How to Control Night Time Humidity in Grow Room
In the growing industry, night time humidity in grow room is a problem that many growers care about but often overlook. Why does humidity rise quickly after the lights go off? What hidden risks can high humidity at night bring? Can traditional dehumidifiers still work well during the night? These questions affect not only plant health but also the final yield and quality.
This blog will explore these common questions. We will explain what causes humidity changes at night, what risks they may lead to, and why traditional control methods may not be enough. In the end, we will also introduce a more efficient and professional solution. It can help growers keep the climate stable at night and make the growing process more reliable.
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How Does Night Time Humidity in Grow Room Differ from Daytime?
Humidity in a grow room does not stay the same all day. Many growers notice a big difference between day and night humidity levels. After the lights go off, the humidity often rises quickly. In this section, we will look at how humidity changes between day and night in a cannabis grow room.
Typical Daytime Humidity Levels in Grow Rooms
To understand night time humidity in grow room environments, we first need to look at what happens during the day. This helps explain why humidity changes so much at night. Daytime plant activity plays a key role.
Humidity Range During Lights-On Phase
Cannabis plants need different humidity levels at each growth stage. During the day, plants perform photosynthesis and transpiration. These are the main processes that affect humidity. In the vegetative stage, plants grow new leaves and stems quickly. They also release more water into the air. This means humidity can be higher, usually around 40% to 70%, which helps cell growth and nutrient movement.
When plants enter the flowering stage, they stop growing many new leaves. Instead, they focus on building flowers. At this time, humidity should be lower—around 40% to 50%. This level still supports healthy transpiration while reducing the chance of disease.
Influences of Light and Plant Activity on Daytime Humidity
During the day, cannabis plants are very active. Once the lights are on, the stomata (tiny openings on leaves) open up. This starts the transpiration process. Water from inside the plant moves into the air. As this water builds up in the grow room, humidity levels rise.
If there are many plants in a small space, even more water is released at the same time. In areas with poor airflow, this can cause moisture to build up in corners or under the canopy. These spots can become hidden humidity risks.
Typical Night Time Humidity in Grow Room
After learning about how cannabis plants behave during the day, we can now look at what happens at night. Once the lights go off, the plants change their behavior. These changes are one of the main reasons for rising night time humidity in grow room environments.
Observed Humidity Rise After Lights-Off
When the lights turn off, temperature and light levels drop quickly. The plants go into a rest mode. Their stomata close, and transpiration slows down. At first, it may seem like humidity should go down since plants release less water. But in reality, humidity often goes up. This happens because cooler air can hold less water. So, the moisture stays in the air or condenses, and relative humidity increases.
Night Time Humidity Range
Without special dehumidification at night, relative humidity in grow rooms can rise by 20% to 40%, or even more. The exact rise depends on many things. These include the starting humidity before lights-off, the temperature difference between the air and surfaces, the amount of water stored in the plants, and how much transpiration is still happening after lights turn off.
What Causes Night Time Humidity Changes in Grow Room?
We talked about how night time humidity in grow room often rises quickly after the lights turn off. But why does this happen? Is it just because the dehumidifier is not working? Not exactly. The change in night time humidity is caused by many things. It involves changes in plant behavior and how the grow room system controls the environment.
Reduced Transpiration and Stomatal Closure
During the day, plants open their stomata. They take water from the roots, move it to the leaves, and release it into the air. This helps cool the plants and adds moisture to the air. But at night, after the lights go off, the stomata close and transpiration slows down.
Many people think humidity won’t rise if transpiration stops. But that’s not true. Less transpiration means the water vapor stays in the air. The humidity from the day doesn’t leave. If the HVAC system doesn’t increase dehumidification at night, moisture builds up quickly, making the air humid and increasing disease risk.
Temperature Drop and Relative Humidity Increase
Temperature and humidity are closely connected. When the air cools, it can’t hold as much moisture. For example, 26°C air can hold more water vapor than 21°C air. When the temperature drops after lights go off, even if the amount of moisture stays the same, the relative humidity goes up fast.
