Sadanori Sase

Optimization of vent configuration by evaluating greenhouse and plant canopy ventilation rates under wind-induced ventilation

The effects of greenhouse vent configurations, plant existence, and external wind speeds on ventilation rates and airflow patterns in a greenhouse and plant canopy zone under wind-induced ventilation were investigated. The optimization of traditional vent configuration for a two-span glasshouse for better air renewal, especially in the plant canopy zone, was attempted by three-dimensional numerical simulations using a computational fluid dynamics (CFD) approach. The realizable k-. model was used for a turbulent model, and the existence of the plants in the greenhouse was modeled by a porous medium method. Prior to the optimization, the CFD model was verified with the results of an experimental study of natural ventilation. The CFD model adequately matched those results. The ventilation rates, both in the greenhouse and in the plant canopy zone, were proportional to external wind speed. Maximum greenhouse ventilation rates were achieved when rollup type side vents were used in the side walls and both side and roof vents were fully open (case 3). For example, the ventilation rate for this vent configuration was 6.03 m3 m-2 min-1 at an external wind speed of 1.5 m s-1. The greenhouse ventilation rate for this vent configuration was almost the same as when the butterfly-type side and roof vents were fully open (case 1). However, the use of a rollup side vent considerably improved the ventilation rate in the plant canopy zone. This showed that ventilation in the plant canopy zone was significantly affected by internal airflow patterns caused by different vent configurations.

Measurements of Wind Velocity and Direction Using Acoustic Reflection against Wall

The measurements of wind velocity and direction using an acoustic reflection against a wall are described. We aim to measure the spatial mean wind velocity and direction to be used for an air-conditioning system. The proposed anemometer consists of a single wall and two pairs of loudspeakers (SP) and microphones (MIC) that form a triangular shape. Two sound paths of direct and reflected waves are available. One is that of the direct wave and the other is that of the wave reflected on the wall. The times of flights (TOFs) of the direct and reflected waves can be measured using a single MIC because there is a difference in the TOF between direct and reflected waves. By using these TOFs, wind velocity and direction can be calculated. In the experiments, the wind velocities and directions were measured in a wind tunnel by changing the wind velocity. The wind direction was examined by changing the setup of the transducers. The measured values using the proposed and conventional anemometers agreed with each other. By using the wave reflected against a wall, wind velocities and directions can be measured using only two pairs of transducers, while four pairs are required in the case of conventional anemometers.

A Wind Tunnel Study of Natural Ventilation for Multi-Span Greenhouse Scale Models Using Two-Dimensional Particle Image Velocimetry (PIV)

A two–dimensional particle image velocimetry (PIV) system installed in a large–sized wind tunnel was used to examine the natural ventilation of fully open roof and Venlo–type multi–span greenhouses. Since the PIV system has rarely been used for large–scale, low–turbulence airflow conditions, the PIV system was investigated to improve its performance and accuracy. The PIV accuracy tests were conducted without any greenhouse models in the wind tunnel because it was very difficult to insert the anemometer sensors in the small–scale greenhouse models, and it was also assumed that the sensor itself could affect natural airflow patterns inside the models. Good results were obtained in the PIV accuracy test, and the errors were shown to be mostly in the .5% range. Additionally, the natural airflow in 2– to 10–span greenhouses was investigated using the PIV system. The PIV results indicated that the PIV technique was an effective method for evaluating the relative performance of alternative designs of greenhouse and other structures with turbulent interior air distributions.

