Note: This blog originally appeared on partner Midwest Machinery’s blog “Engineering Tomorrow” on July 13, 2020.
It’s a modern-day gold rush, and the wild west for commercial Cannabis growers right now.
The lucky few who have received cultivation licenses plan to cash in bags of green gold IF they do this one thing right …
Missouri, like many other states, are as humid as the Rainforest in the summer and as cold as the Arctic in winter, growing indoors is the only way to achieve a year-round harvest.
With limited indoor space available, maximizing your crop yield is the key to making a fortune.
One of the best ways to do that is by choosing the right HVAC/air quality system for your indoor space. The right decision can increase your post-harvest crop yield by up to 30%! That’s some serious coin … er green.
Before we start the showdown we must mention – Midwest Machinery sells the equipment for all these options. We have no bias towards a particular solution. This showdown evaluates the scientific and business-related facts for the grower.
Without further ado, let’s cut through the noise and let the showdown begin. Giddyup!
Challenger 1: Traditional “Rooftop” HVAC Units with Portable Dehumidifiers in the Grow Space
The entry-level option. Rooftop air conditioners are installed and sized to handle the cooling load of the room(s) and will remove a small portion of the necessary room moisture during the lights-on growing phase. The portable dehumidifiers will try to make up for the rooftop units’ dehumidification shortcomings.
The dehumidifiers have a very large job to fill that often gets missed as humidity levels are critical. During the lights-off phase of the room, portable dehumidifier(s) are the primary equipment used to remove moisture.
Here’s the problem, when the portable dehumidifiers are in operation, the air temperature leaving those units is 25°F warmer than the air getting sucked in. This causes the rooftop air conditioners to turn on and try to remove that excess room heat and then quickly turn off again when their task has been completed. They are two competing forces.
The frequent on/off of an air conditioner causes the expensive compressors within those units to die much sooner. From the grower’s perspective, this system causes massive temperature and humidity swings within your grow room space. Your plants will be susceptible to browning, mold, and a much smaller post-harvest yield than a finely controlled space. This is a huge headache for someone trying to grow profitable medical-grade Cannabis.
- Cheapest option
- Easy to install
- Simple service
- No precise temperature/humidity control (units are constantly fighting each other)
- Very high utility bills
- Comfort cooling solution for people, not plants
- Odor control and biological-contamination challenges
- No trending or ability to link everything together for a precise understanding of the space conditions
- Often expensive reheat option is still needed to not over cool the rooms
- Changing the temperature on the rooftop unit will mean the dehumidifiers won’t operate the same and you’ll have to adjust each one independently.
Challenger 2: VRF Units with Portable Dehumidifiers in the Grow Space
VRF systems are very similar to the traditional rooftop unit (Challenger 1) with even more challenges for this particular environment.
VRF is a comfort cooling engineered solution. They are designed for offices, hotels, etc. and are installed and sized to handle the cooling load only. Like rooftops, they will remove a small portion of the necessary room moisture during the lights-on grow mode.
There will be a high number of VRF cassettes (The ceiling boxes with vents and fans) in the space delivering cold air to help offset the temperature load of the lights.
Again, dehumidifiers help with the work of the air conditioner in the lights-on mode. The portable dehumidifiers have a very large job that often gets missed as humidity levels are critical.
In lights-off mode, portable dehumidifier(s) are still used to remove the moisture. The problem is the same as challenger 1 when the portable dehumidifiers are in operation, the air temperature leaving those units are 25°F warmer than the air entering. This causes the VRF air conditioners to turn on and try to remove that excess heat and then quickly turn off again when their task has been completed.
Frequent on/off of a VRF outdoor unit causes the expensive compressors within those units to break much sooner. The grower ends up with the same problems, this system causes massive temperature and humidity swings within your grow room space. Your plants will be susceptible to browning, mold, and a much smaller post-harvest yield than a finely controlled space. This is a huge headache for someone trying to grow profitable medical-grade Cannabis.
- Marginally lower utility bills than rooftop units
- “Off the shelf” equipment
- No precise temperature/humidity control (units constantly fighting each other)
- Very high utility bills compared to our premium options
- Comfort cooling solution for people, not plants
- Odor control and biological-contamination challenges
- Lots of units delivering cold air onto the plants will cause condensation to form on the leaf, which can lead to mold
- VERY HIGH levels of refrigerant being pumped around the space, which is extremely unhealthy if there is a leak
- Lots of compressors and fans between the VRF systems and the portable dehumidifiers. This means there are even more failure points and expensive repairs to consider.
