Climate Control Systems

Dr Photon
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Controlling humidity is an important aspect of growing cannabis and has a large impact on plant health and development. Plants use valve like systems on the underside of their leaves called stomata, which controls the uptake, movement and release of water through the plant. This process is called transpiration. Transpiration is important for several reasons. Such as the movement of minerals, as it uses the transpirational stream as a vehicle to transport nutrients from the roots to the shoots. It is also important for sensible heat loss, as it cools its self through evaporative cooling processes. And gas exchange, where the byproducts of photosynthesis (oxygen) is released and co2 absorbed to complete the carbon cycle of photosynthesis.



Temperature is important not just for a plants overall health but especially for the efficiency of photosynthesis, which is highly dictated by temperature and benefits from a well maintained thermal regulation. Low or high temperatures have significant effects on the processes involved with photosynthesis. And so maintaining temperature becomes a top priority for optimal growing conditions.



Co2 is a major component for photosynthesis, which without it would stop photosynthesis entirely. Plants will uptake these gases in significant quantities which require it to be taken into consideration when setting up grow systems. 



Controlling the internal environment is typically done in two ways. A sealed or air exchange systems. Both have advantages and disadvantages which suit a particular growers needs, depending on what they are ultimately looking for. I will cover both in detail here.


Sealed System:

A sealed system is exactly that, a grow environment that is sealed and operated along side conditioning equipment to control the internal air characteristics. Such as humidity, temperature and co2. A sealed system offers more precise control over the environment which is not influenced by the external climate conditions, but at a greater cost. As more equipment and energy is needed to create an environment that is perfect for cannabis. Its this additional cost factor that is the reason why it is typically not suited for small personal grows. And best left for the larger cultivation systems.


Air exchange system:

An air exchange system is where airflow is used, such as with an exhaust, to replace the internal air with the external air. This is a more simple and usually more economical approach to controlling the internal air conditions. As venting hot and humid air, is less energy expensive than using conditioning equipment. However this type of system is limited in its ability to control the internal environment, as it is always fixed to the maximum potential of that of the external air characteristics. What this means, is that you can only ever attempt to bring your internal air to the same condition of that of the external air. And so any fluctuations brought about through natural shifts in weather. Will have a significant effect on the internal air characteristics.



Controlling the internal air with air exchange systems can be improved by using different configurations, equipments or techniques. 


Thermostats, hygrostats and fan controllers:

Thermo and hygrostats are important for more precise control of exhaust and conditioning equipment. Which maximizes the benefits of air exchange systems. Many systems can only control one variable and so must be configured at times to adjust to the climate shifts. Better systems allow for multiple variables such as temperature and humidity to be controlled. With the best systems providing the ability for Multi stage configurations to allow for differential demands of the lighting cycles. 

Speed controllers for fans can help to control environmental conditions, however are limited as they provide no feedback to respond to shifts and require constant manual manipulation and cannot be rationally maintained effectively.


Climate control equipment:

Because air exchange systems depend on the external air for replacement. This means that the internal air qualities are limited to the maximum potential of that of the external air. And if any conditions such as humidity or temperature shift, then so will the internal air. When these external air conditions fall outside the ideal values, the only way to rectify this is by conditioning the air.

Conditioning equipment such as AC units, Heaters, Dehumidifers, humidifiers and co2 supplimentation, can be used with air exchange systems. To provide additional control of internal conditions when the external air is not sufficient. The difficulty with using conditioning equipment with air exchange systems is high, because the air that has been processed can be vented too quickly and provide very little benefit. There must be time allowed for the equipment to process the air before it is allowed to be vented. This requires attention to detail with certain configurations with equipment and switches. Such as hygro and thermostats. The equipment needs to also be powerful enough to make significant changes to the environment for it to be beneficial.


Equipment Placement:

The placement of the conditioning equipment such as heaters and dehumidifiers, depends on many factors that will determine where its best to position them. Such as space availability, exhaust configuration, ambient conditions etc. If there is no space left for conditioning equipment in the grow area, then your only option is to precondition the air in another environment, such as a small room or attic. And then use that air for the intake of your grow system. This preconditioning is a better choice compared to placing the equipment inside the grow system, as it allows more volume for air to be conditioned before being removed by the exhaust system. Providing better uniformity and climate control.


Light Cycles And Seasons:

When its best to run your light cycles, for example during the day or night, will depend on your geographic location and environmental weather characteristics. With seasons or locations where the external temperature is high during the day. It can be best to run your lights during the night, to avoid lowered photosynthetic efficiency due to high temperatures. With seasons or locations where external temperature is low. It can be best to run your lights during the day, to avoid lowered photosynthetic efficiency due to low temperatures. Managing your light cycles for the climate and seasons will provide better control and efficiency of your grow.


So its not a clear cut process when using air exchange systems. There is a never ending issue of fluctuation and requires attention to detail when assessing whats the best way to control it. This can mean changing the configurations several times a year depending on how dynamic your weather conditions are.




Air Exchange System Configurations Based On Seasons Or Geographical locations:

What season you may be in or the geographical locations that dictate your general ambient air characteristics has an impact on what the ideal configurations and systems chosen should be for ventilation systems. And understanding and knowing what these may be, are quite often difficult and unclear. With very little material available on the subject providing clear and definite rules for such situations. Here i attempt to do this, so that you may know what is required in order to at best, control your environment for optimal results in your growing venture. While minimizing wasted energy by using thermo and hygro stats in a configuration that only ventilates the system when required. This is important to prevent preconditioned air from being ventilated too quickly and wasting valuable energy and lowering efficiency.

