As a horticulturist with a career history in ornamental plant production, as well as cannabis, David Risley has acquired greenhouse-growing experience with trial and error over the years. Now, as head grower for Euflora in Denver, Colo.—he’s learned much he’d like to share on the topic of evaporative cooling, which is an efficient way to deliver lower temperatures to your cannabis crop when installed and utilized correctly.
Currently, Risley has a wet wall system installed in a 7,200-square-foot greenhouse, but will be building out his grow space much differently in the company’s 17,000 square feet of additions that are currently in the works. Here are his tips on how to make your evaporative cooling system work best for you:
1. Ensure all parties included in planning and construction of greenhouse are in communication - contractor, manufacturer, architects, etc.
“Most of the design process of Euflora’s first greenhouse was completed by an architect with no previous experience designing a greenhouse,” Risley says. “The subpar design, combined with an oversimplification of the dynamic nature of a CEA (controlled environment agriculture) structure, led to some costly and completely avoidable blunders, of which I now spend a significant amount of time and energy combating.”
“The biggest mistake by far was locating our mechanical room/head house against the end wall of our veg bay in place of cooling pads. Imagine a 40 x 20-foot shaped L,” he adds. “We now have 10 feet of pad in a 30-feet-wide house. In front of the pad is say, 70 degrees (too cold); in front of the mechanical room is much warmer, 80-plus degrees. And in front of the ‘office’ (turned clone room) is well over 90 degrees and has zero air flow, mostly dead space in summer.”
“Inquire with greenhouse manufacturer about taking tours of already completed projects. Learn what they did and why, then improve and adjust for your project,” Risley says.
2. Ensure proper operation of evap pump and perform routine maintenance.
“Adjust flow to distribution pipe accordingly, and the ensure pump is sized properly,” Risley says. “The goal is to use the least amount of water while maintaining a uniformly wet pad surface; areas where water is running down have reduced rates of evaporation.”
“I like to wash pads down with hose end sprayer and soft brush to remove debris and excess salt,” he adds. “I wouldn’t recommend a pressure washer, as it could damage the pads or strip anti-rot salts off. After rinsing, I clean the pump filter, drain and clean up reservoir, then fill it again with fresh water. I do this monthly in veg. Flower has an adequate bleed-off so draining here is only required seasonally. I recommend contacting Schaefer, and research for more tips relevant to a particular greenhouse for quantity and frequency of bleed-off.”
Also, Risley warns not to pump air from one side of the structure. “If possible, locate the pump and reservoir in the center of the area to be cooled, which will ensure even flow through distribution pipe and a uniformly wet pad surface. If your pads have dry spots, do not attempt to modify distribution pipe by enlarging holes. This was a particularly dumb idea I had at one point,” he says.
Risley also recommends checking the top and bottom of evap frame to ensure air tight (within reason) after installation.
3. Properly seal your facility.
“It didn't take long to figure out that our roof vent was poorly sealed. Turning on our veg bays’ second exhaust fan actually increased temps! With an already higher static pressure from the smaller pad, fan No. 2 sucked down extremely hot air from the gable and outside air from unsealed around doors, outside electrical, partition between bays, etc.,” Risley says. “This is all equates to less air through the pads. Install gaskets around the roof vent, ensure vent motors are closed tight, use weather stripping and door sweep the threshold at base of door to seal it. Silicone and foil tape can be used to seal any other gaps and cracks. Although, it is still mostly unbearable on hot days.”
Also, beware of leaks at aluminum joints. “I highly recommend a PVC system,” Risley says, adding that it’s also important to, “Ensure proper function of evap prior to bringing in plants. Check for leaks and a tight fit between components. Pads have a bit of a break-in period so you likely won't expect the full cooling effect for weeks/months.”
4. Utilize light panels. Select appropriate glazing materials to mitigate excess light and heat build-up.
“The intensity of the sun in Colorado and relatively high light transmission of twin wall poly is more than our veg can handle. Installing diffused light poly will reduce light transmission and eliminate hot spots. This will act like shade paint but without the extra fun and mess of applying shade paint. When it’s hot and the sun is blazing, tender transplants will thank you,” Risley says.
5. Circulate the air.
“Invest in quality HAF (horizontal air flow) fans/circulation fans. In dead zones, or areas where it gets hot, utilize portable evap coolers. They’re efficient, and move a lot of air. So they are very helpful, even if ran with a dry pad,” he says.
6. Consider insect screening and light baffles.
“Installing screening 5x the pad area is ideal to minimize the increase in static pressure,” Risley says. Light baffles (for a light deprivation system) are installed behind cooling pads and exhaust fans to exclude light from entering, and will also reduce flow through pads. “Work with your greenhouse manufacturer, or distributor to appropriately size your exhaust fans to accommodate insect screen/light baffles,” he adds.
7. Don’t skimp on control system and components.
“Just don’t!” Risley warns.
8. Get to know your community.
“Build a good relationship with your fire department and regulatory agencies. Request pre-inspection and take advantage of resources to ensure your building and accessory parts are up to code,” Risley says, adding that Euflora recently received a code violation in May, during their peak production period, for having a shade hung at the top of the veg bay. The negative effects from the increase in temps were immediate, and production ground to a halt. “At the beginning of June, we applied shade paint and have moved more plants in the last two weeks than in the previous month,” he adds.