DEVELOPMENT OF VERTICAL WIND AND TURBULENCE PROFILES OF WIND TUNNEL BOUNDARY LAYERS

Ventilation is considered one of the most important factors for livestock and plant environmental control. However, because of the difficulties of conducting field experiments, aerodynamic studies of ventilation and HVAC of agricultural buildings are difficult and expensive to conduct effectively in full-scale buildings. A wind tunnel can be the most powerful technology for studying aerodynamics because it works with real airflow and the boundary conditions can be easily changed. A large, multi-purpose wind tunnel was built at the National Institute of Agricultural Engineering (NIAE) in Korea in 2002. In this research, the formation of boundary layers, such as vertical wind and turbulence profiles, in the test section of the wind tunnel was studied to determine ventilation efficiency and internal airflow characteristics of naturally ventilated buildings. Compared to measured data, it was found that the optimum wind and turbulence profiles of a 20 m boundary layer could not be achieved using the theory and experimental procedures of civil and architectural engineering because that would require several hundred meters of boundary layer thickness. Moreover, it was impossible to achieve 30% turbulence intensity just above the floor. Finally, it was found that lattice and blocks could be effectively used to design an optimum boundary layer for aerodynamic study of agricultural buildings. When using lattice and blocks, the wind and turbulence profiles were seriously affected by the distance between the lattice and the measurement location, by the distance between adjacent bars of lattice, and by the width of the bars.

Wind Tunnel Measurement of Aerodynamic Properties of a Tomato Canopy

This study was conducted to determine the drag coefficient and the relationship between permeability (K) and momentum loss coefficients (Cf) of a tomato canopy for various leaf area densities. The experiments were conducted in a large-scale wind tunnel system with a tomato canopy. The static pressures and air velocity measurements were performed at several heights in the y-direction and various positions in the z-direction in the wind tunnel test section. The relationship between pressure drop and air velocity across the tomato canopy was determined using a porous medium approach. A drag coefficient of 0.31 was obtained for the tomato canopy used in the experiment. The permeability of the tomato canopy ranged from 0.006 to 0.65 for a leaf area density (L) of 4 (m2 m-3), from 0.004 to 0.41 for L = 5, and from 0.003 to 0.3 for L = 6 as Cf changed from 0.1 to 1. Thus, a mature tomato canopy having L = 6 could be used with a canopy permeability of K = 0.017 and a momentum loss coefficient of Cf = 0.245.

An infrared-based coefficient to screen plant environmental stress: concept, test and applications

By introducing a reference dry leaf (a leaf without transpiration), a formerly proposed plant transpiration transfer coefficient (hat) was applied to detect environmental stress caused by water shortage and high temperature on melon, tomato and lettuce plants under various conditions. Results showed that there were obvious differences between leaf temperature, dry reference leaf temperature and air temperature. The proposed coefficient hat could integrate the three temperatures and quantitatively evaluate the environmental stress of plants. Experimental results showed that the water stress of melon plants under two irrigation treatments was clearly distinguished by using the coefficient. The water stress of a tomato plant as the soil dried under a controlled environmental condition was sensitively detected by using hat. A linear relationship between hat and conventional crop water stress index was revealed with a regression determination coefficient R2 = 0.97. Further, hat was used to detect the heat stress of lettuce plants under high air temperature conditions (28.7°C) with three root temperature treatments (21.5, 25.9 and 29.5°C). The canopy temperature under these treatments was respectively 26.44, 27.15 and 27.46°C and the corresponding hat value was -1.11, -0.74 and -0.59. Heat stress was also sensitively detected using hat. The main advantage of hat is its simplicity for use in infrared applications.

Thermal condition in a compact sunroom for fresh vegetables production

Thermal conditions in a 3 m2 sunroom attached to a residence building were estimated from a vegetable production perspective. The set points of the air temperature were 12–24 °C, an appropriate temperature range for most vegetables. The air temperatures in the full scale model sunroom could be maintained over 12 °C with up to 417 W supplemental heating for the measuring period. In the sunroom, the averaged overall heat loss coefficients between the sunroom and the outside and between the sunroom and the residence building for 24 days during nighttime in February and March were 2.6 and 13.0 W/m2 °C, respectively. The tendency of the diurnal range of air temperature in the sunroom could be roughly simulated for the measuring period except in some daytime cases in February, although the simulation method was a simple and approximate energy balance model with the averaged overall heat loss coefficients.

