Characteristics of Cooling Effect Depending on Operation of Forced Ventilation Systems in a Single-span Plastic Greenhouse

Abstract

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.

Multivariate Analysis of the Phenological Stages, Yield, Bioactive Components, and Antioxidant Capacity Effects in Two Mulberry Cultivars under Different Cultivation Modes

“…Phenology is critical for the implementation of management practices at specific stages of crop development (crop irrigation, fertilization, protection, pollination, harvesting, and pruning) that are predominantly impacted by the temperature. The phenological period of mulberry trees in the greenhouse was obviously earlier than those in the field, which is consistent with the findings of previous studies [12]. The differences identified in phenology in this study may be related to differences in temperatures.…”

“…Therefore, information on the agronomic characteristics of mulberry trees under greenhouse conditions is necessary for producers to understand the cultivars that are most ideally suited to their applications. While greenhouse cultivation has been investigated for its commercial value on black mulberry fruit over the past several years [12][13][14][15], a limited number of studies have focused on China's main cultivated mulberry species. Moreover, few studies have evaluated the characteristics of fruit yield and quality arising from different cultivation modes.…”