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Hot Weather Growing – Cannabis Cultivation in Extreme Climates

There are so many options for climate control in cultivation facilities, and it’s possible to implement an affordable, energy efficient system that meets your budget and lasts for decades - even in hot weather cultivation climates. Start by choosing a qualified, experienced mechanical engineer like Surna for your team to help evaluate those options and ensure that you stay on the path to profitability, even under the extreme conditions of the Arizona desert.
December 16, 2020

We all know that American politics have been a bit volatile over the last several years (speaking of being hot outside), and the only thing predictable in this election cycle was that it would lead to arguments on social media. (Do we win an award for understatement with that sentence?). However, regardless of which side of the aisle you sit, one thing we can probably all agree on is that the most recent election cycle resulted in a lot of good news for our industry. We know we weren’t the only ones cheering for those hard-won victories in Arizona, New Jersey, South Dakota, Mississippi and Montana.

The cannabis industry is unique in that each new market comes with its own regulatory environment. State by state, and even city by city, the rules of engagement are variable from cultivation to processing to distribution and retail. The same is true of the climate in each new market. It’s our job at Surna to understand in precise detail what cultivating in a new climate will require of the environmental control system. With that in mind, we thought it might be helpful to speak to some of the specific requirements and challenges of climate control in unique geographies, which we’ll be doing periodically over the coming months.


Cultivating in Arizona means managing extreme climate conditions of hot weather growing. Some areas of Arizona also experience extreme cold, which we will discuss later in this series. When designing for controlled environment climate systems in hot weather cultivation climates, mechanical engineers must understand how the heat and humidity impact the load calculations inside the building, as well as how the equipment outside the building will be affected.

Climate control systems designers need to understand which climate control approaches are most suitable for hot weather cultivation to ensure that growers consistently meet their target parameters while minimizing energy use and upfront costs. This requires expertise in both the intricacies of designing for controlled environments, and of doing so in extreme climates. That kind of expertise only comes with experience doing both


High ambient conditions impact the design of the climate control system in several ways. First, the load calculations must consider the additional solar gain and ambient heat load that will raise the temperature of the building. The impact of outdoor heat on an indoor cultivation environment is a fraction of the overall heat load.

The primary driver for sensible heat is the lighting in the space, but it can still add up quickly, especially when conditions are extreme. Extreme hot weather can be mitigated by more efficient insulation of exterior walls but will always have some impact and will need to be accounted for in the load calculations.

Even more significant is the derating of the climate control equipment outside the building. Most climate control systems in cultivation facilities are air cooled. This means that heat is absorbed from the building through a chilled water or refrigerant system, then removed from the cooling media and rejected outside when the outside air passes over the air conditioning unit’s condenser coils. The hotter it is outside, the less heat can be rejected, and the less effective air cooling the condenser coils becomes.

HVAC systems are rated for output based on specific nominal conditions, and as temperatures exceed those conditions, their cooling capacity decreases. Put simply, the hotter it is outside, the less cooling output they’re capable of producing. Extreme ambient heat can derate air cooled systems by as much as 30%, which must be accounted for when sizing air conditioning compressors or chiller plants.

Some cultivators opt to utilize water-cooled condensers to avoid the worst impacts of equipment derating in extreme heat. These systems utilize water, as opposed to air, over the condenser coils as a method of heat rejection. Water is more conductive than air, and has higher heat capacity than air, which allows the condensers to reject heat more quickly than with air cooled unit. This increases energy efficiency and minimizes the effects of derating in extreme heat.

However, water cooled condensers also result in higher upfront costs, and more complex maintenance, so they only make sense in certain applications. Make sure you work with an experienced mechanical engineer who can help you evaluate all the options to ensure that you’re making the right decision for your unique facility.


Apart from equipment derating, growing in hot weather is simply harder on the equipment. The use of electricity and the operation of moving parts create heat just by nature of the equipment’s operation. When you add extreme outdoor temperatures, the associated wear and tear increases. It’s important to consider ambient conditions when selecting equipment, and that industrial grade equipment intended for year-round use in these kinds of conditions be selected. Otherwise, the cultivator is likely to face early failure and excessive service calls.

Equipment that utilizes refrigerant is also susceptible to fluctuations in refrigerant pressures related to the outdoor conditions. Certain pieces of equipment might require the addition of extreme high ambient kits so the owner can be assured that it will continue to function during the hottest months of the year.


In high heat or desert climates, ambient relative humidity is extremely low during most of the year. Because of this, it’s likely that cultivators will need to humidify cultivation environments during the vegetative growth phase and often into early flower. However, many new cultivators are unpleasantly surprised by how much dehumidification they’ll need during flowering growth.

When cultivating on a commercial scale, even in very dry environments, there is so much water being transpired during flowering growth that humidity will still need to be carefully managed by the climate control system. Understanding this is one of the many reasons to work with engineers with a strong background in cultivation facilities.


In new geographies, prevalent biosecurity risks may be different. It’s very common for experienced cultivators to be surprised by an outbreak of one pest or fungus or another, after having no experience with it in previous facilities. If this occurs, the team has to identify mitigation and operating protocols that they may not have previously considered. This can impact quality and yield in those early harvests.

As your cultivation practices evolve, HVAC-D system performance will also require dialing-in. The performance of the climate control system is calculated at the engineering level based on cultivator inputs. These inputs include irrigation schedule and volume, lighting schedules and intensity, and desired parameters. If there are deviations in practice from these early stage assumptions during design (and there almost certainly will be), adjustments will be required. Ideally, you’ll have worked with an experienced HVAC-D designer like Surna who can help you plan for these contingencies affordably at the design level.


There are so many options for climate control in cultivation facilities, and it’s possible to implement an affordable, energy efficient system that meets your budget and lasts for decades – even in hot weather cultivation climates. Start by choosing a qualified, experienced mechanical engineer like Surna for your team to help evaluate those options and ensure that you stay on the path to profitability, even under the extreme conditions of the Arizona desert.

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