Building the ‘Dream Greenhouse’

Photos courtesy of RII

Mattel first introduced “Farmer Barbie” in 2018, adding to the doll’s already extensive career list. However, even with the plethora of jobs she has held, there has yet to be a “Greenhouse Operator Barbie,” let alone an accompanying playset that matches the famed toy’s Dreamhouse. But that doesn’t prevent us from imagining what our very own “Dream Greenhouse” would look like.

So, let’s explore the features and systems that could go into a near-perfect “Dream Greenhouse” optimized for resource efficiency. Of course, it’s important to note that there are real-world considerations and limitations that would preclude a business from building a structure perfectly optimized for resource efficiency and production, including location, budget constraints, pending technology advancements and zoning regulations.

While some of the ideas and concepts we consider may seem impossible to implement today, they are included as part of the “Dream Greenhouse” vision we have. The key to getting as close to a perfect build as possible is to think about resource efficiency early on in the design phase, to work with what you have around you, and to be ready to evolve as new technologies become commercially viable.

Location & energy sourcing

As with any farming and real estate project, the first consideration is location. Where a greenhouse is situated will determine everything from lighting and climate control systems to energy sources and the amount of automation you can implement. In a dream scenario, the greenhouse would be located near consumers, so plants could be harvested at peak readiness or ripeness and quickly delivered to the store or distribution center, maximizing shelf life.

As solar-collecting structures, greenhouses are more prone to overheating than being too cold.

“The dream would be to have a high plateau, flat land for no excavating and high elevations,” says Kurt Parbst, president of Borlaug, a resource efficiency-focused engineering consulting firm in the controlled environment agriculture industry and RII member company. “The dream would be a flat mountaintop with a breeze and no pests around it with plenty of fresh, clean water and plentiful access to inexpensive electricity and natural gas. That’s the dream site.”

Zoning limitations may force greenhouse operators to locate in lower farmlands, near other agriculture businesses. This isn’t ideal, Parbst notes, as fields can be filled with thrips and whiteflies that will require more investments into IPM strategies.

Matthew Paris, a project manager at design-build firm and RII member company ARCO/Murray, adds that the dream resource-efficient greenhouse would be located in a mild climate to help maintain ideal greenhouse conditions.

“The milder climate you build in, the less transition temperatures you have day to day and year over year, which can help with overall energy consumption,” he explains.

Ideally, greenhouses should look to co-locate near a waste heat-generating industry, Parbst continues.

“Whether those are oil refineries, cement factories, glass manufacturers, power generators, there are a lot of industries that waste 20% to 50% of the energy that goes into their plant,” he notes. “It’s a tremendous opportunity to put greenhouses near these facilities.”

On-site power generation is another great opportunity to consider in tandem with selecting a greenhouse’s location to help increase circularity opportunities. Fossil-fuel combined heat and power (CHP) systems can help growers generate electricity, heat and CO2 for on-site use.

Beyond CHP systems, Paris would look to implement anaerobic digesters downstream of his dream greenhouse operation. Anaerobic digesters break down organic material in the absence of oxygen, producing biogas (a mixture of methane and carbon dioxide) and digestate (a nutrient-rich residue). They are used for waste management and energy production, converting materials like agricultural waste, manure, food waste and sewage sludge into renewable energy and valuable byproducts.

Anaerobic digesters are “becoming more feasible as we look for new ways to generate power and deliver to the grid,” Paris says. “Regenerative farming is more sustainable, and anaerobic digesters get us back to this more regenerative cycle.”

However, these units require different types of organic inputs, not just plant biomass, limiting their usability today.

“There’s going to be locations where this makes more sense, specifically rural locations where we have dairy farms, traditional farming and greenhouses producing thousands and thousands of pounds of organic waste,” Paris explains. “We must ask ourselves, ‘What is the most practical way to discharge greenhouse organic waste?’”

Tapping into solar energy beyond greenhouse lighting is another way to get free renewable energy.

“Photovoltaics have come a really long way since solar panels were first introduced, because we have a fully glass greenhouse, and PV glass is something that is likely to happen in the future,” Paris explains.

There are a few companies around the world working to integrate photovoltaic technology into greenhouse glass. System USA, a commercial greenhouse in California, is generating an estimated 107,000 kilowatts through such technology, according to a November 2023 report in PV Magazine.

On-site energy generation can be made even more useful by coupling it with energy storage technologies such as heat retention tanks/ponds and/or batteries. Heat retention ponds and tanks allow operators to store thermal energy generated during the day for recirculation in the greenhouse overnight if temperatures drop beyond target ranges. The energy generated on-site can even be sold back to the grid (if the facility is connected to it).

Battery technology is still in the early stages of development, and efficiency improvements are needed to make their use viable for commercial greenhouses. But, as Paris notes, “in the dream greenhouse, you harness the excess energy, store it efficiently and redistribute.”

Facility & structure design

Both Parbst and Paris agree that when it comes to greenhouse design optimized for resource efficiency, tall, Venlo-style structures are ideal. Taller structures can help keep hot air away from the crops (as hot air rises).

“You have plenty of space to hang equipment such as fans, curtain systems or lamps,” Parbst notes. “A tall greenhouse also means a greater volume of air, which means the temperature changes more slowly.”

