24 tips to improve greenhouse efficiency

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For your greenhouse facility to operate at its best, you must properly plan in advance to ensure that the structure and its components are well-maintained and functioning properly.

Here, you’ll find tips for ensuring adequate airflow, facility cleanliness, evaluating fixtures and shade curtains, as well as a special “lightning round” of miscellaneous tips for additional efficiencies.

Managing Airflow

Air circulation in a greenhouse — a separate concept from ventilation — is best achieved with horizontal airflow (HAF) or vertical airflow (VAF) fans designed for this purpose. Avoid using standard box fans. HAF fans need to be sized correctly for the cubic feet of the air mass and installed in sufficient numbers to make a circular current in your greenhouse. Air has weight, so momentum will carry it with little energy input from the fans once it flows in this pattern.

The total fan capacity in cubic feet per minute for this circulation pattern should equal one-fourth of the greenhouse volume, according to the text “Greenhouse Engineering,” a Cooperative Extension publication by Robert A. Aldrich and John W. Bartok, Jr. Ideally, these fans should be integrated into your control system so that they shut off when the ventilation fans are cooling the room. Otherwise, they will create turbulence that will disrupt the parallel flow across the greenhouse, reducing the cooling efficiency.

The advantage of VAF fans is that they can pull air upwards through the canopy, reducing stagnant air in the lower foliage. Typical installations for cannabis are one fan for an area 30 to 50 feet in diameter (707 square feet to 1,964 square feet). The bottom of the VAF fans should be at least 3 feet above maximum height of the canopy. VAF and HAF fans should not be used at the same time.

Circulation air velocity should be a minimum of 50 feet per minute (fpm). At the very least, you should see some flutter in your leaves at their maximum height and density.

Cleanliness

Keep the walls and roof clean, but don’t have your team clean it. Estimated light-transmission loss from dirty greenhouse roofs ranges from 5% to 10%.

Here’s a scary, but true story: At the university greenhouse I managed for 20 years, I made a policy that no one but me could have their feet higher than 6 feet off the ground on a ladder or scaffolding. This was after being shaken by news that an employee cleaning the glass roof of another university facility was seriously injured when she fell through the glass and landed on the metal benches inside.

I’d recommend hiring an insured, professional greenhouse service team to clean your coverings if you have a large range. For gutter-connected houses, robotic units (which roll along the peaks, scrubbing and rinsing) can be purchased. If you take this task on yourself, rent power lifts and have your staff certified to use them for pressure-washing the glass or rigid plastic, at the very least. Avoid the use of ladders or “walking the gutters,” since there is nothing to tie yourself to for safety.

Clean sidewalls, inside and out, annually. Glass or rigid plastic with heavy scale deposits can be pre-treated with a sulfuric acid product registered for greenhouse use before pressure-washing. For routine glass cleaning, use glass cleaner and squeegees on extension handles for best results. Avoid getting cleaning solutions on plants.

Light Fixtures

Tracking operation hours of your bulbs, either in your written log or using the control computer, will ensure you change them before their output decays below 80% (20,000 to 24,000 hours, typically). An old HPS bulb will often appear darker orange when illuminated than a newer one. HPS bulbs that sporadically turn off every few minutes need to be replaced immediately, before they burn out the igniter in the fixture. Fixtures with loud, buzzing transformers are a true nuisance to your employees, who must work in the room several hours per day. Failing fixtures can be repaired, but only by someone certified to discharge a capacitor and work with high voltages.

Tip-Top-Shape Shade Systems

Employing motorized, shade-fabric systems is an excellent way to regulate light intensity and daily light integral; but these systems are expensive to repair, as the labor costs to make even the smallest fix is several times the cost of the component, especially if you need a power lift to reach it.

Therefore, it pays to buy quality fabric and maintain the system routinely. Buy fabric from established manufacturers. Compare warranties and ask if the warranty is pro-rated — meaning each year the replacement value diminishes — and also ask if the warranty pays you back money or just allows for a discount toward your next purchase. These questions will give you a good idea of who stands behind their products. (Bonus tip: Consider a white fabric designed to diffuse light, as research suggests this will increase the number of photons reaching lower foliage.)

Lube rack and pinions annually with a dry moly aerosol lubricant spray. Avoid grease, as it allows dust and grime to collect and gum-up the gears.

Inspect your curtains to make sure circulation fans are not blowing directly on them. This will cause them to vibrate constantly on the support wires, wearing them thin quickly.

The ‘Lightning Round’— More Tips! Below are more tips — that don’t fit tidily into other categories — for an efficient building and operation:

Consider contracting annual maintenance to an experienced greenhouse company. This resolves the safety issues and allows you and your staff to concentrate on growing and delivering quality product to your customers. It will ensure the maintenance is performed, as these tasks are typically not prioritized, despite best intentions.

The same dry moly aerosol lubricant mentioned for shade curtains’ rack and pinions should be applied to vent rack and pinions annually.

A rivet gun will help you fix loose louvers.

Apply floor coatings to cement, making it resistant to algae buildup. The room needs to be empty and dry to apply the coating, and it takes two to three days for application and suitable drying; but it is well worth it, even if only in your propagation area or under evaporative pads.

Irrigation pipes and hoses should be cleared of biofilms annually, using a product labeled for this use. This will reduce clogging of drippers and nozzles. One method to prevent clogging and biofilm accumulation is to install clean-out valves on the ends of the dripper feed lines to force full-pressure water through every week or so. Some growers replace their drip systems once or twice a year to resolve the biofilm problem.

Label each outlet with the circuit breaker that controls it. I use a labeler with weatherproof, adhesive printing tape to color-code them according to outlets that are controlled by timers (versus those that are always on). These labels will improve safety, communication and efficiency of repairs and installations.

Consider single-table light-deprivation systems for crop-scheduling flexibility. This may help you utilize space more efficiently. I have used excellent single-table systems that allowed us to conduct experiments with differing photoperiods.

Determine the best method to consolidate maintenance and repair records in a format that can be shared with your team and is available by smartphone. Develop your own Google Docs or consider other third-party software.

Use signal tapes and flags to improve communication between staff about a clogged dripper, for example, or which plants have pests or are being flushed, etc.

Make repairs more efficient by maintaining a parts list and keeping spare parts on hand.

Anything made of plastic in a greenhouse, such as a fertilizer injector, should be shielded from direct sunlight exposure to protect them from cracking or disintegration. Reflective bubble wrap is a good solution.

Assemble job-specific tool kits for a grab-n-go response to problems: a kit for plumbing repairs and a kit for electronics repairs. Also, an emergency submersible pump with flexible hose fittings can quickly replace an evaporative pad pump until you can plumb in one properly.

Invest in rolling safety ladders with side rails for reaching high places.

Consider buying a used power lift from an equipment rental company, if you can’t afford a new one. I bought one for $6,000 that has lasted more than 10 years.

Place two 20-gallon trash cans everywhere you currently have a standard 32-gallon trash can. Yes, this takes up more space, but will save your staff back strains when they get overfilled, as the smaller cans hold one-third less material.

Editor’s note: This article was first published in the March 2021 issue of Cannabis Business Times magazine.