This is because relative humidity measures how full the air is with moisture at a certain temperature. So, as temperature drops at night, relative humidity can rise from 50% to 75% or higher, even without adding any new water to the air.
Lower System Activity or Shutdown
After lights go off, the heat load in the grow room goes down. Many growers reduce HVAC operation. But in most systems, dehumidification only works during cooling. If cooling slows down, dehumidification slows too.
If there is no separate dehumidifier running at night, moisture stays in the air. Without proper control settings for night time humidity in grow room, humidity can quickly build up.
Plant Density and Growth Stage Factors
The more plants you have, the more water they release into the air. If this moisture isn’t removed during the day, it will collect at night and cause high humidity.
Also, different growth stages affect humidity. During the vegetative stage, plants transpire more, and the room fills with moisture during the day. This causes a faster rise in humidity at night. In the late flowering stage, plants transpire less, but water builds up inside the plants. This makes it harder to remove moisture from the air, and night time humidity in grow room can become harder to manage.
What Risks Come with Sudden Spikes in Night Time Humidity in Grow Room?
We have already discussed how reduced transpiration, falling temperatures, and weak system operation can all cause night time humidity in grow room to rise quickly. It may seem like just a small humidity increase, but if it is not controlled in time, it can lead to serious problems. These include plant health issues, system stress, and higher operating costs.
Increased Risk of Mold, Mildew, and Botrytis
High humidity brings a higher risk of plant disease. When humidity stays above 70% for a long time, mold, mildew, and Botrytis are more likely to appear on plant surfaces. At night, airflow is weaker. Water may condense on leaves and buds, making them wet and creating a perfect place for fungus to grow.
Botrytis is one of the most common and harmful diseases in cannabis growing. It often shows up in late flowering. If it spreads, it can lower your yield or even ruin your whole crop.
VPD Imbalance: Transpiration Disruption and Nutrient Stress
High night time humidity in grow room can break the balance of VPD, which controls how plants breathe and move water. In humid air, the difference in water pressure between leaves and the air becomes small. This slows transpiration and makes it harder for plants to move water and nutrients from roots to leaves.
When this happens, plants may not get enough nutrients. You might see signs like soft leaves, dry edges, or yellowing. In the long run, flower growth can also be affected.
Compromised Bud Quality and Yield
Flower quality and yield depend on a stable climate. High night time humidity in grow room can hurt flower shape and weight. Moisture in the air can make buds swell and become loose. This lowers their density and dry weight.
If moisture stays inside the buds, it can lead to mold, even if the outside looks fine. Also, high humidity reduces the plant’s ability to absorb key nutrients. This affects the production of terpenes and flavonoids, which lowers flavor, quality, and value. Over time, this may reduce your total yield and profits.
System-Level Consequences of Humidity Surges
When humidity rises fast at night, the HVAC and dehumidifiers must work harder. At night, the cooling load is low, so HVAC systems run less. This also lowers their ability to remove moisture. As a result, systems turn on and off more often. This causes faster wear and reduces efficiency.
Dehumidifiers may still run, but if the humidity load is too high, they must work at full power for too long. That shortens their lifespan. Also, moisture may form on cold parts like ducts, coils, and lights. If water cannot drain out, it may lead to rust, mold, or even electrical risks.
Increased Energy Costs and Climate Instability
If night time humidity in grow room is not under control, systems must keep adjusting. HVAC and dehumidifiers may run at full speed for a long time. Or they may start and stop too often. This wastes energy and raises power bills.
Humidity swings also make it hard to control both temperature and moisture. The indoor climate becomes unstable. This affects plant growth and lowers the overall control accuracy.
The Limitations of Traditional Humidity Control Solutions at Night
In cannabis grow rooms, humidity control is an important part of climate regulation. Many growers still use traditional methods. These methods work well during the day. But when night time humidity in grow room rises quickly, the weaknesses of these systems become more obvious.
What Constitutes Traditional Humidity Control in Grow Rooms?
To manage humidity, growers often use several types of common systems. Each method has its own strengths and limits. Their designs and results are different in practice.
