여름철에 자연환기는 온실의 온도를 낮추는데 중요한 역할을 한다. 온실의 형태, 환기창 종류, 환기창의 위치 등은 자연환기 성능에 큰 영향을 미친다. 본 연구에서는 전산유체역학(CFD)을 이용하여 다양한 천창구조에 대하여 측창에 따른 부력환기 효과를 비교분석 하였다. Boussinnesq 가정을 사용하여 전체 계산영역에 대한 부력효과를 시뮬레이션 하였다. 또한 RNG $K-{\varepsilon}$난류모델을 사용하였다. 일사량 효과를 시뮬레이션 하기 위해 Solar ray tracing과 함께 Discrete originates (DO) radiation 모델을 사용하였다. 실험온실 내부의 온도를 측정하여 CFD모델을 검증하였으며, 실험값과 계산값이 잘 일치하는 것으로 나타났다. 7가지의 천창구조에 대하여 온실의 내외부 온도차이와 환기횟수를 비교하였다. 내외부온도의 차이는 $3.2{\sim}9.6^{\circ}C$ 범위로 나타났고, 환기횟수는 $0.33{\sim}0.49min^{-1}$ 범위로 나타났다. 고깔형 천창구조 온실의 경우 내외부 온도차이가 $3.2^{\circ}C$로 가장 낮았고 환기횟수도 $0.49min^{-1}$로 가장 높게 나타나 환기효과가 가장 우수한 것으로 나타났다.
여름철에 자연환기는 온실의 온도를 낮추는데 중요한 역할을 한다. 온실의 형태, 환기창 종류, 환기창의 위치 등은 자연환기 성능에 큰 영향을 미친다. 본 연구에서는 전산유체역학(CFD)을 이용하여 다양한 천창구조에 대하여 측창에 따른 부력환기 효과를 비교분석 하였다. Boussinnesq 가정을 사용하여 전체 계산영역에 대한 부력효과를 시뮬레이션 하였다. 또한 RNG $K-{\varepsilon}$ 난류모델을 사용하였다. 일사량 효과를 시뮬레이션 하기 위해 Solar ray tracing과 함께 Discrete originates (DO) radiation 모델을 사용하였다. 실험온실 내부의 온도를 측정하여 CFD모델을 검증하였으며, 실험값과 계산값이 잘 일치하는 것으로 나타났다. 7가지의 천창구조에 대하여 온실의 내외부 온도차이와 환기횟수를 비교하였다. 내외부온도의 차이는 $3.2{\sim}9.6^{\circ}C$ 범위로 나타났고, 환기횟수는 $0.33{\sim}0.49min^{-1}$ 범위로 나타났다. 고깔형 천창구조 온실의 경우 내외부 온도차이가 $3.2^{\circ}C$로 가장 낮았고 환기횟수도 $0.49min^{-1}$로 가장 높게 나타나 환기효과가 가장 우수한 것으로 나타났다.
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 dy...
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 $9.6^{\circ}C$ depending on the different studied roof vent types. Moreover, the ventilation rate was within the range from 0.33 to $0.49min^{-1}$. Our findings show that the conical type roof ventilation has minimum inside-to-outside air temperature difference of $3.2^{\circ}C$ and a maximum ventilation rate of $0.49min^{-1}$.
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 $9.6^{\circ}C$ depending on the different studied roof vent types. Moreover, the ventilation rate was within the range from 0.33 to $0.49min^{-1}$. Our findings show that the conical type roof ventilation has minimum inside-to-outside air temperature difference of $3.2^{\circ}C$ and a maximum ventilation rate of $0.49min^{-1}$.
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제안 방법
2. For this study, the first step pre-processing was conducted using Google SketchUpTM pro ver. 2015 software to prepare 3D models of greenhouses. Further, meshing was carried out in the ANSYS mesh component.
Further analysis was performed using the gothicshaped conical type roof vent greenhouse with different commonly used natural ventilation configurations which included: only roof-vent opening, only side-vent opening, and combined side and roof-vent openings. The results are illustrated in Fig.
In this research, we used ANSYS Fluent, a CFD tool, to study the effect of different roof vents designs combined with side vents on the inside thermal environment of a single-span greenhouse. Here, we considered the buoyancy-driven natural ventilation effect exerted on the greenhouse internal air temperature and ventilation rate, in the absence of the wind or at an exceedingly low wind speed.
Moreover, the weather parameters were recorded around the solar midday of July. The outside weather data was collected to use as an input in CFD model and greenhouse internal air temperature were measured for the validation of the CFD results. The characteristics of the weather data are presented in Table 1.
(2004b) investigated the effects different greenhouse vents configurations on natural ventilation rate of a two-span greenhouse. This study further studied the ventilation efficiency of a greenhouse while using a combination of side and roof vents. Interestingly, Shklyar and Arbel (2004) used a CFD code to explore the air flow pattern in a pitched-roof single-span greenhouse.
대상 데이터
The experimental greenhouse was a rectangular-based, round-roofed, east-west oriented, single-span greenhouse covered with a 0.15 mm thick polyethylene (PE) film, located at Daegu (latitude 35.53°N, longitude 128.36°E, elevation 48m), South Korea.
이론/모형
The program used the finite method to numerically solve the Navier-Stokes equations, i.e., the mass, energy, and the momentum balances, permitting the calculation of the air velocity and the temperature. The Boussinneq hypothesis was adopted to simulate the buoyancy effect to the whole computational domain.
성능/효과
and in the only roof-vent opening greenhouse internal air temperature was very high 50℃ (less reduction in internal air temperature) comparing other configurations. From the results obtained, we concluded that side vents contributed more to the natural ventilation of singlespan greenhouse, and the combined roof- and side-vent openings achieved the highest reduction in the air temperature.
Further, the efficiencies of the different greenhouse roof vents types were assessed by observing the reduction in the internal air temperature and ventilation rate. Our results showed that, for all the cases studied in this study, the gothicshaped greenhouse with a conical type roof vent combination with side vents is the best as it achieved the lowest air temperature of 30.05℃ and highest air exchange rate (0.49min-1). The results presented in this paper are from specific cases with the particular boundary conditions.
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