High energy prices over the past winter led many growers to switch off their SON-T lighting or to continue production using only LED lighting, even in greenhouses equipped with hybrid systems. But LED lighting produces much less radiant heat, which means the heat input in the greenhouse can fall by as much as 40 percent.

This reduced heat input must often be compensated by additional heating in the pipe system. Climate consultant Bart Bakker explains that growers should consider other solutions first, such as installing an additional energy screen or improving air circulation.

“You often see growers slightly increasing heating again after installing LED lighting,” Bakker says. “In the end you still use somewhat less energy overall, but that extra heat still has to come from somewhere and it costs money. It is often smarter to invest in an additional energy screen. That improves insulation without necessarily adding more heat to the greenhouse.”

Latent heat and dehumidification

When the growing area becomes more insulated, but the illuminated crop continues to produce moisture, the need for dehumidification increases. Mechanical dehumidification systems can return latent heat to the greenhouse air, but they may also consume a significant amount of electricity.

“That electricity is not free,” Bakker notes. “If you generate it yourself, you cannot sell it back to the grid. During cold periods the recovered heat can be useful, but in autumn or spring you often don’t need it.”

In crops such as gerbera, where growers have recently switched to full-LED lighting, new climate challenges can appear. Dense crops combined with LED lighting and double screens can lead to stagnant air in the microclimate.

“If you then introduce heating pipes under the crop, you may increase root pressure too much,” Bakker explains. “That can create a negative spiral you actually want to avoid. You want air movement, but without stimulating excessive evaporation or root pressure, especially during the night and early morning.”

Managing absolute humidity

A better approach is to exchange air above and below the screen and create vertical air movement through the crop. This helps remove moisture through convection and maintain a more balanced greenhouse climate.

“What growers previously achieved by heating pipes – essentially drying the air by heating – can be done far more efficiently with a vertical fan,” Bakker says. “A minimum pipe temperature of 30 to 35 °C can easily require 25–30 W/m² of heat input, while a vertical ClimaFlow fan delivering the same effect uses about 1 W/m².”

Heat from heating pipes also tends to accumulate near the roof of the greenhouse, where it is less useful. Vertical air movement can bring that heat back down to crop level, making better use of the available energy.

Vertical ventilation

Vertical ventilation also allows growers to maintain slightly higher humidity levels without compromising crop health.

“Reducing humidity always costs energy,” Bakker explains. “If you create gentle air movement within the crop, you can tolerate a slightly higher relative humidity. That means you don’t have to ventilate through roof vents as often, which saves energy.”

The key principle remains simple: create a uniform greenhouse climate.

“Try to avoid opening screen gaps wherever possible,” Bakker says. “They often create cold air drops and an uneven climate. Instead, look at how vertical ventilation combined with a double screen can produce a more stable climate and give you much more precise climate control.”

Pay attention to light transmission

Growers who cultivate crops without supplementary lighting should pay close attention to the light transmission of screens, particularly when installing a double screen system.

The NEN standard for light measurement offers an objective method for comparing screen properties, including light transmission and diffusion.

“Every percentage of extra light counts,” Bakker concludes. “We can calculate what an additional one, two or three percent of light transmission means in terms of energy savings and production. With double screens the difference can be significant – sometimes up to 10 percent. In winter, when light levels are already low, every percent matters. So make sure you get good advice before investing.”