Greenhouses Close the Curtain on Energy Costs
Source: Questline
Greenhouse operators are always looking for ways to reduce expenses, including energy costs. One solution is to install curtain systems, otherwise known as shades, screens or thermal blankets. These energy curtains are movable fabric panels that can be manually or automatically opened or closed to optimize indoor conditions.
Curtain systems are effective in reducing heating and coolings costs. They help save energy in four ways:
- Reducing the volume of air that must be heated
- Trapping an insulating layer of air within the heated space
- Reflecting heat back into the greenhouse
- Providing shading to reduce cooling load
Most new greenhouses are constructed with built-in energy curtains. Although these curtains add up to 10% in construction costs, the payback can be as short as three years. Installing an automated system provides the quickest return on investment.
For older greenhouses, special supports may be needed for overhead pipes and lights if curtains are installed parallel and close to the glazing. Otherwise, external curtains can be installed.
Fabric and installation considerations
Materials used for curtain systems include knitted white polyester, non-woven bonded white polyester fiber and composite fabrics. The type of fabric chosen depends mainly on what crop is grown and also determines how much heat is retained and how much fuel is saved.
Greenhouse orientation plays a part in how the curtains are installed; the goal is to have the minimum possible shadow when the curtain is fully open. Other factors include the type of cooling and heating systems and the location of other equipment. System operation occurs from either gutter-to-gutter or truss-to-truss, depending on the width of the greenhouse and gutter height.
Using curtains for shading
A semi-porous curtain made of aluminized materials and used for shading can reduce greenhouse temperature by up to 10°F. This reduces the cost of using fans or evaporative cooling and may improve plant quality. It also reduces daytime temperature fluctuations which can stress plants.
Some growers install a second curtain for flexibility with different crops. The second curtain might be porous for summer shading. In other cases, one curtain may provide 100% light block, while the other curtain provides some light transmission for normal summer lighting control.
Installing a light meter integrated with an environmental control system helps ensure that temperatures are always at optimal levels.