Limi Okushima

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.

WINDWARD WINDBREAK EFFECTS ON AIRFLOW IN AND AROUND A SCALE MODEL OF A NATURALLY VENTILATED PIG BARN

Wind tunnel tests of 1:20–scale windbreak models placed in a windward position from naturally ventilated pig barns were performed to examine the capability of windbreaks to trap air contaminants emitted from livestock buildings. The airflow surrounding the windbreak and the building was measured. Dispersion of air contaminants was predicted with the proposed parameters PU, PV, and PW, which are related to airflow momentum in the leeward direction and to horizontal and vertical plume sizes, respectively. Windbreaks included a solid wall, a net screen, and another pig barn. With a solid wall as a windbreak, air emitted from the building was exhausted in the windward direction. Compared to a net screen or another barn, the solid wall resulted in the lowest airflow momentum. A high–concentration odorous area was predicted to be located between the windbreak and the building. Sprinklers in this area could possibly trap the air contaminants. When a building was placed in the windward position as a wind barrier, the dispersion of odorous air behind the leeward building was predicted to be the smallest compared to a solid wall and a net; moreover, a smaller plume width was seen. When a net screen was used, the airflow between the wall and the building moved only in the leeward direction.

Wind Induced Isothermal Airflow Patterns in a Scale Model of a Naturally Ventilated Swine Barn with Cathedral Ceiling

The airflow patterns in naturally ventilated barns are important for the air velocity that the animals are exposed to under windy conditions. Thus animal welfare may be affected by the sidewall configuration, i.e. size and position of the ventilation openings. In order to get more knowledge of the effect of the sidewall configuration, the air velocities in the animal zone of a growing/finishing pig house were measured in a wind tunnel. A 1/20 scale model was used for the experiments. The model was placed within the boundary layer of the wind tunnel. Low 3.2 m/s, medium 5.5 m/s, and high 7.5 m/s free wind speeds were applied with a corresponding roughness coefficient for the wind profile of n = 0.11, 0.18, and 0.20. Airflow patterns and air velocities in the scale model were determined with the wind perpendicular to the sidewall. There were full–length ventilation openings in both sidewalls and no ridge opening. The experimental variables were the ventilation opening height and the position of the ventilation openings in the sidewall. The experiments showed that the height of the wall between the ventilation opening and the ceiling was most important for the airflow patterns in the building model and thus on the air velocities in the animal zone. When the inlet was flush with the ceiling or the wall height between the ventilation opening and the ceiling was small, the supply jet attached the ceiling on entry. In this case the air velocity in the animal zone could be estimated by use of relationships between wind velocity and height of the ventilation opening. When the wall height between the ventilation opening and the ceiling became larger than a critical value, the supply air jet attached the floor on entry. For the same outside condition and the same ventilation opening height, the down–jet resulted in considerably higher air velocities in the animal zone than the up–jet.

Network-Controlled Measurement of Mean Spatial Temperature Using a Sound Probe with a Long Baseline

An acoustical method for temperature measurement of large-scale spaces in a wind field is described. The real-time thermometry in a long span of 100 m was realized by the adoption of a bidirectional sound probe as a temperature sensor and a wireless local area network for controlling sensors. The probe mainly consists of two loudspeakers and two microphones. An accurate mean spatial temperature was measured without the interference of the wind in the area by the bidirectional probe. We carried out numerical simulations to confirm the validity of our method. The mean temperature was satisfactorily measured by this principle under various distributions of wind velocity. In field measurements, mean spatial temperature along a 100-m-long baseline was measured by the system with a conventional thermometer as a reference. The temperature change over one hour at 30 s intervals was compared to the change in the reference temperature at the center of the baseline. The results indicated that the system recorded a long periodic change in air temperature without the effects of local turbulence and wind. The advantages of the proposed system compared to a conventional thermometer are real-time, wireless and noncontact measurements.

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.

Precision irrigation system based on detection of crop water stress with acoustic emission technique

A computerized and automatic precision irrigation system based on estimation of crops water stress with acoustic emission (AE) technique was developed in the modern greenhouse. The system can automatically acquire the real-time AE signals and transpiration data from tomato crop respectively with AE sensor and electronic balance, The system also can automatically obtain environment parameters of the greenhouse, such as temperature, air humidity, the density of the sunlight and CO/sub 2/ density, and then according to an optimum control algorithm, the system automatically carried out precision irrigation. The experiment results have shown that AE events increase gradually with the increase of transpiration speed of crops to some extent. The system has the potential to implement optimum and automatic irrigation based on the information acquired from the crops with acoustic emission, but the system is easily to be affected by noise of environment.

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.