Additionally, Venlo-style greenhouses can offer crop choice flexibility. “If you start with a tall greenhouse, you’re already compatible with supporting a vine crop in the greenhouse,” Parbst continues.

Any supplemental lighting would be done via high-efficiency LEDs, the layout of which would not interfere with natural sunlight delivery. In an idyllic resource-efficient greenhouse, maximizing sunlight is crucial, and single-pane glass often will offer the best results in that regard.

As noted in RII’s “Facility Design & Construction Best Practices Guide,” single-pane glass can have a light transmission rate as high as 93%, while double-paned glass can have a rate as low as 75%. High-quality, single-pane polycarbonate coverings can also achieve light transmission rates above 90%.

No matter the material chosen, Parbst stresses the importance of having high-light transmission and diffusion glazings. Diffusion “takes heat off the upper part of the canopy, and it drives photons deeper into the canopy, which can help with overall photosynthesis,” he notes.

Additionally, “high light transmission is favored in the glazing, but high transparency generally means poor insulation. The dream greenhouse has well-sealed insulating curtains used throughout the night," he says.

Beyond coverings and structure type, the dream greenhouse also integrates packaging and storage in the same facility.

“Localizing all of your cultivation production, packaging, storage, everything into one facility, to me, is the optimal way to operate,” Paris says.

Parbst also includes an area to conduct R&D experiments at a smaller scale to continue exploring novel efficient technologies and practices.

“Carve out a little space for R&D so you can try new things at low risk before making tremendous investments in new technologies,” he says.

Materials, plants and workflow circuits are critical to smooth operational efficiency, whether harvests are seasonal or perpetual. Layout designs should consider the workday, seasonality and unit efficiency. The dream facility would have high utilization of workers and tools and minimal traffic jams.

Systems & automation

The dream greenhouse optimized for efficiency would incorporate the most cutting-edge automation and controls, from artificial intelligence (AI)-powered environmental control systems to conveyance units that quite literally take the load off employees.

Controls leveraging AI can automate and coordinate lighting, shading, climate control and irrigation systems to maximize production and minimize energy and water usage. It has the potential to improve the current smart algorithm technology by integrating crop models, utility rates, weather forecasting and historical weather data.

For example, meshing AI with grower knowledge and targets can help growers “transition from the hottest parts of the day to the cooler parts of the day into the night in real time,” Paris describes.

Coupling an AI system with crop sensors and cameras can also help growers “read the plant’s health and dial in the climate system for higher yields,” Paris continues. “There’s an incredible amount of data and plant care techniques that we have available to us now that can be imported into the system that can influence climate decisions on a real-time basis.”

AI controllers can also stage cooling systems from most resource efficient to most energy intensive, helping growers maintain target environmental conditions cost effectively. Parbst explains that the dream greenhouse would utilize different cooling and airflow systems, starting with passive cooling.

“If we can, from an engineering perspective, you would rather have definable conditions where you can turn fans on and know exactly how the wind’s going to blow,” Parbst says. “The first thing to do with respect to cooling is to ventilate or exchange air.”

The next stage would leverage adiabatic (i.e., evaporative) cooling such as “pad and fan” or fogging systems. The dream greenhouse using pad-and-fan systems would reduce wasteful bleed-off of the reservoirs by using sensors to control the release of water with accumulated minerals, or by using rainwater with low mineral content.

“Fog is a little bit more difficult to make uniform and to control,” Parbst notes, “and with pad and fan, you have a temperature rise from inlet to exhaust that you have to contend with, but we can design with these things.”

Restricting solar radiation is generally the next step in the cooling hierarchy. The dream shading is one that transmits PAR light but restricts infrared (heat). Retractable shading is a plus, as it is deployed only when needed.

The dream greenhouse would have control over the 24-hour average daily temperature, and, in some cases, 48-hour and 72-hour averages. Managing the average means limiting the daytime peak temperature and correcting the night temperature with night cooling, which requires much less energy than during sun hours.

Temperature control is intimately linked to humidity control. The dream greenhouse would deliver full control of maintaining vapor pressure deficits (VPD) within preferred ranges. The least resource-efficient crop is the one that is ultimately thrown away due to poor quality or too short of a shelf life after all resource inputs are committed.

Advanced AI controllers can also control shading curtains to cut heat while ensuring plants receive their target daily light integral (DLI) levels using a rolling five-day average. Only when necessary would the advanced controller turn on mechanical cooling, or for nighttime climate control.

“I am in favor of correcting the conditions at night using mechanical cooling because you can solve quality problems and plant disease problems, and you can do it with much less energy than in the day because you’re not fighting the sun as you do in the day hours,” Parbst explains. “You can apply mechanical cooling at night in combination with dehumidification to keep the canopy dry and increase your output because you’re maintaining quality and avoiding loss.”

The dream greenhouse presented here, while perhaps not entirely attainable today, serves as a blueprint for the future of sustainable agriculture. By prioritizing resource efficiency from the outset and embracing innovative technologies, growers can inch closer to this ideal.

The key lies in thoughtful design, strategic location and the readiness to adapt as advancements emerge, ensuring that the vision of a resource-efficient, productive greenhouse becomes increasingly realistic.

Rob Eddy is the Resource Innovation Institute’s resource efficiency horticulturist. He has more than 30 years of experience in plant growth facility management, plant research and commercial production.  rob@resourceinnovation.org