While greenhouses allow certain crops to be grown throughout the year, excess temperature, solar radiation and high vapor pressure deficit can cause problems during the summer months. With conventional solutions, such as shade screens, often being labor intensive and reducing the quality of light within the growing space, Canadian company Sunarc has a developed a new liquid foam shading system that mimics cloud cover to automatically shade greenhouses. As the liquid foam filters the sunlight, it reduces solar radiation and controls temperature, but doesn’t deprive the plants of vital light spectra they require for photosynthesis.
Shade panels are made from two layers of polyethylene film between which the foam is pumped as required – the more foam deposited the more shade produced. A sensor system, which monitors the microclimate within the growing space, regulates the foam and sprinklers as conditions demand. Software is programmable to local needs and may be monitored and operated by remote computer control.
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The technology produces conditions that can be varied between 20 percent and 45 percent shade. At night, or on cool overcast days, the foam drains away from the roof and side panels into a storage reservoir. The variable shade systems allows for plants to have a little shade (20-25 percent) in the morning and afternoon and more shade (30-35 percent) in the middle of the day when heat stress would normally be an issue. The foam has been found to reduce the temperature within the greenhouse by up to 6 percent compared to conventional shade-cloth structures. This is particularly important as many plant species will shut down their photosynthesis process during the hottest part of the day due to heat stress.
The system has been tested over a two year period using tomato and sweet pepper plants with two shading strategies: a conventional nonmovable shading curtain compared to the liquid foam shading system. The research team recorded data on the greenhouse microclimate (global solar radiation, air temperature, and relative humidity), the canopy microclimate (leaf and bottom fruit temperatures), and ventilation (opening/closing).
According to the results of the tests, benefits of the technology included an increase of up to 12 percent in greenhouse relative humidity, a decrease in the frequency of roof ventilation operation, and an increase in the length of time bottom fruit temperature remained cool after shading ended. Sunarc claims a possible crop yield increase of 10-20 percent could be achieved by using the system over traditional shade methods.