Top 5 ‘must haves’ for Better IAQ in Controlled Environment Horticulture

Brian D. Anderson, AIA

Co-Founder & Principal
Anderson Porter Design

Chair Emeritus of the
NCIA Facility Design Committee

Top 5 Must Haves:

I recently was invited to speak on a panel for Indoor Ag-Con with some esteemed colleagues in the cannabis industry discussing Indoor Air Quality (IAQ) in CEH*. This blog post explains in further detail some of the facility related measures addressed. 

1. Box within a Box

   Both boxes matter! There is a lot of building science embedded in this idea, but the concept is simple. The outer box is the building, whether it is new construction or renovated, it is the first layer of defense against microbial contamination and plant pathogens getting into the controlled environment. It must be air and watertight, and in most states, it also must be thermally insulated to the level required by code. Exterior doors and most interior doors must have sweeps at the base and automatic closers to shut them after each use. Do not prop doors open to get a nice breeze in as the inner box is the grow environment and must be sealed tight. Consider adopting a standard from the housing industry – we recommend conducting a blower door test on grow rooms during construction. One standard is 0.5ACH @ 50Pa, (.6 or even .75ach could be used). Non-cavity walls are better than cavity walls for avoiding mold growth, Insulated Metal Panels (IMP) are an example of non-cavity walls. There is no hidden place for mold to grow, they come with the insulation already in them (thus the eponym) they go up faster than light-gage metal studs and wall board (please do not use GWB!), the joints can be sealed, and the surface can be specified with a material that is durable, cleanable and mold resistant.

2. You must have ceilings (and floors)!

   This is part of the box within a box of item 1 above, but it is worth pointing out on its own. Please do not leave exposed trusses in the grow environment. Keep in mind a box is 6-sided, with four walls, floor, and ceiling. The floor and ceiling are as important as the walls in the science of how you protect the plants in CEH. If you are renovating an existing warehouse with steel trusses, consider that those trusses are exposed or directly connected with the exterior cladding. As a result, heat is transferred via conduction. If the external temperature is freezing or below, that temperature is conducted thru the truss, causing the humid air in the grow room to condense on the steel truss and begin to drip on your plants. Floors play a significant role as well, do not ignore the floors! Many flooring options depend upon what your base building presents you with. Do not leave exposed concrete. Work with your team to find a sealant, epoxy, or solid surface that will be durable, cleanable, and slip resistant.

3. Quarantine

   It is not just for covid anymore! Prior to covid-19, we have heard many debates about what a quarantine room should be used for in CEH. It is no longer up for debate, do not bring “stuff” into your grow environment that does not belong there, use a quarantine room as a buffer. First, strip all packaging in the shipping/receiving bay and push it back out and dispose of it. Store in-bound materials in quarantine for a period based on your protocols, develop and follow SOPs and SSOPs. We have employed heat treatment as well in these rooms. Line the walls with resistive materials and heat to a temperature that will kill stored-product insects. (62° C, or 143.6° F) Kansas State Entomology Paper.

4. Cascading airflow plus Air-locks

   Create a detailed plan with the Engineering team to cascade the air from positive areas to negative areas. Slightly positive pressure in grow rooms is typical, often with a range between 200 – 300 cfm. Corridors can be neutral or somewhat negative pressured. The system should be tied into the whole-building ventilation system and pushed out through one point of discharge, which should be considered this part of your odor control plan. Airlocks should be used between use types (functional areas) and at the ends of corridors depositing to the exterior. Locating airlocks between functional areas is vital to control IAQ and cross-contamination. integrated facilities typically have 3 use groups: business, manufacturing, horticulture. (International Building Code (IBC) chapter 3; use and occupancy classification) Planning and design efforts should be made to keep staff and products localized to the functional area, avoiding moving through one to get to another. WHO Technical Report Series No. 961, 2011.

5. CO2 matters, more for plants than for people, but you cannot ignore the people.

   To perform photosynthesis, plants need three things: Carbon dioxide, water, and a light source with the appropriate DLI and PPFD. To achieve the desired levels, CO2 systems are now very commonplace. A common, safe system places a vendor-supplied tank outside the facility piped to an injection system designed to put the CO2 directly into the Air Flow for each grow room. Most growers target between 1200 to 1500 ppm of CO2 for enriched environments. Building codes target 5,000 ppm as the harmful level to human health. A ubiquitous sight is a CO2 ejection system. It is commonly argued that it is code required, either by the Engineer of Record or by the Fire Marshal. I may be going out on a limb here, but there is a convincing argument against an emergency purge system. 

   1. There are too few gardeners in a grow room when CO2 is present to warrant the measure. I believe a monitor tied to an audible and visual alarm inside and outside a room is sufficient to protect the lives of employees. 

   2. The dump of enriched, conditioned air out into the neighborhood poses a sometimes-greater threat to the operator. That threat being an unwanted odor nuisance. Neighborhood odor mitigation is often a hard-fought battle at special permit hearings. 

   3. More penetrations in a roof mean greater chances of water leaks. 

   4. The system takes up floor space displacing plants. 

   This argument may be controversial because a human life cannot be measured against a plant. But I believe the alarm system is a valid security measure.
   

*The panel was Titled Airing It Out: Creating & Maintaining A Clean Production Room Environment Sponsored by Indoor Ag-Con. It was wonderfully moderated by Dr. Nadia Sabeh, PhD. on March 24, 2021. My co-panelists were Jeremy Schechter, Director of Cultivation, Buckeye Relief and Trent Thiel, Industrial Molecular Filtration Product Manager for North and South America, Camfil Americas. The ideas here do not necessarily represent those of the other panelists.