Optimal Design Of Pipe Ventilation And Its Validation For Nursery Pig House In Cold Region

As the potential growth area for pig breeding,the breeding facility engineering is developing towards standardization and intellectualization in Northeast China.Ventilation is one of the key technologies of breeding facility engineering,and it is also the main means of regulating the environment of closed pig house.But most of the northeast belongs to the severe cold area,so the contradiction between ventilation and heat preservation of piggery is prominent,to solve this problem,the ventilation model of closed pig house in cold area in winter was studied to improve the environmental quality of pig house and ensure the healthy growth of piglets.At the nursery stage,the piglets'autoimmunity is not perfect and the growth state is susceptible to environmental influence,in addition,the contradiction between ventilation and heat preservation is more pronounced in the nursery pig house because the space is relatively small.Therefore,it is more representative to research on the environmental ventilation regulation of nursery pig house in winter in the severe cold area.On the basis of comprehensive analysis of various ventilation modes,through field investigation,numerical simulation,data analysis,testing verification and other methods,the uniformity principle of air supply duct was explored,and the combined ventilation system with air supply and exhaust ducts was designed innovatively.Through the performance evaluation,the combined ventilation system with air supply and exhaust pipes can effectively regulate the environment of pig house.The main contents and conclusion are as follows:(1)Environmental monitoring and data analysis of experimental piggeryThe nursery pig house of a large-scale pig farm was selected as the experimental pig house in Heilongjiang Province.Environmental monitoring sensor nodes were designed based on Lo Ra wireless communication technology,can collect temperature,humidity,ammonia and carbon dioxide concentration data in the piggery.And based on the principle of wind-induced vibration and pressure power generation,the self-power supply system of sensor node was designed by using electro-mechanical coupling method.Based on the analysis of monitoring data of experimental piggery and environmental standard of nursery pig house,under the condition that the ambient temperature of pig house was suitable for the growth of nursery pigs,concentration of CO₂and relative humidity were determined as input variables of environmental control.On the basis of data comparison and analysis,it was determined that the ventilation volume obtained can meet the requirements of environmental regulation by calculating the concentration of CO₂as a variable.In the ventilation state,the temperature will be greatly affected in the piggery,the main factors affecting the environmental heat balance of piggery were explored,so as to provided a reference for the subsequent design and optimization of combined ventilation system with air supply and exhaust pipes.(2)Theoretical analysis and design of combined ventilation and ventilation of air supply and exhaust pipesThe principle of uniform ventilation and the main factors affecting uniform air supply were analyzed,and the design idea of combined ventilation system with air supply and exhaust pipes was put forward.Computational fluid dynamics(CFD)was used to simulate the air flow field in piggery,the distribution law of airflow field in each fence under combined ventilation mode of air supply and exhaust pipes was analyzed,so as to verify the feasibility of the ventilation system for local environment regulation.Considering the cold stress of nursery pigs caused by low temperature of air supply in the pipes,a three-stage preheating ventilation system was designed,which consists of corridor preheating,heat exchange and heating compensation.The simulation results showed that the preheating ventilation system could ensure that the air supply temperature was suitable for growth of nursery pigs,which provides a technical guarantee for the practical application of pipe ventilation.(3)Optimization of ventilation systemInfluence rules of ventilation pipe diameter,ventilation speed and Angle on airflow field and temperature field were analyzed,computational fluid dynamics(CFD)was used to simulate the air flow field,the uniformity and distribution law of air flow field and temperature field of horizontal section of nursery pig's back and north-south vertical section in the center of the concrete floor were explored.The results showed that when the diameter of ventilation pipe increases from 0.2m to 0.4m,the airflow uneven coefficient of each fence generally increases,but the temperature field is gradually uniform.The distribution of air flow field was gradually uniform with the increase of wind speed at the opening of the air supply and exhaust pipes,but there was no significant difference in temperature field distribution at the horizontal section of nursery pigs'back.The Angle of air supply has a great influence on the distribution area of airflow field and temperature field,but the temperature was within the appropriate range under the setting of each ventilation Angle.When the air supply Angle was reduced from 60°to 45°,the maximum wind speed area of the air flow field shifted from one side of the cement floor to one side of the leaking floor,which is more conducive to the discharge of moisture and dirty gas.The results of comprehensive comparison and analysis showed that when the diameter of the ventilation pipe was 0.3m,the Angle of the air supply pipe was 45°,and the wind speed at the opening of the air supply and exhaust pipe was 1.5m/s and 2.0m/s respectively,the airflow field and temperature field were evenly distributed,and the dirty air in piggery was easier to discharge,and the wind speed and temperature were suitable for the healthy growth of the nursery pigs.(4)Fuzzy control strategy for ventilationBased on the analysis results of experimental piggery environment data and fuzzy control theory,under the condition that the ambient temperature of pig house was suitable for the growth of nursery pigs,the relative humidity and CO₂concentration were used as input variables,and speed control mode of the fans were used as output,and fuzzification and defuzzification were processed.The quantization factors of the input variables K_Hand K_Cwere 0.5,and the quantization factor of the output was 1.According to the needs of local control with fence as ventilation unit in the piggery,the fuzzy control rules were established.The fuzzy control system model was established by MATLAB,to verify the feasibility of ventilation control of variable and variable speed,which laid a foundation for the automatic ventilation control of environment in piggery.(5)Evaluation of ventilation energy efficiencyTo verify the performance of combined ventilation system of air supply and exhaust pipes,The experimental piggery was modified,on the basis of monitoring data of the control piggery and experimental piggery,the airflow uneven coefficient,significant difference,temperature and humidity index(THI),air exchange efficiency,energy consumption,economy and growth performance of nursery pigs were used as indexes to evaluate the ventilation performance..Compared with the control pig house,in one nursery cycle,the cumulative weight gain of nursery pigs in the experimental pig house was 2.23kg more and feeding conversion rate was 1.68%higher.The comprehensive evaluation results showed that all the data of the experimental piggery were as follows:temperature was at 22?to 25?,humidity was at 60%to 70%,concentration of CO₂was at 850mg/m³to 1070mg/m³,concentration of NH₃was at 0.5mg/m³to 3.0mg/m³,the airflow uneven coefficient was lower than 0.1.The experimental pig house was more suitable for the growth of nursery pigs,and he combined ventilation system of air supply and exhaust pipes has obvious long-term economic benefits.