Here we cover most if not all environmental conditions and the suitable configurations for managing your internal grow space for ideal air quality. This includes balanced, cold and hot climates with either high or low ambient humidities. Allowing you to control your system in nearly any climate state.


Balanced Ambient Climates:

Balanced ambient climates are ideal for growing, as cannabis thrives best in warmer environments and demands less energy from additional heating or cooling systems. This can enable the most simplest form of climate control, when conditions are all optimal. And only a single exhaust fan is required to vent additional transpired moisture from plants, and any heat from lights. With the exhaust fan connected to a thermo and or hygrostat for consistent climate control.

In balanced climates with high humidity, a dehumidifier can be used to condition the moisture of the air. Combined with a hygrostat to provide seamless control and response to environmental shifts.

In balanced climates where humidity is low, humidifiers with hygrostats can also be used to effectively increase the humidity of the dry air.


Hot Ambient Climates:

Hot climates where temperatures exceed that of ideal growing conditions, creates problems that adds additional complexity and cost to the grow. If temperatures exceed 30°C, then cooling systems such as air conditioning units may be used in order to prevent excessive reduced rates in photosynthesis and growth.

These air conditioning systems are best controlled with a thermostat (ideally with the sensor in the grow space) and the exhaust with a hygrostat. This combination allows the system to vent only when necessary and the conditioning system to have maximum effect, instead of being wasted by the exhaust. Since the external air temperature exceeds the ideal levels for growing, applying a thermostat on the exhaust is not recommended and will be venting air continually in the fight to bring down temperatures, which will be impossible when the temperature of the air being replaced is already high.

In hot climates with high humidity, a dehumidifer can be used to condition the moisture of the air. Combined with a hygrostat to accurately control these levels. 

In hot climates where humidity is low, humidifiers with hygrostats can also be used to effectively increase the humidity of the dry air.

When dealing with extreme conditions such as these, where high heat is problematic and ambient humidity levels are inconsistant. There can reach a point where the cost is too great and the external air is offering no benefit. And a closed system is more ideal for your situation. Where all internal environment conditions are controlled by equipment such as heat pumps and humidity control equipment. So you must asses this to see whether you benefit from a completely closed system, rather than a air exchange one.


Cold Ambient Climates:

Cold ambient conditions can be just as difficult as hot climates, where several systems are used in order to maintain the internal air quality. In cool climates, exhaust systems are best connected with hygrostats. To allow the system to only ventilate when necessary and limit the amount of heat loss through ventilation. This prevents excessive loss of valuable heat energy and improves the efficiency as much as possible.

To bring low temperatures above ambient, a heater with a thermostat (ideally with sensor in grow space), such as a oil heater is used. This will allow the internal temperatures to be raised at ideal levels for optimal growing conditions.

When cool climates are humid, an additional dehumidifer with a hygrostat can be used to condition the airs humidity levels to satisfactory values.

With cool climates that are dry, a humidifier with a hygrostat can be also used to condition the airs humidity levels for optimal growing.

Just as with hot climates with unpredictable humidity characteristics. You may need to asses whether a closed system is better suited for your environment, rather than a air exchange system where the external air offers little value to the grow.


As always please comment your thoughts or any questions on the subject.


Being wrong, is an opportunity for getting things right.
Posted : 04/11/2019 7:15 pm SHODAN, Tommydjohnsonjr, Cali510 and 8 people liked
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Dr Photon
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Updated with further information on configurations.

Being wrong, is an opportunity for getting things right.
Posted : 09/12/2019 5:45 pm
Dr Photon
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Posted by: Rob123

Ok. So it shouldnt be too big of a problem for my reservoir temp to go up (within reason i assume). What temp would be too high for a drip system?

I ohnestly wouldnt worry about temperature at all. Using oxygenated solution with soilless substrates is just a, why not. But it wont really make a difference. Under deep water culture when plant roots are continually saturated in nutrient solution, temperature is of concern. Because the primary source of oxygen is through that which is dissolved in the solution. And so oxygen is continually being removed from the solution and replaced by pumping atmospheric rich oxygen into solution. Dissolved oxygen in water is limited to around 8%. So maximizing this is essential, as it directly effects plant development.

This is not the case with soilless culture. As the primary source of oxygen is from the porous structure of the media. And depends on the diffusion of gas from the atmosphere, to transfer oxygen to the media and replace what is taken up by the plants directly from the air filled structures or indirectly through dissolved oxygen through diffusion transfer.

Any oxygen that is stored in nutrient solutions and given to soilless grown plants. Will be quickly consumed within minutes. We are talking about 1% of the daily required oxygen content. The rest is sourced directly from the atmosphere through gas diffusion into the air filled pores within the media. Continually being removed by roots and replaced by gas diffusion.

Being wrong, is an opportunity for getting things right.
Posted : 01/02/2021 6:17 am takjr1976, Rob123 and CrackBabies liked
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Dr Photon
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This has been updated.

Being wrong, is an opportunity for getting things right.
Posted : 03/08/2021 6:43 pm