Canadian Consulting Engineer

The cannabis industry’s need for better HVAC

February 12, 2020
By Geoff Brown

Central chillers aren’t working out. Is there a better way?

Cannabis grow room

Photo courtesy Agronomic IQ.

Scalable HVAC systems are essential for the cannabis industry as it continues to ramp up production across Canada and in the U.S. While central chillers have provided a tried-and-true solution for projects requiring large refrigeration capacity in college campuses, hospitals and office buildings, among other facilities, they have fallen short in this particular industry, where grow rooms need specific, variable conditions and redundant infrastructure. This raises the question: is there a better way to design HVAC systems for these rooms?

What’s wrong with chillers

Many cannabis growers are building out their facilities in phases. This is a practical requirement in some jurisdictions where growers must already have some harvests before they can receive a production permit; so, they build just one phase to satisfy the requirement, then build out the facility further after receiving government approval.

This strategy is not so feasible with a central chiller. A chiller and its supporting infrastructure are impractical to expand. Instead, it will need to be built to its full size for day one of production, even though the facility will only be in partial occupancy for a long time. This means high upfront capital costs.

Even if the facility needs to expand later on to meet increasing market demand, the expense of adding capacity to a central chiller will be difficult, if not altogether prohibitive.

Additionally, a central chiller creates a central point of failure. When it goes down, crops in every room are at risk of potentially devastating loss. Grow rooms are different from most other indoor facilities in terms of their requirements for strict conditions. Even a slight change could have big impact on the crop. Losing HVAC control due to mechanical failure could spell disaster.

By way of example, one cannabis grower in Ontario encountered these issues after constructing its facility with a central chiller for cooling and dehumidification, built for full size. The results were disappointing starting with the first phase of cultivation. While sensible demands in the space were easily met, the humidity levels were out of control, with flowering rooms up to 75% relative humidity (RH).

Humidity is one of the most important aspects to control. Without a handle on it, growers risk losing their entire crop—either because (a) there is not enough humidity and the plants’ growth slows due to drought resistance mode or (b) there is too much humidity and the plants are at risk, e.g. of mould disease. While the Ontario facility has not yet reported serious crop issues, the grower must now be mindful of the potential impact of the central chiller on harvest quality.

Careful consideration is needed before selection. Typical chilled-water system designs can get their coils cold enough to lower the air temperature sufficiently, but often lack the elements necessary to effectively condense water out of the air. A properly designed dehumidifier coil, on the other hand, is capable of both air conditioning and dehumidification.

Also, a chilled-water system capable of adequate dehumidification for a typical flower room will also require full-time reheating to ensure the air delivered to the plants is not shockingly cold, which could stunt their growth or kill them altogether. Adding a reheat source, however, adds complexity, cost and inefficiency, which does not serve growers well when they are under pressure to reduce energy consumption.

How unitary systems solve problems

Compared to central chillers, a unitary setup is more agile. A facility can commence cannabis production with the minimum capacity it needs for its start-up phase, then add more units in the future as required. They are generally cheaper to install than a central system and offer additional reliability and efficiency benefits.

The primary business advantage to this approach is cash flow, as it spreads out costs over time, rather than requiring a large, immediate expense of constructing an entire facility and chiller for day one.

Growers can also enjoy more control over their crop by installing multiple units to provide varying conditions, on a room-by-room basis, instead of relying on a single system that can only provide one condition.

Flowering rooms containing different strains of crop may require different conditions, so it is beneficial for them to be served by their own units to provide variability. Meanwhile, rooms that need uniform conditions could be served by one common unit. There is plenty of flexibility possible with this approach.

Some growers have opted to install multiple units for the same room, which maximizes redundancy in case one of the units fails. A cannabis facility in the Montreal area, for example, went in this direction with its HVAC system. Rather than build everything in one shot, the facility was set up with a unitary design that used multiple units for the grow rooms. The units were sized to provide more capacity than is currently required in each room, which means more plants and lighting can be added in the future if desired.

This grower expects to build more rooms in a future phase, so it was important to deploy an ‘intelligent’ HVAC system that could accommodate the increased capacity, which will be accomplished simply by adding more units.

After making a significant initial investment in this facility, the grower was also averse to the risk of losing any crops due to mechanical failure; hence the need for a system of independent grow room control.

Multiple small systems can also represent a better return on investment (ROI). For one thing, downtime for maintenance is minimal, as parts are easier to switch out than with a large, central system. For another, some units can recycle the heat created by the dehumidification process and then efficiently reheat their cold discharge air, helping keep the space’s temperature consistent without needing supplementary heaters. There is also the option of economizer cooling, which can reduce or even eliminate compressor use during winter, by using chilled water provided from an outdoor dry cooler.

Facing limitations

As demand for cannabis production continues to increase, many growers across North America are looking to expand their businesses by adding new facilities or augmenting existing ones. Faced with the limitations of traditional chiller systems in terms of flexibility, scalability and redundancy, they will need to find more intelligent systems. There are benefits to considering the unitary equipment approach.


Geoff Brown is director of Agronomic IQ, which provides temperature and humidity control equipment for grow rooms, and a contributing member to the American Society of Agricultural and Biological Engineers’ (ASABE’s) X653 guideline, HVAC for Indoor Plant Environments Without Sunlight. For a free copy of his new book, Getting Grow Rooms Right, visit to order a digital or printed edition.


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