Stable planning of supply air temperature control in the Hydro-Grow

Introduction

In hydroponic cultivation, cannabis reacts particularly quickly to climatic errors. Without a substrate buffer, abrupt changes in temperature and humidity have an almost immediate effect on transpiration. This is precisely why air temperature control is a climate issue in its own right: it is not only the amount of fresh air that counts, but also the temperature and humidity at which it enters the room.

Supply air that is too cold or too warm creates local stress zones, unstable leaf surface temperatures and strong fluctuations in evaporation behavior. This can lead to imbalances more quickly in the hydro system than in soil, because the plant reacts more directly to climate changes. At the same time, it is important not to lose sight of the basic hydro values: reservoir 18-22°C, good oxygen supply to the roots, clean reservoir hygiene and precise control of pH 5.5-6.0 and EC.

Why supply air is trickier in Hydro-Grow

Fresh air is necessary, but its entry can cause problems if it hits the plants or system unchecked.

Typical consequences of poorly managed supply air:

• Cold air jets lower the leaf temperature locally and push transpiration unevenly.
• Very dry supply air** abruptly increases the evaporation pressure; plants react with stress.
• Warm supply air** can increase heat build-up, especially in dense stands.
• Direct air flow on hydro components** can unintentionally influence the reservoir or pipes.

This is critical in hydro cultivation because climate changes quickly affect water uptake and nutrient dynamics. Climate control must therefore be calmer and more uniform than simply "lots of air in, lots of air out".

Target area for plant-compatible supply air

The supply air should be brought as close as possible to the target area of the room before it reaches the canopy area. Large jumps between outside air and room air are problematic.

Practical rules:

• Do not direct supply air directly at the canopy.
• First mix and distribute the incoming air, then direct it to the plants.
• Keep temperature differences between incoming air and room air as small as possible.
• Particularly critical are cold winter air intake and hot summer air intake.

For the room itself, the Hydro-Grow usually makes sense:

• Vegetation: about 24-27°C during the day, 21-24°C at night
• Flowering:** around 22-26°C during the day, 19-22°C at night
• Keep night setbacks moderate; sharp drops put unnecessary strain on the climate.

How to defuse problematic supply air

Never use the inlet as a point jet

A single hard air jet almost always causes localized problems. Better is

• larger inlet area
• Introduce air via an anteroom, duct or deflection
• Direct the supply air against a wall or into a free mixing zone, not directly onto plants

Preheat cold supply air

If the intake air is clearly too cold, it should be tempered before it enters the plant room. Solutions that raise the air evenly instead of creating hot spots are suitable. The aim is not to overheat, but to avoid abrupt cold zones.

Relieving warm supply air

With hot intake air, it helps to design the air flow so that it does not build up directly in the canopy. At the same time, the exhaust air must reliably dissipate the heat load. In hydro rooms, you should also check whether warm supply air indirectly heats up the reservoir.

Consider day and night operation separately

Supply air often behaves completely differently during the day and at night. Therefore, intake, exhaust air and any temperature control should be evaluated separately for both conditions.

During the day

• Heat input and transpiration are higher.
• Supply air may bring fresh air, but must not create hotspots or dry aisles.

At night

• Cold intake air increases the risk of sharp temperature drops.
• Cooling down too quickly promotes a sluggish, humid microclimate.
• Keep the night values stable instead of allowing large jumps.

Control via VPD instead of just RH

When evaluating the supply air, VPD is often more meaningful than relative humidity alone. An air mass can suddenly appear very dry after heating, even though its absolute humidity has remained the same. This is exactly what often happens with cold outside air in winter.

Orientation values:

• Young plants/cuttings: approx. 0.6-0.9 kPa
• Vegetation:** approx. 0.8-1.1 kPa
• Early to medium flowering: approx. 1.0-1.3 kPa
• Late flowering: approx. 1.2-1.5 kPa

If supply air changes the VPD abruptly, the air flow must be adjusted, not just the target value on the controller.

Hydro-specific warning signs

Pay particular attention to the following signs:

• Plants near the inlet act differently than the rest of the stock
• Leaves only show stress symptoms on one side of the room
• Room temperature appears correct, but individual zones are significantly cooler or drier
• Reservoir temperature drifts out of the range 18-22°C due to unfavorable air flow

Conclusion

In the Hydro-Grow, good supply air is not just fresh air, but controlled temperature and cleanly distributed fresh air. The aim is to achieve a uniform climate without sharp jumps in temperature and humidity. If supply air flows in calmly, mixes before it comes into contact with the plants and is evaluated separately day/night, transpiration remains more stable and the entire hydro system runs much more reliably.

Pro Tips

• Compare sensors near inlet and crown height
• Never point the supply air directly at plants
• Shield reservoir from cold or warm supply air
• Always check winter intake air for VPD effect
• Gradually implementing climate change at Hydro