Journal of the Society of Agricultural Structures, Japan

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Air leakage reduces the effectiveness of CO₂ enrichment in unventilated greenhouses. In this study, a windbreak that can be directly attached to an existing greenhouse was developed to reduce the air leakage; the windbreak was termed a ‘windbreak attachment’. The specifications of the windbreak attachments were examined for two small greenhouses. Pipes were erected at 0.4 m away from the wall of each greenhouse and connected to the eaves of the respective greenhouses with fastening apparatus to form overhangs. The sides of the overhangs were covered with plastic nets, which were used as the windbreak attachments. The windbreak attachments were applied to the sides of the greenhouses for some tests while leaving the ends without windbreaks, and to both the sides and ends of the greenhouses for other tests. The leakage rate was measured in the unventilated greenhouses by the tracer gas technique using CO₂ as a tracer gas. The leakage rates of the greenhouses correlated significantly with outside wind velocity, consistent with many previous studies. The air leakage of the greenhouse with windbreak attachments on both the sides and ends was less than that of the greenhouse with windbreak attachments on the sides, as evaluated effectiveness in reducing air leakage using the ratio of the slopes of the regression lines. Therefore, we concluded that windbreak attachments were needed not only on the sides of the greenhouse but also on the ends. The effect of the windbreak attachments on the leakage rate of the greenhouse was also evaluated for a medium-sized greenhouse. As a result, the leakage rate of the greenhouse with windbreak attachments installed on both the sides and ends was reduced to 53.5 % of that the same greenhouse without windbreak attachments.

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