As the progressive libertarian movement fumed by the 60’s post-modernism has found zeitgeist momentum in the new generations, it has been successfully reconciled with a neo-humanism ideology in an ostentation fashion (contrary to Michel Foucault’s views on the subject). Aimed at affirming the dignity of each human being and the maximisation of individual liberty, the movement tipped the scale of public opinion on many fundamentally conservative policies in favor of libertarian persuasions.

Enter Cannabis.

“As per the World Drug Report 2019 released by the United Nations, cannabis was the most widely used drug in 2017, with 3.8% of the global population, or 188M people, having used it in the previous year… A white paper published by Euromonitor International in February 2019 estimates that the current global market for cannabis is US$150B.”

The door to the $150B industry has been cracked open not only for businesses in the sector, but also for all the auxiliary industries that have a claim for arguably a larger share of the cannabis market. As Mark Twain observantly asserted: “During the gold rush it’s a good time to be in the pick and shovel business”.

The cannabis industry is just coming out of puberty and while the legal market is being suffocated by strict quality control, over-taxation and an inadequate retail space, the black market is flourishing. In 2018, the Canadians paid $115 million for legal cannabis products and spent an estimated $4.9 billion on the black market. And as 2019 comes to a close, California, home to the world’s largest cannabis market, totaling close to $12 billion in estimated sales, $8.7 billion of that is changing hands in the illicit market. Most of the products sold on the black market are contaminated with fungus-related diseases and would fail State laboratory tests or GMP standards. A 2017 UC Davis study discovered multiple bacterial and fungal pathogens even within California legal medical marijuana products. The majority of the contamination issues are related to poorly designed climate control systems. Maintaining temperature and humidity levels below 72F/40%RH is crucial in preventing powdery mildew, Botrytis, and other fungal diseases.

There are few factors that are as important to cannabis cultivation as climate control, and the HVAC industry needs to go to great lengths in order to adapt to the rigorous and challenging environmental conditions of cannabis cultivation. Inadequately selected AC systems and poor air distribution are the main reasons why cannabis plants are being contaminated with fungi and other pathogens during late flowering and post-production (drying and curing). While the sensible load in the indoor cannabis cultivation facilities can reach 200 Btuh/sf and the latent load as much as 100 Btuh/sf of canopy, keeping specific humidity levels below 0.006 (70F/40%RH) during the late flower cycle is an extremely energy demanding and difficult task for most of the traditional cooling technologies, especially during extreme ambient temperatures. It requires the processed air to be chilled to around 40F in order to effectively perform dehumidification and subsequently be reheated to 60-62F in order to avoid stressing the plants.

flower-cycle

SPLIT SYSTEMS
Small and medium ductless HVAC units allow for quick owner installation at relatively low cost. These systems lack direct dehumidification control and are designed for comfort cooling application, although split systems provide some indirect dehumidification capability, they do not allow the grower precise control of neither the supply air temperature nor the indoor relative humidity and must be augmented by stand alone dehumidifiers. Split systems are a viable option for very small-scale facilities.

  • Acquisition cost: $
  • Operational efficiency: ★
  • Temperature and humidity control: ★
  • Applicability constraints: ★★★★

PACKAGED SYSTEMS
RTU’s (rooftop units) are a common choice of medium size facilities. This is generally an inexpensive option with mid-range energy efficiency, but can present challenges associated with excessive ductwork, redundancy, low temperature operation and requirements for building ventilation.

VRF’s (variable refrigerant flow) systems exhibit higher energy efficiency and they are more effective at dehumidification than RTU’s, but it costs comparatively more to acquire and install them. Both RTU’s and VRF’s require hot gas bypass to increase the temperature of the dehumidified air to above 60F. Hot gas bypass is often insufficiently designed for maintaining the indoor cultivation conditions and tend to overcool the space. These systems are more suited for an office environment than for cultivation facilities.

