“Hermetic screens offer more energy saving”

Climate screens are the perfect tool to save energy. The recent energy crisis and the climate objectives have once again draw attention to this. As a result, the (energy-saving) properties of climate screens are being investigated in increasing detail.

Recent research by the WUR within the Energlik project shows that a hermetic screen combined with a dehumidification system proves to be a good energy-saving duo. Phormium, therefore introduces Hermetic Clear: an air and moisture-tight, transparent energy screen, extremely suitable for reducing the energy consumption of greenhouses.

Porous screens
The screens we know today were first used in the 1970’s because of the oil crisis. As is often the case with novelties, they also bring challenges. The screens may have saved energy at the time, but they also caused a dead greenhouse climate: relative humidity reached high levels, and natural ventilation was cut down.

Consequently, the screen was only used when it was necessary. To solve this, manufacturers made the screens porous. This means that the screens were not completely tight but permeable to some extent. This was possible by incorporating yarns (threads) into the textile.

Today, these typical yarns are still present on most screens and have a double function. On the one hand, they drain moisture by absorbing condensation at the bottom of the screen, then transporting it via capillarity to the top of the screen, where the moisture evaporates again. On the other hand, the yarns also create many tiny holes in a screen. These holes allow warm, moist air to find its way through them, which makes it possible to control the climate.

The downside
The downside of these porous screens is their energy loss. The latent and sensible heat loss through the screen, along with moisture and warm air, contribute to the greenhouses’ energy consumption. Nowadays, considering the latest energy crisis and climate objectives, increasing attention is being given to how to eliminate this loss.

Dehumidification & hermetic screens
Thanks to the strong technological evolution in the horticultural sector, dehumidification systems saw the light of day. These systems offer an alternative to the classic way of ventilation through the windows. They keep the relative humidity under control by removing the moisture from the greenhouse air under a closed screen. Because the energy loss to the outside is greatly reduced (no ventilation through the vents + a closed screen), a lot of energy can be saved. In addition, energy can sometimes also be regained from the drained moisture.

A dehumidification system allows the – at present porous – screen to be closed longer, which saves a lot of energy. But it can be done even better by replacing the porous screen with a tighter screen. The more

the screen is closed, the more energy it will save as less sensible and latent heat can escape through the screen.

Therefore, in addition to this porous screen, Phormium developed a hermetic screen called Hermetic Clear. This screen doesn’t contain moisture-transporting yarns and is much less permeable to moisture and warm air than a typical porous screen.

Whereas in the absence of a dehumidification system, this would be seen as a disadvantage, in combination with a dehumidification system, it is a definite advantage to use a hermetic screen. The energy that has been preserved via the screen stays in the greenhouse, reducing energy consumption.

Hermetic screens and a homogeneous climate
Hermetic screens offer, next to a higher energy saving, other advantages that were discovered through research performed by the founders of Plant Empowerment.

More than porous screens, hermetic screens ensure a stable greenhouse climate by preventing unwanted air flows through the screen. These air flows create cold and hot spots in the greenhouse, which is not desired. In cold spots, there is an increased risk of crops getting wet. Which increases the risk of the development of fungal diseases. A colder crop also causes less growth and reduced nutrient absorption. These are some good reasons to pursue an as equal as possible greenhouse climate with the help of a hermetic screen.

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