Evaluation On Winter Ventilation Efficiency Of Freestall Dairy Barns In Heilongjiang Province

Natural ventilation system of dairy barns was evaluated using environment measurement and air moving scheme at two large-scale dairy farms in order to grasp air moving scheme of the free-stall dairy barns accurately, and provide theoretical foundation for the design and transformation of ventilation system of dairy barns.Environment measured index included the diurnal change of air temperature and relative humidity of dairy barns, and the spatial distribution of air temperature, air velocity, ammonia, and carbon dioxide. Results showed that during the winter the relative humidity to most of the time, most areas maintained at 100% for the dairy barns of Wondersun dairy co., LTD. Spatial distribution of air temperature in the dairy barn was very uniform,and the average air temperature from the ground 0.3 meters, 0.8 meters and 1.5meters height in the distance were 3.7℃, 3.8℃ and 4.0℃ respectively. Carbon dioxide concentration is far more than the national standard of 2496 mg/ m3, and the carbon dioxide concentration from the ground 0.3 meters, 0.8 meters and 1.5meters height in the distance were 4392mg/ m3, 4395mg/ m3 and 4464mg/ m3 respectively, and the difference between different level was significant(P<0.05). Air velocity was lower, and the air velocity from the ground 0.3 meters, 0.8 meters and 1.5meters height in the distance were 0.18 m/s, 0.13 m/s and 0.12m/s respectively, and the difference between different height was very significant(P<0.01). The environment for the dairy barns of Yuda animal husbandry co., LTD was similar to the results of Wondersun dairy co., LTD, but relative humidity was higher, carbon dioxide concentration was out of limit seriously, and air velocity was lower.The ventilation system of dairy barns was conducted with standard deviation of indoor air temperature and air moving scheme. Movement of air in the cowshed was visualized with smoke. Results showed that standard deviation of indoor air temperature for the dairy barns of Wondersun dairy co., LTD and Yuda animal husbandry co., LTD was 1.56 and 1.53 respectively, both of them was more than 1.4, and ventilation efficiency mark 3, which indicated that ventilation for these two dairy barns is unsatisfactory, and important ventilation openings are closed。Results with smog experiment showed that air moving scheme for both of dairy barns was similar, fresh air entered into dairy barn from the gap of windows and doors, and then fresh and cold air was warmed by heat produced from dairy cows, after that it become lighter and went up to the roof. A portion of the air runoff from the crevice of ridge, a portion of the air refluxed from cold roof to dairy barns and developed turbulence, and a portion of the air suspended beneath the roof. The lower heat insulation of the external building envelope was the primary reason for poor ventilation, and the close of inlet and outlet was the subsidiary reason.