A simulated investigation to measure acoustic emissions caused by root growth

Monitoring root growth in greenhouses is essential for planned application of growth inputs to the plants and control of the growth environment. A possible method for detecting root growth is to measure the Acoustic Emissions (AE) caused by root-soil interaction. The use of such a technique necessitates a thorough understanding of the AE patterns caused by the root at each growth rate under controlled conditions. Because a real root cannot be controlled to grow at a constant rate, a dedicated root growth simulator was developed to push a probe into the soil at preset rates and thus simulate root growth. The simulator consisted of a stepper motor, allied driver circuitry, a timer module to control the penetration rate, and a hydro-mechanical transmission element. The simulation was conducted in a sand bath, which was instrumented with three AE sensors connected to a conventional AE monitor. Beforehand, the sensors were calibrated for their sensitivity using an AE generator built for this purpose. AE was measured in a noise proof environment in sand under both dry conditions and 10% moisture, with the simulated root growth varied at three levels of 0.5, 1.0, and 1.33 mm h –1 . Emissions from wet or dry sand were periodic and of high intensity. Spectral analysis techniques were used to recognize the dominant frequency at each level of growth rate. Simultaneously, the acoustic attenuation of sand was also measured and correlated with that of the AE signals to study the influence of sensor placement on AE detection. When AE measurements from real root growth were acquired and analyzed, the observed dominant frequencies varied in the same range acquired from the simulations. Hence if more relevant data on AE under simulated studies are acquired, possibilities do exist for this method to be useful for detecting real root growth.

Evapotranspiration Rate Measurement by Energy-balance Equation in a Single-span Greenhouse

An energy balance equation was used to estimate evapotranspiration in a greenhouse, and an instrument for this purpose was developed. It was found that the present method is simpler than that using the Penman-Monteith equation and the estimated values by this method were in good agreement with measured data. It is also reported that normal radiation sensor measurements on a horizontal surface are not adequate for measuring radiation received by a plant canopy in a greenhouse.

Effects of Buoyancy and Wind Direction on Airflow and Temperature Distribution in a Naturally Ventilated, Single-Span Greenhouse using a Wind Tunnel

Experiments were performed in a wind tunnel to study the effects of buoyancy and wind direction on airflow patterns and temperature distribution within an empty, naturally ventilated, arched-roof, single-span greenhouse (open roof, open screened sidewalls). Archimedes Number was used for similarity to determine the necessary wind tunnel air speed and greenhouse floor-tooutside air temperature difference (T) for the 1/15 scale model. Buoyancy effects were studied for three T (10, 20, 30iAEC) and two wind directions (90iAE, 270iAE). Particle Image Velocimetry (PIV) was used to measure airflow vectors. Dimensionless velocity [U(x), V(x)] and dimensionless temperature (¥eT) were analyzed. At 90iAE (roof opening facing wind), the velocity of the downward flowing air from the roof (V = -0.232) created a strong circular airflow pattern that caused the influx of air through the windward sidewall to be significantly small (U = 0.06). At 270iAE (roof opening opposite to wind direction), the velocity of air entering the windward sidewall (U=0.158) was greater than from the roof (V=0.010), creating a more horizontal airflow pattern. Although there was no significant difference in the mean ¥eT inside the greenhouse model based on wind direction, the center and leeward sections were significantly greater for the 270iAE wind direction (p<0.001). Also, T did not have a significant effect on mean ¥eT inside the model. ¥eT was significantly lower at the windward side of the model for all treatments. For the 90iAE wind direction, the center of the model had the significantly highest mean ¥eT. For 270iAE wind direction the center and leeward sections were significantly higher than the windward side. Although the floor was heated, the highest temperatures were observed in the middle of the model, where airflow was minimal. If insect screens had a coarser mesh, more air could enter through the sidewalls to cool the center zone. Results from this experiment will be used to study positions for high-pressure fog cooling nozzles in the full-scale greenhouse.