Journal of the Society of Agricultural Structures, Japan

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The purpose of this study is to investigate changes in temperatures and CH4, N2O, and NH3 emissions during the early stage of dairy manure composting using a time-varying intermittent aeration system that automatically controls arbitrary set times of aeration and interval according to the compost temperature range. The experiment performed time-varying intermittent aeration with six different ON/OFF settings in the laboratory-scale composting device and compared it to conventional composting with continuous and intermittent aeration. Our results showed that the modified aeration system increased the duration of high compost temperature above 55 °C compared to conventional composting and simultaneously increased the maximum temperature during composting by up to 5.0 °C. Depending on the setup conditions of the system, even an approximately 80 % reduction in the percentage of aeration time reduced greenhouse gas emissions by up to 58 % compared with conventional continuous aeration composting and simple intermittent aeration. Additionally, this system reduced the NH3 emissions generated during the thermophilic phase of composting by up to 93 %. There is the possibility that the time-varying intermittent aeration method is more effective than the conventional method in suppressing environmentally hazardous gases. The method may also contribute to more hygienic compost production.

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The wind pressure coefficients Cp on multi-span greenhouses with different eaves were evaluated by wind tunnel test to elucidate the influence of eave height on Cp. In this research, the three-span greenhouses were targeted with eave height of 2 m, 4 m and 6 m, respectively. For the experiment, 1:20 scale models were used. The Cp distribution was obtained for various wind directions θ from 0° (normal to the ridge line) to 90° (parallel to the ridge line) at an increment of 5°. The Cp at the center of the greenhouse showed complicated distribution when θ = 0°. The negative Cp on the windward roof increased in magnitude with an increase in eave height. The local minimum values behind windward eave were -0.23, -0.82 and -1.43 in order of eave height. On the other hand, the influence of the eave height on Cp decreased on leeward roof and leeward wall. For the model with eave height of 4 m, the minimum Cp value was about -3.02 near the ridge corner when θ = 30°. For other models with eave heights of 2 m and 6 m, the minimum Cp were -2.62 (θ = 20°) and -3.56 (θ = 30°), respectively. The extreme Cp value was also affected by eave height. Applying extreme Cp value to the wind load on the roof near the gable wall contributes to the reasonable design for three-span greenhouses, especially for ones with high eaves.

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