| Low profile cross ventilated (LPCV) dairy cattle barns, as a main building style in dairy cattle barns, are increasingly applied. The most obvious benefit of LPCV buildings is the ability of controlling the cows’living environments during all seasons of the whole year, but the desired effect is hard to achieve in actual operation. The objective of this paper is to find and solve the technical problems of why high-temperature, high-humidity and uneven distribution of indoor airflow appeared in the LPCV barns in eastern China in summer. To achieve this goal, computational fluid dynamic (CFD) and particle image velocimetry (PIV) were used to investigate the distribution and variation of the temperature, humidity and airflow inside one of the LPCV barns, on the basis of field measurements of the main experimental parameters. Optimization scheme of the LPCV barn was proposed and practiced in four barns of one farm. These studies all contribute to provide theoretical basis and technical support for the design optimization and environment regulation of LPCV dairy cattle barns in China. The main conclusions of this paper are as follow.1. Field measurements of the main environmental parameters in the selected LPCV barn were conducted systematically and comprehensively in eastern China in summer. The distribution and variation of the temperature, humidity and airflow inside the barn were obtained. The filed measurements indicated that environmental problems such as high-temperature, high-humidity and uneven distribution of indoor airflow generally exited in the LPCV barn. The mean temperature and relative humidity of the8sensors inside the barn was27.5℃and99.38%respectively and the mean temperature-humidity index (THI) was81.5. The wind speed differed greatly between the two sides of the feed-drive alley. The wind velocity of the windward side was1.5m/s higher than that of the other side.2. The effect of various environment inside the selected LPCV barn on the physiological indexes and behavior of the cattle was analyzed by continuously measuring virginal temperature and observing behaviors of dairy cattle. Test results indicated that the virginal temperature of dairy cattle was influenced by both temperature and relative humidity inside the barns. There was significant difference of virginal temperature of the cattle between the two areas around wet pads and fans, respectively. The difference of air velocity in the barn had significant effect on the time of cattle lying-on-the-bed, and those cattle in the lower velocity areas had shorter time lying-on-the-bed than others.3. The3D CFD simulation was carried out to simulate the distribution of main environmental parameters inside the selected LPCV barn, thus to investigate the relationship among the temperature, relative humidity and airflow. Simulation results showed that the key reason for the uneven flow distribution in the barn was the interactional positions of the wind deflectors and the feed manager walls. The CFD model was validated via comparing with the field testing results. High agreement was found between simulation and the measurement proving the reliability and feasibility of the model.4. Based on the similarity theory, an experimental model for the barn with cattle was made by the scale of1:15, and PIV technology was applied to measure the flow field inside the barn. Testing results with model presented the distribution of air flow and the effect of facilities on the air distribution and also validated how accuracy CFD model was again.5. Optimization designs of the wind deflectors on both locations and angles were proposed, aims to decrease the value of the uneven coefficient and also increase the wind speed in cattle area. The effectiveness of optimization scheme was proved by modifying the exiting barns. This study will provide the theoretical and engineering references for designing LVPC dairy cattle barns in the future. |
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