Resource Innovation Institute’s ‘Dream’ Indoor Cannabis Facility

Most cannabis growers have their own ideas of what makes the perfect grow facility. The plethora of options in lighting fixtures, environmental control systems, ideal air and soil temperatures, humidity levels, airflow velocities, and nutrient delivery systems and recipes available in the marketplace can accommodate just about any personal taste.

That’s because there is no one perfect indoor cannabis facility. Depending on production goals, final product outputs, and market conditions, one grower’s dream facility is another one’s albatross.

While we may agree to disagree when it comes to the finer details, in the spirit of the Resource Innovation Institute’s mission of promoting resource efficiency and sustainability in agriculture, we offer here some of the features of our own dream indoor cannabis farm: one that maximizes resource efficiency.

Facility Design & Layout

Efficient use of resources starts with efficient use of facility space. For example, long ductwork tracks can waste thermal energy and put an unnecessary load on your HVAC equipment. Similarly, long electrical feeders add cost and are less efficient due to voltage drop.

With that in mind, efficiency principles are ideally built into the facility’s design. “Centrally locating critical systems like the electrical room, mechanical room, and fertigation room, relative to the growing rooms is important in optimizing facility design and reducing construction costs. This minimizes the length these systems have to reach,” says Holden Orler, a regular speaker at RII webinars who serves as director of operations for ARCO/Murray’s CEA design-build construction team.

A way to maximize resource efficiency through better use of your building’s footprint is to remove as many mechanical systems from the floor space as possible. “That may mean upsizing roof framing to support the load from rooftop HVAC units,” Orler says. “Designing the structure to support mechanical equipment frees up floor space for cultivation and shortens duct runs, which saves on construction costs and reduces inefficiencies from duct leaks.” Early engagement with design stakeholders can help proactively plan facility design for maximum resource efficiency.

Resource efficiency goes beyond eliminating unnecessary power and includes optimizing water usage. Water circularity systems can be more difficult to retrofit, so planning for them early on is crucial to ensure your facility is operating (or can operate eventually) at peak efficiency. One simple step that can lead to both energy and water waste savings is testing incoming water quality to determine the optimal water treatment system for the facility.

Some operators default to reverse osmosis (RO) systems, thinking it’s best to start with water that has been completely stripped of all ions. But RO systems can be some of the most energy-intensive pieces of equipment, in addition to generating a significant amount of waste stream.

There also are ways to minimize energy use when reclaiming HVAC and dehumidifier condensate. Most of that condensate is high-quality–most of the time, it only needs a filtration process to remove any metals it collected from being in contact with the mechanical system’s coil.

When building an energy-efficient condensate reclaim plan, Orler suggests trying to design the facility so pumps are not needed to collect condensate recovery. “Utilizing gravity to flow back to a collection point and reduce the number of times that water needs to be pumped can help create a more efficient and reliable water recirculation solution,” he shares. Using gravity flow can be done overhead with rooftop units but can also be done through underground plumbing if the equipment is at ground level.

Rainwater capture is another feature cultivators looking to build the most efficient indoor facility need to consider early on for it to be successful. Orler says. “If rainwater reuse is going to be utilized, it should be coordinated with the civil stormwater design and local authorities, so it’s crucial to consider this early in the site planning and due diligence phase,” Orler says.

Lighting

Light-emitting diode (LED) fixtures currently are the most energy-efficient systems available to the horticultural market. Additionally, because of the crop’s high value, cannabis growers have had early access to some of the most advanced LED solutions developed. The most resource-efficient indoor cannabis farm would utilize these advanced technologies’ features to the fullest to minimize resource use relative to crop productivity.

A feature to look out for in advanced LED systems is tunable intensity. Being able to fine-tune light intensity will allow operators to deliver exactly what the plant needs, when it needs it without wasting energy on delivering PPFD levels that aren’t as needed in a given growth stage.

Cannabis has yet to find its light input ceiling, but there are economic factors that create a point of diminishing returns. High-intensity discharge (HID) lights such as high-pressure sodium (HPS) fixtures typically have an average photosynthetic photon flux density (PPFD) of 800 due to technological limitations. This is the minimum threshold LED lights must match to match crop productivity according to RII Lighting Working Group member Casey Rivero, a cannabis solutions architect with Fluence.

