Research On Precise Ground Channel Ventilation System For Large-scale Pig Farm

Reasonable ventilation mode is considered as one of the important strategies to ensure the best productive performance of large-scale pig farms.The ventilation mode of traditional large-scale pig house is relatively extensive,which leads to a low somatosensory wind speed in summer.Moreover,poor air quality,insufficient preheating of outdoor cold air in winter and large indoor temperature differences in different areas and different times are frequently seen.All of these result in poor animal welfare,health level and productive performance.What’s worse,the problem of bad working environment and high energy consumption of ventilation is more prominent.For the common problems caused by the ventilation design of the above-mentioned in large-scale pig farms,the present study applied the precision ground channel ventilation system to large-scale pig houses to improve the air distribution in pig houses and the reduce the ventilation energy consumption.The influence of different ventilation modes on the temperature fluctuation,distribution and gas pollutant removal capacity under winter conditions was studied by comparison test of two ventilation modes:ground channel ventilation and ceiling ventilation(traditional ventilation mode).The energy-saving effect of tunnel ventilation system in large-scale sow farms and its influence on the thermal environment comfort of pregnant sows in winter and summer was analyzed by the application of ground ventilation system in large-scale sow farms.CFD technology numerical simulation of the gestation house with ground ventilation system was carried out to study the influence of the tunnel wind system on the temperature field and wind speed field in the gestation house in summer.Optimization plan was made and the field test method was conducted and verified.The main research results were as follows:(1)The tests of the ground channel ventilation and the ceiling ventilation showed that the winter thermal environment and the air quality environment of the nursery in the ground channel ventilation and ceiling ventilation both met the requirements of the national standard.The temperature fluctuation in the ground channel ventilation was1.7℃,and the temperature difference in the length direction was not significant(P>0.05).The temperature fluctuation in the ceiling ventilation was 4.6℃,and the temperature in the length direction was significantly different(P<0.05).The ground channel ventilation was more efficient in removing gas pollutants according to the lower indoor concentration of gas pollutants,and the average ventilation volume was35%lower than that of the ceiling ventilation.(2)The field test of the ground channel ventilation system in a large-scale sow farm found that the neutral temperature of the ground channel for cooling and preheating the fresh air was 11.5℃.The ground channel ventilation system provided an additional average heating power of 56.1 W/m~2 for the pig house in winter and an additional average cooling power of 39.0 W/m~2 for the pig house in summer.The average effective body temperature of sows in winter was(26.0±0.6)℃,the respiratory rate was between 20 and 30 times/min,the average effective body temperature of sows in summer is(26.4±1.2)℃,and the respiration rate was between49 and 52 times/min.Slight heat stress was found in sows,indicating that this ventilation system need to be further optimized in large-scale sow houses.(3)Numerical simulation of the summer environment of the underground ventilated pregnant pig house using CFD technology found that the air flow direction of the pig house was vertical upward,the temperature stratification in the vertical direction was obvious,and the temperature at the height(0.5 m)of the pig activity area was slightly higher than that of the human activity area(1.5 m).The temperature in the pig crates was about 28℃in the animal occupied zone,and the temperature in the aisle was about 27℃.The air velocity of the ground channel air outlet was evenly distributed,which can ensure that each pig can breathe fresh air,but the air flow was not sufficiently mixed with the air in the pig pen.The wind speed in the pig pen was about 0.3 m/s,and the corridor wind was about 0.7 m/s.In summer,the high temperature in the house had a negative effect on the heat dissipation of pigs in the crates.(4)Through the numerical simulation analysis of the optimization scheme of the ground channel ventilation pig house,it was found that the temperature of the pigs’active area in the pigpen was about 27℃,the wind speed was about 1.0 m/s,and the temperature and wind speed were evenly distributed after the pipeline ventilation was added.The result of field verification of the optimized scheme showed that the optimized ground channel ventilation system can achieve a good result of average effective body temperature(21.2±0.4)℃,average body surface temperature(31.1±0.6)℃,average respiratory rate(40±6 times/min)in hot summer(average(35.1±0.5)℃ outdoor,average(77.1%±1.5%)RH).No heat stress happened on pigs under this ventilation mode.