Rooftop chillers, made by Surna.
By Steven P. Fuhr
Most growers know the basic formula for a winning crop. Start with solid genetics, add a proven feeding, pest management and watering schedule, wrap all it all up in a carefully-controlled environment from beginning to end, and you will consistently produce high-quality product. However, the reality of executing these deceptively simple steps is complex; on a commercial scale, it can also be extremely expensive to accomplish.
A grower can start with the best strains on earth, feed them top-of-line nutrients, and use only the purest spring water, but if your environmental controls aren’t dialed in perfectly, your crop is destined for costly failure. Fortunately, recent innovations in building systems are providing some noteworthy environmental solutions for large-scale grow operations.
Controlling an indoor agricultural environment falls into two main areas. Insulating your “envelope” prevents heat transfer, but it can also shield you from unwanted outdoor pathogens and spikes in moisture levels. There are hundreds of great articles on this subject, in addition to volumes upon volumes of International Building Code (IBC), but two years of obsessively searching for the ultimate materials to build a cannabis production building, the answer may have been found in the most unlikely of possibilities: Soy.
Insulating a building’s envelope is often required by the Washington State Energy Conservation Code and IBC, with some exceptions for agricultural buildings like greenhouses. In the end, most counties will require insulation for occupied commercial structures. This is a little different for every area based on average weather, but for most of people, walls need to be at least R-21 and ceilings R-38. Recent bids to completely cover both ceilings and floors of a new, 5,000-square-foot building to that level were between $25,000 and $50,000, so there’s a wide range of options — most of which would be the wrong choice for high-moisture grow rooms. This is where the new innovations come in, and soy.
Everybody has heard the stories of people growing in metal buildings that rain inside, and we know that doesn’t work, but I will never forget when I first walked in a grow that had fiberglass insulation on the walls and ceiling. The black mold was evident everywhere, and the stained surface was obviously un-washable. However, the real shocker was in the ceilings. As the fiberglass absorbed moisture, large bags of retained water would form — bags that periodically burst over the plants and lights below as they got too heavy. Rodents and insects often made spaces to nest in these fibers too. Many other common insulators do the same or worse, like plastic-based “open cell” foam and pure cellulose (wood) fiber. The solution we found is a “closed cell” spray foam that is impervious to moisture, mold, mildew, insects and rodents.
Because the base is sugar and soy beans, it is certified food grade, and it’s so strong, it increases tensile strength of walls by up to 200%. Best of all, at R-7 per inch, it’s a thin, light structural load on walls. To meet one-hour fire wall code requirements, you can either sheetrock over the top or spray a special one-hour fire retardant paint over the foam. This spray-on fire retardant is expensive, but if you don’t have the load strength in your building to handle the weight of sheetrock, you may find it’s much cheaper than structurally retrofitting your whole building. The final result of this foam is an airtight, moisture-proof envelopment that is perfect for indoor agriculture.
One final note about this foam insulation: there are only a few companies in the Pacific Northwest that have the expensive truck-mounted system required to spray it on, and a couple are gaining a solid reputation for specializing in grow-room jobs. I try not to promote specific companies publicly, so if you want to know the contractor we chose, send me an email and I will forward their contact information. Two of the four Washington contractors I called firmly said they will not do “pot” farms, so I suggest being up front with your intended use when you put this out to bid. Keep in mind I get no compensation for referring anyone to any sources. I make these offers to help others purely so our industry as a whole can thrive.
Once the envelope has been insulated and sealed, it’s time to regulate the temperature inside. The goal is to keep your room cool when the lights are on, warm when they aren’t, with moisture levels consistently in check. The key is consistency, with the gold standard being plus or minus 2 degrees on your desired temperature levels at all times, and plus or minus 2% on moisture levels, with no peaks or valleys. Many old-school growers cobbled together venting systems to do this, but that never works in rooms with more than a half dozen lights, or in moist climates. More enlightened growers invest in traditional air conditioners, which work well, but even standard HVAC systems bring their own set of problems.
First and foremost, traditional HVAC is expensive. For our 5,000-square-foot grow, we had HVAC bids as high as $180,000, with the average being around $100,000. Secondly, condensing air and cooling it is extremely inefficient and power hungry, which means it’s costly to run. If you think HID lights suck a lot of juice, go take a look at the power use on your HVAC air-chillers. The reason is that with standard HVAC you’re either taking air from the outside and making it cooler, or cooling the inside air with a closed-loop system. From a thermodynamic standpoint, water transfers heat five times more efficiently than air. As a result, water-cooling towers are the way many large commercial buildings go; however, standard water-cooled systems often use evaporative water-cooling towers that do not work well in damp climates. Not to mention evaporative water-cooling towers tend to start at $200,000 for a small system, and the cost goes up from there — way up.
There is a new system now that one could go so far as to say is designed just for high-humidity, high-temperature environments, but it’s not HVAC — it’s process cooling. More accurately, it’s an old technology with a new application, and it has been engineered specifically to work in high-temperature/high-humidity rooms. The principle of this new application is simple — take the heat out of the room before it heats the air. This mean no air ducts, no filtering air from the outside, no burnt-out mini-split motors covered in resin. If it’s done right, not only do you get a system that costs two-thirds what traditional HVAC costs, it’s much less expensive to run and maintain. Best of all, you end up with a truly sealed grow room that is less likely to inhale problems or exhale smells.
This system uses air handlers that have water lines running to them with chilled water. The warmed water is sent to chillers outside the building that can either passively and more economically dump the heat when it’s below 45 degrees outside, or actively cool it with standard condensers. No evaporative cooling takes place, so it works well in damp or cold climates, and because you are cooling water instead of air, the whole system is five times more efficient to run. This same system can even be linked to hydro-nutrient tanks to cool root water. Cooler roots lets you keep room temps higher while keeping root rot and aphids at bay. Interestingly, the company we chose just developed a new, commercial-grade, water-cooled hood that takes 60% of the heat out at the light, which will be available this spring.
And much like the insulation companies, it’s worth mentioning that of four different process-cooling contractors, half said they would not do business with a cannabis grow. As frustrating as that can be, these companies do make the bid process a whole lot easier.
No matter what systems you go with in the end, I can say for certain you want to start by doing your homework on the different products before choosing one. Then make 100% sure it meets the requirements of your local building department and fire inspector. Finally, hire a contractor that understands the special challenges of our industry, and is willing to work on a cannabis farm.
Steven P. Fuhr is a managing member of AgroPack LLC. He can be contacted with questions at AgroPackWA@gmail.com.