Single-span Plastic Greenhouses Research Articles

Evaluating the Ventilation Performance of Single-Span Plastic Greenhouses with Continuous Screened Side Openings

Natural ventilation is the most cost-effective environmental control method for protected horticulture. To overcome the issues associated with high temperatures in greenhouses, analyzing their ventilation characteristics and maximizing their natural ventilation performance are essential. Therefore, in this study, the natural ventilation performance of arched single-span plastic greenhouses with screened side openings was empirically investigated. Three identical single-span plastic greenhouses were used in this study, each with different side-opening heights. Temperature and wind-speed data were collected, and the ventilation-volume flow rate was calculated considering both buoyancy and wind forces. The natural ventilation performance of the greenhouses was strongly and positively correlated with the ventilation-area ratio and outdoor wind speed. The ventilation rate increased linearly with an increase in the ventilation-area ratio and high outdoor wind speeds. However, the association between ventilation performance and indoor–outdoor temperature differences was not strong. When the ratios of ventilation areas in the greenhouse were changed to 0.08, 0.19, and 0.29, the average indoor–outdoor temperature differences were 14.0, 10.1, and 7.7 °C, respectively, and the ventilation rates were 0.0081, 0.0196, and 0.0315 m3 s−1 m−2, respectively. The proportion of wind in the total ventilation performance was high with a low ratio of ventilation openings and high outdoor wind speeds. However, the proportion of the buoyancy was high, with a high ratio of ventilation openings and a large indoor–outdoor temperature difference. Overall, this study provides foundational insights for optimizing the design and evaluation of ventilation openings in greenhouses, considering the outdoor wind speed.

Effects of Uplift Resistance on Continuous-Pipe-Foundation of Single-Span Plastic Greenhouse by Steel Plate Pipe Connector

The single-span plastic greenhouses are affected by strong winds which generate uplift resistance causing the bending of members, damage to protective films, and damage to crops. This study performed a field test using the static axial tensile load method to present basic data to prevent damage to a single-span plastic greenhouse. Three representative areas were selected, and the effects of pipe connectors, rafter spacing, and embedding depth were tested. In the field test results, it was found to be greatly affected by the pipe connector. The pull-out resistance at the site fixed by welding instead of the pipe connector was measured as 4.5 times the sliding resistance standard value of the Rural Development Administration. In other sites, the measurement was below the standard value of the sliding resistance of the pipe connector. It was confirmed that the uplift resistance is determined by the sliding resistance of the pipe connector, the rafters, and the crossbar pipe. Therefore, it seems possible to increase the uplift resistance of a single-span plastic greenhouses continuous foundation through the reinforcement of the pipe connector. The field test results can be utilized as basic data for the reinforcement of the commercialization of single-span plastic greenhouses and new standards.

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

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

Efficiency of Different Roof Vent Designs on Natural Ventilation of Single-Span Plastic Greenhouse

In the summer season, natural ventilation is commonly used to reduce the inside air temperature of greenhouse when it rises above the optimal level. The greenhouse shape, vent design, and position play a critical role in the effectiveness of natural ventilation. In this study, computational fluid dynamics (CFD) was employed to investigate the effect of different roof vent designs along with side vents on the buoyancy-driven natural ventilation. The boussinesq hypothesis was used to simulate the buoyancy effect to the whole computational domain. RNG K-epsilon turbulence model was utilized, and a discrete originates (DO) radiation model was used with solar ray tracing to simulate the effect of solar radiation. The CFD model was validated using the experimentally obtained greenhouse internal temperature, and the experimental and computed results agreed well. Furthermore, this model was adopted to compare the internal greenhouse air temperature and ventilation rate for seven different roof vent designs. The results revealed that the inside-to-outside air temperature differences of the greenhouse varied from 3.2 to 9.6oC depending on the different studied roof vent types. Moreover, the ventilation rate was within the range from 0.33 to 0.49 min-1. Our findings show that the conical type roof ventilation has minimum inside-to-outside air temperature difference of 3.2oC and a maximum ventilation rate of 0.49 min-1.

