CFD simulation of temperature and humidity distribution in low profile cross ventilated dairy cattle barn

Abstract: With the ever increasing scale and intensivism in pasture in China, low profile cross ventilated (LPCV) dairy cattle barn, as a main building style in cattle house, is increasingly applied. The most obvious benefit of LPCV building is the ability to control the cow's environment during all seasons of the year. It increases the percentage of time cows are in the thermal neutral zone, which allows both milk production and feed efficiency to be increased. However, during the hottest period in eastern China, the hot and humid climate, reduces the control effectiveness inside the building. In order to understand temperature and humidity distribution inside, the field experiment, which measured the parameters including environment temperature, humidity and surface temperature of dairy cattle, was conducted. The experimental dairy houses were located in the east part of China, with the demotions of length 376.6 m×width 90.4 m, and a slop roof of 1/12.5 pitch. Measured results showed that in the LPCV cattle house in eastern China, when the outdoor temperature and relative humidity were 36.2℃ and 55.5% respectively, the wet pad system could cool the air with a decline of up to 7.7℃, but increase the relative humidity to 99.9%, which led to a high temperature and high moisture condition. Meanwhile, three-dimension computational fluid dynamics (CFD) method was carried out to simulate thermal condition inside the cattle building. Multiple parameters of cattle were included in the CFD model to effectively express the heat and moisture released from cattle bodies as well as provide more realistic air flow patterns. In order to save the computer resource, a model of simplified cattle was considered to reduce the number of meshes with the legs and tails in the original. The temperature of the surface of cattle and building was measured by thermal camera in the field experiment. Multi-phase transport model was adopted to calculate the moisture generation. Simulated results showed that the indoor temperature and humidity were influenced by fluent field and unevenly distributed. Low temperature was found in place that had high air velocity, and humidity was significantly coupled with temperature variation. With the air movement, temperature increased by 0.014℃ while humidity decreased by 0.04% per meter in width dimension. Temperature-humidity index (THI) was applied to analyze and estimate environment comfort in different locations inside the cattle building. The THI had a same tendency with the change of environment outdoors. When the wet pad worked properly, THI increased in width dimension. Inlet position had a better thermal condition than outlet position, and THI increased by 0.025 per meter in this dimension (width dimension). The CFD model was validated via the comparison with the field experimental results at the same locations where the temperature and relative humidity sensors were installed. Comparison between simulations and measurements showed that the average relative error between simulated and measured results in temperature and humidity were 0.89% and 0.59%, respectively. Theoretical heat generation of dairy cow was calculated, and the discrepancy between calculated and simulated values was 14.5%. The high agreement in simulation and measurement proved the reliability and feasibility of the model and boundary condition in the simulation. And this study can provide references for the optimization design and environment regulation of LPCV dairy cattle barn in China.