"Lower your operational expenses for the long-term sustainability of your business"

The North American greenhouse lettuce market grows more competitive every year. "Incorporating efficiencies into your lettuce greenhouse and growing systems from the start helps you lower your operational expenses (OPEX) for the long-term sustainability of your business", says Burk Metzger, general manager produce growing at Prospiant. Together with Tony Abbas, director of business development - produce they discussed several technological advancements making lettuce greenhouse production more efficient in a recent webinar.

Mobile Gutter Systems (MGS)
"Mobile Gutter Systems enable growers to automate high-density plant production to net more yields per square foot/meter at much less cost to produce in lettuce greenhouses", says Tony. "In simplest terms, MGS are closed-loop setups that use specialized gutters or gullies to autonomously transport plants through the various cultivation stages."

In a fully automated system, a robotic seeder sows seeds directly into plugs or gutters, and the MGS then moves them to the seed germination area. Once the seedlings emerge, the system transfers them to a propagation area where they can develop a strong root system. After propagation, the system transports the gutters filled with young lettuce plants to the growing or cultivation area, which runs the length of the greenhouse. The gutters move from one side of the greenhouse to the other. As the plants mature and require more growing space, the system autonomously adjusts the spacing between the gutters accordingly. Once workers harvest the plants, the system cleans and sterilizes the gutters before returning them to the seeding area.

According to Tony, autonomous spacing offers a couple of advantages. "It allows for enhanced air movement at the plant level because growers can push air from underneath the plants to create a comfortable growing environment. Growers can also maximize production per square foot/meter by planting at a higher density."

"Additionally, MGS systems require less labor to operate and help decrease input use. On the food safety side, they prove more sanitary than traditional NFT systems because human interaction with the plants remains minimal."

ETFE roof systems as an alternative to glass
"With cost benefits ranging from reduced shipping weight and superior durability to high light transmission and energy efficiency, ETFE roof systems offer a feasible alternative to glass for covering greenhouses", Burk Metzger, General Manager-Produce Growing continued. "ETFE roof systems prove especially advantageous in areas prone to severe weather events such as hurricanes, earthquakes, hailstorms, and high winds."

Tempered glass shatters into small pieces when it breaks, presenting a food safety hazard. "This situation necessitates the removal of a considerable number of plants. Clean-up becomes complicated and time-consuming, especially in greenhouses with lettuce growing systems."

He adds ETFE panels, being pre-stretched and possessing high impact resistance, stand out because they do not shatter like glass. "Their ease of repair and maintenance further contributes to their appeal. This feature makes them especially attractive to greenhouse growers situated in remote locations without convenient access to maintenance services or to those who prefer to self-maintain their greenhouses."

Boal Systems offers an ETFE roof system branded as F-Clean for Venlo-style greenhouses. "F-Clean has a higher rate of light and UV transmission than glass, polyethylene, or polycarbonate. It sheds dirt and debris easily and comes in clear and diffused versions."

Advanced climate conditioning solutions
"Crispness, flavor, head size, freshness — so much of the quality of lettuce and other leafy greens depends on maintaining ideal greenhouse temperatures around the clock, but achieving this goal can prove costly", says Burk. "We can create innovative custom solutions to provide constant, even climate conditioning to increase crop quality and yields at the lowest necessary cost for production. Using new technologies, including absorption chillers, heat pumps, and high-efficiency fans, we guarantee to have a climate solution to address specific crop needs and adapt to various growing locations."

An example of one solution centers around a climate corridor concept, which allows growers to pull air from the interior or exterior of the greenhouse using air handlers and crossflow heat exchangers. "This gives them the flexibility to choose the optimal conditioning source (interior air, exterior air, or a bit of both) to meet their needs, thus facilitating reduced energy consumption."

Absorption cooling uses waste heat to create cooling capacity
Growers often use their natural gas boilers for CO2 supplementation in the spring or summer by redirecting a portion of the flue gas into the greenhouse for distribution."Due to reduced heat demand in the summertime, absorption chillers can make use of the waste heat generated by the boilers to turn the hot water into cold water", says Tony. "Excess cold water not used for current cooling demand can be stored in a water-buffer tank for later use."

He adds while the OPEX savings gleaned from absorption cooling depend on your location and its utility rates, it can offer benefits when for example the climate is too hot and humid for traditional evaporative cooling. "Or when the proposed cooling system has a dehumidification and active cooling phase. We also find the situation sometimes the chiller plant doesn’t operate during peak hours (4 hours per day)."

Tony adds water-cooled chillers prove significantly more efficient than air-cooled chillers. "Including absorption chilling in a chiller plant eliminates the need to install a CO2 system or incur costs for liquid CO2 supplementation. Growers benefit from lower operating costs and higher efficiency, as well as energy savings."

Focus on efficiency for OPEX savings
It has been discussed more often recently: operating a successful greenhouse is not just about the initial costs or investments, it's about the OPEX and the final results as well. "These innovations can collectively increase yields, improve sustainability, and lead to greater operational efficiency, indicating a broader employment of them in future lettuce greenhouse installations. We make it a priority to bring you the tools and technology that keep you competitive and profitable now and in the future", he concludes.

Click here for the complete “Lettuce Cultivation 101” webinar.

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