Part III: Getting the right HVAC solution design
Commercial cannabis is an evolving industry that presents a number of unique challenges for business owners. The past two issues of Marijuana Venture addressed the importance of properly evaluating the true needs of a space in order to make the best decision about HVAC equipment sizing, but how can growers be sure they’re getting the right solution design?
There are different approaches and contrasting technologies that can be applied to achieve the desired grow room conditions. But what approach is the best? What type of equipment will give the best result? What manufacturers will deliver the best solution? What’s the smart money decision?
There is a natural “solution bias” in the engineering community toward traditional HVAC solutions, a tendency to use familiar models that have been applied successfully in the past. But are they truly the best solutions for a grow room application?
When Does a Central Plant Makes Sense?
Most projects requiring 1,000 tons or more of installed refrigeration capacity — roughly 80,000 to 100,000 square feet of facility — have typically utilized a central plant for heating and cooling. This would apply to a typical college campus, hospital complex or data center; for these facilities, it would be unfathomable to use smaller unitary air conditioners.
Because a large grow room can require a similar amount of refrigeration, many engineers naturally want to apply the same central plant approach. And they do so because they are familiar with that approach and don’t consider contemporary, “purpose-built equipment” for grow rooms.
What’s the difference? Why should they consider purpose-built equipment instead of traditional and more familiar solutions? The reason is that grow rooms really are different. They have a much higher latent load (moisture/dehumidification load) than almost any other large-scale environment. Latent load refers to the actual moisture or dehumidification load as opposed to air conditioning (cooling) load for a similar capacity requirement.
For a comparison, consider a computer data center. It has a similar raw cooling power requirement for a given room size as a grow room, but typically no need to dehumidify — in fact, most data centers add humidity to ensure they don’t have any static electricity buildup. This means they’re able to use chilled-water air handlers to effectively cool the space, with no need for reheat or auxiliary heat. Thus, a two-pipe system that’s relatively easy to install and equipment that’s reasonably priced makes perfect sense. You’d have a hard time arguing that it wasn’t the right solution for that space.
Traditional thinking (or solution bias) would say to apply the same approach to grow room spaces, which also have large, sensible cooling requirements.
However, the issue with a grow space is the humidity. To properly control the conditions and dehumidify effectively, the air needs to be cooled much more in order to condense the humidity off the cooling coil. That means the chilled water temperature needs to be much colder than is traditional, which turns out to be very inefficient when using the typical chilled-water air handlers and chillers mentioned previously. Furthermore, in lights-out mode, growers need to be able to not just dry the air but then to reheat it, to avoid overcooling the grow room. That reheat could use free energy captured from the dehumidification process to accomplish that with the right system. If you don’t, add that to your operating costs.
Simple Gets Complicated
This type of setup means growers now need to add a boiler for reheat capability, along with another set of pipes and a more complicated and expensive installation, instead of just a simple chiller-based central plant.
The inexpensive two-pipe system now becomes a much more costly and complicated four-pipe system. A chiller would also need to be run well below its most efficient operating point; you then have to add heat from a boiler and sophisticated systems to control it all, as well as redundancy to your chiller, pumps and boiler so that no single point of failure can affect your entire complex.
Electrical Power Consumption
Another often-overlooked complication is that most grow facilities are painfully underserviced by electrical utility capacity. A single, large plant is going to have a much higher single point load, which your electrical engineer and local permit officials aren’t going to appreciate.
The other obvious challenge with central plant design is that many growers want scalable production capacity with the ability to expand their facilities as their business grows. Knowing this, how do you size your central plant? Do you size, spend and build for current needs or oversize it now and hope expansion absorbs excess capacity? Scaling central plants and the supporting infrastructure is a complicated and expensive process. Central plants are by design not scalable.
The Purpose-Built System
Unitary, purpose-built grow room dehumidification and climate control systems can solve all these challenges and more. By utilizing a unitary compressorized system, you can cool and dehumidify effectively and intelligently reject heat out of your building when needed. You can easily size the equipment to match the room and create built-in redundancy in a number of ways. Expansion is 100% manageable with relatively short equipment lead times. Installation is simple and heat rejection is even simpler with low-risk, scalable, redundant dry coolers. Additional rooms can easily be added at will — entirely independent of the rest of the facility.
The other benefit of purpose-built, unitary systems is that the right ones are far more energy efficient than having separate dehumidification, cooling and heating components. Using separate components, that in some respects actually fight each other, requires careful control systems to minimize wasted energy. On the other hand, purpose-built unitary solutions leverage the latent heat of evaporation to recycle energy with high efficiency and tightly integrated controls.
It’s essential to have a solid understanding of your HVAC options as well as the costs, limitations and advantages of different design scenarios. You want to also weigh the advantages of a more modular, scalable and redundant approach to HVAC control for your facility, relative to traditional central plant considerations. Good vendors will be happy to have an open and honest conversation about the options available to you and which might be most suitable for any given facility.
Business owners need to be more deeply involved in their mission-critical HVAC and dehumidification decisions. There are too many potential areas where third-party specifications and purchase decisions can underserve the bottom line and the long-term interests of shareholders. HVAC equipment decisions must be carefully evaluated against important ROI considerations that have significant impact on budgets well beyond the initial purchase and one-year warranty period.
Business owners also should be thoughtful, diligent and explicit in setting out temperature, humidity and air-change specifications for every stage of growth and every type of potential crop in order to get load calculations done correctly. They should also ask for specific details about HVAC design criteria, why certain solutions are being recommended, what alternatives are available and what the pros and cons of each solution are. Once they are clear and comfortable with the solution design, they should carefully evaluate vendor recommendations and brand decisions based on important considerations that often don’t show up on mere technical specifications.
Equipment selection should be based on the merits of the equipment and evaluated using all of the facts in a straight-up comparison of all value factors over a multi-year ownership cycle, not merely lowest cost to meet specifications on contractor bid day.
Geoff Brown is the brand and product manager for the Agronomic IQ Series of dehumidifiers, specifically designed for growing cannabis in every size of grow room. He started his HVAC career more than 15 years ago and has honed his expertise, dealing in every aspect of dehumidification throughout his career. Prior to managing the Agronomic IQ brand, he was a senior sales manager and sales engineer, who consulted on and managed various successful dehumidification projects.
For additional information about Agronomic IQ’s purpose-built, unitary grow room humidity and temperature control solutions, visit AgronomicIQ.com, or contact the company at ContactUs@AgronomicIQ.com.
This article is the conclusion of a three-part series on the biggest HVAC challenges of modern grow rooms. Parts I and II of the series were published in the February and March issues of Marijuana Venture, respectively. They can be found at www.MarijuanaVenture.com.