design into their initial facility design.

Temperature Control

Probably the most critical job of your HVAC system will be to control the temperature of your cultivation facility. While this is by no means its only job, it is undoubtedly its most significant.

Many elements can impact the temperature of your grow room, such as whether the room is sealed, where the room is located, and the type of lights being used. All of these are important considerations to take into account when deciding which HVAC system works for you.

A completely sealed grow room, for instance, will rely entirely on HVAC for all air supplied to the room. This means that an HVAC unit will be responsible for pumping fresh air into the room, as well as cooling or heating the air as necessary and sending old air out of the room, either to be recycled or released. In an open environment, such as a vented greenhouse or unsealed grow room, vents or windows may allow fresh air into the room, meaning the HVAC unit will only be responsible for pulling old air out of the room.

Your grow room’s location will play a significant role in determining your HVAC needs as well. A grow room situated in a cool mountain environment, for example, will require less from its cooling systems than one located at sea level. Likewise, a grow room situated in a desert (whether in a house or on a commercial property) will likely require evaporative cooling to increase humidity while requiring less from its dehumidification systems come flower time.

Temperature and Lighting

The type of lighting being implemented will drastically affect grow room temperatures as well. Many cultivators who employ HID (high-intensity discharge) lamps such as metal halide or high-pressure sodium bulbs require ducting to cool the fixtures which house their lamps. These cumbersome fixtures are tough to hang but work surprisingly well at maintaining temperatures, conveying away much of the heat generated by the lamp through ducting.

LED growers will deal with heat buildup issues less than HID growers but still must consider the temperatures their lights will generate. Most LED lighting is still coupled with ballasts, which generate a decent amount of heat on their own, causing the lights to run hotter than one might expect. For this reason, most LED growers are still forced to utilize HVAC systems of some kind.

Humidity Control

Your HVAC system will be primarily responsible for maintaining a consistent grow room humidity as well. Cannabis plants thrive in high humidity during vegetative growth, but during flower, the same humidity can cause mould, mildew, or prove a breeding ground for pests. Therefore, humidifiers and dehumidifiers, though often not incorporated into a larger HVAC system, still play a crucial role in the operation and successful implementation of HVAC.

Maintaining proper humidity levels can make or break your entire grow operation. Plants require moisture to transpire or pull water in through the roots and release it through stomatal openings in the leaves. Necessary to avoid damage and maintain optimal plant growth, transpiration aids in many of the plant’s metabolic processes, including photosynthesis.

Humidity can prove an issue with relation to HVAC as growers will often find that the vast majority of their moisture can be easily sucked out by their exhaust fan, leaving their grow room a dry, barren desert. Similarly, the failure of exhaust to carry humidity from the grow room can result in overly humid conditions, essentially turning your grow room into a rainforest.

Many cannabis cultivators opt to use automated controllers to help monitor their grow room’s humidity levels. Relative humidity controllers, for example, measure the amount of water vapour currently in the air versus how much the air can hold. Similarly, vapour pressure deficit (VPD) controllers measure how much more water vapour the air can hold. With these climate controls automated, HVAC systems can operate only when necessary, reducing operating costs, boosting energy savings and increasing sustainability.

Automated controllers can be set to turn on and off when relative humidity reaches or dips below a certain percentage. Likewise, dehumidifiers can be set to kick on when relative humidity gets too high, a perfect solution to prevent excess moisture when flowering.

While humidifiers and dehumidifiers are not often built-in to an HVAC system, per se, their presence is undoubtedly a helpful addition, allowing growers to further dial in their HVAC settings to maintain a proper climate.

Air Flow and Circulation

Another of your HVAC system’s main jobs is to ensure that your plants receive a steady supply of fresh air. The way in which this is achieved will vary between setups, but the principles are the same regardless of the size of the operation.

Depending on various factors, such as the location of the grow room and the weather, growers may choose to rely on a fresh air intake or recycle the air in their grow room. Either way, the air being pushed into the grow room (whether fresh or recycled) must be treated and, in most cases, cooled before entering.

Once in the grow room, it is the responsibility of fans to circulate the air throughout, as plants will be unable to utilize stale air and will wilt or develop disease. Like humidifiers and dehumidifiers, fans are typically not considered a central component of a standard HVAC system, but their contribution to air circulation is invaluable.

An unobstructed outlet is equally essential for air circulation, allowing old, stale air to be sucked out of the room, either to be expelled or recirculated. Depending on the size of the operation, the outlet may be as small as a four-inch exhaust fan or as large as an industrial-sized compressor. Regardless of size, the purpose of removing old and used-up air from the room remains the same.

Air Filtration/Odour Abatement

Still another significant role of HVAC in cannabis cultivation is the scrubbing or filtering of air as it moves through the system. Of course, this doesn’t just mean removing particulate from the air, but odours as well.

Any HVAC system worth its weight will be equipped with at least one or two filters. Like any home furnace or AC unit, these filters trap particles before they are allowed into the condenser, helping optimize your unit’s performance and ensuring that your vents aren’t blowing dust all over your plants.

Perhaps the most interesting filter in the world of indoor cannabis cultivation, though, is the air scrubbing filter designed to reduce the odour of marijuana as it reaches flowering and its peak potency. Typically an activated carbon (or charcoal) filter, this device attaches to the air outlet, usually via ducting, and passes the exiting air through a thick layer of filtering material to collect and destroy the smell emanating from your cannabis.

While air scrubbing was undoubtedly of more significant concern during prohibition times, there are still many, many growers who do not wish to broadcast to their entire neighbourhood what they’re up to in the grow room. Some growers just want to be a good neighbour and not offend with their plants’ odours.

HVAC: Your Best Bet for Maintaining Proper Conditions

One more thing that should be noted on the matter of HVAC is the cost. If you’re planning to set up a large or commercial grow room, you should be well prepared: the price of a solid, reliable HVAC unit can be overwhelmingly high. But growers must remember that this is an initial investment that will pay for itself over time.

While it may seem like a lot upon initial startup, the costs of a reliable HVAC unit are minimal compared to the upkeep and maintenance that will be required of an unreliable one. Like many things in life, you’ll ultimately get what you pay for with an HVAC unit, and spending less now might mean paying more later. In addition, higher quality units tend to be the most energy-efficient, helping to reduce that all-important bottom line for any cannabis business.

Post author
Michael Richey
Michael loves to grow cannabis and write about what he learns along the way. His best friends are his dogs and marijuana.
See more from Michael Richey

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