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Most multi-span greenhouses now employ energy/shade screens. To provide maximum energy conservation and get uniform shading, they need to be adjusted, cleaned and maintained at least once a year. This extends their life and reduces operational problems.

System adjustment

• Monofiliment and steel support cables will stretch over time. This allows the screen to sag and affects closure. The cables should be tightened at least once a year. A good device is a ratchet- type tensioner in each cable.
• Good seals are important to get maximum heat savings. As the cold moist air above the screen tends to fall through any openings and allows heat from the growing area to escape upward by the chimney effect, all openings should be closed. I have been in houses that the temperature was warmer above the extended screen than in the growing area. The leading edge needs to seal tight against the truss. Some manufacturers apply a foam seal to give a good seal where hardware may interfere.
• The perimeter edge seals are sometimes difficult to seal. The screen is usually installed so that the material rides on a narrow shelf made with fire retardant material to prevent fire spread. Some installers fail to seal the space between the shelf attachment to the greenhouse frame and the glazing. This can allow considerable air exchange. Foam with an adhesive backing or for larger gaps, foam pipe insulation has been used with good success.
• The gear motors are generally trouble-free. Check for tight drive connections, gear box oil level and secure electrical connections.

Screen material maintenance

• The screen material usually has a service life of 8-12 years. After that the material may start to tear, aluminum foil on the polyester strips may flake off and ultraviolet from sunlight weaken the fabric. Wear from mechanical drive equipment, HAF air circulation systems and shrinkage of the fabric can also cause deterioration. Repair of tears can be done by cutting a large enough piece to cover the area, covering it with UV stabilized, double sided tape and attaching it to the top of the screen. In some states, the National Resource Conservation Service (NRCS) EQIP program may provide incentive payments for screen replacement.

Cleaning

• Dust accumulation and algae formation can decrease material life. Algae formation is common when a screen remains wet for a period, especially during the overnight when humidity levels rise. Leaving the screen extended early in the morning to allow the sun to provide drying should be a first step. If algae persists, L.S. Svensson (manufacturer of most of the screen material used in the U.S.) recommends extending the screen and spraying on a dilute solution of hydrogen peroxide. This will kill the algae. There is no need to rinse it with water. Don’t use a high-pressure sprayer or try to clean the screen with a vacuum as this will damage the material.

Fire safety

• Screen material is available as Firebreak (FB) or Fire Retardant (FR). Firebreak, with a strip of firebreak material on the edges limits the screen-to-screen fire spread. Flame Retardant material has a different formulation and is required by many building codes and insurance companies for installation in garden centers, school greenhouses or where there are a large number of employees.
• Although fires are rare in greenhouses, you should check to see that the material is not in contact with sources that could start a fire. Electrical wiring should be in metal conduit. Lighting fixtures and bulbs should have a minimum clearance of 24 inches for FB material and 8 inches for FR material. Heating system flue pipes require a 3’ clearance or the use of double wall pipe. If a fire starts, call the fire department, retract the screen, close all vents and shut off any operating fans. A 5- or 10-pound ABC extinguisher should be convenient to control small fires.