Photo: DryGair Energies, Ltd.
Winter is almost here. Temperatures are dropping, and days are growing shorter. This can pose a challenge for greenhouse growers, as they lose heat and are forced to battle the cold. However, with some optimization, many continue growing effectively and efficiently, and even improve yields and reduce expenses as they do so.
How is this done? In a nutshell, by improving insulation, using thermal screens, and installing active dehumidification to control humidity without introducing external air.
Ventilation Spikes Energy Costs
Many popular crops, including vegetables, flowers, potted plants, and more, require a warm environment. So, traditionally, the wintertime would bring with it significantly higher heating expenses.
This has a lot to do with ventilation. Greenhouses of all sizes and crops rely on ventilation as an integral part of their operation. It’s used to exchange air and adjust the temperature when outdoor temperatures are favorable.
However, the main reason growers keep the windows, ceiling, and vents open is to release moisture, which inevitably builds up in a closed greenhouse.
But when temperatures outside drop, ventilating becomes less effective and less efficient. Besides releasing moisture, it also releases heat, which is often expensive to produce. Growers essentially run large heating systems, while leaving the windows open.
While this is obviously an inefficient method to deal with humidity, it’s been the leading solution for decades, and many around the world still operate this way.
Optimizing the Greenhouse for Winter
Many modern growers are adopting new operation methods that drastically reduce heating requirements, creating optimal growing environments, at a much lower cost. One popular method is introducing dehumidification systems, such as DryGair, combined with insulation measures, including thermal screens and curtains.
This combination may not seem intuitive to some, but these two elements actually provide complementary benefits.
Thermal screens, sometimes referred to as energy screens, have been around for a long time. They provide a simple, yet effective and dynamic form of insulation. By deploying a screen, you can significantly reduce heat loss, which has a big impact on the need for heating. Many growers even opt for more than a single screen, amplifying the effect.
However, screens and ventilation conflict, especially during the winter. One is made to reduce air exchange and retain heat, while the other allows air to be let out, introducing cold air into the space. In some cases, the two aren’t even technically possible at the same time.
The Need for Active Dehumidification
Of course, the logical conclusion would be to avoid ventilation and double down on insulating screens. But this raises a separate issue – humidity. Without releasing moisture, relative humidity will spike, quickly reaching 100%.
One grower who has tackled this issue is Martijn van Geel, of Van Geel Group Nursery in the Netherlands. Van Geel Group produces high-quality chrysanthemums and orchids on approximately 25 acres of greenhouse space.
In an interview with Royal Brinkman, Martijn says, “We’re keeping our windows closed more often and have added a third layer of insulating screens. To keep the greenhouse closed longer, we’ve also installed additional LED lighting. But this all leads to humidity issues.”
Any experienced grower knows that’s a big problem. High humidity leads to mildew outbreaks, stunted growth, low fruit development, and overall low output and low quality.
The solution is rather simple: adding dehumidifiers. Dehumidification actively removes moisture from the air, reducing humidity inside the greenhouse. It therefore allows growers to gain full control over the conditions inside, without needing to ventilate, reaping the energy benefits of proper insulation.
Martijn van Geel adds: “To solve our humidity issues and retain heat, we use dehumidifiers. Changing outdoor conditions no longer affect our operations. We don’t need to rely on cold external air, so there’s no need to reheat it.”
Reaping the Benefits of Efficient Cultivation
The benefits you can gain from dehumidification don’t end there, however. Maintaining an ideal humidity range, as well as providing optimal airflow, creates an active climate that stimulates growth and development. It leads to proven yield improvements, both in terms of size and quality.
Growers all over the world are adopting this cultivation protocol, which is gaining more and more popularity. It has also received quite a bit of backing from major research centers and universities, such as the Netherlands’ Wageningen University & Research (WUR), and is even included in the U.N.’s Food and Agriculture Organization’s GAP protocol for greenhouse vegetable production.