Effects of the spacing of roof ventilation devices on the environment and the yield of oriental melons in single-span plastic greenhouses

The purpose of this study is to provide the standard for the proper installation of roof ventilation devices in single-span plastic greenhouses. The amount of ventilation was 19,140 m3 h-1 in the greenhouse with fans installed at intervals of 15 m, and 15,845 m3 h-1 with fans installed at intervals of 20 m. The amount of ventilation was 14,961 m3 h-1 in the greenhouse with stacks installed at intervals of 6 m, and 13,414 m3 h-1 with stacks installed at intervals of 8 m. As a result of analyzing changes in average day-time temperature during June, a high-temperature period, it was found that the narrower the spacing of ventilation devices, the lower the air temperature; and that air temperature in the greenhouse with fans was lower than that in the greenhouse with stacks. As a result of examining the yield of oriental melons per the span of greenhouse (605 m2), it was found that the yield in the greenhouse with fans installed at intervals of 15 m was 5,075 kg, 8.6% more than that in the greenhouse with fans installed at intervals of 20 m. And the yield in the greenhouse with stacks installed at intervals of 6 m was 4,405 kg, 7.2% more than that in the greenhouse with stacks installed at intervals of 8 m. As a result of analyzing economic efficiency according to roof ventilation device treatments, taking into account the value of oriental melon production, the depreciation of ventilation devices, the electric charges, and the expenses for selection and packaging, it was found that income increased KRW 865,450 in the case of spacing fans 15 m apart, compared with the case of spacing them 20 m apart; and that income increased KRW 660,690 in the case of spacing stacks 6 m apart, compared with the case of spacing them 8 m apart.

Effects of an Improved Side Vent on Yield of Oriental Melon and Temperature in Single-span Plastic Greenhouse with Roof Ventilation Fans

Effects of an Improved Side Vent on Yield of Oriental Melon and Temperature in Single-span Plastic Greenhouse with Roof Ventilation Fans

Investigating air leakage and wind pressure coefficients of single-span plastic greenhouses using computational fluid dynamics

Air leakage from greenhouses not only influences heating load and the carbon dioxide supply, but also affects wind loads on the greenhouse structure. Quantitative evaluation of the greenhouse air leakage is essential to estimate variable costs and achieve reasonable designs for greenhouses with adequate strength. In this study, greenhouse leakage rate was estimated through a combination of CFD simulation of the external pressure coefficients of the greenhouse cladding and modelling of airflow through leakage paths on the greenhouse walls. The simulation results of the leakage rate were validated by the experimental results obtained from two greenhouses with the same structure but different orientation. The correlation coefficients between the simulated and measured values ranged from 0.82 to 0.99, and the RMSE of the simulated leakage rate ranged from 0.014 to 0.052. The simulation results indicated that a strong transverse wind created lower leakage rate and internal pressure coefficient. These findings and methodology will be helpful for designing light-weight greenhouses in windy regions.

Effects of Modified Installation Methods of Roof Ventilation Devices in the Single-span Plastic Greenhouses on Yield and Fruit Quality of Oriental Melon

Effects of Modified Installation Methods of Roof Ventilation Devices in the Single-span Plastic Greenhouses on Yield and Fruit Quality of Oriental Melon

박과작물 재배 단동 비닐하우스의 천장 환기시스템 설치 실태조사

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 <TEX>$85.0m^3/min$</TEX>, 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.

Analysis of Safety Wind Speed and Snow Depth for Single-Span Plastic Greenhouse according to Growing Crops

Analysis of Safety Wind Speed and Snow Depth for Single-Span Plastic Greenhouse according to Growing Crops

Development of Single-span Plastic Greenhouses for Hot Pepper Rainproof Cultivation

Development of Single-span Plastic Greenhouses for Hot Pepper Rainproof Cultivation

Wind Loads on Single-span Plastic Greenhouses and Solar Greenhouses

Wind tunnel tests were conducted in an NH-2-type wind tunnel to investigate the wind pressure coefficients and their distribution on the surfaces of a single-span plastic greenhouse and a solar greenhouse. Wind pressures at numerous points on the surfaces of the greenhouse models were simultaneously measured for various wind directions. The critical wind speeds, at which damage occurred on the surfaces of single-span plastic greenhouses and solar greenhouses, were derived. To clearly describe the wind pressure distribution on various surface zones of the greenhouses, the end surface and top surface of the plastic greenhouse and the transparent surface of the solar greenhouse were divided into nine zones, which were denoted as Zone I to Zone IX. The results were as follows: 1) At wind direction angles of 0° and 45°, the end surface of the single-span plastic greenhouse was on the windward side, and the maximum positive wind pressure coefficient was near 1. At wind direction angles of 90° and 180°, the entire end surface of the single-span plastic greenhouse was on the leeward side, and the maximum negative wind pressure coefficient was near −1. The maximum positive wind pressure on the end surface of the single-span plastic greenhouse appeared in Zone IV at a wind direction angle of 15°, whereas the maximum negative pressure appeared in Zone VIII at a wind direction angle of 105°. 2) Most of the wind pressure coefficients on the top surface of the plastic greenhouse were negative. The maximum positive and negative wind pressure coefficient on the top surface of the plastic greenhouse occurred in Zones I and II, respectively, at a wind direction angle of 60°. 3) At a wind direction angle of 0°, the distribution of wind pressure coefficient contours was steady in the middle and lower zones of the transparent surface of the solar greenhouse, and the wind pressure coefficients were positive. At a wind direction angle of 90°, the wind pressure coefficients were negative on the transparent surface of the solar greenhouse. A maximum positive wind pressure coefficient was attained at a wind direction angle of 30° in Zone IX, whereas the maximum suction force occurred in Zone VII at a wind direction angle of 135°. 4) The minimum critical wind speeds required to impair the single-span plastic greenhouse and solar greenhouse were 14.5 and 18.9 m·s−1, respectively.