Standalone Dehumidifiers
Standalone dehumidifiers are one of the most common devices. They are often used in small and medium-sized grow rooms. These machines are designed to remove moisture from the air.
They are easy to install and cost less. But they often only cover part of the space. When placed in one corner or side of the room, some areas stay too humid. These are called dead zones.
HVAC Systems
HVAC systems are mainly built to control temperature. Dehumidification is only a side function. It works by cooling the air so that water condenses and drains away.
Ventilation-Based Humidity Dilution
Some growers use ventilation to control humidity. This method brings in fresh air and pushes out humid air.
It can work well in dry seasons or dry regions. But in humid places or sealed rooms, it often fails. It may even bring more moisture inside. Also, ventilation cannot control humidity very precisely. It is not good for dense plant setups or stages with strict humidity needs.
Why Traditional Systems Struggle with Night Time Humidity in Grow Room Environments
We have looked at several traditional humidity control systems commonly found in grow rooms, but most of these systems are designed for daytime conditions. When night time humidity in grow room rises quickly, these systems usually respond too slowly. They also remove less moisture and waste more energy.
Coupled Load: Cooling Reduction Lowers Dehumidification Capacity
Most HVAC systems remove moisture while cooling the air. At night, when grow lights turn off, the room gets cooler. The HVAC system stops because it reaches the set temperature.
But plants still release moisture slowly. When the air cools, it holds less water. This causes the humidity to rise. Since the system sees the temperature is okay, it does not turn back on. So it also stops removing moisture.
Lack of Real-Time Feedback or Smart Controls
Most traditional dehumidifiers follow simple rules. They turn on only when humidity is higher than a set level. They do not adjust based on real-time changes.
At night, humidity can rise suddenly. If the system cannot sense this quickly, humidity stays high for too long. This increases the risk of plant disease. Without smart controls, the system cannot adjust from far away or react to plant growth needs.
High Energy Consumption Due to Inefficient Cycling
Traditional air conditioners and dehumidifiers often work against each other. The dehumidifier adds heat while removing moisture. Then the air conditioner needs to cool down the extra heat again.
This cycle wastes energy. The machines turn on and off too often. This lowers efficiency and raises energy bills. The result is unstable temperature and humidity. That hurts the plants’ growing environment.
Poor Spatial Distribution of Dehumidification
Standalone dehumidifiers or HVAC systems with poor airflow cannot cover all areas evenly. Wet spots often appear in corners, under racks, or between plants.
At night, air moves more slowly. Moisture can stay in these spots and create high humidity zones. Mold may grow there. Without good airflow design, the system may not detect these risks. That makes control harder.
Achieving Efficient Dehumidification with Altaqua Grow Room HVAC System
Traditional humidity control methods have limitations when dealing with night time humidity in grow room environments. To solve this issue better, a modern integrated HVAC system is more suitable for the strict climate needs of cannabis growing.
Dew Point-Based Dehumidification: Going Beyond RH Control
In a grow room, looking at only the relative humidity is not enough to know the real amount of water in the air. Relative humidity changes with temperature, even when the actual moisture in the air stays the same. This can lead to wrong judgments.
For example:
When the temperature is 27°C and the relative humidity is 90%, the dew point is 25.2°C.
If the humidity drops to 80% but the temperature is still 27°C, the dew point becomes 23.2°C.
If the temperature rises to 30°C and the humidity goes back to 90%, the dew point becomes 28.2°C.
On the surface, the changes in relative humidity seem small. But the actual moisture level, the chance of condensation, and the need for dehumidification are all different. If you only use relative humidity to decide whether to dehumidify, you may respond too slowly because of temperature changes.
Altaqua Grow Room HVAC System uses dew point-based control. It looks at the real amount of water in the air. When the current dew point is higher than the target, the system turns on the compressor to remove moisture. It keeps working until the dew point drops to a safe level. This method is more accurate and not easily affected by temperature changes.
