Active Dehumidification is Better Than Humidity Mitigating Greenhouse Designs
Modern horticulture techniques let us grow food, medicine, and beautiful ornamentals, faster, and more efficiently than ever. Progress in this sector never stops, and new innovations constantly hit the market. With so many ways to deal with different greenhouse issues, it’s often hard for growers to know what the right solution is for them. This article will discuss the benefits of active dehumidification, in comparison to humidity mitigating greenhouse designs.
The Problem with Greenhouse Humidity
There’s no doubt that high humidity is a serious problem for greenhouse growers. The fact that all plants transpire water vapor, as part of their activity, means that any closed growing environment will eventually become very humid.
High humidity is a very serious issue. It can lead to devastating disease and mildew outbreaks, like botrytis, or powdery mildew. But it also affects plant metabolism. When relative humidity is too high, plants will grow slower, smaller, and weaker.
Over the past decade, commercial growers have started using dehumidifiers to actively reduce the humidity in their greenhouses. At the same time, new greenhouse designs started popping up, offering different design techniques to mitigate the negative impacts of humidity.
So, what’s the best way for greenhouse growers to deal with high humidity?
What Are Humidity Mitigating Greenhouse Designs?
“Humidity mitigating greenhouse designs” refers to various design techniques that help growers deal with the negative effects of humidity, without using a dehumidifier.
The biggest distinction is that, in most cases, these solutions are passive, and don’t actually reduce humidity. Rather, they offer a way to reduce the impact of humidity.
One of the most common techniques is natural ventilation, including roof vents. This is the traditional method to reduce humidity – releasing humid air from the greenhouse through windows or vents.
New natural ventilation designs make use of physics to increase their effectivity. But the underlying problem remains the same. Using ventilation to reduce humidity relies heavily on the weather outside. Releasing humid air only works when the air outside isn’t humid. So, in certain climates, and during rainy, humid, or cold days, this method may fail to provide a solution, leaving growers with no option to deal with their humidity.
Additionally, ventilation may be energetically inefficient, even when it’s effective. Greenhouse operators invest a lot of energy into heating, in order to maintain ideal temperatures for their crops. But by releasing air, they lose this heat, requiring constant reheating. So, while this may help control humidity, it doesn’t provide an economically beneficial solution.
Some growers use mechanical vents that allow a greater air exchange. This can double the capacity and improve the effectivity of ventilation, when conditions outside are favorable. However, this type of ventilation doesn’t improve the effectivity when conditions outside are humid or too cold.
Ventilation with Heat Exchangers
Efficiency is one of the most critical issues when it comes to humidity control, which is why some modern ventilation systems come with heat exchangers.
Heat exchangers help recoup some of the heat that would be lost in traditional ventilation, by passing the cold incoming air adjacent to the released warm air, transferring some of the heat.
In theory, this is a great way to reduce some of the heat loss. But in practical terms, these systems provide only double the efficiency of natural ventilation, and land at about 1.5 liters of moisture extraction per kW. This is much better than ventilation alone, but still only a third or fourth of the efficiency DryGair, and half of the efficiency of other active dehumidifiers.
Vertical fans are often mentioned in the humidity control discussion. Using vertical fans lets growers keep their greenhouse closed, with ventilation occurring in the gap between the thermal screen and ceiling. The vertical fans then push the air from this gap downward, into the greenhouse, through dedicated openings in the screen.
This method relies on the fact that the air above the screen is often dryer than that inside the greenhouse, but is more controllable than air from the outside.
One of the main reasons growers turn to vertical fans is to help cool the greenhouse when it’s warm. For example, when using intense grow lights that emit too much heat.
Above screen ventilation and vertical fans are a better solution than traditional natural ventilation, but still have the same downsides. When the air outside is humid, so will the air above the screen, and growers won’t be able to get a humidity reduction in the greenhouse.
Greenhouse Roof Designs to Eliminate Condensation Drips
Water vapor condensing on the ceiling, and causing drips, is one of the biggest hazards in a greenhouse. As greenhouse roofs are normally colder than the interior, the ceiling tends to be cooler as well. So, under humid conditions, the ceiling and railings are some of the first places where water begins to appear.
Condensation drips are hazardous because they get the plants wet, which is a serious catalyst for diseases.
Roof designs that eliminate drips can reduce mold outbreaks and can even be routed to collect some water. But overall, they can’t provide a solution to humidity, and are only a last line of defense once humidity already reaches saturation (dew point).
Additionally, the protective materials used to prevent condensation drips wear down quickly, and require frequent replacement to retain effectivity. This means extra costs, and a greater negative impact on the environment.
What is Active Dehumidification?
Active dehumidification means using dehumidifiers to physically remove water vapor from the air. As opposed to the techniques mentioned so far, active dehumidification reduces the overall humidity in the greenhouse.
Dehumidifiers are effective at lower relative humidity levels as well, ensuring growers can maintain comfortable conditions. Using dehumidification reduces the need for special designs to negate the impact of humidity and provides a complete solution.
DryGair dehumidifiers are designed specifically for horticulture use, and are extremely efficient. A single DG unit can remove 45 liters of water from the air, per hour, running on only 10 kW (4.5 liters/kW).
Using active dehumidification prevents condensation. Not only on the ceiling, but everywhere, including the plants themselves.
Active Dehumidification in Closed vs. Semi Closed Greenhouses
Semi closed greenhouses, as opposed to completely closed greenhouse discussed so far, have a separate room dedicated to air treatment. In this separate chamber, growers can treat the air and reduce humidity using any of the methods mentioned above.
The problem with semi-closed greenhouses is that transporting the treated air back to the greenhouse requires a lot of energy. It also creates uneven conditions in the greenhouse, as the air changes temperature the further it travels in the ducts.
When using DryGair, it’s recommended to place the unit inside the greenhouse, rather than a separate room. This harnesses the DryGair’s ability to create a uniform climate, and saves the energy required to tunnel the treated air from the separate chamber to the greenhouse.
However, DryGair is still highly efficient at extracting water vapor, compared to other dehumidifiers, even when air circulation isn’t engaged. Growers may choose to utilize their units for dehumidification alone, and still enjoy the benefits of effective humidity control.
Stimulating Plant Activity with Active Dehumidification
DryGair can provide a lot more than disease prevention. It’s a tool that stimulates plant activity and improves growth and quality. They do so by letting growers maintain the humidity level ideal for their plants.
Growers can approach this by monitoring VPD (vapor pressure deficit), rather than relative humidity. VPD measures the pressure differences between the amount of water vapor currently in the air, and the saturation point – the maximum amount of moisture the air can carry at its current temperature.
This pressure is what drives plant transpiration. It affects both metabolism and photosynthesis. So, by monitoring and maintaining an ideal VPD, growers can stimulate their plants, leading to better and faster growth, and enjoy higher quality produce.
Benefits of DryGair
Using DryGair has numerous additional benefits. By dealing with humidity from inside the greenhouse, growers gain more control over their environment, and are less susceptible to bad weather. This means they can grow under the best conditions, throughout the entire grow cycle.