단동 플라스틱 온실의 천창 환기효과와 설치기준 분석

Dimensions, operation conditions and improvement items for round roof windows were investigated in arch shape single-span plastic greenhouse with roof vents, and natural ventilation performance was analyzed based on the ventilation theory. Diameter of round roof windows was mostly 60 cm, and chimney height projected on roof was average 30 cm. Installation space was mostly 5 to 6 m but farmhouse of 10 m and over was 16.7% also. A round roof window which has 60 cm diameter was installed to 6 m space generally and 80 cm diameter was installed to 10 m space, but correct standards did not exist. There were a lot of opinions that ventilation effect of round roof windows is fairly good and user satisfaction is generally excellent. It is problem that there is few effects in summer and that vinyl around each vent tears well and rainwater leaks, and improvement hope item required development of automatic control system. In the wind speed of 0.3 m/s, it was estimated that natural ventilation rates were 0.69, 0.55, 0.50 and 0.48 volumes per minute in case of 2, 4, 6 and 8 m installation space for round roof windows, respectively. It was analyzed that the ratio of ventilation due to buoyancy out of total ventilation were 65.2, 41.9, 29.9 and 22.8% in case of 2, 4, 6 and 8m installation space, respectively. By the round roof windows installed at space of 6 m, ventilation rate was estimated to 0.5 volumes per minute, and we can expect the increase in ventilation rate of 30%. In order to meet the recommended ventilation rate for summer season, we have to install the round roof windows at space of 1 to 2 m. However, it is difficult to apply those installation space because of falling productivity due to lower light transmittance as well as rising costs. It is estimated that the installation space of 6m is appropriate for spring or fall season. Therefore it is necessary to encourage installing the roof windows in single-span plastic greenhouses.

우리나라 단동 비닐하우스와 북미지역 하이터널의 비교

Structural characteristics for standard models of single-span plastic greenhouse in Korea and high tunnels in North America were analyzed, and comparative analysis for greenhouse environments measuring in Korean farmhouse and Rutgers high tunnel was carried out to find structural and environmental improvements of single-span plastic greenhouses that occupy most of Korean greenhouse. Widths of high tunnels are similar to single-span plastic greenhouses but their heights are high comparatively and their side heights are fairly higher than single-span plastic greenhouses specially. Rafters, which are main frames, section sizes of high tunnels are bigger and their intervals are wider than single-span plastic greenhouses. Relative bending resistances compared with representative Korean greenhouse were analyzed by 0.92 to 1.42 in single-span plastic greenhouses, and 1.38 to 2.96 in high tunnels. Frame ratios of single-span plastic greenhouses were 6.8 to 8.6%, and those of high tunnels were 5.5 to 8.7%. We analyzed air temperatures and solar radiations measured in single-span plastic greenhouse and high tunnel on clear days in late March. There were outside temperatures in generally similar range, and judging by rise of indoor temperatures, ventilation performance of high tunnel is more excellent than single-span plastic greenhouse. Solar radiations of two areas were no big difference but light transmittance of high tunnel was a little bit higher than single-span plastic greenhouse. Single-span plastic greenhouses are disadvantageous in environmental managements such as ventilation performance and light transmittance because distance between greenhouses is too narrow and length of greenhouse is too long compared to high tunnels. To get the environmental improvement effects as well as to increase the structural resistance of single-span plastic greenhouses are achievable by widening the width of greenhouse in possible range, widening the space between rafters, and enlarging the section size of rafters. Also, we need to secure enough distance between greenhouses and to restrict the length of greenhouse by maximum 50 m in order to improve the ventilation performance and the light transmittance.