ISHS Acta Horticulturae 801: International Symposium on High Technology for Greenhouse System Management: Greensys2007
DEVELOPMENT OF A NATURAL VENTILATION MODEL FOR A TALL, GUTTER-VENTED, MULTI-SPAN DOUBLE-LAYER POLYETHYLENE GREENHOUSE |
| Authors: | M.S. Borhan, X. Hao |
| Keywords: | Regression, wind speed, tracer gas, temperature difference, greenhouse climate control |
| DOI: | 10.17660/ActaHortic.2008.801.52 |
| Abstract:
The ventilation and leakage rates of an one-acre tall, double-polyethylene (D-poly), air-inflated, gutter-ventilated and 9-span commercial greenhouse at Leamington, Ontario, Canada were measured under various weather conditions. The objective of the study was to develop a ventilation model for naturally ventilated D-poly greenhouses to optimize CO2 enrichment under ventilated conditions. Continuous injection method with carbon dioxide (CO2) as tracer gas was used to determine the air exchange rates at various levels of roof vent opening (5, 10, 20, 30, 40, 50, 60, 80, and 100%). The air exchange rates were calculated based on the CO2 concentrations inside and outside the greenhouse and the rates of CO2 injected into the greenhouse. Two meteorological stations were devised and installed inside and outside the greenhouse to monitor climate and CO2 concentrations. The influence of wind speed, wind direction, and the temperature difference inside and outside the greenhouse on air exchange rates were analyzed for each level of roof vent opening. Wind speeds had a large influence (linear) on air exchange rates while wind direction did not affect the air exchanges. When the temperature difference inside and outside greenhouse exceeded 8°C, it affected air exchange rates even if the wind speed was above 3 m s-1. A linear regression model describing the relationship between air exchange rates and the product of two variables (wind speed and vent opening coupled with leakage rate) was developed, calibrated and validated. The average accuracy and standard error of prediction were 84.45% and 1.95 h-1, respectively. This study has demonstrated that the ventilation and leakage rates of a tall, gutter-ventilated, D-poly commercial greenhouse can be predicted by a simple linear regression model with reasonable accuracy. | |
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