If a grower is wondering where to start with a greenhouse, the answer might surprise them. It's not fans. Not wet walls. Not even heating.

Rather, it's a shade screen. A simple, retractable cloth, drawn horizontally across the inside of a greenhouse, operated by a single gear motor.

This one system can shade a full hectare of crops in under three minutes, cut heating bills by 30 to 50%, and respond automatically to changing weather conditions throughout the day.

It's also super cost-effective. No other single investment gives that kind of return across so many dimensions.

Two jobs, one system
A shade screen does two jobs, and it does both of them remarkably well. The first is shade (when it's needed).

In warm climates with high solar radiation, closing the screen shades a crop the way an awning shades a patio. But growers need control over when to shade their crops. That's why Vegtech Netafim only sets up retractable screens.

These screens, controlled by the greenhouse climate computer, open and close automatically based on radiation sensors and temperature readings. Clouds pass over the sun, the screen opens. The sun comes back, the screen closes. Growers get the light without the heat stress.

For all that movement across 10,000 m², only a single gear motor is running. Compared to the alternative — extraction fans, circulating fans, and wet wall pumps running continuously — the electricity bill is but a fraction. The motor turns, moves the screen, and stops. It doesn't use power while the screen is in place.

The second job is energy conservation.

Picture a greenhouse at night: the peak of the roof might be six or seven metres tall, but the crop only occupies the lowest metre or two. Without a screen, the heating system is trying to warm that entire volume of air, including the metres of empty space.

Close the screen, and it effectively divides the greenhouse into two compartments. The warm air is trapped below, around the plants. The cold air sits above the screen, unheated.

That's why screens typically deliver 30 to 50% savings on heating costs. Some multi-layer installations achieve even more. The screen closes in two or three minutes, and growers get the benefit all night long without drawing another watt. In cold climates, it would be hard to find a commercial greenhouse without one.

Screens typically pay themselves back in two to four years, and in many cases, less — just by reducing energy costs.

Choosing the right cloth
The right cloth depends entirely on the climate and the crop.

For growers in a warm climate where heating isn't a concern (like parts of Mpumalanga, Limpopo, North and East Africa), a permeable, open-weave cloth is best, because it allows hot air and humidity to pass through the fabric and vent out of the greenhouse.

Using an impermeable cloth in a hot greenhouse traps heat and moisture instead.

In cooler regions, the opposite applies. An impermeable, closed-weave cloth creates a thermal blanket effect that seals the warm air below and keeps the cold air above. This is the cloth needed in the Western Cape highlands, the Free State, or any winter production environment.

Beyond open-versus-closed weave, screen cloths can also be engineered to manipulate how light passes through them.

Some cloths diffuse direct sunlight, scattering it more evenly across the canopy. This is brilliant in glass greenhouses, where direct light through glass panels can cause uneven crop growth. In plastic greenhouses, it's a great way to upgrade light quality without replacing the roof cover.

The shade factor varies widely. A 30% shade cloth handles moderate radiation. A 50% cloth suits higher-intensity conditions. The right specification depends on the crop, the climate, and the season.

Why quality matters
A screen system is a mechanical installation with moving parts. It's not like installing a shade net and walking away. The cloth moves back and forth every day, sometimes several times a day, driven by motors and cables that must all work together reliably for years.

That's why the quality of the components and the design of the system matter as much as the cloth specification. Poorly designed slip blocks, loose cable tension, or substandard profiles lead to uneven closure, cloth wear, and maintenance headaches that eat into the savings the screen was supposed to deliver.

Vegtech Netafim partners with Alweco, a Dutch manufacturer that has been designing and building greenhouse screen systems for over 35 years. Alweco develops many of its components in-house, including the Ultra Lock screen profiles and Ultra Delay slip blocks that ensure a tight seal when the screen is closed. It's a partnership Vegtech Netafim chose specifically because Alweco's engineering focus matches how Vegtech Netafim approaches greenhouse design: get the details right, and the system performs for years without constant attention.
 

Source: www.floraldaily.com