Masahisa Ishii

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.

Micrometeorology Measurement by Acoustic Method

In this paper, we describe a visualization method of wind velocity and direction distributions for micrometeorology measurement. The wind velocity and direction were measured in a noncontact mode within a measurement area using acoustic probes, on the basis of differences of the time of flight of sound. To reconstruct a two-dimensional distribution, eight acoustic transducers were installed at equal intervals along the circumference of a turntable. The reliability of the system was tested in a wind tunnel. The test was performed for two patterns: increasing wind velocity under a constant wind direction, and rotating wind direction under a constant wind velocity. For the two experimental patterns, two-dimensional distributions of the wind velocity and direction could be reconstructed. Compared with a reference measured with an ultrasonic anemometer, our results showed good agreement.

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.

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.

Evaluation of Lettuce Cultivars Suitable for Closed Plant Production System

There are many cultivars in butterhead lettuce (Lactuca sativa L.) and if some of them can perform well in the relatively low light and high temperature condition, the commercial lettuce production become feasible because of the lower electric consumption in the plant factory. Eighteen cultivars were grown in the summer greenhouse under 50% shading condition, and the growth indices of seedling stage were examined in relation to the quality of final products (Expt.l). These cultivars were classified into two groups, namely unsuitable (lower qualities) and suitable (higher qualities). The ratio of leaf length to width and chlorophyll content in the seedling stage closely related to the quality of the final products. Twelve cultivars of both groups were selected from the previous experiment and grown in a closed production system to evaluate the productivity and the quality (Expt.2). The performance of the plants showed a similar tendency with those under the greenhouse condition. Thus, the ratio of leaf length to width and chlorophyll content in the seedling stage were found to be an effective index for the evaluation of the performance of lettuce cultivars.