  • Acquisition cost: $$$
  • Operational efficiency: ★★
  • Temperature and humidity control: ★★★
  • Applicability constraints: ★★★★★

CHILLED WATER SYSTEMS with heat recovery offer efficient temperature and dehumidification control. They provide higher levels of system redundancy and are capable of efficient load distribution based on an alternate day/night grow room schedule. Chilled water systems (especially water-cooled) come with a high acquisition, installation and maintenance cost and they are usually price-prohibited for small and medium operations.

  • Acquisition cost: $$$$$
  • Operational efficiency: ★★★★
  • Temperature and humidity control: ★★★★
  • Applicability constrains: ★★★

ABSORPTION CHILLERS
Though these systems are effective in maintaining the design criteria, they are costly, exhibit low COP and require significant amount of thermal energy. Because of these drawbacks, the use of the absorption chillers is limited to the facilities that employ cogen systems.

  • Acquisition cost: $$$$$
  • Operational efficiency: ★★★
  • Temperature and humidity control: ★★★★
  • Applicability constrains: ★

GEOTHERMAL
These systems are energy cost-effective and have low-maintenance. However, their geographical applications are limited, they require a large investment and they are mostly employed as a supplemental source of cold in greenhouses.

  • Acquisition cost: $$$$$
  • Operational efficiency: ★★★★
  • Temperature and humidity control: ★
  • Applicability constrains: ★

INDIRECT EVAPORATIVE COOLER (IEC) WITH DIRECT EXPANSION (DX) are either RTU’s or VRF’s with an additional indirect evaporative stage coil to improve operating efficiency of the systems. In dry climates, they can save up to 30% of energy in comparison with traditional systems. Similarly to standard RTU’s and VRF’s, a hot gas bypass mode is required.

  • Acquisition cost: $$$
  • Operational efficiency: ★★★
  • Temperature and humidity control: ★★★
  • Applicability constraints: ★★★★

IEC WITH DESICCANT DEHUMIDIFICATION AND DX OR CHILLED WATER BACKUP
This is the most efficient and effective system for maintaining a conducive to cannabis cultivation environment. While the cost of installing this system is at a premium, depending on the climate, this approach can save as much as 60% of operating cost compared to the traditional systems, which translates in $250,000-$350,000 annually for a 22,000 sf of canopy license in CA.

cooling

The thermodynamic advantages of this approach are clear on the psychrometric chart below. At the first stage, a desiccant rotary dehumidifier removes humidity from the processed air while introducing the heat of condensation and the residual heat of desiccant regeneration into the airflow. Subsequently, the processed air is sensibly cooled by IEC stage to the temperatures, close to the wet bulb of the ambient air. Depending on the climate, IEC stage is sufficient to remove the heat of dehumidification and cool the processed air to 60F-66F the largest part of the year. When IEC stage comes short in its capacity, the DX or Chilled water coil is activated to provide additional cooling potential.

Cooling-Air2O

There have been significant developments recently in the IEC technology industry and companies like Air2O, Intelligent Cooling offer packaged systems that greatly outperform VRF’s and RTU’s in many categories and provide a considerable advantage in operating efficiency with up to 70% energy savings. On the downside, these systems are larger and heavier than traditional packaged units and the rotary desiccant dehumidifiers require natural gas connection.

  • Acquisition cost: $$$$
  • Operational efficiency: ★★★★★
  • Temperature and humidity control: ★★★★★
  • Applicability constraints: ★★★

Grow-Product

There is no single solution in selecting the right climate control system for commercial cannabis cultivation and many factors must be considered: budget, geographical location, energy cost, facility structural constrains, ROI, etc. Choosing experienced cannabis cultivation HVAC design firm is a crucial step in securing the operational success.

The cultivations that strive to produce top grade product while lowering the operating expenses should opt for IEC systems augmented by desiccant dehumidification.

This article was written by Air2O’s Cannabis Cultivation Cooling Engineer, Iggy Kogan.

References:

Oppenheimer Cannabis Primer 08/2019.

https://americanhumanist.org/what-is-humanism/definition-of-humanism/

https://www.mercurynews.com/2019/11/30/california-pot-industry-calls-for-help-from-state-leaders/

https://health.ucdavis.edu/health-news/cancer/uc-davis-study-finds-mold-bacterial-contaminants-in-medical-marijuana-samples/2017/02