Controlling and reducing greenhouse humidity is one of the greatest challenges of modern commercial agriculture. Though it’s a much-discussed topic, it is also a complicated one. Growers often ask about the differences between dehumidifiers, fans and ventilation, in regard to controlling humidity in the greenhouse, struggling to find what best fulfills their needs.

Though all of these technologies can assist in achieving and maintaining your optimal climate, they are not true alternatives to one another. Rather, they are complimentary to each other.

The difference between dehumidifiers, ventilation and fans

In order to make the decisions that best suit your greenhouse’s needs, it’s important to understand the difference between these closely related terms.

Dehumidifiers – Technologies used to physically remove water vapor from the greenhouse air. These units work directly to reduce the actual amount of humidity found in the greenhouse.

Ventilation – Opening the greenhouse in order to exchange air with the outdoors. This is the traditional approach to controlling greenhouse humidity. By letting the humid air out, and introducing new air, you can achieve a reduction in humidity.

Fans – Used to create airflow within the space. In the context of humidity control, fans help the air reach different areas of the greenhouse and reach further into dense foliage. Fans alone do not remove water vapor or reduce the absolute humidity in the growing space.

Greenhouse fans or vents are not a complete climate control solution

Traditionally, fans were designed to push air horizontally in a single direction. These days, there is a huge variety, including vertical fans and air circulators. These can improve air movement in large spaces and inside the foliage, helping to combat local pockets of humidity build-up.

But there is one important distinction to make. While fans may help disperse pockets of high humidity, they do not actually reduce the amount of water vapor found in the greenhouse. In a saturated environment, with 100% relative humidity, fans will not reduce the humidity level.

Ventilation, as a means to reduce greenhouse humidity, is a viable and efficient method under certain circumstances. But, as venting utilizes air from outdoors, it has very strict limitations and does not always achieve its purpose.

New generation of fanning and ventilation

The past few years brought some innovation to the greenhouse fan and vent fields. One of the leading concepts being upper layer ventilation. These are fans located above the thermal, shading or blackout screens.

These fans attempt to bridge the gap between traditional humidity control and more modern approaches, taking plant empowerment into consideration.

Above screen ventilation allows growers to ventilate, while keeping their screens rolled out. This way, you can ventilate without compromising control over lighting, and to some extent, climate control.

But these technologies still suffer from some of the same problems that traditional ventilation faces. In order to effectively reduce humidity, they still rely on outdoor conditions, which are often unsuitable and unreliable.

Ventilating in order to reduce humidity requires conditions to be drier outdoors, which is not the case during rainy periods, humid days, nighttime and in tropical climates.

Additionally, venting can negatively impact the greenhouse temperature. During cold periods, using above screen fanning will still lead to a drop in temperatures, requiring excessive heating to maintain optimal temperatures. Even worse, it may cause dew point condensation, which can lead to disease outbreaks such as botrytis or powdery mildew.

A complete approach to reducing greenhouse humidity

The best way to approach greenhouse climate control is not by using one piece of technology. But rather, an array of equipment.

During periods of fair weather, it is definitely recommended to open the greenhouse and ventilate in order to reduce humidity. But, when weather is not fit for ventilation, such as overnight, or especially during dusk and dawn (when conditions outdoors change rapidly), it’s best to close the greenhouse and treat the climate inside.

This is best done by closing windows or vents and deploying thermal screens. In this situation, you can efficiently control the temperature. Without treatment, closing the greenhouse would lead to a spike in relative humidity, due to transpiration from the plants. Ventilation alone cannot reduce this humidity, but a greenhouse dehumidifier can easily control it.

light dep greenhouse

Closing the screens while using DryGair reduces light pollution. Credit: https://flickr.com/photos/8431398@N04/4179696789

Climate control is not yet complete though. To avoid condensation occurring in at-risk positions, such as inside the dense foliage, it’s important to provide enough airflow. This can be done by combining dehumidification with fanning.

DryGair’s dehumidifiers are equipped with a unique hood design to create air circulation, spreading the dried air to all corners of the growing space in a circular fashion. Air circulation helps to homogenize the climate conditions throughout the greenhouse. Combined with dehumidification, it ensures a condensation-free growing facility.

Dehumidification provides more than humidity control

Using a dehumidifier provides more than just humidity control. It allows growers to close the greenhouse without risking disease outbreaks, creating a more controllable environment, with greater energy efficiency.

By rolling out thermal screens and blocking off any air exchange, growers can control their temperature with much greater efficiency. This can help reduce most greenhouses’ energy expenses by as much as 50%.
The same is true for radiation. With dehumidifiers allowing you to close the greenhouse, you can control your lighting to a greater extent. By enabling a risk-free deployment of shading or blackout screens, growers can allow sunlight in only when it is desirable, and not due to humidity build-up.

When coupled with air circulation, dehumidification helps maintain an active climate and stimulate the plants. By maintaining a good, in-range VPD level, you can maximize the crops’ growth potential.

The complete solution

Ventilation, fans and dehumidification are closely related, but they are not interchangeable. The only way to efficiently gain total control over the greenhouse environment is by utilizing all three and understanding how and when to use each piece of equipment.

For more information on combining these technologies to gain maximum environmental control, while minimizing expenses, visit the DryGair solution.