Determining the optimal light intensity depends on numerous factors, not the least of which is the facility’s production and financial goals. At a commercial scale, “we need to make so many dollars per square foot of production, and then we work back from there,” Rivero says. “What do I need to do and implement to make sure that I am generating X dollars per square foot per year? That will determine how much light I give it, what type of nutrients I give it, and all those things that go into that process. Right now we're seeing typical averages of 1,000-1,100 with upper levels of 1,200 to 1,300 PPFD.”

Turning to third-party testing organizations such as the DesignLights Consortium (DLC) can make system comparisons easier. DLC offers a “worst-case scenario” measurement of the fixtures it tests, meaning the lights are rated at their worst performance rather than their optimal or average outputs. (Some jurisdictions also mandate that fixtures be on the DLC’s qualified product list (QPL) to be eligible for incentives and rebate programs.)

The lighting fixture choice is in the top three most important decisions a facility operator will make, as lights are “the reaction driver dictating what happens on the rest of the systems,” Rivero stresses. For example, latent heat loads will be greatly minimized when leveraging LED systems, so growers converting from HID fixtures will need to adjust their HVAC setpoints by 1-1.5 degrees Celsius.

“With the HID systems, … we would typically see a set point of 70 to 74 [degrees Fahrenheit]” to maintain optimal leaf surface temperatures, Rivero says. ”The cool thing about LED technology is we're able to increase that temperature requirement of the HVAC system to promote an efficient VPD [vapor pressure deficit], and also lower the requirement of that commercial equipment so we're not utilizing the equipment as heavily as we needed to with the high-pressure sodium system.”

Environmental Control

Integrated HVAC and dehumidification (HVAC-D or HVAC&D) systems typically are going to have a better overall energy efficiency rating than standalone units that do not communicate with each other. Per RII’s HVAC Best Practices Guide, HVAC systems “that fully integrate cooling and dehumidification offer integrated control of both air conditioning and dehumidification sequences. While standalone plug-in dehumidification units are inexpensive, they reject heat back into cultivation spaces and require air con

ditioning systems to work harder and more often.”

However, depending on the volume of moisture that needs to be removed–a factor determined by number of plants in a room, crop development stage, as well as temperature and humidity setpoints–added standalone dehumidification units can be a good option to lighten the load on the integrated system, especially if integrated with the HVAC system through a smart controller.

“A lot of times in the veg cycles, you don't need a whole lot of dehumidification, maybe only during the six hours of lights out,” explains RII HVAC Working Group member Randy Lenz, an application engineer at Anden. “Then as you transition into flower, you might need more and more dehumidification. Having a piece of equipment that is dedicated to doing that gives you your best control of the humidity and the best control of your vapor pressure deficit.”

Dehumidifiers can reject heat into the cultivation area (an issue that can be mitigated with ductwork removing that hot air from the environment), but they can also help make environments easier to cool. “The wetter the air is, the harder it is to cool,” Lenz says. “Because the coil is so wet, it loses some of its ability to remove the heat from the space. Having a drier coil due to the dehumidifier pulling the water out makes its cooling more efficient,” he says.

The metric to consider when evaluating systems to suit your dehumidification needs is their liter per kilowatt rating, Lenz notes. The higher the figure, the more efficient the system is at removing moisture in a given period.

HVAC and dehumidification can make up the second largest energy input in your cultivation operation (with lighting often making up the first biggest energy consumer). Having a well-built and well-insulated building will help avoid extra heating or cooling loads. “Making sure that the grow has been built properly so you have six plus inches of insulated panels and everything sealed and caulked … so that you're containing that room and ensuring the outdoors doesn't have a factor on your heating and cooling loads” is crucial to having a highly efficient indoor farm, Lenz notes.

In a facility where resource efficiency is the main goal, having combined heat and power (CHP) systems with CO₂ that can be captured, cleaned, and recirculated into the cultivation environment offers the highest return on investment. “CHP is being used to power a facility. Recapturing the CO₂ off of that and delivering it to the rooms is a great way to increase resource efficiency,” Orler notes. Similar setups can be designed with facilities using boiler systems, as well.

This is not an exhaustive plan to build the most resource-efficient indoor cannabis farm by any means. However, every cannabis operation can identify ways to make better use of its space and systems by keeping a critical eye on existing processes, budding technologies, and industry best practices. From new builds to existing retrofit projects, the principles and setups outlined here can help any operation become a better steward of our shared resources while maintaining, or even increasing, profitability.

Robert Eddy, M.S., is Resource Efficiency Horticulturist at Resource Innovation Institute.