Simultaneous Temperature and Humidity Regulation
In traditional grow rooms, temperature and humidity are controlled by different machines. These machines do not work together. When humidity changes fast, the systems cannot keep up. You may fix the temperature, but the humidity goes up. Or you fix the humidity, but the temperature becomes unstable. This makes it hard to keep the grow room steady.
Altaqua Grow Room HVAC System has an all-in-one design. It puts cooling, heating, dehumidifying, and air circulation into one unit. The system has four modes: dehumidifying with cooling, dehumidifying with heating, dehumidifying with temperature control, and air circulation mode. These modes help manage both temperature and humidity at the same time.
When night time humidity in grow room environments rises while the temperature drops, the system does not keep cooling. It changes to dehumidify + temperature control mode. This mode removes extra moisture and adjust temperature to the target. During the day, when temperature increases, the system switches to dehumidify + cooling mode. It removes water and cools the air at the same time. This way, the system can handle day and night changes and help plants grow in a steady environment.
WiFi Control Provides Easy Access and Control
In grow rooms, fast reaction and easy control are very important. Altaqua Grow Room HVAC System has WiFi control. Growers can use the internet to check the system anytime. They can see real-time data about temperature and humidity. They can also change settings even if they are not in the grow room.
This 24/7 online control helps keep the system running well. It also saves time and lowers service costs. If humidity levels are wrong or if there is a system problem, the unit sends out a warning. This helps the grower take quick action before the problem gets worse.
The system also works with Modbus protocol. It can connect to a building management system (BMS). For large grow rooms or big projects, this makes control easier. It also helps reduce mistakes and saves labor.
Built-In Redundancy for Mission-Critical Reliability
If a climate system breaks down in a grow room, the plants can be harmed quickly. To avoid this, Altaqua has specially enhanced the "built-in redundancy" capability in the design of the HVAC system in the grow room. Even if one part stops working, the system can keep running and protect the environment.
The system uses separate control circuits. Important parts like EC fans, electrical controls, and compressors each have backup units. If one circuit fails, the others keep working. This design makes sure the system is stable, even if problems happen at night. It helps control night time humidity in grow room spaces without interruption.
Conclusion
Night time humidity in grow room settings is often not taken seriously. But it is a key factor for healthy plants. By understanding how humidity works, avoiding the limits of old systems, and using smart and efficient climate control, growers can better manage night time conditions. This helps protect the plants and improves both quality and yield.
FAQ
1. Why does night time humidity in grow rooms increase after lights go off?
When lights turn off, air temperature drops, reducing its ability to hold moisture—this raises relative humidity. At the same time, plant transpiration slows, and HVAC systems often reduce cooling, leading to less dehumidification. These combined effects cause humidity to rise at night.
2. What is the ideal humidity range at night for cannabis grow rooms?
The optimal night time humidity in grow room settings vary by growth stage. During the vegetative phase, 50–60% RH is typically ideal, while flowering requires lower levels around 40–50% RH to prevent mold and botrytis. Sudden spikes beyond this range, especially above 60%, can lead to serious plant health issues.
3. Can high night time humidity cause bud rot or mold?
Yes. Night time humidity in grow room environments that exceed safe thresholds create a breeding ground for mold, mildew, and botrytis (bud rot). Lack of airflow, high RH, and cool surfaces at night accelerate condensation and spore growth, especially during late flowering when buds are dense and sensitive.
4. Why do traditional HVAC systems struggle with night time humidity control in grow rooms?
Most traditional HVAC systems link dehumidification to cooling. At night, reduced heat load causes the system to scale back cooling, and therefore, its dehumidification drops. This results in poor night time humidity in grow room control. Additionally, these systems often lack smart feedback, coordination between humidity and temperature, and targeted moisture removal in all room zones.
5. How does dew point control help manage night time humidity in grow rooms?
Unlike relative humidity, dew point offers a more stable measurement of moisture content in the air. Controlling night time humidity in grow room setups by targeting dew point ensures precise activation of dehumidification regardless of temperature changes. This method prevents under-dehumidification that can occur when relying only on RH values that fluctuate with temperature.
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