Your Cultivation Goals will Guide Your HVAC Technology Choice

When given the opportunity to work with some of our design and construction peers to put together a design/build resource for the industry, we jumped at it. The result was “Build Your Grow,” which you can read here. However, we thought it would also be helpful to do a quick recap of the top takeaways for a quick read.
August 20, 2020

One of the first questions clients ask us is which HVAC technology will be best for their facility. Although there are some categories we can narrow it down to very quickly, it’s important to understand that selection of the right approach for your facility is a consultative process that requires a detailed understanding of the facility itself. This includes architectural, electrical, civil and geographic details. 

At Surna, we spend a lot of time understanding cultivation methodology, irrigation strategies, desired climate parameters through the life cycle of the plant, and the overarching business goals of the cultivator. 

We are meticulous about extracting these details, because they are vital to the implementation of a climate control system that meets ALL the cultivator’s goals, not just some. Once those variables and goals are well understood, we complete performance and load calculations, review budgets, and then decide with our client which type of system is most appropriate for their goals.

In today’s post, we’ve summarized the most common categories of HVACD technologies utilized in cultivation facilities. That’s not to say these are the only options, just that they’re the most commonly applied in our experience. Also, keep in mind that there are nearly unlimited options within options in each of these categories—from energy efficiency to filtration to economization and more. This blog is not intended to give you enough information to decide what is best for your facility. It is only intended to arm you with information for conversations with your design team.

It will always be our strong recommendation that you employ the services of a qualified mechanical engineering firm who can review all these details with you, and work with you to determine the best approach for your facility. And remember, if you don’t have one identified, you can always call us—we work all over the world. If you do have one identified, you can still call us—we help other engineering firms navigate the intricacies of HVACD design in cultivation facilities on a regular basis.

HVAC Systems with Stand Alone Dehumidification

This approach describes systems that have no integrated dehumidification option and must be utilized in conjunction with stand-alone dehumidifiers for humidity management. You can find our blog with additional details on stand-alone dehumidification systems here.

DX Systems

This type of system describes a typical split, mini-split, or rooftop unit (RTU). Historically, this approach has been the most commonly applied system category in cultivation facilities, largely because of their wide availability in comfort cooling applications and the familiarity of “old school” cultivators with the technology (primarily due to a historical lack of engineering in cultivation facility design). However, they are beginning to fall out of favor with cultivators as reduction of operating costs becomes a bigger priority in the industry.

These systems are designed for comfort cooling applications and are not intended for the year-round, industrial grade performance demanded by cultivation operations. Thus, they tend to fail early and require substantial maintenance during their life cycle. These systems do not have direct humidity control and require the use of stand-alone dehumidifiers to manage humidity, which creates an increase in the overall electrical infrastructure on the building, and air handling options are limited. This approach is generally among the highest electrical consumption options. However, this approach is usually at the lower tier in capital costs and can be deployed relatively quickly in comparison to other technologies, which is why it remains on the table as an option for cultivators focused solely on reduction in construction costs.

2-Pipe Chilled Water Systems

This describes a system in which chilled water, as opposed to refrigerant, is utilized as the primary means of heat exchange in the cultivation space. From a climate management perspective, it operates very similarly to DX systems. However, it has a number of advantages over DX systems, including longevity, redundancy and electrical infrastructure reductions.

With this type of approach, air handling systems operate independently of the compressors, allowing one central plant to operate multiple rooms without mixing air between rooms. This results in the ability to reduce electrical infrastructure requirements (particularly when flowering rooms are “flipped,” or operating on opposite light cycles), and offers greater opportunities for redundancy at lower cost. Further, chillers are generally designed for heavy commercial or industrial applications, resulting in less maintenance and a much longer life cycle. Lastly, in cooler environments, economization options that do not require ventilation are available, which can dramatically reduce operating costs.

Cultivators who select this option should expect to pay slightly more for their system than those who select DX and should expect longer equipment and installation lead times. These systems are generally most applicable for cultivators who have mid-range budgets and for whom longevity, air handling flexibility, reduced electrical infrastructure, and options for improved energy efficiency are a priority.

HVAC Systems with Integrated Dehumidification

This approach describes more sophisticated climate control systems with integrated humidity management, which do not require the addition of stand-alone dehumidifiers for humidity control. Additional information is available in the blog link under HVAC Systems and Stand Alone Dehumidification.

DX with Hot Gas Reheat

These systems are typically either split or packaged, where the refrigerant circuit is routed through the airstream twice—once to remove BTU’s (heat and humidity) from the air, and then to replace the heat back into the airstream to make dehumidification operations temperature neutral. This allows cooling and dehumidification to be accomplished with a single piece of equipment.

These units are generally simple to install and operate, although they carry longer lead times than standard DX systems. They also require sophisticated controls, often supplied by the manufacturer with the units themselves. Electrical infrastructure is reduced with the elimination of stand-alone dehumidifiers, and precise conditions can be maintained, particularly when modulating hot gas reheat is selected (more on that later in this blog series). Longevity is generally superior to standard, comfort cooling-style DX systems as these systems are intended for cultivation applications.

Equipment costs for this type of approach are among the highest of all options, but installation is fairly simple and adds limited cost. This approach is usually most applicable for cultivators who have a robust capital budget and are seeking precision, improved energy efficiency, and relatively simple installation.

4- Pipe Chilled Water Systems

4- pipe chilled water combines the strongest advantages of 2-pipe chilled water and modulating hot gas reheat systems. These designs consist of a cooling coil followed by a reheat coil, which is utilized for cooling and dehumidification. Reheat is accomplished with either high efficiency boilers, or by utilizing heat recovery from the chiller plant.

These systems are complex and expensive, but usually include the tightest precision, most redundancy, highest flexibility (in both air handling options and achievable results), lowest electrical infrastructure requirements, and longest overall lifespan of all options. These systems allow for multiple energy efficiency options, and when utilized with the correct controls system, can provide great visibility into the operation of the climate control system. This allows for minimized maintenance as well as providing the cultivator insights into how they might make minor adjustments within their cultivation practices to reduce energy consumption associated with the HVAC system.

In general, the equipment for this type of system will be less expensive than with most hot gas reheat systems, but the installation is complex and can add cost. This approach is usually most applicable for cultivators who have a robust capital budget and are seeking the best as it relates to precision, energy efficiency, flexibility, electrical infrastructure, redundancy, and business insights.

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