ISHS Acta Horticulturae 801: International Symposium on High Technology for Greenhouse System Management: Greensys2007
EFFECT OF INSECT SCREEN CONFIGURATION ON NATURAL VENTILATION IN A SINGLE-SPAN GLASSHOUSE |
| Authors: | S. Sase, L. Okushima, M. Suzuki |
| Keywords: | airflow, air temperature rise, tracer gas, ventilation rate, vent opening |
| Abstract:
Field experiments were carried out using identical single-span glasshouses equipped with continuous hinged ridge vents and sliding-door type side vents without plants growing. A 55% porosity screen was used for the experiments. Three cases of screen configuration were simultaneously compared: 1) screens on the side and ridge vent openings, 2) screens on the side vent openings and a screen installed horizontally at an eaves height in the glasshouse, and 3) no screen as control. The environmental conditions including the natural ventilation rate were continuously monitored. Preliminary results showed that the horizontal installation of a screen (case 2) improved the natural ventilation rate and the air temperature rise compared with the installation of screens on the ridge vent openings (case 1). The average natural ventilation rates of cases 1 and 2 were 40% and 77%, respectively of the control (case 3) when all vents were fully open on a nearly clear day with an outside solar radiation peak of 782 W m-2. The average inside air temperatures of cases 1 and 2 were 1.5°C and 0.5°C higher, respectively than the control. When the outside solar radiation remained roughly constant at approximately 400 W m-2 and the wind velocity ranged from 0.5 to 1.2 m s-1, the effect of side vent opening was investigated. It was shown that when the side vents were closed, the air temperatures for cases 1 and 2 were 1.6°C and 0.9°C higher, respectively than case 3. The differences in the air temperature difference between cases 1 and 3 remained fairly constant, whereas the difference between cases 2 and 3 tended to decrease as the side vent opening was open wider. The observed values showed a non-linear relationship between the natural ventilation rate and the air temperature rise as expected from the energy balance. | |
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