• Korean Journal of Agricultural Science
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• v.28 no.2
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• pp.99-107
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• 2001

It is difficult to install a ventilation window on the roof of single span greenhouses of arch shape. Investigation on the roof ventilation structures for those greenhouses was conducted. In small greenhouses with spans of 5 to 8 m, circular or chimney type ridge vents made of plastic were employed. In large greenhouses with spans of 12 to 18 m, even span roll-up ridge vents made of steel pipe were employed. The effect of roof ventilation was evaluated by comparative experiments between greenhouse installing ridge vents and having controlled side vents only. Roof ventilation contributed greatly to restraint of temperature rise and maintenance of uniform temperature distribution in greenhouses. And ventilation efficiency was analyzed by experiments on the opening and closing operation of the ridge and side vent. There were no temperature differences according to opening and closing sequence of ventilation window. But for greenhouse temperature control by ventilation, it is desirable to open side vents after ridge vents and to close ridge vents after side vents.

• Journal of Bio-Environment Control
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• v.31 no.3
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• pp.143-151
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• 2022

This study was carried out to investigate quantitative characteristics of the cooling effect in a single-span arch greenhouse with roll-up side vents depending on operation of circulation and exhaust fans during ventilation, in order to suggest a practical strategy regarding installation or operation of forced ventilation systems. The examination was conducted under 3 different ventilation conditions (side vents only, side vents + circulation fans, and side vents + circulation fans + exhaust fans). In each condition, variations of internal and external air temperatures and exogenous environmental factors were recorded during ventilation, and the cooling effects were investigated by comparing the normalized temperature difference (NTD) of each ventilation condition. In the morning time (11:00-12:00), a temporary peak in the temperature difference was observed at the beginning of ventilation regardless of ventilation methods. The time taken to the maximum NTD was decreased from 340 s to 110s, and the NTD was dropped from 1.158 to 1.037 as the more forced ventilation systems were operated. The more operations caused the passing time over specific NTD values reduced by 60% as the time was reduced from 1,030 s to 550 s at NTD = 0.8, 1,610 s to 915 s at NTD = 0.6, and 2,315 s to 1,360 s at NTD = 0.4. The temporary peak in NTD was not observed in the afternoon time (14:00-15:00) but it was dropped as quickly as the ventilation started. Also the more operations resulted in the passing time over specific NTD values reduced by 70% as the time was reduced from 560 s to 345 s at NTD = 0.8, from 825 s to 540 s at NTD = 0.6, and from 1,145 s to 810 s at NTD = 0.4. Conclusively, the intervention of the forced ventilation system is recommended in the morning time or in high thermal conditions to achieve more effective and economical ventilation.

• Korean Journal of Agricultural Science
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• v.40 no.4
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• pp.317-323
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• 2013

This research was conducted to obtain the basic information for establishment of standard guidelines in the design and installation of roof ventilation system in single-span plastic greenhouse. To achieve this, the greenhouse structure & characteristics, cultivation status, and ventilation system were investigated for single-span greenhouse with roof ventilation system cultivating the Cucurbitaceae vegetables, watermelon, cucumber, and oriental melon. Most of single-span watermelon greenhouse in Haman and Buyeo area were a hoop-style and the ventilation system in those greenhouses mostly consisted of two different types of 'roof vent (circular or chimney type) + side vent (hole) + fan' and 'roof vent (circular type) + side vent (hole or roll-up type)'. The diameter of circular and chimney-type vent was mostly 60cm and the average number of vents was 10.5 per a bay with vent spacing of average 6.75m. The ratio of roof vent area to floor area and side vent area in the single-span watermelon greenhouse with ventilation fan were 0.46% and 7.6%, respectively. The single-span cucumber greenhouse in Haman and Changnyeong area were a gable roof type, such as even span, half span, three quarter and the 70.6% of total investigated single-span greenhouses was equipped with a roof ventilation fan while 58.8% had a circulation fan inside the greenhouse. The ratios of roof vent area to floor area in the single-span cucumber greenhouse ranged from 0.61 to 0.96% and in the case of the square roof vent, were higher than that of the circular type vent. On average, the roof ventilation fan in single-span cucumber greenhouse was equipped with the power input of 210W and maximum air volume of $85.0m^3/min$, and the number of fans was 9.75 per a bay. The number of roof vent of single-span oriental melon greenhouse with only roll-up type side vent ranged from 8 to 21 (average 14.8), which was higher than that of other Cucurbitaceae vegetables while the vent number of the greenhouse with a roof ventilation fan was average 7 per a bay.

• Journal of Bio-Environment Control
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• v.31 no.2
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• pp.90-97
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• 2022

This study was carried out to investigate the effect of side vent heights on temperature and relative humidity inside and outside the single-span plastic greenhouse (W: 7 m, L: 40 m H: 3.9 m) during natural ventilation. Four different heights (120, 100, 80, 60 cm) of the side vent were used as an experimental condition. Variations of temperature and relative humidity inside and outside the greenhouse and the differences between heights were compared by using one-way ANOVA. In the daytime, the difference in temperature between inside and outside the greenhouse was dropped from 14.0℃ to 7.1℃ as the side vent height increased. The temperature difference in the nighttime was less than 0.2℃ regardless of the height. One-way ANOVA on the temperature difference between heights presented that the statistical significance was founded between all of the combinations of height in the daytime. The difference in relative humidity between inside and outside the greenhouse was grown from -13.8% to -22.2% with a decrease in the side vent height. The humidity difference in the nighttime was less than 1% regardless of the height. One-way ANOVA on the humidity difference revealed that most of the side vent heights showed significance in the daytime but between 100 and 80 cm was not significant. It seemed because the external air became cooler during the experiment with a height of 80 cm. Conclusively, this study empirically demonstrated that the higher side vents resulted in the decrease of differences in temperature and relative humidity between inside and outside the greenhouse, and also the effect of side vent height was statistically significant. This study may be helpful for deciding the height of the side vent effective for controlling temperature and relative humidity in a single-span greenhouse during natural ventilation.