ENERGY CURTAIN STUDY (Harrow ’07 update)
By Dave Harrison
How beneficial are these systems in greenhouse pepper production?
How beneficial are energy curtains in greenhouse pepper production?
That’s the focus of a current research project by Dr. Tom Papadopoulos and co-workers Dr. Xiuming Hao and Shalin Khosla.
Energy curtains are quite common in glass greenhouses, because they’re not as energy-efficient as double-poly units. “The way growers compensate for this is to apply energy curtains.”
Energy curtains, however, are not widely utilized in pepper greenhouses. That could soon change, depending on the results of this research. “That’s the purpose of the study,” explained Dr. Papadopoulos, “to see what we would gain and what we would lose (by using curtains).”
The trials are being conducted at two test sites within Del Sol Greenhouses in Kingsville, a short drive from the Greenhouse and Processing Crops Research Centre (GPCRC). The study features four replicates with energy curtains and four without. A number of plant growth parameters are being constantly recorded via a number of sensors placed throughout the crop. Recorded are the air, leaf and fruit temperatures, along with humidity, condensation and light levels. Researchers will also compare harvested fruits from both greenhouses.
Curtains not only save energy, they can also help optimize crop conditions. “Energy efficiency is one thing, “ said Dr. Papadopoulos, “but the improved environment, logically, should result in improved productivity and quality.”
At night in a greenhouse with the curtains applied, radiation from the plants is trapped and bounces back to the crop. In a greenhouse without curtains, the radiation rises to the cover and some will pass through. This means the leaf and canopy temperature in a greenhouse with curtains will be warmer than in a greenhouse without curtains. “You will be able to maintain the same canopy temperature, but while using less energy.”
Curtains can also modify the environment. Peppers prefer a more humid environment than do tomatoes, for instance. “By having an energy curtain in place, you will trap more of the moisture within the canopy,” noted Dr. Papadopoulos.
The cooling effect of curtains in the summer is also important. Plants have upper and lower limits temperatures within which they perform best. In the summer, the upper limit is sometimes exceeded. “If the plant’s transpiration capacity is exceeded, it cannot cool itself sufficiently and it will become over-heated. If it can’t supply itself with sufficient water, it is stressed for water.” Such conditions can lead to such problems as blossom end rot.
However, while curtains keep things cooler in the summer, they also block some of the light. Depending on the fabric, light losses could range up to 40 per cent.
The double-poly greenhouse environment is not as harsh in the summer compared to that of glass houses. “There is more direct light coming in with glass houses, whereas with double poly, the light is more diffused. This means a gentler environment in the summer compared to glass houses.”
In another facet of the project, infrared cameras have been installed to record crop canopy temperatures. These readings will be compared to those made by the individual sensors strategically placed within the crop. “Another part of this project is to determine which system is more stable and representative of the crop conditions,” said Dr. Papadopoulos. “Is there a difference in their readings?”
While such cameras are now quite expensive, prices will probably drop once more people begin using them.
The project began in January and is expected to wrap up late this year. This study is sponsored by the Ontario Greenhouse Vegetable Growers, with funding assistance from the Canada/ Ontario Research and Development (CORD) program.
“If the report shows that energy curtains are beneficial, more pepper growers will install them.”