Climate Control Systems

Dr Photon
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Completed Grows

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Why We Must Use Climate Control Systems:

Humidity and transpiration:

No matter what kind of system you have, you are always going to need to remove at least some level of moisture that is created through transpiration. Plants transpire large amounts of water which if left unmanaged, can create problems such as fungal and bacterial diseases. So the removal of this humid air, is likely the number one priority with any air control systems. But you must also maintain ideal humidity levels because humidity has a direct influence on the transpiration rate (ignoring the temperature effect of VPD for this). Too low or high humidity can impact a plants overall health as the shift in transpiration can effect the levels of fluid and nutrient mobility and negatively effect the overall health of plants. 



Naturally when using high powered light sources such as LED, sodium and halide discharge, a large volume of energy is converted to heat through inefficient electrical conversion. This heat can be detrimental to the plants health, as high internal plant temperatures drastically influences photosynthetic effeciency.  We must also prevent low temperatures as this also has an influence on photosynthetic effciency.



Air that is not supplimented or replaced with new air, impacts plants as they require co2 to be able to complete the synthesis part of photosynthesis. AKA calvin cycle. Old air that has not been replaced can drop its concenteation of Co2 and limit photosynthesis and overall plant development.


Types Of Air Control Systems:

Controlling the internal environment is typically done in two ways. A Sealed system or a air exchange system. 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 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 its typically not suited for small personal grows. And best left for the larger cultivation grows.


Air exchange system:

An air exchange system is where a airflow system is used, such as an exhaust, to replace the internal air with the external air. This is a more simple and economical approach to controlling the internal air conditions. However this type of system is limited in its ability to control the internal environement, 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 conditon 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.


Control Techniques For Air Exchange Systems:

Controlling the internal air with air exchange systems can be improved by using different configurations, equipments or techniques. There is no simple setup that allows a fixed configuration and can handle all external environmental shifts. You will have to at times, adjust for these shifts in external weather to the best of your ability. 


Thermostats, hygrostats and fan controllers:

Thermostats and hygrostats are important for more precise control of exhaust and conditioning equipment. Which maximizes the benefits of air exchange systems. Speed controllers for fans also help control the exhaust systems and maintain an ideal air replacement rate for your conditons.


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 air quality factors such as humidity or temperature shift, then so does 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 the room your tent occupies if you are using tents.. And use that air for the intake of your grow system. This preconditioning is a better choice compared to placing the equipment inside the internal environment, as it allows more time for the air to be conditioned before being removed by the exhaust system and improves the distribution and uniformity of the conditioned air.



The seasons will change how your system may be configured and will not always be a static setup that is entirely dependent on sensor switches. You may have to constantly change your systems configuration, depending on the dynamics of external air characteristics.


Light Cycles:

When its best to run your light cycles, for example during the day or night, will depend on your geographic location and environment 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 temperature. 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.


Growth Stage:

The stage of growth can change the ideal configuration that is chosen with air exchange systems. For example, during vegetation, high humidity is less of a concern so systems can be configured to suit. During flowering, more so in the last half. High humidity is not ideal, so the system must be configured to control this.



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 Systems Configurations:


Air Exchange Systems 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.

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 warm, cold and hot climates with either high or low ambient humidities. Allowing you to control your system in nearly any climate state.


Warm ambient climates:

Warm ambient climates are ideal for growing, as cannabis thrives best in warmer environments and demands less energy from additional heating or cooling. This can enable the most simplist 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 heat from lights. With the exhaust fan connected to a thermostat for consistant temperature control.

In warm 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 warm 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 nesscary and the conditioning system to have maximum effect, instead of being wasted by the exhaust.

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.


Cool Ambient Climates:

Cool 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 nessecary 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 Tommydjohnsonjr, Cali510, Simplefarmer and 7 people liked
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Dr Photon
Member Moderator
Expert Grower
Completed Grows

Updated with further information on configurations.

Being wrong, is an opportunity for getting things right.
Posted : 09/12/2019 5:45 pm
Dr Photon
Member Moderator
Expert Grower
Completed Grows
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 Rob123 and CrackBabies liked
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