- No trending data or ability to link everything together for a precise understanding of the space conditions
- Changing the temperature in the VRF system will mean the dehumidifiers won’t operate the same and you’ll have to go adjust each one.
Challenger 3: Chilled Water System
We’re getting into better options for grow rooms now that can be specifically designed for the application. However, we still believe a chilled water system is not the best option most of the time.
Imagine buying all the parts to a car and assembling a unique vehicle for the first time. This is the analogy for using a chilled water system on grow rooms.
Every building must be designed/configured by highly skilled engineers that have extensive experience with indoor grow rooms. For room controls, they must be custom coded by skilled programmers. There are very few programmers at standard controls companies that are familiar with the control of indoor grow spaces.
Room temperature and humidity are controlled with an array of heat exchangers. Chillers make cold water and send it to air handling units (big metal boxes with fans and coils). Air handling units blow air across the cold-water coils to send cold air into the grow space. To keep from overcooling the space, a massive amount of “reheat” is necessary. This is often in the form of electric reheat coils (this is a huge energy hog). The chiller also needs help from large cooling towers that sit outside of the building.
There will also be an extensive amount of water piping throughout the building and pumps that send the water through the pipes. All these pieces will be tied together by a controls contractor, who doesn’t work for the same company as any of the equipment.
Sometimes when there is a problem, every equipment provider and trade point their fingers at each other and the customer is left in the middle with no answers.
For grow rooms, we cannot recommend a chilled water system in most cases.
- High energy efficiency
- Expandability (if planned)
- Potential for very robust equipment
- Higher crop yield can be achieved
- Complex system design
- Potential redundancy issues if the chiller breaks
- Extremely expensive repairs for large equipment
- Specialized service companies required for maintenance and service
- Third party controls contractor not associated with the equipment (finger-pointing if something isn’t working)
- Owners can’t change settings easily without involving the controls contractor to write new software
- The high cost of electricity due to reheating necessity
Costly as is large commercial/industrial equipment
Challenger 4: DesertAire™ GrowAire™ Environmental Control System
A DesertAire™ GrowAire™ purpose-built (all-in-one) environmental control system is a fully integrated solution that performs the work of the air conditioner AND the dehumidifier by using highly advanced, Cannabis industry designed control logic to handle the temperature and humidity … All in one package!
Since this option is all-in-one, the system controls can easily remove heat or add it back into the indoor space as required during both lights-on and lights-off cycles.
These units use a compressor to help cool the air to handle the temperature load. Part of the refrigeration cycle that allows them to cool the air also gives these units the ability to reheat when necessary. This means we don’t need any extra reheating equipment. We call this “free reheat” because the energy was already created when removing the heat to cool the air.
All of this is built into the computer controller and because the controller is handling it all, you can easily change setpoints without fear of causing the system to fight itself.
This can be a set-it-and-forget-it system where the computer does all the work for you and manages the equipment, or the grower has complete fine-tuned control to their desires. Grow rooms using this system typically see very healthy and robust plants. In some installations we have seen a 30% increase in post-harvest crop yield vs. other system options.
- Purpose built system
- Purpose built controls system
- Extremely precise temperature and humidity control
Controls system built by the manufacturer of the equipment (no finger pointing)
- Higher up-front cost (offset by energy rebate)
- Planning required to avoid equipment production lead times
- Free Reheat – no need to pay for a unit to cool and another unit to heat (dehumidify)
- Electrical company rebates are easily acquired.
- Equipment can be maintained by a multitude of contractors.
- Remote support from the factory available at a moment’s notice (AireGuard)
- Reduced total number of pieces of equipment (less to maintain and fail)
Higher crop yield and profit potential
There you have it, folks! A purpose-built system like DesertAire™ GrowAire™ is the best option based on science, long-term cost analysis, and maximum post-harvest margin. If you’re longing for more information, don’t hesitate to download our ultimate grow room related documents below or contact Desert Aire () to start planning your room design.
Read our Vapor Pressure Deficit and HVAC Design Application Note: ()
Download Desert Aire's Questionaire for Grow Rooms: